Medical Coding Guides

Coding Fundamentals

How to Choose an ICD-10-CM Code: A Step-by-Step Coding Workflow

Start from the provider’s documented diagnosis, find its main term in the Alphabetic Index and follow every subterm and cross-reference, then verify the code in the Tabular List — the only place laterality, 7th characters and the instructional notes can be confirmed. Report the code at its highest available specificity, sequence it by the encounter’s rules, add every code the notes require, and validate the set against the code relationships before it goes out.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Code Relationships & Conventions

Excludes1 vs Excludes2: When Two ICD-10-CM Codes Can Be Reported Together

An Excludes1 note means the two codes describe conditions that cannot occur together, so they are never reported together — unless the documented conditions are genuinely unrelated, in which case both may be coded. An Excludes2 note means the excluded condition is simply not part of this code, and both codes may be reported when the patient has both.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Sequencing

Sepsis, Severe Sepsis, and Septic Shock: How Many Codes, and Which Goes First

Sepsis alone takes one code, for the underlying systemic infection — A41.9 when the organism is not specified. Severe sepsis takes at least two: the infection first, then a code from R65.2-, plus a code for each associated acute organ dysfunction. Septic shock is severe sepsis with R65.21. A code from R65.2- can never be the principal diagnosis.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

Common Clinical Coding Problems

How Do I Code Diabetes With Chronic Kidney Disease?

Diabetes with chronic kidney disease takes at least two codes: the diabetes combination code for CKD (E11.22 for type 2, or the .22 code of the applicable E08–E13 category) followed by the N18 code for the documented stage. The Index links the two through “with,” so the relationship is presumed unless the provider says the CKD has another cause. Add a Z79 code for the control agent; with hypertension documented, the CKD is also coded through I12 or I13.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Code Relationships & Conventions

The “With” Convention: When ICD-10-CM Presumes Two Conditions Are Related

When the Alphabetic Index or a code title links two conditions with “with” or “in,” ICD-10-CM presumes one causes the other — and they are coded as related without the provider saying so. The provider statement that changes the coding is the one saying they are unrelated.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Code Relationships & Conventions

7th Character A, D, or S: “Initial” Does Not Mean First Visit

The 7th character follows the phase of care, not the visit count: A while the patient is receiving active treatment, D during routine healing or recovery after active treatment is complete, S when a late effect of the injury is being treated. A new provider seeing the patient for the first time changes nothing.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How to Choose an ICD-10-CM Code: A Step-by-Step Coding Workflow

Start from the provider’s documented diagnosis, find its main term in the Alphabetic Index and follow every subterm and cross-reference, then verify the code in the Tabular List — the only place laterality, 7th characters and the instructional notes can be confirmed. Report the code at its highest available specificity, sequence it by the encounter’s rules, add every code the notes require, and validate the set against the code relationships before it goes out.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Symptom Code or Confirmed Diagnosis: When an R Code Is Right, and When It Is Not

A symptom or sign code is correct when the provider has not established a related definitive diagnosis by the end of the encounter — the Guidelines call such codes “acceptable, even necessary.” Once a diagnosis is confirmed, a symptom routinely associated with it is not coded separately; one that is not routinely associated is coded after the diagnosis. Inpatient and outpatient rules differ for “probable” diagnoses.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

“Other” vs “Unspecified,” NEC vs NOS: Which Residual Code Fits the Record

An “other” or “other specified” code is for a condition the record describes in detail for which no specific code exists — NEC, “not elsewhere classifiable.” An “unspecified” code is for a record that does not give enough detail to pick a more specific code — NOS, “not otherwise specified.” They answer opposite documentation situations, and where a category has no unspecified code, the “other” code covers both.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

“See” vs “See Also” in the Alphabetic Index: When You Must Follow the Cross-Reference

A “see” cross-reference must be followed — the term you are on has no code, and the correct code is under the term it names. A “see also” cross-reference is optional: the term you are on may already give the code, and the other term is offered in case it holds additional entries you need.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Combination Codes: One Code for Two Conditions, and When a Second Code Is Still Needed

A combination code is a single code that classifies two diagnoses, a diagnosis with an associated manifestation, or a diagnosis with an associated complication. When it fully identifies the documented conditions, or the Alphabetic Index directs to it, it is assigned alone — multiple coding is not used. When it lacks the specificity to describe the manifestation or complication, an additional code follows it.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Principal Diagnosis vs First-Listed Diagnosis: Which Term Applies, and How Each Is Chosen

Principal diagnosis is the inpatient term: the condition established after study to be chiefly responsible for the admission. First-listed diagnosis is the outpatient equivalent: the condition chiefly responsible for the services at that visit. They are chosen by different sections of the Guidelines, and uncertain diagnoses are handled in opposite ways.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Sepsis, Severe Sepsis, and Septic Shock: How Many Codes, and Which Goes First

Sepsis alone takes one code, for the underlying systemic infection — A41.9 when the organism is not specified. Severe sepsis takes at least two: the infection first, then a code from R65.2-, plus a code for each associated acute organ dysfunction. Septic shock is severe sepsis with R65.21. A code from R65.2- can never be the principal diagnosis.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

Code First, Use Additional Code, and Code Also: What Each Note Requires, and Which Ones Set the Order

Code First and Use Additional Code are two halves of one sequencing instruction: the code carrying Code First goes second, after its underlying condition; the code carrying Use Additional Code goes first, with the secondary code after it. Code Also means a second code may be needed to describe the condition fully, but it gives no sequencing direction — the order depends on the encounter.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Manifestation Codes: What Goes First, and Why It Can’t Be the Manifestation

A manifestation code reports a condition caused by something else, and the classification requires the underlying etiology to be sequenced first. Manifestation codes are never first-listed or principal — Medicare’s inpatient editor rejects 422 of them outright, and the tabular’s paired notes say the same thing.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

Excludes1 vs Excludes2: When Two ICD-10-CM Codes Can Be Reported Together

An Excludes1 note means the two codes describe conditions that cannot occur together, so they are never reported together — unless the documented conditions are genuinely unrelated, in which case both may be coded. An Excludes2 note means the excluded condition is simply not part of this code, and both codes may be reported when the patient has both.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

The Placeholder “X”: When a Code Needs It, and Why Leaving It Out Invalidates the Code

The X is a placeholder that fills a character position so that later characters — above all a required 7th character — sit in the right place. It appears where the classification left room for expansion, most visibly in the T36–T50 drug codes. Where a placeholder exists it is mandatory: a code written without it is not a valid code.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Laterality: Right, Left, Bilateral, or Unspecified — and What Happens Across Two Encounters

When a code carries laterality, report the side the record documents: right, left, or bilateral. If both sides are affected and no bilateral code exists, report right and left separately. When a bilateral condition is treated one side at a time, the bilateral code applies until one side is resolved, then the unilateral code for the side that remains. Unspecified-side codes are for the rare record that cannot be clarified.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Includes Notes, Inclusion Terms, Parentheses, Brackets, and “And”: How to Read a Tabular Entry

Four small conventions decide what a tabular entry covers. An Includes note under a three-character category defines or exemplifies its content. Inclusion terms under a code are conditions the code is used for — synonyms or, under “other specified” codes, a list — and are not exhaustive. Parentheses enclose nonessential modifiers that do not change the code; brackets hold synonyms in the Tabular and mark manifestation codes in the Index. “And” in a title means “and” or “or.”

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

The “With” Convention: When ICD-10-CM Presumes Two Conditions Are Related

When the Alphabetic Index or a code title links two conditions with “with” or “in,” ICD-10-CM presumes one causes the other — and they are coded as related without the provider saying so. The provider statement that changes the coding is the one saying they are unrelated.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

7th Character A, D, or S: “Initial” Does Not Mean First Visit

The 7th character follows the phase of care, not the visit count: A while the patient is receiving active treatment, D during routine healing or recovery after active treatment is complete, S when a late effect of the injury is being treated. A new provider seeing the patient for the first time changes nothing.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Many ICD-10-CM Codes Are There? Counts by Fiscal Year, FY2016 to FY2027

The FY2027 ICD-10-CM order file lists 98,403 entries, of which 74,879 are valid codes that can be reported and 23,524 are category or subcategory headers that cannot. It takes effect October 1, 2026. The first ICD-10-CM year, FY2016, had 91,737 entries and 69,823 valid codes.

Foundational · FY2027 · CURRENT · Updated September 8, 2026

Which ICD-10-CM Chapters Carry the Most Excludes1 Notes? A Census of the Tabular List

The FY2027 ICD-10-CM tabular carries 5,411 Excludes1 note lines at 2,648 locations and 2,529 Excludes2 lines at 1,172 locations. Chapter 18 (symptoms, R codes) has the most Excludes1 lines, 477; Chapter 10 (respiratory) is the densest for its size. Only the skin and injury chapters carry more Excludes2 than Excludes1.

Intermediate · FY2027 · CURRENT · Updated September 8, 2026

Which ICD-10-CM Codes Have Been Retired? A Twelve-Year Lifespan Census

Across the twelve ICD-10-CM fiscal years published so far, 99,085 distinct codes have appeared in a CMS order file and 75,909 of them have been reportable at some point. Of those, 1,030 are no longer reportable: 619 were deleted from the file and 411 remain in it as non-billable parent categories. No code has ever been withdrawn and later restored.

Intermediate · FY2027 · CURRENT · Updated September 14, 2026

How Much Does ICD-10-CM Change Each Year? Eleven Years of Additions, Deletions and Revisions

Across eleven annual updates, FY2017 through FY2027, ICD-10-CM has added 7,348 codes, deleted 682, revised the description of 1,265 without changing the code, and flipped the billable status of 413. The years are not alike: FY2017 and FY2023 each added and deleted far more than a typical year, and description revisions are heavily front-loaded into the first three years after adoption.

Intermediate · FY2027 · CURRENT · Updated September 15, 2026

Which ICD-10-CM Chapters Have Grown the Most Since FY2016? Twelve Years by Chapter

ICD-10-CM is not evenly distributed across its 22 chapters. Chapter 19 (injury, poisoning and certain other consequences of external causes) alone holds 41,187 valid codes in FY2027, 55 percent of the entire code set; the top five chapters together hold 80.8 percent. Growth since FY2016 is just as uneven: Chapter 4 (endocrine) grew 44 percent while Chapter 1 (infectious diseases) grew 1 percent, even though Chapter 19 added more raw codes, 1,324, than any other chapter.

Intermediate · FY2027 · CURRENT · Updated September 15, 2026

Poisoning, Adverse Effect, or Underdosing: Which T36–T50 Column, and What Goes First

The T36–T50 codes carry the substance and the circumstance in one code, and the 5th or 6th character picks the column: 1–4 for poisoning by intent, 5 for adverse effect, 6 for underdosing. Poisoning is sequenced first with its manifestations after; an adverse effect is sequenced after the code for the reaction it caused; underdosing is never principal or first-listed.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

Acute and Chronic Together: When Both Codes Are Reported, and Which Goes First

When the same condition is documented as both acute (or subacute) and chronic, and the Alphabetic Index lists acute and chronic as separate subentries at the same indentation level, report both codes with the acute code first. When the classification instead provides a single combination code for the acute-with-chronic form, that one code is reported alone.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

What Are the Medicare Code Editor Edits, and Why Do Individually Valid Codes Fail Them?

The Medicare Code Editor (MCE) is the software CMS applies to Medicare inpatient claims; its edits are CMS edits, distinct from any commercial payer’s rules. Most diagnosis edits restate a classification rule as a machine check: an invalid code, an external cause or manifestation code as principal, a status or symptom-type code on the unacceptable-principal list, a diagnosis impossible at the patient’s age. Two valid codes fail when their combination or position breaks one of those rules.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Assign the Present on Admission (POA) Indicator? Y, N, U, W and the Exempt List

The POA indicator is reported for each diagnosis and external cause code on an inpatient institutional claim. Appendix I of the FY 2027 ICD-10-CM Official Guidelines defines present on admission as present when the inpatient admission order occurs, so a condition that develops in the ED, observation or outpatient surgery is POA. Assign the codes first, then give each Y, N, U or W; leave the field blank only for a code on the CDC/NCHS exempt list.

Intermediate · FY2027 · CURRENT · Reviewed October 5, 2026

How Do I Code a Sequela (Late Effect)? Two Codes, the Residual First, and the 7th Character S

A sequela is the residual effect left after the acute phase of an illness or injury has ended; there is no time limit on coding it. It generally takes two codes: the residual condition first, then its cause, as an injury code with 7th character S or a dedicated sequela code such as I69.- or B90–B94. A sequela code that already includes the residual stands alone. The acute-phase code is not reported with the late effect.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Arthropathy, Osteopathy and Myopathy “in Diseases Classified Elsewhere”

These six musculoskeletal families code a joint, bone or muscle problem caused by a disease coded elsewhere. Pick the family from the mechanism, code the underlying disease first, then read the Excludes1 — it routes whole groups of patients, diabetic ones especially, out of these categories entirely. Check the subcategory too: within M14 and M02 the manifestation rules apply to some and not others.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code a Flu Shot or Other Immunization Visit? Z23 for the Encounter, Z28 When the Vaccine Is Not Given, Z28.3 for Underimmunization Status

A flu shot or any other vaccination visit is Z23, Encounter for immunization: first-listed when the vaccination is the reason for the visit, secondary when it is part of a routine well-child or preventive examination, which leads. Z23 records only that immunization was the purpose; the vaccine and its administration are procedure codes. A vaccine due but not given takes a Z28.0–Z28.9 reason code; underimmunization status is Z28.3-, secondary only.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Screening or Diagnostic? When a Z Screening Code Applies and When the Symptom Leads

A screening code (Z11, Z12, Z13, Z36) is for testing a seemingly well person for a disease or its precursors. When a patient has a sign or symptom and the test is to rule out or confirm a suspected diagnosis, that is a diagnostic examination, not a screening — the sign or symptom is coded as the reason for the test. A condition found on screening is added as an additional diagnosis.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Aftercare vs Follow-Up: Healing Care (Z42–Z49) or Surveillance After Treatment Is Complete (Z08–Z09)

Aftercare codes (Z42–Z49 and related categories) describe continued care during the healing or recovery phase after the initial treatment of a disease. Follow-up codes (Z08, Z09) describe surveillance after treatment is complete and the condition no longer exists. Neither is used for injuries, which take the injury code with a subsequent-encounter 7th character.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Status or Complication? When a Z Status Code Gives Way to a Complication Code

A status Z code says something is present and affects care without being a current problem: a pacemaker, a transplant, a stoma. Once the record documents a problem with it, the complication code from T80–T88 or the body-system chapters takes over and the status code is not reported beside it; the Guidelines say the status code adds no information the complication code lacks. Routine attention to a device or opening is a third case, with its own Z codes.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

History Codes (Z80–Z87): When Is a Condition “History Of” Rather Than Current?

Personal history codes (Z85–Z87 and the Z91.- history subcategories) report a past condition that no longer exists and is not being treated but may recur; family history codes (Z80–Z84) report a family member’s disease that raises the patient’s risk. Both are sequenced after the reason for the encounter and pair with the follow-up and screening codes: Z85 carries Code First for Z08, Z86 and Z87 for Z09. A condition still present or still treated is not history.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Status Codes: When Should a Z Status Code Be Reported?

A status code reports that a patient carries a disease, has a residual of a past condition, or has a prosthetic or mechanical device from past treatment — information that may affect care without being a current illness. It is not reported with a body-system code that already includes the information, it is distinct from a history code, and Medicare’s inpatient editor rejects most status codes as principal diagnosis.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

When Can a Z Code Be the Primary Diagnosis?

A Z code can be the first-listed or principal diagnosis when the circumstance it describes is itself the reason for the encounter. Status codes like Z93.6 almost never qualify — and Medicare’s inpatient editor rejects them — while their Z43.- “attention to” counterparts usually do.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Artificial Opening Coding: Status, Attention, or Complication?

Every artificial-opening encounter lands on exactly one of three families: a complication code (J95.0-, K94.-, N99.5-) when something is wrong with the opening, Z43.- when the opening is being serviced, or Z93.- as a secondary code when the opening is merely present. The note’s verbs decide which.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Acute Kidney Injury (AKI)? N17.9, Acute Tubular Necrosis, and AKI on Top of Chronic Kidney Disease

Nontraumatic acute kidney injury is coded to category N17: N17.9 for AKI or acute kidney failure without further detail, N17.0 for acute tubular necrosis, N17.1 or N17.2 for cortical or medullary necrosis. With chronic kidney disease, the N17 code and the N18 stage code are both reported, sequenced by the circumstances of the encounter. N17 carries a Code Also note for the underlying condition; “renal insufficiency” without “failure” or “injury” is N28.9, not N17.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code a Myocardial Infarction? I21 for Four Weeks, I22 for a Second MI Within Them, and I25.2 After

An acute myocardial infarction is coded from category I21 for four weeks from onset: I21.9 when type and site are unspecified, I21.0–I21.3 for a type 1 STEMI by site, I21.4 for a type 1 NSTEMI, I21.A1 for a type 2 MI with its cause coded first, I21.A9 for types 3–5. A further type 1 or unspecified MI within those four weeks adds I22. After four weeks, continuing care takes an aftercare code; a healed infarction needing no care is I25.2.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

After a CABG: Z95.1 Bypass Graft Status, I25.7- and I25.810 Graft Atherosclerosis, and Z48.812 Aftercare

After coronary artery bypass grafting, Z95.1, Presence of aortocoronary bypass graft, is a secondary status code while the grafts are functioning. Once the grafts are diseased, the code is I25.7- (atherosclerosis of the bypass graft with angina, by graft and angina type) or I25.810 without angina, and Z95.1 adds nothing the disease code does not say. Surgical aftercare during recovery is Z48.812, which may accompany Z95.1 to name the surgery.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code COPD? Uncomplicated, With Exacerbation, or With a Lower Respiratory Infection

COPD is coded from category J44: J44.9 uncomplicated, J44.1 with a documented acute exacerbation, J44.0 with an acute lower respiratory infection, which carries a Code Also note for the infection itself. An exacerbation is a worsening of the chronic condition, not an infection; when both are documented, J44.0 and J44.1 may both be reported with the infection code. Other specified forms are J44.8-. Every J44 code carries a Code Also note for the type of asthma (J45.-), if applicable.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

How Is “Threatened Labor” Coded? O47 False Labor, Not O60 Preterm Labor

Threatened labor is coded to O47.0-, False labor before 37 completed weeks, with the trimester character — category O47’s Includes note names “threatened labor,” and O60 Preterm labor carries an Excludes1 sending “threatened labor NOS” back to O47.0-. O60.0- applies only when the record documents that labor actually began before 37 weeks.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Traumatic, Pathological, or Stress Fracture: Which Family, and the Osteoporosis Rule

A fracture belongs to exactly one family. Traumatic fractures take the injury codes by site (S02–S92); fractures from diseased bone take M80 (osteoporosis), M84.5 (neoplasm), M84.6 (other disease) or M84.4 (unspecified pathological); stress fractures take M84.3-. The families exclude each other by Excludes1, and a patient with known osteoporosis who fractures after a minor fall is coded to M80, not to an S code.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Venomous Insect Sting or Bite: A T63 Toxic-Effect Code, Not an Injury Code — and No W57

A venomous sting or bite is a toxic effect: a T63 code from the Table of Drugs and Chemicals — bee T63.44-, wasp T63.46-, other arthropod T63.48- — sequenced first, with intent in its 6th character and manifestations such as anaphylactic shock (T78.2) after it. No external cause code is added; the W50–W64 block excludes T63 outright. A nonvenomous insect bite is the opposite: a superficial injury S code by site, with W57 as the external cause.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

Retained Foreign Body: T81.5 Left During a Procedure, Z18 Fragment Status, or T15–T19 Through an Orifice

Three code families describe a foreign body in a patient, and they exclude each other. T81.5- is a complication of care: something accidentally left in the body during a procedure. Z18 is a status code: a fragment that remains embedded, usually from an injury, and is not being treated as a complication. T15–T19 is an injury: a foreign body that entered through a natural orifice — eye, ear, airway, gut, genitourinary tract — with a W44 external cause code.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Diabetes With Chronic Kidney Disease?

Diabetes with chronic kidney disease takes at least two codes: the diabetes combination code for CKD (E11.22 for type 2, or the .22 code of the applicable E08–E13 category) followed by the N18 code for the documented stage. The Index links the two through “with,” so the relationship is presumed unless the provider says the CKD has another cause. Add a Z79 code for the control agent; with hypertension documented, the CKD is also coded through I12 or I13.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Diabetes With Retinopathy? Severity, Macular Edema, and Laterality

Diabetic retinopathy is one combination code that carries three documented facts: the retinopathy type (E11.32 mild, E11.33 moderate, E11.34 severe nonproliferative, E11.35 proliferative, or E11.31 unspecified), whether macular edema is present (6th character 1 with, 9 without), and — for E11.32 through E11.35 and E11.37 — the eye as a 7th character: 1 right, 2 left, 3 bilateral, 9 unspecified. No separate retinopathy code is added.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Diabetes With Neuropathy? E11.40 to E11.49 and the Charcot Joint

Diabetic neuropathy takes one combination code chosen by the documented type: E11.40 when the record says only “diabetic neuropathy,” E11.41 mononeuropathy, E11.42 polyneuropathy (including diabetic neuralgia), E11.43 autonomic neuropathy (including diabetic gastroparesis), E11.44 amyotrophy, E11.49 other. Neuropathic arthropathy — the Charcot joint — is a separate combination code, E11.610. The link to the diabetes is presumed through “with.”

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Diabetes With Hyperglycemia or Hypoglycemia? E11.65, E11.64-, and the E16.A Level

In a patient with diabetes, hyperglycemia is E11.65 — not R73.9, which the E10 category excludes as “hyperglycemia NOS.” Hypoglycemia is E11.649 without coma or E11.641 with coma, and E11.64- carries a Use Additional Code note for the hypoglycemia level (E16.A1–E16.A3) when the level is documented. E16.2, Hypoglycemia, unspecified, carries an Excludes1 for diabetes with hypoglycemia and is not used.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Secondary Diabetes? E08 Due to an Underlying Condition, E09 Drug-Induced, or E13 Other Specified

Secondary diabetes, caused by another condition or event, is coded to E08, E09 or E13, each with E11’s complication structure. E08 (due to an underlying condition) carries a Code First note for that condition; E09 (drug- or chemical-induced) carries a Code First note for a poisoning and a Use Additional Code note for an adverse effect; E13 is other specified diabetes, including postpancreatectomy and postprocedural. The three exclude each other and E10, and E11’s Excludes1 note lists all three.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Diabetes With Multiple Complications? One Code Per Complication, and When E11.8 or E11.69 Applies

A patient with several diabetic complications gets several diabetes combination codes — one for each documented complication — sequenced by the reason for the encounter. E11.69, other specified complication, is for a documented complication the category has no code for and asks for a code identifying it. E11.8, unspecified complications, is for a record that says “with complications” and names none. Neither replaces the specific codes when the complications are documented.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Respiratory Failure? Acute, Chronic, or Acute-on-Chronic — and Can It Be Principal?

Respiratory failure is coded by its course — J96.0- acute, J96.1- chronic, J96.2- acute and chronic (the tabular’s term for acute-on-chronic) — with a 5th character for hypoxia (1), hypercapnia (2), or unspecified (0). Acute or acute-on-chronic respiratory failure may be the principal diagnosis when it is the condition established after study to be chiefly responsible for the admission; with another acute condition, the circumstances of admission decide, and a query settles an unclear record.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Anemia in Chronic Disease? D63.0, D63.1, D63.8 and the Code First Rule

Anemia documented as due to a chronic disease is coded to category D63, “in chronic diseases classified elsewhere,” and each of its codes carries a Code First note: D63.0 anemia in neoplastic disease (the neoplasm first), D63.1 anemia in chronic kidney disease (the N18 code first), D63.8 anemia in other chronic diseases (the underlying disease first). As manifestation codes, they are never principal or first-listed. Anemia with no cause documented is D64.9.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Heart Failure? Type, Acuity, and the Hypertension Combination Codes

Heart failure is coded from category I50 by type — I50.2- systolic (HFrEF), I50.3- diastolic (HFpEF), I50.4- combined — and acuity: unspecified, acute, chronic, or acute on chronic. “Congestive heart failure” with no type is I50.9. When the patient also has hypertension, the Guidelines presume the relationship: I11.0 (or I13.- with CKD) is assigned and leads, with the I50 code after it as the Use Additional code identifying the type.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Pneumonia? Organism, Influenza First, Aspiration, and Ventilator-Associated

Pneumonia is coded by the documented organism — J13 pneumococcal, J15.- other bacterial, J12.- viral, J18.9 when none is documented — and the pneumonia categories carry two instructions: Code First an associated influenza (J09.X1, J10.0-, J11.0-) at J12–J16 and J18, and Code Also an associated abscess (J85.1) or aspiration pneumonia (J69.-). Ventilator-associated pneumonia, J95.851, is assigned only when the provider documents it, with a B95–B97 code for the organism and no J12–J18 code.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Transplant Complication or Transplant Status? T86 vs Z94, and CKD After a Kidney Transplant

A functioning transplanted organ is a status, Z94.-. A complication or rejection that affects the transplanted organ’s function is coded to T86.- plus a second code for the complication itself; conditions that do not affect the organ’s function are not transplant complications. Chronic kidney disease after a kidney transplant is the standard case: N18.- with Z94.0, not T86.1-, unless failure, rejection or another complication is documented. The status code is not added to the complication code.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Hypertension With Chronic Kidney Disease? I12, I13, and the N18 Stage

When both hypertension and chronic kidney disease are documented, the classification presumes the CKD is hypertensive: assign I12.9 for CKD stage 1–4 or unspecified, or I12.0 for stage 5 or end-stage renal disease, followed by the N18 code for the documented stage. If heart disease is also present, a code from I13 replaces both I11 and I12. The presumption is broken only when the provider states the CKD is not related to the hypertension.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Active Cancer or “History Of”: When a C Code Becomes Z85

The malignancy code stays active for as long as treatment is directed at the site — surgery, chemotherapy, or radiation. Z85 personal-history codes take over only when all three parts hold: the primary has been excised or eradicated, no further treatment is directed to that site, and there is no evidence of disease there.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

How Do I Code Postpancreatectomy Diabetes Mellitus?

Postpancreatectomy diabetes mellitus takes three codes working together: a code from category E13 as the principal or first-listed diagnosis, E89.1 (postprocedural hypoinsulinemia), and a Z90.41- code for the acquired absence of pancreas — an explicit instruction in the Official Guidelines, not an inference.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

Bilateral Knee Osteoarthritis: One Code or Two?

When both knees have primary osteoarthritis, assign the single bilateral code M17.0 — not M17.11 plus M17.12. The two-unilateral pattern is only correct when the classification provides no bilateral code, and for primary knee osteoarthritis it does.

Foundational · FY2027 · CURRENT · Reviewed October 1, 2026

What Does an NCCI Correct Coding Modifier Indicator of 0, 1 or 9 Mean?

The indicator says whether a modifier can ever permit the pair to be reported separately. 0 admits no exception. 1 allows one where the encounter supports it. 9 means CMS has marked the edit not applicable. It never says whether your documentation supports separate reporting.

Intermediate · FY2027 · CURRENT · Reviewed October 1, 2026

What Does an MUE Adjudication Indicator of 1, 2 or 3 Change?

The indicator decides what the published unit value is compared against. Under 1 each claim line stands alone. Under 2 and 3 the units are summed across every line carrying that code on one date of service, which is a stricter comparison. The value alone does not tell you which.

Intermediate · FY2026 · HISTORICAL · Updated September 13, 2026

Your Diagnosis Is Not on the NCD’s List. Does That Mean Medicare Will Not Cover It?

No. A code’s absence from a policy’s published list does not establish non-coverage by itself; whether it does depends only on what that policy states. Absence can also mean the list was never published for that policy, or that a mapping existed and CMS ended it.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

Why the Same Inpatient Claim Can Group to a Different MS-DRG

Because the date of service chooses the grouper. CMS publishes a grouper package per fiscal year and, for most years, a point release partway through it. The formula tables, code attributes, exclusions and hospital-acquired condition lists all belong to one package, so two dates can classify the same facts differently.

Advanced · FY2027 · CURRENT · Reviewed October 1, 2026

What Is an HCC, and What Does the CMS-HCC V28 Mapping Tell a Coder About an ICD-10-CM Code?

A Hierarchical Condition Category (HCC) is a group of diagnoses that CMS’s risk-adjustment model treats as one condition. The CMS-HCC V28 mapping, published by CMS for payment year 2026, assigns some ICD-10-CM codes to a category; most codes are assigned to none. The mapping is a consequence of the code, not an instruction to select it: code what the provider documented, to the specificity the record supports, and the category follows.

Advanced · FY2027 · CURRENT · Reviewed October 5, 2026