N15.1

Renal and perinephric abscess

A renal abscess is a localized collection of purulent material within the renal parenchyma, often as a complication of severe pyelonephritis. When the infection extends through the renal capsule into the space between the kidney and the surrounding Gerota's fascia, it is defined as a perinephric abscess. These conditions represent serious, potentially life-threatening infections of the upper urinary tract. Most renal abscesses result from ascending urinary tract infections caused by gram-negative organisms like Escherichia coli or Klebsiella species. However, hematogenous spread from distant sites, such as the skin or heart, can lead to abscesses primarily caused by Staphylococcus aureus. Patients with diabetes, renal calculi (stones), or structural abnormalities of the urinary tract are at a significantly higher risk. Diagnosis is typically confirmed via contrast-enhanced CT imaging, which reveals a well-defined, low-attenuation fluid collection. Management requires a combination of prolonged intravenous antibiotic therapy and, in many cases, percutaneous or surgical drainage of the abscess collection.

Clinical Symptoms

Unilateral or bilateral flank pain
High-grade fever
Chills and rigors
Costovertebral angle (CVA) tenderness
Palpable abdominal or flank mass
Dysuria
Malaise and generalized fatigue
Nausea and vomiting
Weight loss
Night sweats
Tachycardia
Persistent leukocytosis
Hematuria

Common Causes

Ascending urinary tract infection
Acute pyelonephritis
Nephrolithiasis (kidney stones) causing urinary obstruction
Diabetes mellitus
Hematogenous bacterial seeding from skin infections or endocarditis
Vesicoureteral reflux
Structural urinary tract abnormalities
History of urological surgery or instrumentation
Polycystic kidney disease with cyst infection
Immunocompromised status

Documentation & Coding Tips

Specify the causal infectious organism to allow for secondary code assignment.

Example: Patient with right-sided renal abscess found to have Escherichia coli on aspirate culture. Assessment: Right renal abscess (N15.1) due to E. coli (B96.20). Billing Focus: Identification of the specific pathogen. Risk Adjustment: The presence of an infectious agent increases the clinical complexity of the encounter.

Billing Focus: Infection etiology and pathogen linkage.

Document the precise anatomical location and laterality even if the code N15.1 is not specific by laterality.

Example: CT imaging reveals a 4cm multiloculated abscess in the left renal cortex and extension into the perinephric fat. Assessment: Left renal and perinephric abscess (N15.1). Billing Focus: Anatomical specificity for surgical planning and CPT linkage. Risk Adjustment: Higher severity linked to extra-renal extension.

Billing Focus: Laterality and specific renal compartment involvement.

Clearly document any underlying obstructive conditions such as nephrolithiasis or ureteral strictures.

Example: The patient presents with a renal abscess secondary to an obstructing 8mm stone in the proximal ureter. Assessment: Renal abscess (N15.1) with calculus of the ureter (N20.1). Billing Focus: Comorbid obstructive uropathy. Risk Adjustment: Multiple related renal conditions indicate high medical decision making and chronic disease management.

Billing Focus: Causal obstructive factors.

Link systemic inflammatory response syndrome (SIRS) or sepsis if clinically present.

Example: Patient presents with fever, tachycardia, and leukocytosis. Clinical diagnosis: Sepsis due to renal abscess. Assessment: Sepsis due to E. coli (A41.51) and renal abscess (N15.1). Billing Focus: Sepsis as the primary diagnosis. Risk Adjustment: High-tier HCC 2 (Sepsis) with N15.1 as the underlying source.

Billing Focus: Systemic manifestations of the localized abscess.

Detail the clinical status of associated diabetes mellitus, which is a common risk factor.

Example: Patient with Type 2 DM and chronic kidney disease stage 3 presents with renal abscess. Assessment: Renal abscess (N15.1), Type 2 DM with CKD (E11.22), CKD stage 3 (N18.31). Billing Focus: Diabetic complications. Risk Adjustment: Comorbid diabetes with CKD and acute infection creates a very high-risk profile.

Billing Focus: Underlying metabolic comorbidities.

Relevant CPT Codes

99214 - Office or other outpatient visit for the evaluation and management of an established patient, which requires a moderate level of medical decision making
Typically used for follow-up of a renal abscess requiring ongoing antibiotic monitoring and review of imaging.
99204 - Office or other outpatient visit for the evaluation and management of a new patient, which requires a moderate level of medical decision making
Initial consultation for a complex renal infection with potential for surgical intervention.
49405 - Image-guided fluid collection drainage by catheter (eg, abscess, hematoma, seroma, lymphocele, cyst); visceral (eg, kidney, liver, spleen, lung/mediastinum), percutaneous
Standard procedure for draining a renal abscess larger than 3-5 cm.
74177 - Computed tomography, abdomen and pelvis; with contrast material(s)
Gold standard for diagnosing and characterizing the extent of renal and perinephric abscesses.
50020 - Drainage of perirenal or renal abscess; open
Required for complex or multiloculated abscesses that fail percutaneous drainage.
10061 - Incision and drainage of abscess (eg, carbuncle, suppurative hidradenitis, cutaneous or subcutaneous abscess, cyst, furuncle, or paronychia); complicated or multiple
Used for external drainage of associated subcutaneous tracks if the abscess ruptures through the flank.
99213 - Office or other outpatient visit for the evaluation and management of an established patient, which requires a low level of medical decision making
Used for stable follow-up of a resolving abscess with a straightforward course.
50391 - Instillation(s) of therapeutic agent into renal pelvis and/or ureter through established nephrostomy, pyelostomy, or ureterostomy tube
Occasionally used for direct antibiotic delivery in refractory cases.
76770 - Ultrasound, retroperitoneal (eg, renal, aorta, nodes), real time with image documentation; complete
Often the initial screening tool for renal masses and collections.
87070 - Culture, bacterial; any other source except urine, blood or stool, with isolation and presumptive identification of isolates
Essential for identifying the pathogen and determining antibiotic sensitivity.