83540

Iron, Serum

CPT code 83540 describes a quantitative clinical laboratory test performed to measure the concentration of iron within the serum portion of a patient's blood. Serum iron refers specifically to the iron that is currently being transported in the blood, almost entirely bound to the protein transferrin. This measurement is a fundamental component of what is collectively known as iron studies, which provide a comprehensive view of a patient's iron metabolism and storage. Iron is an essential element for human health, as it is a central component of hemoglobin in red blood cells, which facilitates oxygen transport, and myoglobin in muscle tissue. The procedure involves a standard venipuncture to collect blood, typically in a serum-separator tube (SST) or a plain red-top tube. In the laboratory, the blood is centrifuged to separate the serum. The analytical process involves several biochemical steps: first, the iron is dissociated from its carrier protein, transferrin, using an acidic reagent. Next, the ferric iron (Fe3+) is reduced to ferrous iron (Fe2+). Finally, a chromogenic reagent is added which reacts with the ferrous iron to produce a colored complex. The intensity of this color is measured via spectrophotometry at a specific wavelength, and the concentration of iron is calculated by comparing the absorbance to a known standard. Results can be affected by diurnal variation, recent dietary intake, or iron supplementation, which is why fasting morning samples are preferred for clinical accuracy. This test is essential for diagnosing iron deficiency anemia, monitoring iron overload conditions like hemochromatosis, and evaluating chronic illnesses that sequestration iron.

Clinical Indications

  • Diagnosis of iron deficiency anemia
  • Evaluation of suspected hemochromatosis (iron overload)
  • Monitoring patients on iron replacement therapy
  • Screening for lead poisoning in pediatric patients
  • Differential diagnosis of microcytic anemias
  • Assessment of nutritional status in malabsorption syndromes
  • Evaluation of chronic fatigue and weakness
  • Monitoring patients with chronic kidney disease
  • Investigation of suspected liver disease

Procedure Steps

  1. Verify patient identity and ensure appropriate pre-test preparation (e.g., fasting).
  2. Perform venipuncture to collect a venous blood sample into a serum-separator tube or red-top tube.
  3. Allow the blood specimen to clot completely at room temperature.
  4. Centrifuge the specimen to separate the serum from the cellular components.
  5. Aspirate the serum and transfer it to an analyzer-compatible aliquot tube.
  6. Introduce the serum into an automated chemistry analyzer.
  7. Apply an acidic buffer to dissociate iron from the transferrin protein.
  8. Add a reducing agent to convert ferric iron to its ferrous state.
  9. Mix with a chromogen (such as ferrozine or bathophenanthroline) to create a color reaction.
  10. Measure light absorbance using spectrophotometry.
  11. Calculate the serum iron concentration based on the absorbance values and calibration curves.
  12. Report the final concentration in micrograms per deciliter (mcg/dL).

Coding Guidelines

  • CPT 83540 should be reported for the measurement of serum iron only.
  • Do not use 83540 to report total iron-binding capacity (TIBC); use CPT 83550 for that measurement.
  • Ferritin measurement is reported separately using CPT 82728.
  • Transferrin measurement is reported separately using CPT 84466.
  • If a collection of iron-related tests is performed, check for specific panel codes, although serum iron is frequently billed as a standalone component alongside TIBC.
  • Phlebotomy (36415) may be reported separately depending on the payer and the setting in which the blood was drawn.
  • Modifier 91 may be applied if a repeat iron test is medically necessary on the same day for the same patient.

Associated ICD-10 Codes