Pathology/Lab Coding Alert

Answer: The D-dimer test code is 85378 (Fibrin degradation products, D-dimer; qualitative or semiquantitative) or 85379 (… quantitative), depending on whether the test involves a quantitative measure.

Whether the lab report lists the result as positive or negative, you’d use 85378 for the first test because the test simply indicates a qualitative or semiquantitative finding, typically with a break point of greater or less than 0.50 mg/L of fibrinogen equivalent units (FEU). However, as you state the measured value of the second test was 0.7 mg/L FEU, a better code choice for that test would be 85379.

Multiple units: You should be able to get paid for two D-dimer tests on the same date of service. The National Correct Coding Initiative (NCCI) Medically Unlikely Edits (MUE) lists the code limit as two.

Also, the MUE Adjudication Indicator (MAI) for these codes is 3. The NCCI Policy Manual states that Medicare contractors may bypass MUEs with an MAI of 3 during claims processing if they “have evidence (e.g. medical review) that UOS [units of service] in excess of the MUE value were actually provided, were correctly coded, and were medically necessary.”

Solution: Even though you haven’t surpassed the MUE limit, your payer may expect you to list the additional lab test code with modifier 91 (Repeat clinical diagnostic laboratory test). Follow your payer’s guidance on this point to get paid for correctly performed and documented lab tests.