CPT code 85379 – D-dimer quantitative test

Key takeaways

CPT code 85379 covers quantitative D-dimer testing, meaning any assay that reports a numeric result.

Qualitative or semiquantitative assays take 85378, or 85380 when the assay is ultrasensitive.

Paired ICD-10 codes include R79.1 (abnormal coagulation profile), I26.x (pulmonary embolism) and I82.4x (DVT).

Only one code from the 8537x family belongs on a claim per specimen, and billing two for one specimen is a bundling error.

Pabau’s claims management software flags bundling conflicts and incomplete diagnosis pairings before submission.

CPT code 85379: Official descriptor and code category

CPT code 85379 is a Pathology and Laboratory code published by the American Medical Association (AMA) under the Hematology and Coagulation subsection (codes 85002-85999). Its full official descriptor is: Fibrin degradation products, D-dimer; quantitative.

The code has remained stable across recent code-year updates. It covers any laboratory method that produces a numeric D-dimer result, including high-sensitivity quantitative assays. Common methods are latex-enhanced immunoturbidimetry and ELISA. A qualitative or semiquantitative screen belongs to 85378, or to 85380 when the assay is ultrasensitive.

Clinical indications: When CPT 85379 medical necessity applies

Payers recognize CPT 85379 as medically necessary when the clinical record documents a specific sign or symptom driving the order. The most common reasons payers accept as medical necessity include:

• Pulmonary embolism rule-out: Pleuritic chest pain, sudden dyspnea, or hemoptysis, particularly when combined with a Wells score calculation documenting pre-test probability
• Deep vein thrombosis workup: Unilateral leg swelling or calf tenderness, with or without a Wells DVT score
• DIC monitoring: Suspected disseminated intravascular coagulation in the context of sepsis, major trauma, or obstetric complications
• Post-operative VTE surveillance: Serial D-dimer after orthopedic or major abdominal procedures in high-risk patients
• Sepsis-related coagulopathy: Rising D-dimer as part of an acute-phase coagulation panel in ICU or hospital settings

A symptom-based ICD-10 code is acceptable when PE or DVT has not yet been confirmed. Payers understand that the test is ordered during the diagnostic workup, before a definitive diagnosis exists. What matters is that the ordering rationale appears in the physician’s note.

CPT 85379 vs 85378 vs 85380: Choosing the right code

Selecting the wrong code from the 8537x family is a frequent billing error on D-dimer claims. The correct code depends entirely on the methodology the laboratory used, not on the clinical result or the ordering context.

Check the lab report first. If the result is a single number in ng/mL FEU or μg/mL with no tier or range qualifier, CPT code 85379 is correct. That holds for high-sensitivity quantitative assays too, because 85380 is not a quantitative code. Confirm with the laboratory before billing if the report wording is ambiguous. The decision path below shows how the report format settles the code.

ICD-10 codes commonly paired with CPT 85379

Every CPT code 85379 claim requires a paired ICD-10 diagnosis that establishes why the test was ordered. Missing or non-specific diagnoses are another frequent denial driver. Check your Medicare Administrative Contractor (MAC) Local Coverage Determination for D-dimer or coagulation testing, since covered diagnosis lists vary by jurisdiction. You can look up the full descriptor for each diagnosis below in the ICD-10-CM code library.

Code the confirmed diagnosis once it is documented. A sepsis patient with confirmed DIC, for example, is billed with D65 on later serial D-dimer claims rather than R79.1.

Medicare and commercial payer reimbursement for CPT 85379

CPT code 85379 is reimbursed under the Medicare Clinical Laboratory Fee Schedule (CLFS), not the Physician Fee Schedule (MPFS). Clinical laboratory tests such as 85379 are paid under the CLFS, although some pathology services pay under the MPFS. Check the CMS Clinical Laboratory Fee Schedule files for the current national limitation amount, since CLFS rates are updated each year.

Medicare pays the lower of the CLFS national limitation amount or the billed charge. Commercial payers may reimburse above or below the CLFS rate depending on their contracted schedule. When you submit through a clearinghouse, the electronic remittance advice confirms which CLFS-based rate was applied. Billing teams can then reconcile payment without cross-referencing the CMS fee file by hand.

Documentation requirements to support medical necessity

A lab order slip alone does not satisfy payer audit requirements for CPT code 85379. The medical record must show the full chain from symptom to result. Follow medical billing compliance best practices and make sure each of these elements appears in the chart before submitting:

• Ordering physician’s clinical rationale: A note entry naming the symptom or sign that prompted the order, such as “acute onset pleuritic chest pain, SpO2 94%”
• Pre-test probability scoring: A Wells score or modified Wells DVT score in the note strengthens medical necessity for PE or DVT indications. Payers increasingly expect it in outpatient settings
• Lab report confirming quantitative output: The result must show a numeric value (ng/mL FEU or μg/mL), not a positive/negative flag. That confirms CPT 85379 rather than 85378 was the correct code
• Treating provider’s interpretive note: A sentence in the progress note or assessment that references the D-dimer result and explains how it influenced the clinical decision
• Repeat testing justification: If the test is ordered more than once in a short period, the note must document what changed clinically. That could be a rising result with unchanged symptoms, or a new clinical event

For Medicare patients, check whether your MAC has issued a Local Coverage Determination for D-dimer or coagulation testing. LCD criteria vary by jurisdiction, so a diagnosis that satisfies one MAC’s covered-diagnosis list may not satisfy another.

Common claim denial reasons for CPT 85379 and how to fix them

CPT code 85379 denials are predictable. The same five patterns recur across payers, and each has a defined corrective action. Effective denial management workflows catch most of these before the claim leaves the practice.

• Wrong code billed (85378 or 85380 instead of 85379): Pull the original lab report. If the result is numeric, rebill with 85379, whatever the assay’s sensitivity. Attach the lab report if your payer accepts it as a supporting document. If the assay was qualitative or semiquantitative, the denial is correct and 85378 or 85380 is the right code.
• Missing or non-specific ICD-10 pairing: A claim submitted without a diagnosis, or with an unrelated diagnosis such as a routine check-up code, will deny. Append R79.1, I26.x, or I82.4x as appropriate and resubmit. Verify the paired code against your MAC’s LCD before resubmitting.
• Medical necessity not documented: When the payer requests records, submit the physician’s note showing the specific symptom, any Wells score, and the interpretive note. If the chart lacks these elements, a retrospective addendum by the ordering physician may support the appeal. Prospective documentation is always preferable.
• Duplicate billing: Two 85379 claims for the same patient on the same date will trigger an edit. If the repeat test was clinically justified, document the changed clinical circumstance in the chart and file an appeal with that documentation attached.
• Panel unbundling error: If a panel code that already includes a D-dimer component was also billed, 85379 will deny as a component of the panel. Review whether a DIC or coagulation panel code was submitted in the same claim and remove the unbundled line.

For systematic denial prevention, your pre-submission workflow should check two points before the claim is batched. One is the code family, with one 8537x code per specimen, and the other is the ICD-10 pairing. A clean claim submission that passes payer edits first time costs far less to process than one that needs an appeal.

Bundling rules and code combinations for CPT 85379

Only one code from the 8537x D-dimer family belongs on a claim for a single specimen. Billing 85378 and 85379 for the same specimen is a bundling error under the National Correct Coding Initiative (NCCI). If two separate specimens were genuinely tested, check the pair’s modifier indicator in the current NCCI tables before billing both.

CPT code 85379 can generally be billed on the same day as other coagulation tests when the clinical situation warrants a full coagulation panel. Common partners are 85610 for prothrombin time, 85730 for partial thromboplastin time, and 85384 for fibrinogen. However, NCCI edit tables are updated quarterly. Verify current edit pairs via the CMS NCCI tool before billing any combination. A pairing that was permitted last quarter may become an edit in the next update.

• One of 85378, 85379 or 85380: Only one D-dimer code per specimen
• Compatible with PT (85610): Commonly billed together in DIC panels and VTE workups
• Compatible with PTT (85730): Standard coagulation panel combination
• Compatible with fibrinogen (85384): DIC monitoring typically includes D-dimer and fibrinogen together
• Check panel codes: If a panel CPT was also billed, confirm 85379 is not already part of it before adding a separate line

Use the AAPC Codify CPT lookup to check current NCCI edit status for any code pair before billing.

Prior authorization and ABN requirements

CPT code 85379 does not typically require prior authorization for acute inpatient or emergency presentations. When a patient presents with acute chest pain or leg swelling, most payers process the claim on a standard medical-necessity review after the fact.

Outpatient and repeated testing is a different story. Some commercial payers require prior authorization for serial outpatient D-dimer testing. This applies particularly when the test is ordered more than twice in a 30-day period. Check the specific plan’s coverage policy before submitting a series of claims.

For Medicare patients, an Advance Beneficiary Notice of Noncoverage (ABN) may be required when the clinical indication may not meet your MAC’s LCD coverage criteria. Common triggers include ordering 85379 for a non-covered indication or when repeat testing lacks documented clinical justification.

Consult the CMS ABN instructions or your compliance officer for the specific situations that require an ABN in your jurisdiction. The CMS CLFS files give you the current national limitation amount to quote when issuing an ABN for this code.

How claims management software prevents CPT 85379 denials

Many D-dimer denials start before the claim is built. A coder picks a code without opening the lab report, or the diagnosis in the note never reaches the claim line.

Pabau, the practice management platform we build, catches both before submission. Its claims management software flags incomplete ICD-10 pairings, bundling conflicts within the 8537x family, and duplicate billing.

Clean claims then go out through Pabau’s Claim.MD integration, which reaches thousands of US payers. Remittance advice comes back into the same system, so your team reconciles CLFS payments without a separate spreadsheet.

Stop D-dimer claims from denying on first submission

Pabau’s claims management tools flag incomplete ICD-10 pairings, bundling conflicts, and duplicate billing before a claim leaves your practice. See how it works for laboratory billing teams.

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Conclusion

Code CPT 85379 from the lab report, not from the order. A numeric result means 85379, whatever the assay’s sensitivity. A positive/negative or tiered result means 85378, or 85380 when the assay is ultrasensitive.

Build that check into charge entry, and pair every claim with the symptom or diagnosis in the note. Those two habits remove the denial patterns this code is known for. The trade-off is a minute of checking per claim against weeks of appeal work.

Book a demo to see how Pabau checks D-dimer code selection and diagnosis pairing before your lab claims go out.

Continue your research

Need to understand how claims flow through a clearinghouse? Medical claims clearinghouse guide explains how electronic claims are validated and routed to payers.

Want to reduce repeat denials across your lab billing? Medical billing fundamentals covers the full claim lifecycle from charge capture to payment posting.

Got a CARC code back on a D-dimer claim? Denial codes in medical billing maps the most common CARC denial reasons to their corrective actions.

Billing a PTT alongside the D-dimer? CPT code 85730 covers partial thromboplastin time coding, documentation and payment.

Appealing a denied lab claim? Medical appeal form template gives you a structured letter for submitting supporting documentation.

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