85384

Fibrinogen Activity Test

Fibrinogen activity, reported under CPT 85384, is a critical laboratory assay used to quantify the functional level of fibrinogen (Factor I) within the human coagulation system. Fibrinogen is a large, complex, hexameric glycoprotein synthesized primarily by hepatocytes in the liver. It plays a dual role in the body, serving as a key structural component of blood clots and as an acute-phase reactant. During the final stages of the coagulation cascade, the enzyme thrombin (Factor IIa) cleaves small peptides (fibrinopeptides A and B) from the fibrinogen molecule. This enzymatic action converts the soluble fibrinogen into insoluble fibrin monomers. These monomers then spontaneously polymerize to form a mesh-like network, which is subsequently cross-linked by Factor XIIIa to create a stable, solid blood clot. The 85384 procedure typically utilizes the Clauss method, which is the gold standard for measuring fibrinogen activity. In this functional assay, an excess concentration of thrombin is added to a sample of diluted patient plasma. By employing a high concentration of thrombin, the reaction rate becomes independent of any endogenous thrombin inhibitors (like heparin) or other coagulation factors present in the sample, and instead, the clotting time becomes strictly dependent on the concentration of functional fibrinogen. The time elapsed between the addition of thrombin and the detection of a physical clot is measured electronically or optically. This time is then compared against a standard calibration curve to determine the concentration of active fibrinogen in milligrams per deciliter (mg/dL). Clinically, this measurement is vital for diagnosing and managing various conditions. Low fibrinogen levels (hypofibrinogenemia) or the presence of dysfunctional fibrinogen (dysfibrinogenemia) can lead to significant bleeding risks. These may be inherited or acquired through conditions such as disseminated intravascular coagulation (DIC), where clotting factors are rapidly consumed, or severe liver disease, where synthesis is impaired. Conversely, elevated fibrinogen levels are often observed during pregnancy, systemic inflammation, or as a risk factor for cardiovascular disease. Monitoring these levels is essential for patients undergoing major surgery, those with unexplained hemorrhage, or individuals receiving thrombolytic therapy with agents such as streptokinase or tissue plasminogen activator (tPA). Unlike the fibrinogen antigen test (CPT 85385), which measures the total protein mass, CPT 85384 ensures the protein is actually capable of forming a clot.

Clinical Indications

  • Evaluation of unexplained bleeding or bruising episodes
  • Diagnosis of Disseminated Intravascular Coagulation (DIC)
  • Monitoring of fibrinolytic/thrombolytic therapy (e.g., tPA or streptokinase)
  • Assessment of hepatic synthetic function in severe liver disease
  • Screening for hereditary fibrinogen deficiencies (afibrinogenemia, hypofibrinogenemia, or dysfibrinogenemia)
  • Preoperative screening in patients with a history of bleeding diathesis
  • Evaluation of obstetric complications such as placental abruption
  • Assessment of acute-phase inflammatory responses

Procedure Steps

  1. Collection of venous blood into a vacuum tube containing 3.2% sodium citrate (blue top tube) to prevent premature clotting.
  2. Centrifugation of the blood sample at a standardized speed and duration to separate the cellular components and obtain platelet-poor plasma (PPP).
  3. Preparation of a 1:10 dilution of the patient's plasma using a specialized buffer solution to optimize the reaction kinetics.
  4. Warming of the diluted plasma and a standardized thrombin reagent to 37 degrees Celsius.
  5. Addition of a high concentration of bovine or human thrombin reagent to the diluted plasma sample.
  6. Automated or manual measurement of the exact time (in seconds) from the addition of thrombin until the first detection of fibrin strand formation.
  7. Interpolation of the measured clotting time against a laboratory-specific calibration curve, which is created using plasma standards of known fibrinogen concentrations.
  8. Reporting of the result in milligrams per deciliter (mg/dL) or grams per liter (g/L).

Coding Guidelines

  • CPT 85384 should be used for the quantitative measurement of fibrinogen activity (functional assay).
  • Do not use 85384 for the measurement of fibrinogen antigen (protein mass); instead, use CPT 85385.
  • If both activity (85384) and antigen (85385) are performed on the same day for the same patient, both codes may be reported to highlight a discrepancy (as seen in dysfibrinogenemia).
  • This code is a standalone laboratory procedure and is not bundled into the Prothrombin Time (PT - 85610) or Partial Thromboplastin Time (PTT - 85730) codes.
  • Ensure the laboratory is CLIA certified for high or moderate complexity testing as required for the specific methodology used.
  • If the fibrinogen is determined as part of a calculated value from a PT test (derived fibrinogen), check local payer policies, as some may not allow billing 85384 for a non-Clauss, calculated result.

Associated ICD-10 Codes