85730

Thromboplastin time, partial (PTT); plasma or whole blood

CPT code 85730 refers to the Activated Partial Thromboplastin Time (aPTT) or Partial Thromboplastin Time (PTT) test, a functional screening assay used to evaluate the efficiency of the intrinsic and common pathways of the blood coagulation cascade. This procedure involves measuring the time, in seconds, required for a fibrin clot to form in a plasma sample after specific reagents are added. Specifically, the test evaluates several clotting factors, including Factor XII (Hageman factor), Factor XI, Factor IX (Christmas factor), and Factor VIII (antihemophilic factor), as well as factors within the common pathway such as Factor X (Stuart-Prower factor), Factor V (proaccelerin), Factor II (prothrombin), and Factor I (fibrinogen). Clinically, the aPTT is most frequently utilized to monitor the therapeutic efficacy and safety of unfractionated heparin (UFH) anticoagulation, as heparin enhances the activity of antithrombin III, which in turn inhibits factors IIa and Xa, leading to a prolonged aPTT. Beyond medication monitoring, 85730 is essential in the diagnostic workup of patients with unexplained bleeding, recurrent miscarriages (associated with lupus anticoagulants), or a family history of hemophilia. In the laboratory setting, the test is performed on citrated plasma. The addition of a contact activator (such as silica, kaolin, or ellagic acid) and phospholipids (acting as a platelet substitute) initiates the intrinsic pathway, followed by the addition of calcium chloride to trigger clot formation. A prolonged result may indicate a deficiency or inhibitor of one or more of the aforementioned factors, whereas a shortened result may occasionally reflect a prothrombotic state. This code is distinct from CPT 85610 (Prothrombin Time), which assesses the extrinsic pathway.

Clinical Indications

  • Monitoring of unfractionated heparin (UFH) therapy
  • Screening for congenital bleeding disorders such as Hemophilia A (Factor VIII) and Hemophilia B (Factor IX)
  • Preoperative coagulation screening to assess bleeding risk
  • Investigation of unexplained bruising, epistaxis, or excessive surgical bleeding
  • Evaluation of suspected Von Willebrand disease (VWD)
  • Detection of circulating anticoagulants or inhibitors such as lupus anticoagulant
  • Assessment of liver disease impact on coagulation factor production
  • Evaluation of disseminated intravascular coagulation (DIC)

Procedure Steps

  1. Collection of venous blood into a tube containing 3.2% buffered sodium citrate (light blue top tube)
  2. Centrifugation of the specimen at high speed to obtain platelet-poor plasma
  3. Incubation of the patient's plasma with a standardized amount of phospholipid (partial thromboplastin) and a surface activator (e.g., silica, kaolin, or ellagic acid)
  4. Addition of calcium chloride to the mixture to re-calcify the plasma and initiate the clotting process
  5. Measurement of the time interval from the addition of calcium until the visual or automated detection of a fibrin clot
  6. Comparison of the patient's clotting time against a laboratory-established reference range or control sample

Coding Guidelines

  • Report 85730 for a standard partial thromboplastin time (PTT) on plasma or whole blood
  • Do not use 85730 for a PTT substitution/mixing study; instead, use CPT 85732
  • If the test is repeated on the same day for clinical monitoring (e.g., titration of heparin), append modifier 91
  • This code includes the automated or manual calculation of the time to clot
  • When performed as part of a preoperative panel, ensure the appropriate Z-code is listed as the primary diagnosis
  • 85730 is frequently billed alongside 85610 (Prothrombin Time) for a comprehensive coagulation screen

Associated ICD-10 Codes