Prolonged Clot Time Reflexive Profile

Content Review: April 2023 Last Update:
  • Use to evaluate prolonged clotting times such as PT and/or aPTT when cause is unknown
  • Most useful for the workup of patients with unexpected prolonged clotting times
  • Condition-specific testing is preferred when the patient has a known coagulation disorder or a clear bleeding presentation
  • Reflexive panel includes basic clotting times (PT, aPTT, dilute Russell viper venom time [DRVVT]), lupus anticoagulant testing, fibrinogen, and d-dimer

Clotting time tests such as prothrombin time (PT) and/or activated partial thromboplastin time (aPTT) are commonly used for a variety of reasons, including workup of a bleeding tendency, as part of a presurgical evaluation, as guidance for blood product replacement, or to monitor anticoagulant medication.  Prevalence of prolonged clotting time varies depending on the setting and on patient- and laboratory-specific factors. Prolonged clotting times of unclear etiology may require further evaluation to determine cause and to exclude clinically significant bleeding disorders.  The Prolonged Clot Time Reflex Panel provides a comprehensive workup to determine the etiology of prolonged clotting times, including lupus anticoagulants and factor deficiencies or inhibitors. In rare circumstances in which a definitive cause for prolonged clotting time is not identified by testing available within the panel, appropriate follow-up testing will be recommended in the customized panel interpretation.

Typical Testing Strategy

Based on the patterns observed in this reflex test, additional studies may be recommended by ARUP Hemostasis/Thrombosis medical directors, such as coagulation factor assays and von Willebrand factor testing.

Disease Overview


Symptoms associated with prolonged clotting times depend on the underlying etiology.

  • Patients with an LA:
    • May be asymptomatic or may have elevated thrombotic risk  (if LA is associated with antiphospholipid syndrome)
    • Generally are not at increased risk for bleeding
  • Patients with a factor deficiency or inhibitor are at increased risk for bleeding 

Diagnostic Issues

  • This reflexive panel was designed to evaluate prolonged clotting times (as detected by tests such as PT and/or aPTT), particularly in presurgical or other settings where there is not strong clinical or other laboratory evidence that suggests a specific coagulation disorder
  • Panel benefits include:
    • Greater standardization and cost-effectiveness in the assessment of prolonged clotting times
    • More timely diagnosis and avoidance of  multiple rounds of testing and multiple phlebotomies for the patient
    • Expert interpretation by medical directors who supervise the lab performing the testing
  • A patient history form submitted with the test order allows for optimal panel interpretation and correlation with the clinical setting
  • Patients with a known coagulation disorder or strong clinical or other laboratory evidence of a specific coagulation disorder (such as a clear bleeding presentation) should be offered condition-specific testing


  • Clotting times tests, such as PT and/or aPTT, enable evaluation of coagulation reactions and are dependent on :
    • The presence and function of coagulation factors, including fibrinogen
    • Phospholipid support for the coagulation reactions
    • Calcium availability (affected by specimen collection tube/anticoagulant)
  • Problems with any of these components can result in clotting time prolongation

Test Interpretation


  • Reflexive test selection and panel interpretation are performed by ARUP Hemostasis/Thrombosis medical directors
  • Customized panel interpretation includes the clinical significance of any abnormalities identified and recommendations for follow-up testing, if indicated
  • Reference intervals will be provided for each test performed, including age-stratified reference intervals, when appropriate


  • Anticoagulant medications may interfere with testing and cause erroneous results 
  • Recent transfusion or factor replacement may affect results
  • Results may be inaccurate in the event of inappropriate specimen collection and handling
    • Clotted specimens (serum specimen or traumatic venipuncture)
    • Line draws (specimen may be contaminated with heparin or IV fluids)
    • Incorrect anticoagulant (anything other than sodium citrate plasma)