Prolonged Clot Time Reflex Panel

Prolonged Clot Time Reflex Panel 2014318
Method: Electromagnetic Mechanical Clot Detection/Qualitative Hemagglutination/Platelet Agglutination/Microlatex Particle-Mediated Immunoassay

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 a lupus anticoagulant (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 (PT and/or PTT), 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, avoiding multiple rounds of testing and multiple phlebotomies for the patient
    • Expert interpretation by medical directors supervising 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 PTT, 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 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)
  1. Kamal AH, Tefferi A, Pruthi RK. How to interpret and pursue an abnormal prothrombin time, activated partial thromboplastin time, and bleeding time in adults. Mayo Clin Proc. 2007; 82(7): 864-73. PubMed
  2. Kruse-Jarres R, Singleton TC, Leissinger CA. Identification and basic management of bleeding disorders in adults. J Am Board Fam Med. 2014; 27(4): 549-64. PubMed

Last Update: September 2019