Geisinger Medical Laboratories Test Catalog

Order Display Name: Geisinger Epic Procedure Code Or ID CPT Code:  

PT/APTT MIXING STUDIES

Geisinger Epic Procedure Code: LAB2948             Geisinger Epic ID: 14541
       

SPECIMEN COLLECTION
Specimen type:
 Platelet-poor plasma
Preferred collection container:
Alternate Collection Container:
Other size blue-top (3.2% sodium citrate) tubes (e.g., 1.8 mL, 4.5 mL)
Specimen required:
Two (2) 1 mL aliquots
Special notes:
  • If the patient’s hematocrit (HCT) is >55%, the volume of anticoagulant in the tube must be adjusted. Contact a performing location for sodium citrate adjusted tubes or instruction for how to adjust the sodium citrate.
  • When possible, use fresh venipuncture.
  • Avoid prolong tourniquet time (< 1 minute) and hemolysis during collection as this will alter results.
  • If indwelling catheter or butterfly collection device must be used, draw sample from a non-heparinized lumen or flush the line with 5 mL of saline and discard/use first 5-10 mL of blood for other purposes.
  • Tubes should be >90% filled.
  • Immediately mix gently after collection by inverting the tube end over end 5 to 6 times. Avoid vigorous mixing or additional inversion. Observe for the presence of clots or hemolysis and recollect if observed.
SPECIMEN PROCESSING
Specimen processing instructions:
Centrifuge specimen immediately at designated time and speed to obtain platelet-poor plasma (<10,000/µL). Using a plastic pipette, carefully remove plasma from cells, avoiding platelet/buffy layer by leaving a thin layer of plasma on top the cells. The centrifuged plasma should be aliquoted (1 mL per aliquot) into clearly labeled polypropylene tubes. The number of tests ordered will determine the aliquots needed. Check the residual specimen for clot and if present discard sample and redraw specimen. If plasma is icteric, lipemic or hemolyzed a lab comment should be generated to notify staff. Freeze upright in non-thaw freezer. 
Transport temperature:
 Frozen
Specimen stability:
 Room temperature: 4 hours
Frozen (plasma) -20°C: 2 weeks
Frozen (plasma) -70°C: 6 months
Rejection criteria:
 Clotted, hemolyzed, improperly filled tubes, improper anticoagulant ratio (HCT >55% and citrate not adjusted), refrigerated specimens, or stability exceeded.

Note: Specimens suspected of thawing in transport, indicated by slant in aliquot or specimen in lid of tube, will have testing performed, and the comment “interpret results with caution as thawing suspected” added to results.

TEST DETAILS
Reference interval:
 PT or PT heparin neutralized: PT 11.6-15.2 seconds
aPTT or aPTT heparin neutralized: 21-38 seconds
Interpretation guide:
 Correction of PT or aPTT is defined as test returning to reference range after mixture with normal pooled plasma or Rosner Index <15. Correction indicates a factor deficiency(s) state.
Partial or No Correction as seen with a Rosner index >15 suggests an inhibitor. Interpretation guidelines are built into the testing algorithm.
Additional information:
 Mixing study only performed if elevated PT and/or aPTT. If PT and/or aPTT normal only original value will be reported.
CPT code(s):
 85611
Note: The billing party has sole responsibility for CPT coding.  Any questions regarding coding should be directed to the payer being billed.  The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only.
Test includes:
 aPTT(Baseline/Mix); PT (Baseline/Mix), heparin level, heparin neutralization, thrombin time, and fibrinogen.
Baseline = patient plasma only.
Mix = patient plasma + normal control plasma tested immediately after mixing and again after a 60-minute incubation.
Methodology:
Mechanical clot-based
Synonyms:
PT/PTT Mixing Study
50/50 Mixing Study, A5050
Mixing Study
Clinical significance:
This test is used to investigate the cause of a prolonged aPTT and/or PT.
Doctoral Director(s:)
Michelle Grant DO    
Review Date: 03/31/2023

Performing Locations

Geisinger Medical Center

Performing laboratory: Coagulation
Technical Lead: Margaret Knowles-Tuchman
Frequency: Daily, 1st shift
Performed STAT? No

Geisinger Wyoming Valley Medical Center

Performing laboratory: ATL+
Technical Lead: Mary Glazenski    
Frequency: Monday-Friday 0600-1330, Saturday, Sunday 0600-1300    
Performed STAT? No
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