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Test Code Billings Clinic: 2035 Protime (PT), Plasma

Performing Laboratory

Billings Clinic Laboratory: Coagulation

Useful For

Used to screen for hemostatic disorders involving fibrin formation and to monitor the effectiveness of oral anticoagulant therapy.

Methodology

Optical

Specimen Requirements

  • Draw blood in a light blue-top (3.2% sodium citrate) tube.
  • Immediately after draw, gently invert tube(s) at least 6 times to mix well.
  • Spin down, remove plasma, spin plasma again, and place 1 mL of citrate platelet-poor plasma in plastic vial.
  • Glass vial is not acceptable.
  • Double-centrifuged specimens are critical for accurate results as platelet contamination may cause spurious results.
  • Freeze specimen immediately at -20° C.
  • Send specimen frozen.
  • Whole blood in the original blue tube can be sent UNSPUN at Room Temperature if the specimen will arrive prior to 24 hours from time of draw.

Storage/Stability

Specimen Type Temperature Time
Whole Blood Ambient (Preferred) 24 hours
Citrated Plasma Ambient (removed from cells immediately after centrifugation) 24 hours
  Frozen (-20oC) 2 weeks
  Frozen (-70oC) 12 months

Reference Values

Protime:

Call-back value: ≥43 seconds

 

INR:
2-3 (only for patients on oral anticoagulation)
Call-back value: ≥4.5

 

Reference values change with each new reagent lot (about once a year). Check with laboratory or refer to reference range on computer reports.

Day(s) Test Set Up

Daily

Test Classification and CPT Coding

85610 - Prothrombin time
 

LCD or NCD test. ICD-9 code is required for this test. When appropriate, obtain a properly executed ABN and submit the ABN with test order(s). See “Medical Necessity and Advanced Beneficiary Notice (ABN) Policy and Form” under Resources for a copy of a form and additional information.

LOINC Code Information

Reporting Name LOINC Code
Protime 5902-2
INR 6301-6