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Specimen Collection Manual and Test Catalog

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PT INR

Geisinger Epic Procedure Code:  LAB2946    Geisinger Epic ID:  14539

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: 

1 mL


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 the first 10 mL of blood.
  • 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
Processing instructions: 

Only PT INR AND analysis = 24 hours of collection, store and transport as whole blood at room temperature. 

Multiple plasma coagulation assays OR analysis > 24 hours after collection, centrifuged specimen within 60 minutes of collection using the designated time and speed to produce platelet-poor plasma (<10,000/µL platelets). Transfer the plasma to a clean tube and re-centrifuge for 10 minutes to obtain platelet-free plasma. Remove platelet-free plasma into aliquot tubes (see below) and freeze.

  • All aliquot(s) should be 1.0-1.9mL.
  • 1 tube typically yields 1 aliquot. 
  • Multiple tubes, create 1 aliquot for each tube collected plus 1 additional aliquot.
  • Transfer plasma coagulation test(s) to aliquot tube(s).

Transport temperature: 

Whole blood: Room temperature 
Plasma: Frozen on dry ice


Specimen stability: 

Room temperature: 24 hours 
Frozen -20°C: 2 weeks 
Frozen -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: Specimen 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 11.6 – 15.2 
INR 0.8 – 1.2


Critical values/courtesy alerts: 
INR greater than 4.99
Additional information: 

Anticoagulation Impact on Coagulation Tests


CPT code(s):  85610
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: 

PT, INR


Methodology: 
Mechanical clot-based
Synonyms: 

INR, PTINR, Protime, Prothrombin Time, International Normalized Ratio


Clinical significance: 

Screening test used to assess the extrinsic and common clotting pathways. Prolonged PT may be associated with bleeding and could indicate one or more deficiencies of plasma factors VII (most common), X, V, II, and fibrinogen (only if less than 100 mg/dL), and/or a possible inhibitor (factor dependent or lupus anticoagulant) as well as a vitamin K deficiency (from dietary or intestinal reabsorption disorders). Diseases often associated with prolong PT include liver failure and disseminated intravascular coagulopathy (DIC).

Medications may also prolong PT including warfarin, direct thrombin inhibitors, direct Xa inhibitors, vitamin K antagonist and antibiotics that prevent vitamin K absorption. An INR is the standardized measurement used to monitor warfarin.

Warfarin Therapeutic Ranges: 
INR: 2.0-3.0 conventional anticoagulation
INR: 2.5-3.5 high intensity anticoagulation.

If patient has a lupus anticoagulant and a prolong PT, the INR may not be accurate and an alternative test for monitoring warfarin should be considered.


Doctoral Director(s): 
Michelle Grant DO
Review Date:  09/03/2026

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