Geisinger Medical Laboratories Test Catalog

PT INR

• 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.

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.

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.