Davis's Lab & Diagnostic Tests

Prothrombin Time and International Normalized Ratio

Prothrombin Time and International Normalized Ratio is a topic covered in the Davis's Lab & Diagnostic Tests.

To view the entire topic, please or purchase a subscription.

Davis’s Laboratory and Diagnostic Tests Online, powered by Unbound Medicine, provides nurses and students access to 400+ test monographs containing reference ranges, indications, patient preparation and result interpretation. Explore these free sample topics:


-- The first section of this topic is shown below --


Protime, PT, and INR.

Common Use:
To assess and monitor coagulation status related to therapeutic interventions and disorders such as vitamin K deficiency.

Plasma collected in a completely filled blue-top (sodium citrate) tube. If the patient’s hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.

Normal Findings:
(Method: Clot detection) 10 to 13 sec.

  • International normalized ratio (INR) = 0.9 to 1.1 for patients not receiving anticoagulation therapy; 2 to 3 for patients receiving treatment for venous thrombosis, pulmonary embolism, and valvular heart disease.
  • INR = 2.5 to 3.5 for patients with mechanical heart valves and/or receiving treatment for recurrent systemic embolism.
  • For patients receiving anticoagulants, therapeutic levels of warfarin are achieved by adjusting the dosage so the prothrombin time (PT) value is 1.5 to 2.5 times longer than normal or so the INR is between 2 and 3.

-- To view the remaining sections of this topic, please or purchase a subscription --