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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Prothrombin Time/INR

Test Code(s): PROX / PT

CPT Code(s): 85610

Methodology: Mechanical Clot Detection

Days Performed: Daily, 24 hours.

Turnaround Time: Stat: 1 hour.
Routine: 4 hours.

Specimen Requirements

Specimen: Blood

Collection Instructions: The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factors and platelets. Tube MUST be allowed to fill up to "fill" line indicated on tube.

If unable to collect 1.8 ml tube (pediatrics only) please call Core Coagulation Lab at 263-9617 or Special Coagulation Lab at 263-5005 for alternate tube and instructions.

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: 3.5 mL
Pediatrics: 1.8 mL

Sample Analyzed: Plasma

Volume Required: Preferred: 0.5 mL
Pediatrics: 0.5 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma (platelet count should be less than 10K/uL). Separate plasma and transfer to plastic tube or vial. Freeze plasma at -20C or below.

Specimen Transport: Transport whole blood specimen on an unopened tube at room temperature to the laboratory within 24 hours of collection. Specimens that have been opened and spun must be less than 4 hours old when received by the laboratory.  Otherwise, transport frozen plasma aliquot on dry ice.

Unacceptable Criteria: Grossly hemolyzed specimens, clotted specimens, partially filled tubes and specimens greater than 24 hours old when received by the laboratory are not acceptable.

Stability: Ambient: 24 hours if unspun; 4 hours if spun and opened
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Reference Interval:
 0 days - 6 months:  0.8-1.2
 7 months and up:  0.9-1.1

Critical Calls: View

Additional Information:

INR is the International Normalized Ratio which takes into account the instrumentation and reagent system used at UWHC. The INR is intended to standardize reporting of the prothrombin time. For patients NOT on anticoagulants, the reference range for the INR is 0.9 -1.1. The recommended therapeutic range for oral anticoagulant therapy is INR of 2.0-3.0. (Exception: The recommended range for patients with a mechanical mitral valve or patients with mechanical valves in both aortic and mitral position is an INR of 2.5-3.5) Reference: CHEST 2012; 141 pgs e5925-e5945.

PT Protime International Normalized Ratio INR

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