Click here for more information about laboratory operations and procedures
If you have additional questions regarding this test, please call: 415-353-1667
Prothrombin Time (Complete View)
|Test name||Prothrombin Time|
|Test Update Information|
|Test group||Prothrombin time|
|Performed by||Parnassus, Mission Bay & Mt. Zion Hematology|
|In House Availability||Test available 24 hours per day 7 days per week|
|Method||Mechanical clot detection|
|Collection Instructions||1. Check the expiration date on the label of the blue top vacutainer before drawing the patient
2. For blood collection in a sodium citrate blue top, the tube must be filled to above the Minimum Fill Indicator on the tube. It is crucial to wait and allow the tube to stop filling before removing it from the needle.
3. With use of a butterfly needle, draw about 1 cc using a separate blue top to remove air from tubing, discard the first tube and then draw a second blue top tube filled to the full extent of the vacuum.
4. Tubes should not be filled past the Maximum Fill dashed line by either using a syringe or removing the tube cap.
For patients with Hct's ≥ 55% please contact Hematology (For Parnassus patients call 3-1747, for Mission Bay patients call 6-0194) to obtain blue top tubes with adjusted citrate volumes in order to maintain the proper citrate to plasma ratio for coagulation studies.
|Container type||Blue (2.7 mL) or Lt. Blue (1.8 mL) top filled to full extent of vacuum|
|Amount to Collect||
|Sample type||Citrated plasma|
|Preferred volume||1.5 mL plasma|
|Min. Volume||1 mL plasma|
|UCSF Rejection Criteria||Samples collected in outdated blue top vacutainer.
Over-filled or under-filled samples may be rejected.
|Ref Lab Rejection Criteria|
|Normal range|| Parnassus & Mission Bay:
The PT of full-term normal infants does not appear to differ significantly from adults, although factor levels are somewhat lower in the first six months of life (Andrew, M et al. Development of the human coagulation system in the full-term infant. Blood. 70:165-172).
|Critical value||INR ≥ 5.0|
|Synonyms||PT; coumadin; warfarin; INR|
|Stability||Unopened, uncentrifuged specimens are stable for 24 hours at room temperature.|
|Turn around times||STAT 1 hour, Routine 4 hours|
|Additional information|| Current reagents permit the reporting of results up to 100 seconds; if no clot is detected by that time the result will be reported as > 100 seconds.
The International Normalized Ratio (INR) will be routinely reported in addition to the Prothrombin Time in seconds. The reagents, and therefore the reference range in seconds, differ among the various UC affiliated hospitals. However, the INR adjusts for the inherent variability of tissue thromboplastins employed in the assay.
Note: when the prothrombin time is just above the upper limit of the normal range, calculation of the INR can result in a normal INR. This reflects the rounding of decimals utilized in the INR calculation.
The INR is the parameter of choice in monitoring the adequacy of warfarin anti-coagulation, and should in theory remain stable. The appropriate therapeutic range will vary with the disease and treatment intensity desired. The UCSF Hematology Consultation service generally recommends as therapeutic range for warfarin: (a) INR of 2.5-3.5 for most mechanical valves or recurrent systemic embolism, (b) INR of 2.0-3.0 for most other indications. Recommendations for warfarin therapy and monitoring are available through the UCSF Hematology consultation services: for adults, pager 443-4276, for pediatrics pager 443-6966.
The Prothrombin Time contains a reagent that neutralizes heparin up to 2 U/mL.
Per in-house study done 05/2015, the sensitivity of the PT for detecting factor deficiencies is as follows:
In regard to samples drawn through heparinized lines: (i) the PT reagent neutralizes low levels of heparin and (ii) additional heparin neutralization can cause a reduction in coagulation factor levels. For these reasons, heparin neutralization is not recommended for PT measurements.
|LDT or Mod FDA?|
|Include for internal use?|
|Last Updated||6/23/2015 11:06:08 AM|
|Lab Procedure Link|