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Activated Partial Thromboplastin Time
|Performed by||Parnassus & 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 (x3-1747) 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||
Note: If hepabsorption is required draw a full Blue top (2.7 mL)
|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|UCSF Rejection Criteria||Samples collected in outdated blue top vacutainer.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 tubes may be rejected|
An infant reference range has not been experimentally determined using our current PTT reagent. The PTTs of normal infants are longer than those of adults due to lower factor levels in the first months of life; the infant reference ranges provided (5 days, 3 months) are based on published literature (Ref: Andrew M et al. Blood 1987; 70-165). This publication further indicates that although trending longer, PTT values at 3 months may not differ statistically from adult values. If there is concern for clotting factor deficiency or inhibitor in an infant, factor activity assays should be requested if clinically indicated.
|Critical value||≥ 60 seconds if new finding within previous 24 hours. ≥ 80 seconds are always phoned|
|Synonyms||PTT; aPTT; Monitoring Anticoagulation; Monitoring heparin|
|Stability||If the patient is not on heparin, unopened, uncentrifuged specimens are stable for up to 4 hours at room or refrigerator temperature. If the patient is on un-fractionated heparin, the plasma should be separated within one hour and tested within four hours of collection. Plasma may be frozen at -20C if PTT testing must be delayed, but results may be slightly affected.|
|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.
Per in-house study done 01/2013, the sensitivity of the PTT for detecting factor deficiencies is as follows:
Factor VIII level may prolong the PTT when < 33%
Factor IX level may prolong the PTT when < 16%
Factor XI level may prolong the PTT when < 14%
Therapeutic anticoagulation with unfractionated heparin is generally monitored with the PTT. Recommendations for heparin therapy and monitoring are available through the Hematology Consultation service, which can be contacted at pager 443-4276. An overview of recommendations is available in the laboratory manual for reference purposes only in the entry: Heparin Laboratory/Dosing Algorithm. The reagents, and therefore the reference range and therapeutic range, differ among the various UC hospitals. Patients with lupus anticoagulants being treated with unfractionated heparin are usually monitored with heparin levels, rather than with the PTT.
Therapeutic anticoagulation with direct thrombin inhibitors (i.e. argatroban) is generally monitored with the PTT. Recommendations for therapy and monitoring are available through the Hematology Consultation service, pager 443-4276.
For patients not being treated with heparin for whom a sample may be contaminated with heparin, a heparin-neutralizing enzyme can be employed to overcome the effect of up to 2U/mL of unfractionated heparin/mL. Heparin neutralization is no longer routinely available. Performance of an aPTT after heparin neutralization may rarely be necessary for care of pediatric patients, and is subject to approval by laboratory medicine resident or faculty. In these rare circumstances, heparin neutralization may detect a substantial unexpected coagulopathy when a sample is drawn through a heparinized line. Of note, heparin neutralization reduces coagulation factor levels (typically by approximately 10%, but up to a 30% decrease can occur; internal UCSF study, Jan & Apr 2013). Therefore, heparin neutralization should not be used to detect slight abnormalities of coagulation, small changes in clotting times, or when monitoring anticoagulation.
|Medical Necessity?||Yes. Click here for more information|
|Last Updated||5/22/2013 12:23:53 PM|
If you have additional questions regarding this test, please call: 415-353-1667