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Inhibitor Screen for Partial Thromboplastin Time

Item Value
Approval req'd? No. However, the PTT Inhibitor Screen will be performed only if the PTT is abnormal.
Available Stat? No
Test code PTTIS
Test group Inhibitor screen
Performed by Parnassus Hematology
In House Availability Monday-Friday 0800-1400
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 (Parnassus: 3-1747, Mission Bay 6-1094) 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 top filled to full extent of vacuum X 3
Amount to Collect 9 ml blood
Sample type Citrated plasma
Preferred volume 4 mL plasma
Min. Volume 2 mL plasma
UCSF Rejection Criteria Samples collected in outdated blue top vacutainer.
Processing notes Deliver sample to the Hematology Lab ASAP.
Normal range Negative
Synonyms PTT Mixing Study, Inhibitor Screen, Factor Inhibitor Screen
Stability 4 hours
Turn around times Same day or next weekday
Additional information PTT Inhibitor Screen will be performed only if the PTT is abnormal. If the test is ordered on a sample with a normal PTT, the inhibitor screen cannot yield a positive result. "Test not Indicated" will be sent.

The PTT Inhibitor Screen should be used for screening for a Factor 9 specific inhibitor.

The PTT Inhibitor Screen may be of limited value in a number of clinical settings and alternative tests are recommended:

For the evaluation of lupus anticoagulant as cause of a prolonged PTT, specific tests are suggested [Russell's Viper Venom Test (RVVTM) and Lupus anticoagulant by Hexa (HEXA)].

For the evaluation of thrombin inhibitors as cause of a prolonged PTT, a Thrombin Time may be useful.

Screening for Factor 8 or Factor 11 inhibitors, the Modified Inhibitor Titer (MODIT) is suggested.

If unusual findings are noted a pathologist review and interpretation may be performed and separately billed for
CPT coding 85730, 85732 x2
LDT or Mod FDA? Yes
Last Updated 1/29/2015 4:44:31 PM
Entry Number 1581
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