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Platelet Function Analysis (PFA-100)
|Clinical Questions||Does my patient have von Willebrand disease? If so, which type?|
|Test group||Platelet function|
|Performed by||Parnassus Hematology|
|Patient Preparation||Patients should avoid eating fatty foods prior to sample collection. Administration of aspirin or anti-platelet agents may prolong results and should be avoided.
Testing requires simultaneous Hematocrit and Platelet count or drawn within preceding 24 hours of sample collection.
|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.
Use 19-21 guage needle. Draw Lavender top FIRST. Invert tubes gently 3-4 times after collection.
NOTE: Samples for PFA-100 testing CANNOT be delivered via pneumatic tube to the laboratory, they must be hand-delivered within 4 hours of collection.
|Container type||Blue top tubes filled to full extent of vacuum x2 and Lavender top|
|Amount to Collect||8.4 mL blood (Blue top 5.4 mL, Lavender top 3 mL)|
|Sample type||Citrated whole blood & EDTA whole blood|
|UCSF Rejection Criteria||Samples collected in outdated blue top vacutainer. Samples delivered via pneumatic tube. Over-filled or under-filled tubes may be rejected|
|Processing notes||If orders do not include PLT & HCT, CBC or CBCD, order CBC.|
|Normal range|| Closure times:
|Turn around times||Performed 0800-1600 Monday-Friday. Turn around 4 hours.|
|Additional information||Prolonged closure time detected by the PFA-100 may reflect platelet count < 150 x109/L, hematocrit < 35%, platelet function defects, von Willebrand Disease, uremia, medications such as aspirin, and exposure to fish oils found in dietary supplements. A normal closure time does not exclude von Willebrand disease or platelet function defects. Results should be evaluated in conjunction with clinical history and other laboratory findings.
Testing requires that a hematocrit and platelet count is ordered on the EDTA sample. If none ordered a CBC will be added and billed for.
The PFA-100 test can be run if (A) the hematocrit is > 40% with platelets > 110 x 109/L or (B) the hematocrit is 30-40% with platelets > 200 x 109/L. If neither of these criteria are met, the test is cancelled because lower values result in prolonged closure times.
Published studies indicate that the PFA-100 test has variable sensitivity for von Willebrand Disease and hereditary platelet function defects depending on the clinical setting. In published selected patient populations sensitivity was 93% for von Willebrand disease and 81% for hereditary platelet function defects (Haemophilia 2001, 7:170-179). However, in unselected patients referred for evaluation of mucocutaneous bleeding the sensitivity was much lower, 62% for von Willebrand disease and 24% for platelet function disorders (J Thromb Haemost 2004, 2:892-898).
1.Presence of hemolysis may interfere with test results. Therefore, use of hemolyzed blood for PFA-100 testing is not recommended.
2.Certain fatty acids and lipids found in various human diets are widely known to inhibit platelet function and may prolong results. Physicians may wish to advise patients to refrain from fatty foods prior to testing. Neutral lipids, such as cholesterol, generally have no effect on platelet function.
3. Platelet inhibiting agents, such as aspirin and anti-glycoprotein IIb/ IIIa antagonists, directly affect platelet function and may prolong results.
|Last Updated||11/12/2013 3:37:08 PM|