SEPTEMBER CASE STUDY:A known 3 year old hemophiliac patient has being admitted to a small hospital and need to be transferred to your hospital for a possible treatment. A sample is collected and rushed to the special coagulation laboratory. The APTT is run and the result is > 100 seconds. One point is run to quickly give the pediatric hematologist a result and the 1:10 dilution is 32%. This does not correspond to an APTT of > 100 seconds. The complete results are:
1:20 = 54%
1:40= 75%
1:80=98%
What is a possible explanation for this result? Should this patient receive product, based on the APTT result? What is the factor assay telling us? What test can be done to confirm this?
Two possible reasons for the "inhibitor pattern". Most likely the sample contained heparin which as the patien plasma is diluted, the heparin is also diluted causing less interference in the aPTT-based assay. Less likely is a Lupus Anticoagulant. Options - screen for heparin or use Hepzyme. If heparin is not the culprit, do testing for LLI. A Chromogenic Factor VIII assay might also be helpful, but is not available in every lab. The patient should not be treated based upon the prolonged aPTT.