Viral Load Testing and Lab Procedures
Jan 21, 1999
I have now had three viral load tests (PCR, Ultrasensitive). The first was done at the clinic and sent by them to the lab my insurer uses. It was not done because the sample was mishandled. The second was drawn at the lab's service facility, but sent to their lab in the suburbs by courier later that day. How much effect does time spent by the blood sitting unhandled have on the accuracy of the test. And how does freezing affect it? I finally paid the substantial difference and had the test done at a reference lab, since both previous tests were rejected by the lab's processing facility. Is this worth the money? And does handling greatly affect CD4/8 counts as well?
Response from Dr. Holodniy
Excellent and important questions that are not appreciated by some practitioners. Viral load can be affected by the type of blood collection tube the blood is collected in. It is most stable in purple top tubes. Whole blood in purple top tubes can sit on a bench for over 24 hours, without appreciable loss of viral load "signal". The companies who make the tests recommend separation of plasma from whole blood and placment into a freezer within 6 hours of collection. Freezing is actually the best way to store samples. There is no appreciable loss of viral load for many months. Cd4 counts can have wide variability between labs. Samples are recommended to stay at room temperature for shipping. Severe cold or freezing will severely affect the numbers. The type of tube the blood is placed in is also very important. MH
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