My doctor's procedures raise concern about reliability of PCR test that shows "undetectable"
Jan 23, 2004
Hi, Dr. Lee, Nice to have you as an expert on the website!
I'd appreciate your clarifying something which relates to the durability/stability of blood samples for viral load and other PCR testing: my doctor has the tendency, when he draws blood on Fridays, to leave the whole blood samples in his fridge over the weekend. The following Monday afternoon (three days later), the Lab from the hospital with which he is affiliated collects it and it is centrifuged at the Lab so that test can be done on plasma and cells.
My questions are these: I have read that centrifuging should occur within 6 hours of the blood draw - do you think my doctor's procedure could cause a falsely low VL test on plasma?
For PCR DNA testing, would the delays affect those test results?
If the centrifuging did take place within 6 hours and the blood were stored in the fridge, but not frozen, would RNA and DNA PCR test results be affected?
Last question is: could not centrifuging within time and storing unfrozen, but cool for three days affect EIA results? Fales positives or negatives?
Response from Dr. Lee
The simple answer to all of your questions are: Yes, yes, yes and yes. PCR or polymerase chain reaction testing is very sensitive to changes in temperature and other factors. A time delay, particularly a delay in the separation of the living cells from the plasma, or inappropriate storage temperature may effect the results of the tests.
You are certainly perceptive to have noted this situation at your doctor's office. Have you asked your doctor about it? One way to address your personal concerns would be to visit your doctor on Monday morning, so your blood would be more rapidly processed and therefore you could be more certain of the results.
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