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why the same lab contains different cut off OD's for the elisa.

Mar 8, 2010

Hi Sir,

I am Sr. I had sex with girl in november 2008. In 2009 june i got fever and body pains. And i took the tablets for 15 days. after seven days fever went off. At the 28 june I went for total body checkup. At that time hiv status came negative.

In september 2009 I got body pains in extereme range. after two and half months it went off. And i went for the all the hiv related tests and came negative.

In November 2009, I went for hiv elisa and PCR DNAtest. At that time elisa results is test OD - 0.020 and cut off OD is 0.264. And PER DNA came negative. so, elisa test is also negative.

And I went hiv elisa test and PCR RNA again december 26, 2009 and it is different laboratories from earlier. And the results is test OD is - 0.024 and cut off OD is 0.168 So, here also test results came negative.

And I went for all hiv related tests again in 5 th March 2010 and it is same laboratories which i went in december. And elisa test OD is - 0.031 and cut off OD is - 0.145 And all came negative.

I have below mentioned doubts. Could you please answer them.

1. Is elisa contains different metods? 2. why test OD results increasing in my case. 3. And I went for the same lab for testing. but contains different cut off values. 4. I tested after the 17 months and all the results came negative. Is I need to test again? 5. Is anything hiding hiv virus in my body ( because some type of cancers can delay the seroconversions)? 6. Is medicine i took for boady pains and fever is affecting the test results?

Kindly clarify the doubts.

Thanks, Sr

Response from Dr. McGowan


Let me try to address your questions.

1) The Elisa tests are run periodically in the lab, different labs may use different kits to run the test. Each time the test is run the machines are calibrated to provide the cutoff for that run. That is why the cutoff value changes. The conditions for each test are different (temperature, concentration of the solutions, etc can differ microscopically). 2) Likewise, All of your values are below the cutoff of the test, the numbers may not really be increasing since they are too low to accurately measure. This level is within the "noise" of background and should not have any meaning put to it. Usually if someone were indeed developing antibody, the levels would rise very quickly over 2-4 weeks and to high levels, that is not the pattern here. 3) As I just described 4)NO, you do not need to be tested again for HIV based on your past possible exposure. 5) No medication for a cold or fever would not interfere with the results of the HIV test.

Best, Joe

9 months now Dr. Joe

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