Q. Can you explain the results of HIV screening test?

Hi doctor

Hope you are doing great.

Please see attached the reports for the viral markers and VDRL/RPR screening along with this query.

These tests were undertaken after eight months and 19 days of exposure or 263 days post-exposure. I have a few doubts as follows basis my understanding so far:-

(1) I just wanted to confirm if the test used in the attached report from the pathology laboratory for HIV Screening is a 4th generation test.

The heading of the test mentions "HIV 1& 2 antibodies Screening test, Serum," but if we go a notch below in the report, it mentions "HIV 1/2 & P24 Combo test(CMIA)" which implies, as per my understanding that the 4th generation test was used. The rest of the test details, like comments, description, etc., are rather silent and do not explain much about the test performed/technique used, creating confusion in my mind. Since the test is from the pathology laboratory and you might be seeing similar reports in your regular practice, it would be really helpful if you could clear up my confusion/reassure me wrt this.

(2) I would like to know the exact window period for the anti-HCV antibody test for modern methods like CMIA/CLIA etc., which are commonly used these days. The CDC website mentions that "anti-HCV seroconversion occurs on an average of eight to 11 weeks with a reported range of 2 weeks to 6 months". Further, the WHO fact sheet does not contain information about the window period for the HCV antibody test and only talks about the incubation period of the HCV virus in general, which is the same as "two weeks to six months," as mentioned above. Please clarify the window period from a more practical point of view.

(3) What do you think is the most accurate measure of any window period? So, for instance, let us say the window period for HIV I & II - antibodies test is 90 days. Now some experts/health org quote it as 90 days, others as 12 weeks, and some as three months. All of these, though similar, are not the same;

12 weeks equates to 84 days, and when taking three calendar months, we might generally exceed 90 days and may fall around 91/92 days(depending on the month)

So which one should a person follow?

Can one get tested on the 91st day of exposure, or should one wait for three calendar months (that is 91/92 days to complete, depending upon the month) to expire, or are 12 weeks also fine?

Hi doctor,

Thank you for the reply. Just one small followup, as you mentioned above:-

You mentioned previously that the HIV antibodies test in the attached report is a combo test, and it is negative. Does the word 'combo test' implies that it is a fourth-generation HIV test?

Hi doctor,

Thankyou for the reply. So that means that the HIV test in the attached report is a fourth generation one, right?