A new study suggests that thousands of HIV-negative Kenyans and Ugandans were incorrectly diagnosed as positive due to faulty tests at voluntary counseling and testing (VCT) centers, the Daily Nation reports.

The study involved 6,255 people between ages 18 and 60 who sought VCT services at testing sites in both countries. When two different tests were performed on participants, 131 had “discrepant” results where one was positive and the other negative. On the third test, 27 were confirmed to be HIV positive.

Researchers found that rapid tests such as Determine, Uni Gold and Capillus are normally used in poor societies because they are cheap and that confirmatory tests are not usually done at VCT sites in either country. However, assistant medical services director Peter Cherutich maintained that these rapid tests are the best method for countries such as Kenya and Uganda because they are cheap and easy to use and do not require refrigeration.

The risk of inaccurate diagnoses rises when rapid tests are done once without a confirmation test. According to the report, this is because they are “fraught with errors and as such, cannot alone be used to determine whether an individual is positive or not.” Therefore researchers suggest that positive results always be administered with a follow-up test before a diagnosis is made.