“Inappropriate sample collection is the main culprit behind inaccurate testing,” he said. Dr Nisar false negative results are occurring because healthcare providers aren’t collecting samples with enough of virus. This can happen because they don’t insert a swab deep enough in the nose or don’t collect enough of the sample. “False negative can also occur if persons are testing too early or too late during their infection and there isn’t lot of virus in their cells,” he said.
“And, errors can happen if a sample sits too long before being tested which allows the virus to break down,” he added. Dr Nisar said another issue related to PCR test is “false positive result”. “That means people who are uninfected receive positive results for Covid,” he said.
Dr Nisar said the false positive result can be due to contamination either from a positive sample analyzed in the lab at the same time (cross contamination) or more likely from genes amplified from prior positive samples or positive controls (carryover contamination). False positives can also be produced by sample mix-ups or data entry errors.
“False positive results lead to unnecessary sequestration of uninfected individuals and waste of human resources in contact tracing,” he said. “It is important to mention that if the test is not perfect, it does not mean it is not useful. Proper sample procedures, good lab practice standard and using high quality PCR kits could reduce inaccurate results,” said Dr Nisar.