The Director of Research and Head, Microbiology Department, Nigeria Institute of Medical Research, Lagos, Dr. Rosemary Audu, says PCR-based COVID-19 tests can produce false-negative results, warning that such variability might increase the spread of the virus.
The Polymerase Chain Reaction testing method is the only testing technique approved by the Nigeria Centre for Disease Control for COVID-19 testing in the country.
The virologist said on several instances, NIMR had experienced variability from test kits supplied to the institute from the national programme for COVID-19 testing.
Dr. Audu’s position is coming after new research carried out by a team of scientists from Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America, revealed PCR-based COVID-19 tests may have a false negative rate of 20 per cent or more, depending on when it is done and when the sample is taken.
The study, published in the Annals of Internal Medicine on June 6, urged clinicians to consider waiting for 1 to 3 days after symptom onset to minimise the probability of a false-negative result.
The virologist said professionally, it is advised that molecular laboratories should validate test kits and define their cut off that ensures results remain constant and undisputed anywhere.
“That is the best practice anywhere. This is not only limited to the COVID-19 test kit. It is just that we need to come up with the cut-off,” she said.
“For instance, we have had about five different test kits that were supplied to us from the national programme for COVID-19 testing and we validated those kits.
“Using the manufacturer’s guidelines on how to interpret results, we found that some samples will test positive on one kit and another kit will be negative. So we have that variability.
“However, what we advise is that each molecular laboratory needs to draw up their cut off, such that when it is negative, it is negative. And when it is positive, it remains positive.”
Speaking on the dangers variability or inconsistency in results poses to the fight against COVID-19, she said “For those who are infected, if they get a negative result, they are likely to go out and spread the virus.
“And for those who are negative, if they get a positive result, they may be admitted into an isolation ward, and there, they will get infected,” she said.
The expert explained that due to the novel nature of COVID-19, several dynamics are being thrown up and are being studied to have a better understanding of the disease, adding that what manufacturers of the test kits have done is to just use few samples to conclude what the cut off should be in terms of positive and negative results.
Dr. Audu noted that, however, as more people are getting to use the kits, it has been discovered that sometimes, it does not always follow what the manufacturers have specified.
“That is why we have to now redefine the cut-off. So, what we advise is that every laboratory should validate and define their cut off. They don’t have to use what the manufacturers say,” she said.
The virologist further advised that molecular laboratories should ensure to stick to the use of the same test kits to avoid variability in results.
“There was a time in this country when a few people tested positive to COVID-19 and after a few days, they were negative.
“If the same test kits are not used, there will be that variability. It is usually advised that a laboratory should stick to the use of the same test kit for testing.
“However, there might be times when the same test kit might not be readily available for use, but laboratories necessarily need to validate and define a cut off such that whatever result is issued out, when taken elsewhere will remain the same.
“What we expect as a good laboratory practise is for a new kit to be validated before use and a cut-off defined.
“This way, you have your controls for positive and negative results. Especially for those at the borderline that tend to be the ones that will give issues, you have to test them again to be sure they give accurate results,”