Lancet explains conflicting Covid-19 test results

In recent weeks, Lancet has been put on the spot after some of those who went for Covid-19 tests at the facility tested positive and later tested negative at KEMRI.

The most recent case involved 17 members of staff of St Andrew’s Turi who tested positive for Coronavirus but later tested negative when they went for a second test.

Lancet CEO Dr Ahmed Kalebi on Wednesday set the record straight as he sought to explain the conflicting results among patients.

He used an analogy of two photos of a pimpled face taken at different times using different cameras.

“A photo of a face that shows pimple(s) may be looked at differently e.g. expert cosmetic dermatologist may interpret what they see in finer details compared to a non-expert medical person or a layperson.

“The level of knowledge thus affects interpretation of results,” he tweeted.

Dr Kalebi stated that the tests conducted by Lancet are very specific and maintained that positive results are real.

Through a newsletter seen by Ureport, Lancet added that false-negative results may occur in up to 20% of swabs done especially in mild or asymptomatic individuals.

It stated that a low positive result may be followed by a second negative swab if;

• The patient is near the end of their infection
• The second swab was not taken from infected epithelium
• The patient is an intermittent secretor and was not secreting the virus when the swab was taken
• The second result was obtained using a less sensitive assay than the first one

Lancet further said that a negative result can be followed by a positive one if;

• The first swab was taken just before virus secretion begun
• The first swab was not taken from infected epithelium
• The patient is an intermittent secretor and was not secreting the virus when the swab was taken
• The first result was obtained using a less sensitive assay than the second one