UNDER THE MICROSCOPE
Lab hopping is when a patient gets a test result which is not to his liking, whether true or not, and gets another test from a different lab hoping there’s a mistake in the first lab’s result. Often, he doesn’t consult a doctor, who may have ordered the test and can/should be the one to interpret the result in light of the patient’s clinical condition. Often, it’s the immediate impulse of denial, as in, “I can’t (afford to) be sick/positive!”. This is even more cogent during this pandemic when a positive SARS-CoV-2 result will mean immediate isolation for at least 10 days, symptomatic or not. There’s the stigma of having an infectious disease as well.
The common scenario is when he gets a second result which is negative, he goes ballistic on the first lab claiming it gave him a false positive result. He then goes on social media blasting the first lab and telling others not to patronize that lab. Lab gets bad rep. But is it justified?
From a pathologist’s viewpoint, a false positive RT PCR result is highly unlikely. Why? We have a rigid quality system that prevents false positive results. With laboratory testing, we have three phases: pre-analytical, analytical and post-analytical. Each test run has positive controls to insure we can detect positive samples and negative controls to check for possible contamination that might cause a false positive result. Our technicians are highly trained to insure there is no carryover of samples. If in doubt, we even order a repeat test (analytical). When we encode results, these are double checked by another person to avoid errors (post-analytical).
On the other hand, a false negative result is more likely than a false positive one. We have a dictum in medicine: A negative result does not mean absence of disease. It may be a failure to detect it. The pre-analytical phase for COVID-19 swab testing involves sample collection, packaging, transport and specimen identification. Only the last item is within the lab’s control.
There’s a correct technique in swabbing a person. A poorly trained or careless swabber can get an inadequate sample with poor technique or when the patient moves during the collection process. There’s a chance of the patient being injured as well in this scenario. An example was a very indignant mother claiming our lab released a false positive result. She even sent a video of her child being collected during a drive-through testing where the child was clearly squirming and thrashing about while the swabber tried to insert the swab through the child’s nostrils and actually didn’t insert the full length of the swab. That clearly was a failed sample collection and the result certainly can’t be reliable. As the saying goes: Garbage in, garbage out. A review of our test clearly showed a positive result. End of story.
Another case: Patient tests positive at one lab; goes to another lab two days later and gets a negative result. Are the tests comparable? No. When the infection is in the late phase, it can still be detected by RT-PCR. When the viral load goes down to undetectable levels days later, the RT-PCR result will turn negative. You can’t compare tests that are days apart. The same will happen when different kits are used with different gene targets and limits of detection even when tested on the same day. Some kits will detect a lower viral load than others.
From the lab’s point of view with regard to COVID testing, a false positive result, if it ever happens, has lesser consequences of a person being isolated for 10 days. The reverse is true of a false negative result, which can have devastating personal and societal impacts.
If you truly feel there has been an error, ask the lab to check on your result. We gladly entertain inquiries and will check back on the case in question.
Why are some patients adamant on getting a negative COVID test? Usually, the test is done for a certain purpose like travel. That indignant mother had booked flights and hotel rooms for her family and needed a negative swab to travel. Or an executive badly wants to be at an in-person meeting. Others would like to be able to go to work. But there’s a cost to seeking a negative test result.
If you’re truly infected but asymptomatic, you may infect other more susceptible family members who may get severe disease or die. That’s a huge personal cost for a denial of the true state of affairs.
The cost to society is even higher when the person becomes a super spreader and causes an outbreak at his workplace or travel destination. Then the locality is shut down and the local economy suffers at great cost to daily wage earners. At a time like this, we can’t afford to be selfish and insist on getting our way. There is a huge price to pay and we can’t afford it. Let’s be more responsible for each other’s sake.