State Finally Requiring Labs To Report the Most Important Result of a COVID Test
A positive test for COVID-19 reveals little about how sick or contagious the patient might be.
Health officials in Florida recognize this, and the state has taken the important step of requiring labs to include what’s called a “cycle threshold” on all positive test reports.
A positive result sets in motion a long and inconvenient chain of events. The patient and his or her family members are required to drop everything and quarantine. They must inform all of those with whom they’ve had recent contact, some of whom may be forced to quarantine as well.
When one considers the large numbers of Americans testing positive every day, many of whom are asymptomatic, the question becomes whether all of this trouble is really necessary.
People also question the accuracy of the test results. A couple of weeks ago, CNBC reported that Elon Musk, the CEO of Tesla, took four COVID-19 tests on one day. Two came back positive and two were negative.
An article from MIT Medical tells us there is no such thing as a false positive. If an individual receives a positive result on a COVID-19 test, “we can be sure that it has correctly detected genetic material from the SARS-CoV-2 virus, the virus that causes COVID-19.”
The polymerase chain reaction test is the nasal swab with which many of us are familiar. According to MIT Medical, the PCR test “analyzes samples by amplifying viral RNA in cycles. Most tests … use a 40-cycle protocol. If the virus isn’t detected within 40 amplification cycles, the test result is negative. If viral RNA is detected in 40 cycles or less, the PCR machine stops running, and the test is positive. Because you received a positive result, we know that the test detected the virus in your sample by the time it reached its 40-cycle limit.”
However, “this binary way of viewing test results — positive/negative, infected/not infected” — tells us nothing about the size of an individual’s “viral load.”
“After all,” MIT Medical said, “the amount of virus in a sample is directly correlated with the number of amplification cycles needed to detect it, a number known as its cycle threshold (CT). A positive test that comes back positive in 20 cycles contains a greater amount of virus than one requiring 40 cycles. Right now, we just call both results ‘positive.’ But it’s obvious that the first sample came from an individual with a higher viral load. And the greater the viral load, the more contagious the patient is likely to be.”
In other words, an individual might have been exposed to a small amount of the disease and his or her immune system is fighting it. It will soon be gone. However, if the DNA is cycled enough times, even a trace amount will be picked up and the individual will receive a positive test result.
Meanwhile, another person who is severely infected with COVID-19 will also receive a positive result.
Up until now, there has been no way to differentiate between the two.
The Florida Department of Health understands this dilemma. Last week, the Sunshine State became the first to make it mandatory for labs to include the number of cycle threshold values in all test results.
State health officials are essentially saying that not all cases of COVID are equal, and a long quarantine might not be necessary for everyone who tests positive.
Should all of these positive results be included in the total daily number of new coronavirus cases?
If it takes 40 cycles for a lab to detect a trace amount of the virus that his or her immune system is fighting off, should this be counted as a new case of COVID-19?
Or is this level of screening simply skewing the numbers, making them appear higher than they are and thus giving politicians ammunition to enact overly stringent restrictions to combat the virus? Is it providing governors and local leaders with a rationale to call for more draconian lockdowns than are necessary?
The lockdowns, they tell us, are based on the dramatic increase in positive cases. An article in The Lancet, a highly respected medical journal, points out that in April, tests were conducted on mostly severely ill patients and health care professionals. Currently, however, tests are being conducted on far more people. Anyone who may have come in contact with someone who has later tested positive for COVID is being tested. For others, a test may be required before attending a specific event.
“In March and early April, 2020, most people tested in the UK were severely ill patients admitted to hospitals with a high probability of infection,” the Lancet article said. “Since then, the number of COVID-19-related hospital admissions has decreased markedly from more than 3000 per day at the peak of the first wave, to just more than 100 in August, while the number of daily tests jumped from 11,896 on April 1, 2020, to 190,220 on Aug 1, 2020.
” In other words, the pretest probability will have steadily decreased as the proportion of asymptomatic cases screened increased against a background of physical distancing, lockdown, cleaning, and masks, which have reduced viral transmission to the general population.
“At present, only about a third of swab tests [PCR tests] are done in those with clinical needs or in health-care workers … while the majority are done in wider community settings. … At the end of July 2020, the positivity rate of swab tests … remained significantly lower than those in early April, when positivity rates reached 50%.”
The importance of knowing the severity of the viral load an infected person carries cannot be overstated, especially with the sharp rise in testing. It will allow patients, medical professionals, public health officials and political leaders to take appropriate, rather than uncompromising, actions to contain the spread of the disease.
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