“False positives/false negatives” and quality control
At Setolabo Sanitary Inspection Center, we create standard operating procedures and ledgers, and undergo rigorous screening by the public health center, including on-site inspections, to operate as a prefecturally registered sanitary inspection center. Unlike the typical “private inspection companies near train stations,” Setolabo Sanitary Inspection Center performs 95% of its tests as a sanitary inspection center commissioned by the government.
The PCR tests that you take when visiting a medical institution are also conducted at the Sanitary Laboratory, and the tests conducted at the Setolabo Sanitary Laboratory are administrative tests and tests conducted by medical institutions.
The testing centers are open 24 hours a day, but in order to make the testing more accessible to the general public, we have set up saliva collection stations at our testing centers in Nagoya, Kobe, Osaka, Hiroshima, Okayama, Kagawa, Ehime, Kochi, and Tokushima to open part of the hours to the public. The samples that you collect at each testing center are transported to the testing center, where they are tested by nationally qualified testers, including clinical laboratory technicians and doctors.
(When there are a large number of samples, laboratory inspectors and graduate students from national universities may also be temporarily involved in the testing.)
In 2020, the Ministry of Health, Labor and Welfare issued a notice to all testing companies to notify “false positive and false negative results” on their websites. Setolabo Sanitary Testing Center has also received the notice and is notifying people of the possibility of “false positive and false negative results.”
<Efforts to prevent false positives at Setolabo Hygiene Laboratory>
It is said that false positives often occur due to the following reasons. The most common of these is contamination. Contamination refers to the mixing of other positive samples with other samples. At Setolabo Hygiene Laboratory, we perform tests based on the contamination prevention manual, and have been approved by the public health center after having the manual thoroughly reviewed.In addition, as a unique initiative of Setolabo Sanitary Testing Laboratory, we test positive samples twice. By testing until two consecutive positive results are obtained, it takes time, but it prevents false positives. There are other cases where a positive result is given due to the detection of similar viruses or debris.
<Efforts to prevent false negatives at Setolabo Hygiene Laboratory>
It is said that false negatives occur more frequently in specimen collection than in the test procedure. At Setolabo Hygiene Laboratory, false negatives cannot be prevented because specimen collection is done by doctors or patients themselves. However, by raising awareness, we ask all patients to submit saliva samples using the correct collection method.
False negatives are more likely to occur when:
・Early infection period (especially the first 1-3 days after onset)
・Immediately after eating or drinking
・Immediately after gargling with iodine
・When a doctor takes a nasopharyngeal swab in an improper manner
False negatives are common, especially in the early stages of infection. PCR tests are performed at all laboratories using a few microliters of saliva. Therefore, if the coronavirus, which tends to gather in the back of the nose, has not multiplied sufficiently in the back of the nose, the amount of virus contained in the collected saliva may be low. This is why public health center tests sometimes take a long time to perform. On the other hand, when it comes to self-paid tests or tests at medical institutions, people often take the test immediately after developing symptoms such as fever, so for the above reasons, the result may be “negative” even if the person is actually infected.What’s even more troublesome is that if the collected saliva is 1 mL, the amount of saliva actually used in the test is only a few microliters, less than 1/100 of that amount. Therefore, even if the collected saliva contains a small amount of virus, if the saliva used in the test does not contain it, the result may be negative or positive. Therefore, since it is particularly difficult to judge in the early stages of infection, the possibility of a false negative is significantly reduced if you take a PCR test some time after symptoms appear (after the third day).
Setolabo Sanitary Inspection Center generally refuses to accept saliva PCR tests that are purchased online and mailed in the post because they contain a virus inactivation liquid that may destroy the virus’s genes, increasing the possibility of false negatives. Similarly, Setolabo Sanitary Inspection Center generally refuses to accept the pink transport liquid used for mailing because, for the reasons mentioned above, it is not suitable for the early stages of infection and the virus’s genes are destroyed when transported at room temperature.
At Setolabo Sanitary Testing Laboratory, we review our quality control on a daily basis to prevent false positives and false negatives.
In addition, we ask that all those who are able to take the test at their own expense understand that the test is not 100% reliable. If you have a fever, please self-isolate and wear a mask. It is up to each and every one of you to take action to prevent the spread of infection. We believe that PCR tests are there to support that effort.
I will end this column with the hope that this situation will be resolved as soon as possible.
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