Earlier this year, Japan's Ministry of Health, Labour, and Welfare released the results of a study on the use of antibody tests. It was conducted to determine the extent of the spread of the coronavirus and to evaluate the performance of antibody test kits. How reliable are antibody tests and can they be used to trace the origin of the virus? Terrence Terashima explains.

The antibody tests in April, using donated blood samples have raised debates among Japanese medical experts. The purpose of the test was to evaluate the "sensitivity" and "specificity" of the antibody test, using kits from 5 companies.

In the screening, two sets of samples were compared: one thousand blood samples collected after the spread of the virus in Tokyo and six prefectures in the northeastern region and 500 blood donation samples from January to March 2019, before coronavirus was confirmed in Japan.

TERRENCE TERASHIMA Tokyo "So, can the antibody test tell us when the COVID-19 virus entered Japan? Experts say that is difficult to assess. One has to conduct tests of older samples. But at the same time, we do not know how long the antibody remains in the body."

The result for the 2020 samples showed three out of 500 people in Tokyo and two out of 500 people in six prefectures tested positive.

Meanwhile, two samples from 2019, before the first recorded COVID-19 case in Japan, also tested positive.

With a very sample size, nothing much can be concluded according to experts. But they say the investigation indicates that some of the 2020 samples that were tested likely include "false positives".

KATSUNORI YANAGIHARA Professor, Nagasaki University Head of Laboratory Medicine, Nagasaki University Hospital "All in all I think the blood sample they used was too few and using several different test kits would add complications. So it is not surprising if we found false positive results in the overall data."

Researchers say it is important to identify the origin of the test samples and the specificity of antibody tests to understand how the virus is spreading in Japan. Skipping some of the specificity tests likely produced different results.

The antibody test measures antibody production to a specific antigen, which is only a portion of the virus protein configuration.

Seeing which particular antibody is detecting which particular virus antigen is said to be important.

YOSHIHIRO ISHIKAWA Vice President, Research Yokohama City University "Some antibody may be positive but if you use another antibody TEST it may be negative. That's one issue. And also many antibody tests use just a quick yes and no type examination. If it says yes what is the cutoff line? In other words how do you know what the exact level of antibody quantity which is supposed to be positive or negative?"

In any case, medical experts say the government needs to keep a record of antibody tests.

KATSUNORI YANAGIHARA Professor, Nagasaki University Head of Laboratory Medicine, Nagasaki University Hospital "I do not know if the government or health authorities keep a sample of those found positive in the antibody tests held recently. If they do, we should compare and determine how long the antibody remains in the body. Six months, one year or whether it decreases or not."

Detailed data is useful to plan measures against possible second and third waves' outbreak of the virus. Terrence Terashima, CGTN, Tokyo.