After more than two months of COVID-19, there still seems to be some lingering confusion regarding the two main types of tests: RT-PCR, and antibody or serological tests. RT-PCR detects the RNA —genetic material— of the virus, and serological tests detect the antibodies that appear when infected by the virus. But how are the results of these tests interpreted? Which of the two is more suitable, and when?

You can live without knowing the answers to these questions, just as you can live without knowing what the semicircle of the edge of the areas on a football pitch is for, but if you are reading these lines, you are probably a curious person and you would like to know it.

Both tests are handy and informative, so we are going to try to solve it as ties are solved in football games. We’re going to take a five-penalty shootout.

FIRST PENALTY

RT-PCR: It tells you if the virus is in your body. GOAL. 1-0

Antibody test: It tells you if the virus has been in your body. GOAL 1-1

SECOND PENALTY

RT-PCR: A positive indicates that you can spread the disease, and, by isolating yourself, you protect your environment and stop the pandemic. GOAL. 2-1

Antibody test: A positive indicates that you are probably protected from another infection. GOAL. 2-2

THIRD PENALTY

RT-PCR: You need specialized machines and personnel to perform the test. MISS. 2-2

Antibody test: If it is the rapid type, you do not need machines or specialists. GOAL. 2-3

FOURTH PENALTY

RT-PCR: It is very sensitive, it detects very low amounts of the virus. GOAL. 3-3

Antibody test: If it is a rapid test, the sensitivity is lower. If it is a slow test (by ELISA technique), it is more sensitive. POST. 3-3

FIFTH PENALTY

RT-PCR: If you are a «normal» person and without symptoms, you will hardly get a RT-PCR from your health system. MISS. 3-3

Antibody test: They are being done to some collectives, but it is still not very accessible. POST. 3-3

3-3 draw. It would be necessary to continue shooting penalties. There are so many factors and variables that could give goals to one or another type of test, that the penalty shootout can be extended as much as that of the match between Argentinos Juniors and Racing de Avellaneda in 1988, where 44 penalties were taken. Eduardo Galeano wrote about that match in his book Football in the Sun and in the Shadow, in a chapter entitled «Indigestion.» Galeano remembers that, after 44 penalties, when Argentinos Juniors finally won 20-19, there were few people left in the stadium to celebrate.

One aspect that complicates this hard-fought penalty shootout is the phase of the disease in which each test is done. This is what would happen during the four canonical phases of a COVID-19 ²⁸.

Phase 1: Neither viruses nor antibodies are detected.

Newly infected, for just hours or a few days, you will come up as negative in the serological test and probably also in a RT-PCR.

Phase 2: Only viruses are detected.

Symptoms appear and for a few days you will test positive in the RT-PCR test, but negative in the serological test.

Phase 3: Viruses and antibodies are detected.

Between the third and fourth week, the antibodies against SARS-CoV-2 appear, and for a few days, you can test positive in both tests.

Phase 4: Only antibodies are detected.

The virus disappears through the action of your immune system. You will test negative in the RT-PCR test, but positive in the serology one. Antibodies can be detected for months, and perhaps years.

Therefore, you can receive a positive result from both tests over a short period of time. The simultaneous presence of the virus and the neutralizing antibodies that counteract it is something temporary and brief, like the presence of the Charlton brothers in the England team. These were its phases:

Phase 1: Neither Bobby nor Jack.

The four Charlton brothers played on the streets of Ashington, a small town in northeast England. Their most likely future career was at the mine, where their father worked. The football world had yet to discover either Bobby or Jack.

Phase 2: Bobby only.

Bobby played for Manchester United and debuted for the England national team in 1958. Meanwhile, his brother Jack played for Leeds United. Bobby was a powerful goalscoring midfielder, who could strike the ball with either foot. He got the Golden Goal award. There was a period when only Bobby was noticed and Jack seemed not to exist.

Phase 3: Bobby and Jack.

Jack was a tall centre back who took no chances if he had to clear the ball. Surprisingly, at the age of 30, he was called up by the England National Team, along with his younger brother, to play the 1966 World Cup in England, which has been the only one that England has won in its history. They beat Franz Beckenbauer’s West Germany 4-2 in the final.

Phase 4: Only Jack.

Jack, taking advantage of his outgoing and charismatic personality, was a coach for several years, managing to lead Ireland in the 1990 World Cup in Italy, in which they reached the quarter-finals. As proof of Jack’s outgoing character, one documentary tells how, after winning the 1966 World Cup, he partied with a friend in London with a thousand pounds in one pocket and a paper in the other, where he wrote: “This body is to be returned to Room 508, the Royal Garden Hotel.” Jack partied as he played: hard.

Another factor that complicates the interpretation of the tests is the variability of the duration of the disease phases in each individual. The journal Nature Medicine published a detailed study of 12 patients who underwent daily RT-PCR tests²⁹. In some cases, the virus was detectable only over a 12-day period, but in other cases, SARS-CoV-2 was detected for 30 days, although it is probable that it did not have infective capacity then. RT-PCR is such a sensitive technique that it can detect very small amounts of virus, which could give positives, even if they do not have much capacity to spread and infect because the amount of virus (viral load) that one has seems to be correlated with the ability to infect.

If you already knew enough about these tests, and you also knew that the semicircle of the area serves to mark a distance away from the players when a penalty is going to be taken, I hope I have at least entertained you, and I hope this piece has provided you with some detailed information, such as that all crescent points in the area are 9.15 metres from the penalty spot, a distance equal to 10 yards. The penalty spot is 12 yards, eleven metres, from the goal line. Whims of those who invented this game.

THE BOOK, WHICH INCLUDES SCIENTIFIC REFERENCES, IS AVAILABLE WORLDWIDE, IN AMAZON.