Some political leaders are hailing a potential breakthrough in the fight against COVID-19: simple pin-prick blood tests or nasal swabs that can determine within minutes if someone has, or previously had, the virus.
The tests could reveal the true extent of the outbreak and help separate the healthy from the sick. But some scientists have challenged their accuracy.
Hopes are hanging on two types of quick tests: antigen tests that use a nose or throat swab to look for the virus, and antibody tests that look in the blood for evidence someone had the virus and recovered. The tests are in short supply, and some of them are unreliable.
The market has gone completely mad," Spanish Health Minister Salvador Illa said Thursday, lamenting the lack of face masks, personal protection equipment and rapid tests, "because everybody wants these products, and they want the good ones.
The Spanish government on Thursday sent 9,000 rapid antigen tests that were deemed unreliable back to a manufacturer that, according to the Chinese government, had no license to sell them.
British Prime Minister Boris Johnson this week called the rapid tests a game changer and said his government had ordered 3.5 million of them.
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The U.K. hopes the tests will allow people who have had COVID-19 and recovered to go back to work, safe in the knowledge that they are immune, at least for now. That could ease the country's economic lockdown and bring back health care workers who are being quarantined out of fears they may have the virus.
Many scientists have been cautious, saying it's unclear if the rapid tests provide accurate results.
In the past few months, much of the testing has involved doctors sticking something akin to a long cotton swab deep into a patient's nose or throat to retrieve cells that contain live virus. Lab scientists pull genetic material from the virus and make billions of copies to get enough for computers to detect the bug. Results sometimes take several days.
Rapid antigen tests have shorter swabs that patients can use themselves to gather specimens. They are akin to rapid flu tests, which can produce results in less than 15 minutes. They focus on antigens parts of the surface of viruses that trigger an infected person's body to start producing antibodies.
Health authorities in China, the United States and other countries have offered few details on the rates of false positive and false negative results on any coronavirus tests. Experts worry that the rapid tests may be significantly less reliable than the more time-consuming method.
Lower accuracy has been a concern with rapid flu tests. Spanish scientists said the rapid tests for coronavirus they reviewed were less than 30% accurate. The more established lab tests were about 84% accurate.
Those results "would prevent its routine introduction, according to a report by the Spanish Society of Infectious Disease and Clinical Microbiology that triggered the alarms in Spain and spurred the government's rejection of the 9,000 antigen tests.
Similar questions swirl around new antibody tests involving blood samples. Some versions have been described as finger-prick tests that can provide important information in minutes.
Antibody tests are most valuable as a way of seeing who has been infected in the recent past, who became immune to the disease and if done on a wide scale how widely an infection has spread in a community.
The antibody tests also will allow scientists to get a better understanding of how deadly coronavirus is to all people, because they will provide a better understanding of how many people were ever infected, ranging from those who never showed symptoms to those who became fatally ill. The results will also guide vaccine development.
But so much is unknown, including how long antibodies and immunity lasts, and who the blood tests should be used on.
We don't have all the answers," said Dr. Robin Patel, president of the American Society for Microbiology.
For most people, the coronavirus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death. Most people recover.