Clinical diagnostics have been thrust into the spotlight as the United States clamors to test symptomatic and high-risk populations for Covid-19. As new diagnostic developments, testing strategies, and benchmarks are announced, more and more questions surface about what we know about Covid-19 testing, what we don't know, and what we still need to find out.
In our new resource sheet, we answer the top three Covid-19 testing questions we've received from our members:
What are the different types of tests and the use cases for each?
Various types of tests are available to detect Covid-19, with new tests hitting the market at a dizzying pace. At a high level, Covid-19 testing boils down to three main methods: polymerase chain reaction (PCR) tests, antigen tests, and serological (antibody) tests. PCR and antigen tests can both diagnose active cases of the virus—but differ in their accuracy, cost to produce, and time to process. Antibody tests, on the other hand, look for signs of previous infection. To optimize your Covid-19 testing strategy, we break down the differences and tradeoffs among their ability to diagnose, turnaround time, capacity considerations, and best-suited applications.
What evidence is available on the accuracy of diagnostic and antibody tests for Covid-19?
Test performance characteristics, even within the same type of tests, vary. Generally speaking, PCR tests are considered the gold standard for accurately identifying active infection. Another popular diagnostic test, antigen tests, can identify active infection but are less sensitive than PCR, meaning greater risk of false negatives.
Antibody tests can be subject to higher rates of false positives but are also best reserved for detecting previous infection from Covid-19.
How much testing does the United States really need?
Experts' perspectives differ on the number of diagnostic tests required to effectively reopen the United States in the absence of a vaccine or effective treatment. Most estimates range from 2.27–5.88 tests per 1,000 population per day, although specific targets vary by geographic region according to test positivity rate, population vulnerability, concurrent mitigation strategies, and other factors. However, experts agree that PCR testing on its own is likely insufficient due to processing capacity constraints. With the introduction of antigen tests and their expected manufacturing at scale, the country may be closer to testing the millions of people per week some researchers think is required.