More than 100 million COVID-19 tests have been performed in the United States, according to the Centers for Disease Control and Prevention's COVID Data Tracker.
But the true number of tests is unknown because of decentralized accounting and the fact that not all tests were created equally.
"Testing has always been at the heart of how we get out of COVID, because without insights into where infection is spreading, you're flying blind. Our response is heavily based on test results, in terms of which phase of reopenings we're in and whether we have to go into lockdown," said John Brownstein, an epidemiologist at Boston Children's Hospital and ABC News contributor.
The CDC only includes polymerase chain reaction, or PCR, tests in its count. These tests look for presence of the virus and are usually sent away from a doctor's office and processed in a large, centralized lab.
But increasingly, doctors' offices are offering a new generation of 15-minute rapid test, which might not always be counted. A third type of test, antibody tests, also are excluded, but these tests show only if a person was previously infected -- not whether they're still contagious.
Keeping track of diagnostic testing at a national level is essential not only for accurately counting confirmed COVID-19 cases, but also for guiding our efforts to control the pandemic. Unfortunately, it seems that many states either don't report data from antigen testing to the CDC or are not keeping complete data on it.
There's no straightforward answer about whether rapid tests are counted, said Molly Polen, senior director of communications and public relations for the American Association for Clinical Chemistry. One of the most common types of rapid tests is called a nasal-swab-based antigen test -- not to be confused with an antibody test, which requires a blood sample.
"It looks like a number of states combine PCR and antigen testing, but same as with the antibody tests, not all states seem to report antigen test results," Polen added.
That's a problem because it means we may be significantly underestimating the number of people who have COVID-19 at any given time.
"There's a lot of confusion about what gets reported, when it gets reported and how it gets reported," Brownstein said.
Failure to report complete COVID-19 testing data goes against current federal guidelines, but just because doctor's offices across the country are required to report these newer "rapid" COVID test results does not mean they're actually doing so -- or doing so consistently.
The main problem is a lack of efficient and effective infrastructure for centralized data collection, said Blythe Adamson, an epidemiologist and former member of the White House Coronavirus Task Force. "Different states may have different ways they operationalize clinical reporting to different health departments. CDC does not have a standardized infrastructure for all of this."
"So if there's testing but we don't have that data, that gives us major gaps in our understanding and it could force us into making public health decisions that are not aligned with the best possible evidence," he said.
The gap between the reported number and true number of COVID cases will only widen moving forward, as rapid antigen tests are rolled out by the millions.
Antigen tests are being used more and more because they're fast and cheap. They can produce a result in just a few minutes because they don't need to be processed in a lab, whereas PCR and antibody tests may take days. Antigen tests also are significantly less expensive.
There is even talk of using antigen tests at home, similar to pregnancy tests. That would mean we'd have to rely on regular people -- not health care professionals -- to report their own results, which could get complicated. What's more, many antigen tests results need to be confirmed with a PCR test, which could "open up a whole other Pandora's box," said Brownstein.
Testing needs to be ramped up to combat COVID-19, but data from testing needs to be more easily reportable and actionable -- more signals, less noise in the data.
"It requires more infrastructure and thought and care as we think about how to integrate all this data together," Adamson said.
Leah Croll, M.D., a neurology resident at NYU Langone Health, is a contributor to the ABC News Medical Unit. Sony Salzman is the unit's coordinating producer.