Receiving a COVID-19 test result that is neither clearly positive nor negative can be confusing and lead to significant uncertainty. Terms like “abnormal,” “invalid,” or “inconclusive” indicate that the testing process did not yield a definitive answer regarding an active infection with SARS-CoV-2. This ambiguity does not automatically signify a positive result, but it also cannot rule out the presence of the virus. Understanding what these results mean, why they occur, and what steps to take next is necessary for protecting both personal health and public safety.
Defining Positive, Negative, and Inconclusive
A positive test result indicates that the test successfully detected evidence of the SARS-CoV-2 virus in the collected sample. For a molecular test, such as a PCR, this means the genetic material of the virus was found, signifying an active infection. A rapid antigen test returns a positive result when it identifies specific viral proteins (antigens) present in high concentrations during the acute phase of illness.
A negative result means that the test did not detect the presence of viral genetic material or antigens at the time the sample was collected. However, a negative result is not an absolute guarantee of non-infection, as the virus may still be present at levels too low for the test to pick up, particularly early in the course of the illness. This is often the case with less sensitive rapid antigen tests compared to molecular PCR tests.
An inconclusive or invalid result is distinctly different from a negative one because it signifies a technical failure rather than the absence of the virus. This outcome means the laboratory or the test itself was unable to interpret the sample to determine if the virus was present or absent. Therefore, an inconclusive result is not equivalent to a positive finding, but it leaves the infection status unknown, requiring further investigation.
Causes of Ambiguous Test Outcomes
Ambiguous results arise from various issues that interfere with the test’s ability to reliably complete its detection process.
Technical Failure
One primary reason is technical failure, often seen in rapid at-home tests when the control line does not appear. The control line confirms that the test reagents are working correctly and that the sample has properly flowed across the test strip. If this control mechanism fails, the entire result is deemed invalid, regardless of whether a positive line appeared. Laboratory-based molecular tests, such as PCR, can also experience technical issues, including equipment malfunction or cross-contamination, which can lead to an uninterpretable result.
Sample Quality Issues
Other failures relate to sample quality, where an insufficient amount of material was collected during the swabbing process. A swab that is not correctly inserted or rotated enough may not gather the minimum viral particles or human cells needed for accurate analysis. Improper handling or storage of the specimen during transport to the lab, such as mislabeling or contamination, can also compromise the sample, making it unusable.
Low Viral Load
A third category involves low viral load, which can lead to an “indeterminate” or “inconclusive” reading, particularly with highly sensitive PCR tests. This happens when the amount of viral genetic material is present but falls near the test’s limit of detection. The virus may be present at a low level because the person is very early in the infection cycle, or conversely, nearing the end of their illness. While the test detects something, it is not enough to cross the threshold for a definitive positive result, leaving the status ambiguous.
Navigating Next Steps and Retesting
Upon receiving an inconclusive or abnormal test result, the immediate action is to self-isolate, especially if symptoms are present or if there has been a known exposure to someone with COVID-19. Since the test could not rule out infection, public health guidance suggests treating the result as a presumptive positive until a definitive status can be determined. This temporary isolation helps prevent potential transmission if the ambiguous result was masking an early or waning infection.
The next step involves seeking guidance from a healthcare professional or the testing facility that processed the sample. They can provide specific advice tailored to the individual’s symptoms, exposure history, and the type of test originally administered. This consultation is important for individuals with underlying health conditions or those whose symptoms are worsening.
Retesting is necessary to resolve the ambiguity and obtain a clear result. If the initial test was an inconclusive rapid antigen test, a follow-up PCR test is often recommended due to its higher sensitivity, which can more accurately detect low levels of the virus. The recommended timing for a retest is typically within 24 to 48 hours of the initial ambiguous result. Getting a clear positive or negative result from the follow-up test allows the individual to either end isolation or proceed with the recommended protocols for a confirmed infection.