How to read a PCR test result

A PCR test looks for genetic material from a virus in a sample, commonly collected from the nose or throat. The report may say positive, negative, detected, not detected, or occasionally invalid. The wording and the laboratory's reference range matter, so keep the full report available when discussing it.

A positive or detected result means the test found viral genetic material in the sample. It can support a diagnosis of COVID-19 when the test is for the virus that causes it, but it does not by itself describe how severe the illness is or whether symptoms will worsen.

A negative or not detected result means the test did not find enough target material in that sample at that time. A result can be negative if testing is done very early, after the amount of virus has fallen, or if the sample was difficult to collect. An invalid result means the laboratory could not reliably analyse the sample and may recommend another sample.

Check which virus was tested, when the sample was taken, and whether the report includes a note about retesting. Follow the instructions provided by the testing service or clinician. If the result is positive, limit close contact while following current local health advice, especially around people at higher risk of serious illness.

If the result is negative but you have ongoing symptoms or a recent exposure, contact a clinician about whether repeat testing or another assessment is appropriate. A rapid antigen test and a PCR test use different methods, so their results may not be interchangeable in every situation.

Seek urgent medical help for severe difficulty breathing, new confusion, inability to stay awake, or blue, grey, or very pale lips or skin. Do not wait for a PCR result if you feel seriously unwell.

Arrange medical advice promptly if symptoms are getting worse, you cannot keep fluids down, or you have a health condition or treatment that may increase the risk of complications. Take the test report, symptom timeline, and list of medicines with you.

Ask which result wording applies to your sample, whether the timing could affect confidence in the result, and whether you need repeat testing. You can also ask how long to avoid close contact, which symptoms need monitoring, and whether your existing medicines or health conditions change the next step.