PCR Test
Reviewed
Also called: Nucleic acid amplification test (NAAT), Molecular test
PCR (polymerase chain reaction) tests are a reliable and accurate way to diagnose certain infectious diseases, some types of cancer, and certain genetic changes. They detect small amounts of genetic material (DNA or RNA) from a pathogen or abnormal cell in a sample. The test amplifies the genetic material to make it easier to detect. Results are typically qualitative (detected or not detected). Because PCR tests can find disease early, they play an important role in preventing the spread of infections.
Specimen: Blood, saliva, mucus, or tissue
Why this test may be ordered
- To diagnose an infectious disease (e.g., COVID-19, HPV, influenza)
- To identify genetic changes that cause disease
- To detect small amounts of cancer cells that may be missed by other tests
Preparation and collection
No special preparation is needed.
Blood draw, nasal swab (anterior nares, mid-turbinate, or nasopharyngeal), saliva, or tissue sample
Physical risks: Blood draw may cause slight pain or bruising. Nasal swabs may cause tickling, coughing, or gagging. Nasopharyngeal swabs may be uncomfortable and cause coughing or gagging. All effects are temporary. There is no risk of infection from the test itself.
Understanding results
A PCR test looks for genetic material (DNA or RNA) from a specific pathogen, cancer cell, or genetic change. The result is reported as detected or not detected. Your healthcare provider will explain what your result means for your health.
- Not Detected: No genetic material from the target pathogen, cancer, or genetic change was detected. Limitation: This result means the test did not find the targeted genetic material in your sample. It may be a true negative, but if your symptoms strongly suggest infection, a false-negative is possible (e.g., due to early infection or poor sample collection). Next step: If you were tested because of symptoms or exposure, follow your provider’s advice about monitoring for new symptoms and when to return to normal activities. No emergency action is needed.
- Detected: Genetic material from the target pathogen, cancer, or genetic change was detected in your sample. Limitation: This result means the test found the targeted genetic material. It may indicate an active infection, past infection (if only RNA fragments remain), or a genetic change. False positives are rare but possible, especially if contamination occurred during collection or processing. Next step: Contact your healthcare provider promptly to discuss the result and appropriate next steps, which may include treatment, isolation, or further testing. Do not delay if you have severe symptoms or were tested for a condition that requires urgent care.
- May detect genetic material from a past infection even after you are no longer infectious (false-positive for active infection).
- A poor sample (e.g., not swabbing both nostrils or not rotating the swab) can lead to a false-negative result.
What to do next
Your healthcare provider will interpret your result in the context of your symptoms, exposure history, and other tests. Follow-up may include additional testing or treatment if an infection or genetic change is detected.
- What is the specific genetic material (DNA or RNA) being tested for?
- How does this result affect my treatment or isolation recommendations?
- Do I need a repeat test or confirmatory testing?