Health Corner

Why Do Test Results Need to Be Repeated Before a Confirmed Diagnosis?

Currently, there are two main types of COVID-19 testing:

1. Viral genetic testing (PCR test) – the gold standard for diagnosing COVID-19.

2. Antibody (serological) testing – mainly used as a supplementary diagnostic tool.

Each test type has its own advantages and limitations. In general, results may need to be confirmed through repeated testing due to factors such as insufficient viral load or low antibody levels. Details are as follows:

Viral Genetic Test

1. Patients with mild symptoms may begin to recover 10–14 days after onset, during which viral levels decrease, making detection more difficult.

2. The accuracy of results may be affected by the sampling site. If the sample contains too few viral particles, the result may not reflect the actual infection status.

Antibody Test

1. The immune system produces antibodies relatively slowly (usually around 7 days after infection), meaning levels may initially be too low to detect.

2. Differences in reagent quality can reduce test sensitivity.

3. Improper storage or transportation of test reagents can cause them to lose effectiveness.

To minimize missed diagnoses, testing may need to be performed multiple times. Combining laboratory results with clinical symptoms and chest imaging can significantly improve diagnostic accuracy.

What Are False Negatives and False Positives?

To understand this, note that test results do not only indicate positive or negative outcomes. They can also include false positives and false negatives, which represent inaccurate results.

• False Positive (FP): A positive test result even though the person is not infected.

• False Negative (FN): A negative test result even though the person is infected.

Possible reasons include:

• Low viral load during the early stage of infection, resulting in a false negative.

• Sample collected from a site with insufficient viral presence.

• Differences in testing materials between laboratories.

• Improper sample collection technique.

• Degradation of the virus due to environmental conditions.

• Contamination of samples during testing, leading to a false positive.

Highly sensitive tests can detect more true positive cases accurately. In contrast, low-sensitivity tests may produce more false negatives, causing infected individuals to wrongly believe they are virus-free and delaying treatment.

Therefore, repeated testing, along with clinical assessment and lung imaging, is essential to ensure diagnostic accuracy and confirm or rule out infection.