Comparing and contrasting RT-PCR & Rapid Antigen Tests
To get an insight into RT-PCR tests and Rapid Antigen Tests, the Sunday Times contacted Consultant Virologist Dr. Rohitha Muthugala of the Kandy Teaching Hospital.
RT-PCR (Reverse-Transcription Polymerase Chain Reaction) test –
■ The test specimens are from nasopharyngeal ( upper part of the throat) and oro- pharyngeal ( middle part of the throat) swabs. Checks the viral RNA (ribonucleic acid) through an enzyme reaction by amplifying a small amount of RNA.
■ Overall, the sensitivity is 70%, but if the infection is in the upper-respiratory tract, it is 80-90% sensitive and if the infection is in the lower-respiratory tract, it is 60-70% sensitive. Time- wise the testing takes about 4 hours without considering the specimen preparation time.
■ The testing is done in batches ( not individually), in 24, 48 or 96-specimen batches.
■ The advantage is that the test can even find a low viral load but sometimes by that time the patient may not be infective (capable of causing infection).
■ It is a technically difficult test to do and could exhaust both the required material and personnel handling it. It needs a sophisticated laboratory with the personnel needing specialized training.
■ The cost is high.
Rapid Antigen Test –
■ The test specimens are from nasopharyngeal swabs.
■ Checks the viral protein (the jutting out spikes of the virus). There is no amplification involved. Sensitivity is very high when the viral load is high and low when the viral load is low.
Time-wise, it takes only about 20 minutes.
■ The testing can be done individually. As the test finds those having a high viral load, it is good to identify them as they are very infectious at this time. It is a relatively easy test to carry out. It does not need a sophisticated laboratory and can be carried out in a field setting.
■ The cost is low.
Dr. Muthugala added that the RT-PCR Test is the gold standard in diagnosing patients, while the Rapid Antigen Test can be used as a screening tool to detect patients who are in the infectious period, making this an advantage.