A 38-year-old woman from Delhi presents with a 3-day history of fever, cough, and dyspnea. Chest X-ray shows bilateral ground-glass opacities. She is suspected to have COVID-19. Which investigation is the most appropriate for confirming the diagnosis?

Explanation

## Diagnostic Confirmation of COVID-19 **Key Point:** RT-PCR (reverse transcription polymerase chain reaction) targeting the viral RNA is the gold standard for confirming active SARS-CoV-2 infection. ### Why RT-PCR is the Investigation of Choice 1. **Highest sensitivity and specificity** — detects viral RNA during the acute phase (typically days 1–14 of illness) 2. **Nasopharyngeal and oropharyngeal swabs** are the preferred specimen sites for upper respiratory tract sampling 3. **Rapid turnaround** — results available within 24–48 hours in most settings 4. **Gold standard** — recommended by WHO, CDC, and Indian Council of Medical Research (ICMR) for diagnosis **High-Yield:** RT-PCR remains positive for 5–14 days after symptom onset; sensitivity is highest in the first week of illness. ### Timing of Serological Tests | Test | Timing | Clinical Use | |------|--------|---------------| | IgM antibodies | Appears day 5–7 | Late confirmation, not acute diagnosis | | IgG antibodies | Appears day 10–14 | Past infection, immunity assessment | | RT-PCR | Day 1–14 | **Acute diagnosis (gold standard)** | **Clinical Pearl:** In this patient with acute symptoms (fever, cough, dyspnea) and radiological findings consistent with COVID-19 pneumonia, RT-PCR is the definitive test. Antibody testing would be falsely negative in the first 5–7 days. **Warning:** Do not rely on serology for acute diagnosis — IgM may be negative in the first week of illness, leading to false reassurance.