Fig. 3.

Suggested approach to serologic testing of patients without past infection and negative rRT–PCR. Assessment of the patient's clinical condition consists of medical history, symptoms, and CT scan. Contact with suspected COVID–19 case, typical symptoms (fever, dry cough, fatigue) and distinctive CT image (ground-glass opacities, patchy consolidations) suggest a high risk of SARS–CoV–2 infection. For this reason, positive serology can suggest the early or late phase of infection. It is also necessary to exclude the risk of false-negative rRT–PCR study, so repeating the molecular test is advisable. No contact with suspected COVID–19 case, oligosymptomatic or asymptomatic infection, and nonspecific CT image suggest a low risk of infection. Convalescence, a past infection, and false-positive serology should be considered in these cases. Due to no prior disease, negative rRT–PCR, and low risk of infection, it seems unnecessary to perform repeat testing. However, negative rRT–PCR and negative serology indicate the false-negative rRT–PCR and “window period” in cases with high risk of infection. It is advisable to repeat the rRT–PCR test. Insignificant medical history, negative rRT–PCR, negative serology, and low risk of COVID–19 suggest no active and past infection. rRT–PCR – real-time Reverse–Transcription Polymerase Chain Reaction, COVID–19 – Coronavirus Disease 2019, CT – Computer Tomography. SARS–CoV–2 – Severe Acute Respiratory Syndrome Coronavirus 2.