The gold standard for Covid-19 diagnosis is RT-PCR for SARS-CoV-2 from the upper airways. This method suffers from decreased accuracy in more severe disease stages affecting the lower airways. False negative PCR tests in severe cases impose a massive risk to the health system, promoting intra-hospital disease spread in the actual pandemic situation. Reports from China indicate false negative PCR from upper airway samples in severe Covid-19 pneumonia in more than 50% of the cases. Therefore, complementary tests for the detection of these dangerous cases are urgently needed. The value of che...