CD163 and acute respiratory distress syndrome: In COVID-19 patients, secondary HLH and the cytokine storm may be responsible for the unexplained progressive fever, cytopenia, ARDS, neurological and renal impairment.[4] Therefore, mast cell activation syndorome should be considered in a patient with COVID-19 with signs of rapid deterioration of clinical and laboratory-derived parameters.[4] We could not estimate the natural killer cell activity as per the HLH-2004 pediatric diagnostic criteria and the CD163.[4] It seems that we could cover the diagnostic criteria depending on the cell activation value.