2.1. Patients

A case-control study was performed on 70 adult patients diagnosed with COVID-19, confirmed cases on a clinical, radiological, and laboratory basis according to the diagnostic guidelines of the Saudi Ministry of Health. They were admitted to King Abdulaziz Hospital in Jeddah Saudi Arabia between March 2021 and July 2021. Fourteen [14] age- and sex-matched individuals who were apparently healthy were included in this study as a control group.

Inclusion criteria: The patients were admitted to King Abdulaziz hospital, where the blood samples were collected. The patients were clinically and radiologically diagnosed as COVID-19 cases and were confirmed in the Regional Laboratory, Jeddah, KSA through positive testing of respiratory samples for SARS-CoV-2 by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) using LightCycler 480 II Roch, Germany. The control group included healthy healthcare workers who had a negative screening for SARS-CoV-2 using RT-PCR. The limited size of the control group was attributed to the limited number of healthy controls available during the pandemic (those not infected with COVID-19 and not vaccinated), as most of the population were currently or previously COVID-19-infected.

The patients were clinically classified according to the National Health Commission of China’s New Coronavirus Pneumonia Prevention and Control Program July 2020 [28], as follows: mild cases: mild clinical symptoms, with no signs of pneumonia on the imaging examination; moderate cases: showing respiratory symptoms and fever, accompanied by manifestations of pneumonia during imaging; severe cases: for adults, the cases met any of these criteria: oxygen saturation ≤ 93% at rest, shortness of breath with a respiratory rate of ≥ 30 times/min, or an arterial oxygen partial pressure (PaO2)/oxygen concentration (FiO2) ≤ 300 mmHg (1 mmHg = 0.133 kPa); critical cases: any cases that met any of the following criteria: shock, respiratory failure which requires mechanical ventilation, or another organ failure that requires admission to the intensive care unit (ICU). Patients were followed up for the determination of outcome as survivors (hospital discharge) or deceased (in-hospital death).

Patient groups were divided as follows:

Exclusion criteria were chronic infections (HCV, HBV), cancers, any immunological disorders or patients on immunosuppressive drugs or chemotherapy, any underlying hematological disorder, and laboratory and clinical signs of other infections that were not COVID-19.