Plasma Leptin Is Increased in Intensive Care Patients with COVID-19—An Investigation Performed in the PronMed-Cohort

COVID-19 has shaken the world and intensive care units (ICU) have been challenged by numerous patients suffering from a previously unknown disease. Leptin is a polypeptide pleiotropic hormone, mainly expressed by adipocytes. It acts as a proinflammatory cytokine and is associated with several conditions, known to increase the risk of severe COVID-19. Very little is known about leptin in severe viral disorders. Plasma leptin was analyzed in 222 out of 229 patients with severe COVID-19 on admission to an ICU at Uppsala University Hospital, a tertiary care hospital in Sweden, and compared to plasma leptin in 25 healthy blood donors. COVID-19 was confirmed by positive PCR. Leptin levels were significantly higher in patients with COVID-19 (18.3 ng × mL(−1); IQR = 30.4), than in healthy controls (7.8 ng × mL(−1); IQR = 6.4). Women had significantly higher leptin values (22.9 ng × mL(−1); IQR = 29.8) than men (17.5 ng × mL(−1); IQR = 29.9). Mortality at 30 days was 23% but was not associated with increased leptin levels. Neither median duration of COVID-19 before admission to ICU (10 days; IQR = 4) or median length of ICU stay (8 days; IQR = 11) correlated with the plasma leptin levels. Leptin levels in COVID-19 were higher in females than in males. Both treatment (e.g., use of corticosteroids) and prophylaxis (vaccines) have been improved since the start of the COVID-19 pandemic, which may contribute to some difficulties in deciphering relations between COVID-19 and leptin.