PTH and Hypocalcemia: The cause of hypocalcemia in patients with COVID-19 is not clear, but is likely to be multifactorial, including calcium-dependent viral mechanisms of action, hypoproteinemia, imbalanced vitamin D and parathyroid hormone levels in the acute phase of COVID-19 infection, chronic and acute malnutrition during critical illness, and high levels of unbound and unsaturated fatty acids in inflammatory responses.