Critically ill patients, especially those with sepsis, often have low calcium levels and high levels of calcitonin precursors in their blood. A study looked at 101 patients in intensive care and found that as the severity of the illness increased, calcium levels decreased and calcitonin precursor levels increased. This suggests that high levels of calcitonin precursors may contribute to the low calcium levels seen in these patients. Other factors like vitamin D and parathyroid hormone levels did not seem to play a role in this process. Further research is needed to understand how these calcitonin precursors affect calcium levels in critically ill patients with sepsis.