Rosh Internal Medicine Practice Exam

During insulin therapy for diabetic ketoacidosis, electrolytes can shift between the blood and inside cells as glucose goes into cells. Phosphate is especially important because, in DKA, total body phosphate is often depleted from diuresis and poor intake, even if initial serum levels aren’t obviously low. Once insulin is started, phosphate moves into cells along with glucose, which can cause a notable drop in serum phosphate. This hypophosphatemia can impair energy production in muscles, including respiratory and cardiac muscles, and may lead to weakness, respiratory failure, or hemolysis if severe. Because of this risk, phosphate levels should be monitored during treatment and replaced if they fall to a low level or if there are signs of deficiency. While other electrolytes also shift during therapy, phosphate has a distinct and potentially serious impact on organ function when it drops in response to insulin.