Rosh Emergency Medicine Practice Test

Which laboratory finding is essential to obtain before initiating insulin in a patient with suspected diabetic ketoacidosis?

1. Bicarbonate

2. Glucose

3. Potassium

4. Sodium

The correct answer is: Potassium

In managing a patient with suspected diabetic ketoacidosis (DKA), obtaining a potassium level before initiating insulin therapy is crucial. Insulin drives potassium back into cells, which can lead to a significant decrease in serum potassium levels, particularly in patients with DKA who may already have underlying electrolyte imbalances. Many patients with DKA present with a degree of hyperkalemia due to acidosis and cell breakdown, but upon administration of insulin, their potassium levels can rapidly drop, potentially leading to life-threatening hypokalemia. Therefore, it is essential to check potassium levels to guide treatment. If the potassium level is low (below 3.3 mEq/L), insulin administration should be delayed until potassium is corrected to avoid cardiac complications. While glucose, bicarbonate, and sodium levels are all important markers in the management of DKA, potassium is the critical laboratory finding needed to ensure safe administration of insulin and to prevent adverse effects associated with potassium shifts.