Which diagnostic test confirms a diagnosis of hypokalemia?

The serum potassium level is the definitive diagnostic test for confirming hypokalemia, which is characterized by low levels of potassium in the blood. Hypokalemia can lead to various clinical manifestations, including muscle weakness, cramping, and arrhythmias.

Measuring the serum potassium level directly assesses the concentration of potassium in the bloodstream, allowing healthcare providers to determine if the patient is indeed experiencing hypokalemia. Typical reference ranges for serum potassium are approximately 3.5 to 5.0 mEq/L, and levels below this range are indicative of hypokalemia.

Other tests listed do not specifically measure potassium levels. A complete blood cell count evaluates components of blood such as red blood cells, white blood cells, and platelets but does not provide information on electrolyte imbalances. An X-ray film of long bones is generally used to assess structural integrity or abnormalities of bones, not electrolyte levels. Blood cultures are essential for detecting infections but are unrelated to evaluating potassium levels. Therefore, the serum potassium level is the most appropriate and direct test for confirming a diagnosis of hypokalemia.