Which investigation would be most useful for diagnosing hypoglycemia in a diabetic patient presenting with confusion and sweating?

The most useful investigation for diagnosing hypoglycemia in a diabetic patient presenting with confusion and sweating is a random blood sugar test. This is primarily because hypoglycemia is characterized by low blood glucose levels, and a random blood sugar test can quickly determine the patient's glucose status at the time of presentation.

In cases of hypoglycemia, patients often experience symptoms such as confusion, sweating, trembling, and irritability, and a timely measurement of blood glucose is crucial for confirming the diagnosis and guiding immediate management decisions. If low blood sugar is confirmed, appropriate treatment can be initiated quickly to alleviate the patient’s symptoms and prevent further complications.

Fasting blood sugar tests are less appropriate in acute situations because they require the patient to have fasted for a certain period. Electrocardiogram and serum electrolytes, while useful for assessing other conditions, do not provide information on blood glucose levels and therefore are not valuable for diagnosing hypoglycemia specifically. These other investigations might reveal additional concurrent issues but would not address the immediate concern of low glucose levels directly.