A 58-year-old man with diabetes shows symptoms of drowsiness and fatigue. Which initial investigation should be performed?

In the context of a patient exhibiting symptoms such as drowsiness and fatigue, particularly one with a known history of diabetes, the most immediate and appropriate investigation to conduct is a blood glucose measurement. The rationale behind this is that individuals with diabetes are at a heightened risk for both hyperglycemia (high blood sugar) and hypoglycemia (low blood sugar), which can present with similar nonspecific symptoms like fatigue and altered alertness.

Measuring blood glucose can provide quick and crucial information about the patient's current glycemic status. If the blood glucose level is found to be too high or too low, it will guide further management steps, such as administering insulin for hyperglycemia or glucose for hypoglycemia.

While fasting blood sugar can be informative in assessing long-term glycemic control, it is less urgent in acute scenarios where immediate symptoms need to be addressed. Similarly, measuring standing and lying blood pressure can be useful in some contexts, such as diagnosing orthostatic hypotension, but it does not directly address the immediate concerns raised by fluctuating blood glucose levels in a patient with diabetes. An electrocardiogram is typically warranted in cases of suspected cardiac issues, which is not the primary concern in this scenario.

Thus, assessing blood glucose promptly is