A known diabetic patient is admitted with sudden loss of consciousness. What is the initial investigation that should be performed?

In the scenario of a known diabetic patient who experiences sudden loss of consciousness, the most immediate and relevant initial investigation is checking the random blood sugar level. This is crucial because loss of consciousness in diabetic patients can often be attributed to hypoglycemia (low blood sugar) or hyperglycemia (high blood sugar), both of which are acute complications of diabetes.

Determining the blood sugar level quickly can guide the management of the patient. If hypoglycemia is confirmed, immediate intervention with glucose can be instituted, potentially reversing the loss of consciousness rapidly. On the other hand, if hyperglycemia is the issue, further interventions tailored to that condition can be initiated.

Other investigations, such as a CT scan or MRI, are more appropriate in the context of ruling out structural brain issues, but they do not address the immediate concern of metabolic derangement that may be life-threatening. An ECG could help assess cardiac issues but is not specific enough to differentiate the cause of loss of consciousness in a diabetic context. Thus, measuring blood sugar is the most pertinent and actionable first step.