Final answer:
A stumbling, incoherent alcoholic in the emergency room should be assessed for thiamine (Vitamin B1) deficiency, which can lead to neurological issues such as Wernicke's encephalopathy, a condition frequently associated with alcohol abuse.
Step-by-step explanation:
A person known to be an alcoholic who presents with stumbling and incoherence should be checked for a thiamine deficiency, which is part of the Vitamin B complex (specifically Vitamin B1). The clinical condition of severe thiamine deficiency is known as Wernicke's encephalopathy, particularly common amongst alcoholics. Alcohol impairs thiamine absorption and increases its excretion, leading to a deficiency.
Thiamine is critical for nerve function and energy metabolism; its deficiency can cause serious neurological issues such as confusion, ataxia, and ophthalmoplegia, and may develop into Wernicke-Korsakoff syndrome if not treated. Hence, Vitamin B1 levels should be assessed in this case, rather than Vitamin C, iron, or calcium deficiencies, which are less commonly associated with alcoholism.