What is the highest priority deficiency to assess in an 81-year-old woman presenting with confusion and hallucinations?

In assessing an 81-year-old woman presenting with confusion and hallucinations, the highest priority deficiency to evaluate is Vitamin B12. This vitamin is essential for proper neurological function, and its deficiency can lead to significant neurological and psychiatric symptoms such as confusion, memory loss, and hallucinations.

Older adults are particularly at risk for Vitamin B12 deficiency due to factors such as decreased absorption related to atrophic gastritis, the use of certain medications, or dietary insufficiencies. Symptoms of Vitamin B12 deficiency can mimic other forms of dementia or psychiatric disorders, making it crucial to rule this out as a potential cause for the patient's presentation.

While deficiencies in iron, folate, or calcium can have significant health implications, they do not typically present with confusion and hallucinations as prominently as Vitamin B12. Iron deficiency primarily leads to anemia, folate deficiency can result in anemia and some neurological symptoms, but it does not generally cause the acute neurological changes seen in B12 deficiency. Similarly, calcium deficiency may lead to more physical manifestations or muscle cramps rather than specific neurological symptoms. Therefore, assessing for Vitamin B12 deficiency is the most critical step in this clinical scenario.