An otherwise healthy elderly client develops the sudden onset of confusion, lethargy, anorexia, and nocturia. The nurse should expect an order for which of the following lab test to assess this sudden change in health status?

Delirium in the elderly is an acute, fluctuating disturbance of attention, awareness, and cognition that develops over hours to days, often triggered by infection, medications, surgery, or metabolic imbalance. It is common in hospitalized older adults and is reversible if the underlying cause is identified and treated. Rationale: A. In older adults, a sudden change in mental status, such as confusion and lethargy, often indicates an underlying infection rather than primary neurologic disease. A urinary tract infection is a common cause of acute mental status changes in this population, and symptoms may be atypical, presenting without classic urinary complaints. Nocturia may also suggest urinary involvement. A urinalysis is the most appropriate initial diagnostic test to evaluate for infection. B. Anemia typically causes fatigue and weakness but does not usually present with sudden confusion or acute mental status changes. C. Acute hepatitis would more commonly present with jaundice, right upper quadrant pain, and nausea rather than sudden confusion and nocturia. D. Although electrolyte imbalance or dehydration can contribute to confusion, the combination of symptoms (especially nocturia and acute mental status change) is more suggestive of infection in this scenario. Electrolytes may still be ordered, but they are not the primary diagnostic focus here.