Final answer:
To confirm dehydration in a 2-month-old with a history of vomiting and diarrhea, serum electrolytes is the most appropriate test. This blood test can reveal the balance of electrolytes, which is often disrupted in dehydration. Other tests mentioned are less specific or not indicated for diagnosing dehydration.
Step-by-step explanation:
The question pertains to a 2-month-old with a 24-hour history of vomiting and diarrhea, presenting with signs of dehydration such as sunken fontanel and absence of tears. To confirm dehydration, the most appropriate test among the options given is c. Serum electrolytes. This blood test can reveal the balance of electrolytes in the body, which is often disrupted in cases of dehydration due to vomiting and diarrhea. A urine analysis (UA), whether obtained by bag or catheter, can provide information on dehydration but is less specific than serum electrolyte levels. A cerebrospinal fluid (CSF) test is not indicated for dehydration diagnosis.
It is crucial to identify and treat dehydration promptly, as severe dehydration can have significant health implications, especially in young children. If a patient is severely dehydrated, such as the one described, they may require rehydration through intravenous fluids in a medical setting.