Which initial laboratory test is most appropriate for a 30-year-old woman with abdominal pain and diarrhea?

In evaluating a patient with abdominal pain and diarrhea, initiating the diagnostic process often involves obtaining a complete blood count (CBC). This test is valuable because it provides insights into the overall health of the patient, including the presence of anemia, infection, or inflammation. In particular, the CBC can reveal white blood cell counts that may indicate an infectious process, as well as hemoglobin levels that can suggest blood loss or dehydration, both of which can accompany gastrointestinal issues.

While other tests, such as stool cultures or Giardia antigen tests, are specific for particular conditions and can be essential later in the diagnostic process, starting with a CBC helps to quickly assess the patient’s general health status and guides further testing based on the findings. In cases of gastrointestinal distress, recognizing signs of systemic effects and ruling out potential complications is crucial, making the CBC a foundational first step in the evaluation.

Tests like thyroid stimulating hormone (TSH) would be less immediately relevant unless there were strong indications of thyroid dysfunction, which typically presents differently, while focusing solely on parasites or specific bacteria like Giardia may miss other critical underlying issues. Therefore, utilizing a complete blood count first allows for a comprehensive initial assessment that can direct subsequent diagnostic efforts appropriately.