Which diagnostic test is most appropriate in a child suspected of having Kawasaki disease with persistent fever and rash?

In the evaluation of a child suspected of having Kawasaki disease, the most appropriate diagnostic test is the measurement of the elevated erythrocyte sedimentation rate (ESR). This is a common laboratory finding in patients with Kawasaki disease, as it indicates an inflammatory response in the body. Kawasaki disease is characterized by systemic inflammation that affects blood vessels, and the elevated ESR helps provide supportive evidence for the diagnosis in conjunction with the typical clinical features, such as persistent fever, rash, conjunctivitis, and changes in lips and oral mucosa.

Elevated ESR is not specific to Kawasaki disease but can indicate inflammation due to several conditions. However, given the acute and specific context of Kawasaki disease, it contributes significantly to diagnosing this syndrome when integrated with the clinical picture.

The other options, such as measuring N-terminal moiety of B-type natriuretic peptide, are more indicative of heart strain rather than directly associated with Kawasaki disease diagnosis. Mucosal tissue biopsy is not a routine or necessary step in the diagnosis of Kawasaki disease; instead, it is assessed primarily through clinical criteria. Finally, stating that no laboratory tests are necessary overlooks the importance of laboratory findings, like elevated ESR, which can aid in the diagnosis of Kawasaki disease when combined with clinical symptoms. Thus