Which symptom indicates severe dehydration in infants?

The symptom that indicates severe dehydration in infants is the absence of tears when crying. In healthy infants, crying is typically accompanied by tears, as tear production is a sign of adequate hydration status. When an infant becomes severely dehydrated, the body conserves water, which affects the production of tears. This absence of tears is a critical indicator that the infant may be experiencing a significant fluid deficit.

The other symptoms—frequent crying, change in appetite, and increased energy levels—do not specifically signify severe dehydration. Frequent crying can occur for various reasons unrelated to hydration, changes in appetite can happen with several developmental or health issues, and increased energy levels are generally contrary to the lethargy that often accompanies dehydration. Therefore, the lack of tears when crying stands out as a clear and specific symptom of severe dehydration in infants.