A 9-month-old with diarrhea has a slightly depressed anterior fontanel and normal capillary refill. What percent dehydration is most likely?

A 9-month-old with diarrhea has a slightly depressed anterior fontanel and normal capillary refill. What percent dehydration is most likely?

• A. 3%
• B. 5%
• C. 8%
• D. 10%

Answer: (C)

In infants, estimating dehydration relies on clinical signs such as how sunken the fontanel is and how well perfusion appears. A slightly depressed anterior fontanel points to fluid loss, but a normal capillary refill indicates that perfusion is still adequate and the dehydration isn’t severe. This combination fits the range of some dehydration, which is typically around 5–9% of body weight. Eight percent lies squarely in that range, making it the best match. If dehydration were mild (around 3%), the fontanel might not be notably sunken, and if it were severe (10% or more), you’d expect signs of poor perfusion such as delayed capillary refill, tachycardia, or lethargy.

In infants, estimating dehydration relies on clinical signs such as how sunken the fontanel is and how well perfusion appears. A slightly depressed anterior fontanel points to fluid loss, but a normal capillary refill indicates that perfusion is still adequate and the dehydration isn’t severe. This combination fits the range of some dehydration, which is typically around 5–9% of body weight. Eight percent lies squarely in that range, making it the best match. If dehydration were mild (around 3%), the fontanel might not be notably sunken, and if it were severe (10% or more), you’d expect signs of poor perfusion such as delayed capillary refill, tachycardia, or lethargy.