Worldwide, thousands of children die each day from diarrhea and dehydration. Missing a diagnosis of dehydration, miscalculating its severity (and overtreating it), and treating nonexistent dehydration are all associated with substantial morbidity-not to mention considerable cost. A literature review conducted to evaluate the most effective means of assessing hydration status in children five years of age and younger found that under the best of circumstances, dehydration is difficult to diagnose.

Follow the signs.

The study authors determined that the findings of the physical examination, rather than the parents' report-in other words, signs rather than symptoms-were the most important indicators of dehydration and its severity. For example, a parent's assertion that urine output is low and histories of either diarrhea or vomiting were found not to be strongly associated with the likelihood of dehydration. Three signs in particular were found to be the most valuable:

* an abnormal capillary refill time (the time it takes for normal color to return to a superficial capillary bed after it's compressed)

* abnormal skin turgor (a delayed or slow returning of pinched abdominal skin to its normal shape)

* tachypnea

Several of the studies the authors reviewed examined the use of groups of signs and showed that, even though a number of these signs are not particularly sensitive when considered on their own, taken together they were more helpful in determining the presence of dehydration and its severity. These included general appearance, radial pulse, respiration rate, appearance of the anterior fontanelle, systolic blood pressure, abnormal skin turgor, the appearance of the eyes, the presence or absence of tears, and the condition of mucous membranes.

Laboratory testing.

Several studies looked at the specificity of laboratory values in determining hydration status, including blood urea nitrogen (BUN) levels, the BUN-creatinine ratio, the concentration of bicarbonate, the base deficit, the pH level, the anion gap, and the uric acid level. Surprisingly, only the bicarbonate concentration was valuable; a concentration higher than 15 mEq/L or 17 mEq/L (depending on the study) indicated the absence of dehydration in children with gastroenteritis.

The bottom line, as noted by the authors, is that the signs, rather than the symptoms, should guide treatment decisions.-Doug Brandt

Steiner M, et al. JAMA 2004;291(22):2746-54.