EVIDENCE-BASED ANSWER
Routine infant diarrhea requires no lab work or cultures (strength of recommendation [SOR]: C); the degree of dehydration can be determined reliably by percent body weight change (SOR: B). However, bicarbonate may help rule out dehydration (SOR: B); electrolytes and blood urea nitrogen may be useful in evaluating complicated diarrhea with severe dehydration or when intravenous fluids are required; stool cultures are indicated for bloody or prolonged diarrhea, suspected food poisoning, or recent travel abroad (SOR: C).
Oral rehydrating solution is adequate fluid replacement for diarrhea associated with mild to moderate dehydration, followed by prompt refeeding with an age-appropriate diet (SOR: A); intravenous fluids are recommended for severe dehydration (SOR: C). Probiotics have been shown to safely reduce the duration and frequency of diarrhea (SOR: A).
Evidence summary
Evidence is summarized in the Table. Evaluation of an infant with diarrhea usually requires only a thorough history and physical exam. While no clinical trials have tested the impact of blood or stool testing on patient outcome, a recent systematic review suggested the only blood test reliable for ruling out dehydration is a serum bicarbonate greater than 15 to 17 mEq/L.1 Consensus reports have suggested laboratory studies are unnecessary unless dehydration is severe or IV fluids are required; stool cultures are necessary only for bloody or prolonged diarrhea, systemically ill infants, suspected food poisoning, or recent travel abroad.2,3
Effective management of infant diarrhea is based on the degree of dehydration, which can be estimated by percent body weight loss—the difference between the baseline and acute weights, divided by the baseline weight.3 If the baseline weight is not known, prolonged capillary refill time, abnormal skin turgor, and abnormal respiratory pattern are more reliable indicators of dehydration; other physical findings are less precise.1
Infants with diarrhea who are not dehydrated should continue age-appropriate nutrition.4 For infants with mild to moderate dehydration, however, rehydration using oral rehydrating solution is the initial therapy, followed by continued hydration to replace ongoing losses.2,3 A meta-analysis of randomized controlled trials (RCTs) in developed countries demonstrated equivalent efficacy of oral fluids compared with IV fluids, with an overall failure rate of only 3.6% for infants and children treated with oral rehydrating solution (95% confidence interval [CI], 1.4–5.8). There was no significant difference between oral rehydrating solution of varying sodium concentrations, and no increased risk of hypernatremia or hyponatremia compared with the IV treatment arm.5 Continued breastfeeding during the rehydrating phase significantly reduced dehydration (based on case control studies; odds ratio [OR]=5.23; 95% CI, 1.37–19.99; P=.016, limited by sample size).3,6 Breastfeeding also significantly reduced the number of diarrheal stools (found in a small-scale RCT).7 For obtunded or severely dehydrated infants, or those with an ileus or persistent vomiting, expert opinion suggested IV fluids.2,4