Cow's milk associated rectal bleeding: a population based prospective study. 
Isolated rectal bleeding in infants is often attributed to the consumption of cow's milk.  However, the prevalence of this condition has not been described, and its preferred diagnostic methods and management are controversial.  In a prospective population-based study following 13,019 children from birth, 21 infants with isolated rectal bleeding attributed to cow's milk protein consumption were identified.  Following evaluation, parents were encouraged to resume cow's milk protein and infants were followed for reappearance of symptoms and thereafter for 6 yr.  In addition, infants with rectal bleeding were compared to a control group of healthy infants.  The prevalence of isolated rectal bleeding attributed to cow's milk consumption was 0.16%.  All infants were asymptomatic within days of dietary modifications.  Eleven of the 14 infants (78.5%) whose parents reintroduced cow's milk protein to their diet following our evaluation tolerated it with no adverse effects.  Those 11 infants were significantly younger at initial consumption of cow's milk protein (6.7 ± 1.6 months) compared to those who continued elimination diet (17.7 ± 9.2 months), (p = 0.002) while their 1-yr hemoglobin levels were comparable (p = 0.98).  No risk factors for rectal bleeding were identified.  The prevalence of isolated rectal bleeding attributed to cow' milk is low.  The condition is generally benign and resolves quickly with elimination diet.  Reintroduction of cow's milk following resolution of symptoms is often well tolerated and is recommended for confirming the diagnosis and avoiding prolonged unnecessary elimination diets.