A 32-day-old term girl is brought to the ED by her grandparents for ongoing emesis with feeds and weight loss. The patient’s birth history was complicated by limited prenatal care, maternal narcotic dependence, perinatal hepatitis C exposure, and a 14-day stay in the NICU for thrombocytopenia requiring platelet transfusion, with the eventual diagnosis of May-Hegglin anomaly. At hospital discharge she had a normal platelet count, was tolerating 40 to 90mL of formula every 3 hours and had no issues with voiding or elimination. Weight at the time of discharge (13 days of age) was 2.5% below birthweight.

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The patient now presents with frequent projectile, non-bloody, non-bilious emesis within an hour after feeds since discharge. The addition of ranitidine by her pediatrician within days of discharge did not improve her symptoms. Outpatient pyloric ultrasonography was not suggestive of pyloric stenosis. The patient takes approximately 1oz of formula every 3 to 4 hours and now vomits after almost every feed. The family notes decreased wet diapers. Stools have been soft, formed, but not diarrheal. Stool frequency of once per day has been unchanged.

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On initial exam the infant is pale, cachectic and tired appearing. Her weight of 2,560gm is down 21.7% from 3,270gm at birth. The anterior fontanelle is sunken and capillary refill time is 4 to 5 seconds. Heart rate is 176 and respiratory rate 32, with normal oxygen saturation. Her abdomen is soft and nondistended with normal bowel sounds.  The remainder of the examination findings are normal. Lab studies are significant for the following: borderline low potassium of 3.8, low chloride of 92, bicarbonate of 29, and BUN of 24.

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What is your differential diagnosis at this point?

 

Based on your differential diagnosis, which of the options below is likely to be the highest yield next diagnostic step?

(A) Blood culture

(B) Urinalysis

(C) Abdominal x-ray

(D) Head CT

(E) CMP