Oliguria in a 2-year-old Girl

A 2-year-old girl who has had diarrhea and vomiting for about 5 days was brought back to the emergency department for a second visit by her father because he was told that if the frequency of the child’s urination decreased, it could signal severe dehydration. The child has not had any significant pain but did have a low-grade fever and some blood in the stool earlier in the illness, both of which resolved about two days ago. The vomiting has also resolved.

Physical examination: Vital signs are normal except for mild tachycardia. Mucous membranes are moist. The abdomen is soft and non-tender. A rectal exam is deferred. Her skin appears a bit pale. The rest of the physical exam is normal.

TESTING: Blood chemistry results:  

Sodium              120 mEq/L

Bicarbonate         18 mEq/L

BUN                    102 mg/dL

Creatinine             4.4 mg/dL 

CBC                      platelets 42 x 10⁹/L;  Hgb 9.2 g/dL

WBC                     normal but smear shows both schistocytes and burr cells

What do you think is causing these crazy lab results?

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