Case 5: Autoantibodies and an Elevated Creatinine in a 14-year-old Girl

Presentation

A previously healthy 14-year-old girl presents with 2 weeks of malaise and abnormal laboratory results. She presented to her pediatrician 1 week ago with fever and fatigue and received amoxicillin for culture-positive streptococcal pharyngitis. However, she had no improvement and began having daily episodes of nonbloody, nonbilious emesis. One day ago she noted decreased urine output, facial puffiness, and mild abdominal distention. Currently, she reports no headaches, epistaxis, sinusitis, or respiratory symptoms.

On physical examination, she is afebrile, with a heart rate of 78 beats/min and blood pressure of 149/85 mm Hg. She appears well, with normal physical findings except mild facial and lower extremity edema and mild abdominal distention.

Initial laboratory results are:

• Sodium 125 mEq/L (125 mmol/L)

• Potassium 8.5 mEq/L (8.5 mmol/L)

• Chloride 91 mEq/L (91 mmol/L)

• Bicarbonate 14 mEq/L (14 mmol/L)

• Blood urea nitrogen 167 mg/dL (59.62 mmol/L)

• Creatinine 24.2 mg/dL (2,139.28 μmol/L)

• White blood cell count 13,400/μL (13.4 × 10⁹/L)

• Hemoglobin 8.9 g/dL (89 g/L)

Electrocardiography reveals normal sinus rhythm without peaked T waves. Kidney ultrasonography shows enlarged, slightly echogenic kidneys.