A 5-Week-Old Boy with Failure to Thrive, Marked Hyperkalemia, and Hyponatremia

Summary

DOI: 10.1373/clinchem.2015.252320

5-week-old white boy presented to the emergency department after referral from his primary care physician with concerns for failure to thrive. The patient's birth weight was 2892 g at 37 weeks of gestation (10th percentile). He was 2665 g at 5 weeks of age (<second percentile). He had been exclusively breastfed for the first 3 weeks of his life.

Student Discussion

Student Discussion Document (pdf)

Min Xu,^1,2* Carolina Di Blasi,^3,4 Jane Dickerson,^1,2 Rhona Jack,^1,2 and Joe C. Rutledge^1,2

¹Department of Laboratories, Seattle Children’s Hospital, Seattle, WA; ²Department of Laboratory Medicine, University of Washington, Seattle, WA; ³Department of Endocrinology, Seattle Children’s Hospital, Seattle, WA; ⁴Department of Pediatrics, University of Washington, Seattle, WA.
*Address correspondence to this author at: Department of Laboratories, OC.8.731, Seattle Children’s Hospital, 4800 Sand Point Way NE, Seattle, WA 98105. Fax 206-987-3840; e-mail [email protected].

Case Description

A 5-week-old Caucasian boy presented to the emergency department after referral from his primary care physician with concerns for failure to thrive.

The patient’s birth weight was 2892 grams at 37 weeks of gestation (10th percentile). He was 2665 grams at 5 weeks of age (<2nd percentile). He had been exclusively breastfed for the first 3 weeks of his life. At 3 weeks of age, he was introduced to a bottle with expressed breast milk, but showed little interest in the bottle. At a well child check-up at 4 weeks of age, his weight was down, and formula supplementation was recommended. In the last 3 days before the admission, he had been lethargic and had difficulty feeding. He had two episodes of projectile vomiting during that week. There was a noticeable reduction in the amount of stool and urine output during the last two days before admission without fever or diarrhea.

The patient was born at 37 weeks of gestation by spontaneous vaginal delivery. Mother was found to be group B streptococcus (GBS) positive but was not treated prior to delivery, so the patient was monitored for 48 hours in the hospital before discharged home. Mother also had a history of bilateral vesicoureteral reflux and reimplantation surgery. There was no other history of genital, urinary or kidney abnormalities. On exam he was cachectic and lethargic but did have warm extremities, brisk capillary refill (<2 seconds) and good distal pulses. No skin hyperpigmentation was seen and the genitalia were normal. Laboratory tests were significant for potassium (K) 10.2 mmol/L, sodium (Na) 116 mmol/L, chloride (CL) 91 mmol/L, BUN 64 mg/dL (22.9 mmol/L), creatinine 0.7 mg/dL (61.9 μmol/L), and glucose 88 mg/dL (4.9 mmol/L), pH 7.29, pCO2 29 mmHg, total CO2 15.0 mmol/L (Table 1). The specimen was not hemolyzed. Contamination of the specimen with K was originally suspected by the medical technologist. Communication with clinical staff confirmed the quality of the specimen. Electrocardiogram showed no electrolyte-related changes. His blood pressure was 75/41 mmHg (normal interval 65-85/45-55 mmHg). The patient received normal saline boluses to supplement Na, kayexalate to chelate K, and calcium gluconate to antagonize the membrane actions of hyperkalemia. Although he had 2 normal newborn screens, the possibility of congenital adrenal hyperplasia (CAH) was still in the differential diagnoses owing to such high K and low Na. He was started on stress dose steroids after measurement of baseline adrenocorticotropic hormone (ACTH), renin, aldosterone, 17-hydroxyprogesterone (17-OHP), and cortisol. Urinalysis for the possibility of urinary tract infection (UTI) was also performed. One hour later, Na increased to 125 mmol/L and K decreased to 7.9 mmol/L. He was admitted to the neonatal intensive care unit for further evaluation and management.

Questions to Consider

What is the differential diagnosis of a patient with marked hyperkalemia, hyponatremia and metabolic acidosis?
What are the diagnostic tests for CAH?
What are the consequences of neonatal infection of GBS?

Final Publication and Comments

The final published version with discussion and comments from the experts appears in the November 2016 issue of Clinical Chemistry, approximately 3-4 weeks after the Student Discussion is posted.

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