Electrolyte Quiz

Choose the best single best answer

1. An 18-year-old woman presents with a 27-lb weight loss over five months. She is amenorrheic. On examination she is cachectic and has lanugo hair and erosion of the enamel on her upper incisors. Her height is 64 inches, weight 80 lb, pulse rate 42 per minute, blood pressure 75/50 mm Hg. Her initial serum electrolytes are normal. She is admitted to hospital and commenced on a regular diet of 1000 kcal/day, and increased by 200 kcal/day every 2 days. On day 7, she becomes confused and disorientated with auditory and visual hallucinations.

Which of the following statements about this patient is likely to be correct:

A. She is at risk of sudden death

B. Her current condition is caused by inadequate caloric replacement

C. The corrected QT interval on her electrocardiogram is shorter than normal 

D. Her current condition may be corrected with insulin

E. Her total body phosphorus stores are normal

2. An 85-year-old male presents with a 3 year history of diffuse bone pain.

Laboratory Studies

Serum creatinine1.2 mg/dL

Serum albumin3.7 g/dL

Serum calcium9.1 mg/dL

Serum phosphorus1.2 mg/dL

Serum immunoreactive parathyroid hormone (intact) 19 pg/mL (Normal range 10-65 pg/mL)

Serum 25-hydroxy cholecalciferol54 pg/mL (Normal range 9-43 pg/mL)

Serum 1,25-dihydroxy cholecalciferol 3 pg/mL (Normal range 15-60 pg/mL)

Urine phosphorus 15 mg/dL

Urine creatinine 50 mg/dL

The most likely cause of hypophosphatemia in this patient is:

A. Primary hypoparathyroidism

B. Nutritional vitamin D deficiency

C. X-linked hypophosphatemic rickets

D. Oncogenic osteomalacia

E. Malabsorption syndrome

3.A 30-year-old female with HIV infection is maintained with didanosine, tenofovir, ritonavir, trimethoprim-sulfamethoxazole and clarithromycin.

Laboratory Studies

Serum sodium136 mEq/L

Serum potassium 3.2 mEq/L

Serum chloride110 mEq/L

Serum bicarbonate17 mEq/L

Serum glucose 84 mg/dL

Blood urea nitrogen8 mg/dL

Serum creatinine 0.4 mg/dL

Serum albumin 3.3 g/dL

Serum calcium 8.7 mg/dL

Serum phosphorus 0.9 mg/dL

Serum uric acid 1.6 mg/dL

UrinalysispH 6.0, specific gravity

1.015, 3+ glucose, trace protein

Urine phosphorus 26 mg/dL

Urine creatinine 36 mg/dL

The most likely cause of hypophosphatemia in this patient is:

A. Occult malignancy

B. Tenofovir toxicity

C. Insufficient sun exposure

D. Alcohol abuse

E. Malabsorption syndrome

(Questions courtesy of Dr. Alan Yu, Director Kidney Institute and Professor Of Medicine, University of Kansas Medical Center)