ELECTROLYTE QUIZ

A 35 year-old white female presented with a  several month history of hypercalcemia, requiring multiple courses of pamidronate and  calcitonin. Past medical history of cystic fibrosis, type 1 diabetes mellitus, chronic kidney disease secondary to aminoglycosides (CrCl 10-15 mL/min), and refractory hyperphosphatemia.  Medications include insulin, diltiazem, bisoprolol-hydrochlorothiazide, sucralfate, aluminum hydroxide gel, cisapride, pancrelipase. Laboratory data is as follows: BUN 84 mg/dL, serum creatinine 5.3 mg/dL, albumin 3.6 g/dL, Ca 15.6 mg/dL, Mg 1.9 mg/dL, PO₄ 5.5 mg/dL.  iPTH is 17 pg/ml (10-65), 25-vitamin D 20 ng/mL (9-43), 1,25-vitamin D 8 pg/mL (15-60), TSH 4.8 µU/m (0.5-5 ) , 24 hr urine Ca  410 mg, F_eCa 20% , SPEP/UPEP show no monoclonal bands, PTH-rP 0.3 pmol/L (<1.3), vitamin A 63 µg/dL (28-94), bone scan is negative and hand X-ray is normal

The cause of her hypercalcemia is:

A.) Sarcoidosis

B.) Malignancy

C.) Aluminum (aluminium) toxicity

D.) Familial hypercalcemic hypocalciuria

E.) Primary hyperparathyroidism

(case provided by Dr. Alan Yu).

____________

The correct answer is C, metabolic acidosis with respiratory compensation Diarrhea causes loss of intestinal bicarbonate leading to metabolic acidosis.  Reduced arterial pH stimulates carotid body pH receptor leading to compensatory hyperventilation leading to reduced PCO2. The anion gap is normal in this case because in order to maintain electrical neutrality, chloride replaces the lost bicarbonate. There are no exogenous unmeasured anions as would be present if the anion gap were increased. 

A 41-year-old male with a history of severe diarrhea was admitted to the ER after fainting. History of eating “street food” at a parade 1 day previously. Physical exam revealed decreased skin turgor.  Arterial blood gas analysis revealed pH = 7.21; PCO₂ = 26 mmHg; [HCO₃^-] = 10 mEq/L; K⁺ = 2.2 mEq/L with a normal anion gap .   The correct diagnosis of his condition is:      

A.) combined metabolic and respiratory acidosis           

B.) metabolic acidosis secondary to hyperkalemia           

C.) metabolic acidosis with respiratory compensation           

D.) respiratory alkalosis with renal compensation           

E. ) uncompensated metabolic acidosis