NAPLEX® Review Question of the Week: Calcium Conundrum

This week's question will evaluate your ability to determine appropriate calcium concentrations.
NAPLEX® Review Question of the Week: Calcium Conundrum
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IQ, a 61-year-old male, presented to the ED with 3-day history of nausea, vomiting, and constipation. He also endorsed polyuria, fatigue, and generalized weakness. Workup is significant for hypokalemia, hypomagnesemia, as well as EKG showing shortened QT intervals, prolonged PR intervals, and widened QRS complex.

PMH: Hypertension, Bipolar disorder, Alcoholic cirrhosis with ascites

Weight 69 kg, Height 72 in

Vitals: BP 119/78 mmHg, HR 91 bpm

Labs on presentation:

A1c 5.5%

Na 139 mEq/L, K 3.0 mEq/L, SCr 0.9 mg/dL, Ca 10.1 mg/dL

Mg 1.2 mEq/L

Albumin 1.5 g/dL

Current medications:

Chlorthalidone 12.5 mg PO QD

Lithobid 600 mg PO BID

Aldactone 200 mg PO QD

Lasix 80 mg PO QD

What is IQ’s corrected calcium level?

A. 10.1 mg/dL

B. 12.1 mg/dL

C. 2.1 mg/dL

D. 14.5  mg/dL

Answer with Rationale

Electrolytes are naturally occurring charged ions that are essential for many functions in the human body. They can be predominantly extracellular (sodium, chloride, bicarbonate, calcium) or predominantly intracellular (potassium, magnesium, phosphorous). Electrolyte imbalance can occur due to many reasons, including but not limited to malnutrition, GI disorders, cardiac disorders, endocrine disorders, lung disorders, and renal dysfunction. Signs and symptoms can be non-specific, ranging from nausea, vomiting, generalized weakness, etc., to life-threatening arrhythmias. Some patients with electrolyte abnormalities might even be asymptomatic on presentation, especially mild cases. Calcium is involved in many processes in the body, such as platelet aggregation, bone and tooth metabolism, cardiac contractility, neuromuscular activity, etc. The normal range for calcium varies depending on the institutions, but generally is around 8.5-10.2 mg/dL. Hypocalcemia is often associated with hypoparathyroidism or Vitamin D deficiency, while hypercalcemia can occur in patients diagnosed with cancer or primary hyperparathyroidism. Hypercalcemia can also be drug-induced, with thiazides, lithium, vitamin D supplements being the most common culprit. In the body, calcium is primarily bound to albumin; the physiologically active form is the unbound or ionized calcium.

For patients with albumin < 4 g/dL, the process for calculating corrected calcium is as follows:

 

Answers A, C, and D are incorrect. Approximately 40-50% of calcium in the body is bound to albumin, thus, correction for hypoalbuminemia is warranted when albumin is below 4.0 g/dL. Since his albumin was 1.5 g/dL, a corrected calcium must be calculated for IQ to reveal his true calcium level.

Answer B is correct. IQ’s true calcium level, after correction for hypoalbuminemia, is 12.1 mg/dL, as calculated above. This value is consistent with hypercalcemia, which can be explained by the symptoms he presented with.

Generic/Brand: Chlorthalidone (Hygroton), Lithium (Lithobid), Spironolactone (Aldactone), Furosemide (Lasix)

NAPLEX® Core Competencies Covered:

  • 1.1 – From instruments, screening tools, laboratory, genomic or genetic information, or diagnostic findings
  • 1.2 – From patients: treatment adherence, or medication-taking behavior; chief complaint, medication history, medical history, family history, social history, lifestyle habits, socioeconomic background
  • 1.5 – Signs or symptoms of medical conditions, healthy physiology, etiology of diseases, or pathophysiology
  • 2.2 – Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied
  • 4.1 – Patient parameters or laboratory measures

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