Hypocalcemia

Indications for Testing

Suspect when symptoms occur and serum calcium is low

Laboratory Testing

Initial testing – serum calcium and albumin [corrected calcium = measured total calcium +0.8 (4.0-serum albumin)], serum phosphorus, serum magnesium, serum creatinine
- Ionized calcium does not need to be corrected for hypoalbuminemia
Repeat serum ionized calcium testing
Intact PTH
- Elevated PTH, normal or high phosphorus, normal magnesium, high creatinine – renal failure/pseudohypoparathyroidism
- Elevated PTH, normal or low phosphorus, normal magnesium, normal creatinine
  - Low vitamin D 25(OH) – vitamin D deficiency
- Low PTH, normal or high phosphorus, normal creatinine, low or normal magnesium – hypoparathyroidism or hypomagnesemia
- Normal PTH, normal or low phosphorus, normal creatinine, normal magnesium, low albumin – hypoalbuminemia (pseudohypocalcemia)

Differential Diagnosis

Serum calcium, phosphorus and creatinine measure weekly (monthly during initial therapy)
Once stabilized on therapy, measure values 1-2 times/year

Hypocalcemia may be noted either acutely or chronically in hospitalized patients and outpatients.

Epidemiology

Prevalence – occurs in 12-80% of critically ill patients

Etiology

Acute hypocalcemia – intensive care unit patients (acute pancreatitis, sepsis)
Hypoparathyroidism
- Autoimmune hypoparathyroidism
  - Associated with polyglandular syndrome 1
  - Symptoms – chronic mucocutaneous candidiasis, alopecia and vitiligo
  - Autosomal recessive inheritance
- Acquired
  - Surgical removal of parathyroids
  - Radiation-induced parathyroid destruction
  - Metastatic infiltration of glands (rare)
- Pseudohypoparathyroidism
  - Resistance to parathyroid hormone (PTH)
- Genetic syndromes
  - DiGeorge and velocardiofacial syndrome
    - Rare congenital disorder
    - Symptoms – cardiac, facial, thymic and thyroid abnormalities
      - Severe early childhood infections
    - Learning disorders
    - Genetics – rearrangements on chromosome 22 (TBX1 gene)
  - Familial hypocalcemia with hypocalciuria (includes Bartter syndrome subtype V)
  - X-linked hypoparathyroidism
  - Mitochondrial disorders with hypoparathyroidism
Vitamin D deficiency
- Malabsorption
- Inadequate diet/sunlight
Magnesium deficiency
- Malabsorption
- Inadequate diet
- Alcoholism

Pathophysiology

Serum calcium concentration kept within a narrow physiologic range
Control of calcium by parathyroid hormone, vitamin D (1,25), calcium and phosphate

Clinical Presentation

Acute
- Neuromuscular – tetany, paresthesias, muscle spasms (Chvostek and Trousseau signs)
- Neuropsychiatric – anxiety, hallucinations, confusion
- Cardiovascular – bradycardia, ventricular arrhythmias, cardiac collapse
Chronic
- Neuropsychiatric – cognitive deficits, extrapyramidal symptoms
- Dermatologic – dermatitis, dry skin
- Dental – enamel hypoplasia
- Ophthalmologic – cataracts

Treatment

Treat according to etiology
Calcium (may require intravenous calcium depending on calcium level) and vitamin D analogues

Tests generally appear in the order most useful for common clinical situations

Test name: Calcium, Serum or Plasma

ARUP #: 0020027

Methodology: Quantitative Spectrophotometry

Use: Diagnose hypocalcemia

Test name: Albumin, Serum or Plasma by Spectrophotometry

ARUP #: 0020030

Methodology: Quantitative Spectrophotometry

Use:

Initial testing

Test name: Creatinine, Serum or Plasma

ARUP #: 0020025

Methodology: Quantitative Enzymatic

Use:

Initial testing

Test name: Phosphorus, Inorganic, Plasma or Serum

ARUP #: 0020028

Methodology: Quantitative Spectrophotometry

Use:

Initial testing

Test name: Parathyroid Hormone, Intact

ARUP #: 0070346

Methodology: Quantitative Electrochemiluminescent Immunoassay

Use: Diagnose hypoparathyroidism

Test name: Magnesium, Plasma or Serum

ARUP #: 0020039

Methodology: Quantitative Spectrophotometry

Use: Differential diagnosis of hypocalcemia

Test name: Vitamin D, 25-Hydroxy

ARUP #: 0080379

Methodology: Quantitative Chemiluminescent Immunoassay

Use:

Differential diagnosis of hypocalcemia

Additional Tests Available

Test name: Parathyroid Hormone, Intact with Calcium

ARUP #: 0070172

Methodology: Quantitative Electrochemiluminescent Immunoassay

Comments:

Test name: Calcium, Ionized, Whole Blood

ARUP #: 0020140

Methodology: Ion-Selective Electrode/pH-Electrode

Comments:

Available only to University of Utah patients

Test name: Calcium, Ionized, Serum

ARUP #: 0020135

Methodology: Ion-Selective Electrode/pH-Electrode

Comments:

General

Comprehensive Review: March 2011
Last Update: March 2011

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