HYPOCALCEMIA
HYPOCALCEMIA: Excerpt from Differential Diagnosis in Primary Care
The physiologic model of Intake, absorption, transport, regulation, and excretion lends itself well to developing a list of possible causes of hypocalcemia.
HYPOCALCEMIA
Intake
Poor dietary intake of calcium is not often seen in developed countries. However, poor intake of vitamin D may be the cause. Vitamin D facilitates the absorption of calcium.
Absorption
Malabsorption syndrome is often associated with hypocalcemia.
Transport
Anything that lowers the plasma protein may be associated with hypocalcemia. Consequently, nephrotic syndrome, cirrhosis of the liver, malnutrition, and malabsorption syndrome may all produce hypocalcemia on this basis.
Regulation
Hypocalcemia is associated with pseudohypoparathyroidism where the kidney fails to respond to parathyroid hormone. In hypoparathyroidism, there is decreased or absent PTH causing hypocalcemia.
Excretion
In chronic nephritis, hypocalcemia occurs because the kidney cannot excrete phosphates. More phosphates are excreted in the stool blocking calcium absorption and lowering serum calcium. Secondary hyperparathyroidism results aggravating the situation. On the other hand, with renal tubular acidosis, the kidneys do not reabsorb calcium and phosphorus from the glomerular filtrate, causing hypocalcemia. Secondary hyperparathyroidism results here also. Long-term diuretic therapy may induce the same picture.
Approach to the Diagnosis
Determining the serum phosphate and alkaline phosphatase levels will facilitate differentiating the causes of hypocalcemia. The phosphates and alkaline phosphatase are elevated in chronic nephritis but only the alkaline phosphatase is elevated in renal tubular acidosis and malabsorption syndrome. Only the phosphorus is elevated in hypoparathyroidism and pseudohypoparathyroidism. Hypoparathyroidism can be distinguished by a low serum PTH assay result.
Other Useful Tests
- CBC (malabsorption syndrome)
- Sedimentation rate (nephritis, acute pancreatitis)
- Chemistry profile (uremia)
- Urinalysis (chronic nephritis; renal tubular acidosis)
- 24-hour urine calcium (hypoparathyroidism)
- Skeletal survey (rickets)
- d-Xylose absorption test (malabsorption syndrome)
- Serum protein electrophoresis (nephrosis)
- Ellsworth–Howard test (pseudohypoparathyroidism)
- Bone biopsy (rickets, osteomalacia)
- Endocrinology consult
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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