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.
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 PTH. 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 and aggravates the situation. In contrast, 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–H o w a r d test(pseudohypoparathyroidism)
- Bone biopsy (rickets, osteomalacia)
- Endocrinology consult
Pictures
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- 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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