LabMed

Hypoparathyroidism

At a Glance

Hypoparathyroidism is a relatively rare disorder. There are two major causes of hypoparathyroidism:

  • deficient secretion and/or action of parathyroid hormone (PTH)

  • resistance to PTH (pseudohypoparathyroidism)

Deficient PTH action or secretion can result from surgical removal of the parathyroid glands, iron overload, autoimmune disease, DiGeorge syndrome, inherited defects in the PTH gene, and other genetic defects. Transient loss of parathyroid gland function can occur in patients who have hypomagnesemia or surgical injury. The clinical manifestations of hypoparathyroidism are mainly related to hypocalcemia and include increased neuromuscular excitability (i.e., paresthesias, muscle cramping, tetany), mental disturbances, and teeth/bone anomalies. The symptoms are aggravated by alkalosis.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

The basic laboratory work-up should include serum calcium, PTH, albumin, phosphorus, magnesium, blood urea nitrogen and creatinine. 25-hydroxyvitamin D is an appropriate follow-up test, if serum calcium is low but PTH is relatively high.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Low serum albumin can complicate interpretation of serum calcium. In patients with hypoalbuminemia, corrected calcium should be calculated or, alternatively, an ionized calcium measured.

What Lab Results Are Absolutely Confirmatory?

For most cases, no test is absolutely confirmatory. The diagnosis is made based on history and the pattern of laboratory results. Low or undetectable PTH in the face of hypocalcemia, hyperphosphatemia, and normal renal function establishes the diagnosis.

Additional Issues of Clinical Importance

Autoimmune parathyroid destruction may be accompanied by additional manifestations of autoimmune disease. Likewise, iron overload syndromes (e.g., hemochromatosis) can affect multiple organ systems.

Errors in Test Selection and Interpretation

A common error in laboratory work-up of hypoparathyroidism is failure to measure serum magnesium.

Hypomagnesemia is a readily treatable cause of depressed parathyroid function. The differential diagnosis of hypocalcemia differential is broad and includes some common conditions, such as vitamin D deficiency. A thorough consideration of patient history is important in arriving at the right diagnosis.

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