- Author: Mini R Abraham, MD; Chief Editor: George T Griffing, MD more...
Laboratory studies for the diagnosis of pseudohypoparathyroidism (PHP) include serum calcium tests (including measurement of serum total calcium and ionized calcium) to confirm a hypocalcemic state. Serum phosphate levels are elevated in PHP.
Determining the serum concentration of intact PTH, using an immunoradiometric assay (IRMA), is also diagnostic. When the serum concentration of PTH in a hypocalcemic patient is increased, the patient has either a form of PHP or secondary hyperparathyroidism.
Assessment of skeletal and renal responsiveness to PTH is accomplished by measurement of changes in serum calcium, phosphorus, cAMP, and calcitriol concentrations and in urinary cAMP and phosphorus excretion after administration of the biosynthetic N-terminal fragment of PTH.
Consider thyroid function tests and measurement of gonadotropin and testosterone or estrogen levels. Also consider assessment of growth hormone function with insulinlike growth factor-1.
In a study, Freson et al concluded that platelet-based testing can effectively be used in the diagnosis of Gsa defects. In their report, on the use of platelets to diagnose Gsa hypofunction, the investigators found that platelet aggregation responses varied according to Gsa signaling defects, thus providing a reflection of a patient's phenotype and genotype.
A study by Todorova-Koteva et al demonstrated the use of commercially available recombinant PTH injections and concomitant measurement of cAMP in urine to diagnose PTH resistance, especially in nonphenotypically evident pseudohypoparathyroidism.
Radiography of the hand may show a specific pattern of shortening of the bones, in which the distal phalanx of the thumb and the third through fifth metacarpals are shortened most severely. Radiography may also show small soft tissue opacities (calcifications/ossifications). Computed tomography (CT) scanning may reveal calcification of the basal ganglia.
Additional studies in PHP include the following:
Electrocardiogram - May reveal prolongation of the QT interval secondary to hypocalcemia
Analysis of the GNAS1 gene - Helps to identify the specific genetic defect in patients with PHP type 1a
Patients with PHP type 1b may be evaluated for parathyroid-related bone disease. Consider bone mineral density (BMD) testing in this group of patients.
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