What is the role of blood and urinary chemistries in the diagnosis of McCune-Albright syndrome?

Updated: Jan 17, 2019
  • Author: Gabriel I Uwaifo, MD; Chief Editor: George T Griffing, MD  more...
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Answer

Individuals with MAS may have elevated liver enzymes or hyperbilirubinemia. Even after normalization of cortisol or thyroxine levels, these elevations can persist, suggesting the presence of G protein alpha subunit (Gs alpha)–activating (GNAS1) mutations in the liver. Furthermore, hypophosphatemia may result from increased urinary phosphate excretion. Therefore, a complete multichemistry panel should be performed that includes calcium, phosphorus, and liver function tests.

Blood and urinary chemistries show evidence of excessive bone turnover and elevated indicators for bone formation and resorption (eg, urinary N-telopeptide, pyridinolines, deoxypyridinolines). Serum alkaline phosphatase levels (total and bone-specific fractions), osteocalcin, and serum cyclic adenosine monophosphate (cAMP) [37] levels are elevated.

Urinary excretion of hydroxyproline, N-telopeptides, pyridinium X-links, and cAMP is elevated. Depending on the extent of coexisting osteomalacia, serum calcium may be normal or slightly reduced. Typically, the rickets or osteomalacia associated with MAS is hypophosphatemic and hyperphosphaturic.


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