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242 MACROALKALINE PHOSPHATASE, A RARE CAUSE OF ELEVATED ALKALINE PHOSPHATASE: A CASE REPORT A Lazarescu, C Lowe BACKGROUND: Macroalkaline phosphatase has been described in a few case reports as an alkaline phosphatase-immunoglobulin complex that presents with an elevated alkaline phosphatase (ALP) on routine laboratory testing. Precipitating the isoenzymes with polyethylene glycol reveals a normal ALP activity. IgG- and IgA-alkaline phosphatase complexes have both been reported in the literature. Although it is similar to macroamylasemia in that the actual levels of ALP enzyme are not elevated, macroalkaline phosphatase is not commonly considered as a cause of elevated ALP. Aside from the potential for diagnostic error, it is unclear whether it has clinical significance.
Division of Gastroenterology, Queen's University, Kingston, Ontario
CASE: A 60-year old woman was incidentally found to have a persistently elevated ALP in the range of 400-700 U/L (normal 40-120 U/L). She had no history or risk factors for liver disease. Her past medical history included stage 2A Hodgkin's lymphoma treated with chemotherapy and radiation therapy in 1992, aortic regurgitation, a transient ischemic attack, and osteoarthritis. Her physical examination did not reveal any signs of chronic liver disease.
All her other liver tests were normal, including GGT. 5-nucleotidase was borderline elevated. Anti-mitochondrial antibody and anti-nuclear antibody were negative. Bone specific ALP was normal. Serum bile acids were slightly elevated. Ultrasound, CT and MRI of the abdomen did not reveal any liver or biliary abnormalities. There was no evidence of recurrence of the lymphoma.
Further tests on the ALP isoenzymes suggested the presence of an immunoglobulin-alkaline phosphatase complex which accounted for the increase in serum ALP activity. After precipitating the immunoglobulin with polyethylene glycol, the ALP activity decreased by 84% and electrophoresis was normal. This indicated that the elevation in ALP was secondary to it being bound to an immunoglobulin.
CONCLUSION: In this patient's case, the severe elevation in ALP appears to be due to macroalkaline phosphatase, a non-liver, non-bone cause, yet it lead to numerous investigations. Recognition of this entity by gastroenterologists may streamline the diagnostic approach and avoid unnecessary tests.