Innocent elevation of aspartate aminotransferase

Incidental raised transaminases: a clue to muscle disease

Twenty-one patients with incidental hypertransaminasaemia who were eventually diagnosed as muscular dystrophy are described. There were two females and 19 males aged between 2 and 11 years [mean (SD) 6.7 (3.4) y]. Serum alanine and aspartate transaminase levels were between 73 and 595 IU/L (30-35) and 68 and 550 IU/L (30-35), respectively. Muscle disease was suspected when creatine phosphokinase levels were elevated and confirmed in each patient by muscle biopsy. The time interval between incidental hypertransaminasemia and the diagnosis of muscle disease was between 3 and 12 months. Eleven patients were diagnosed as Becker's muscle dystrophy, eight as Duchenne muscle dystrophy and two had sarcoglycanopathy. Long-term elevation of transaminase levels might be a sign of occult muscle disease. Invasive tests such as liver biopsy should not be performed in patients with unexplained hypertransaminasaemia without first determining creatinine phosphokinase levels.

Macro-aspartate aminotransferase in a female with antibodies to hepatitis C virus

Persistent elevation of aspartate aminotransferase (AST) activity in serum due to the presence of a macroenzyme form of AST (macro-AST) may lead to diagnostic confusion in many clinical conditions, particularly those associated with chronic liver disease. We describe a case of macro-AST arising in an adult female with a false-positive hepatitis C virus (HCV) RNA test result that was not accompanied by other biochemical or histologic evidence of liver disease. The presence of macro-AST in serum was confirmed utilizing size-exclusion, high performance liquid chromatography (HPLC) and Protein G-agarose beads to precipitate immune complexes of AST and immunoglobulin G followed by centrifugation and AST activity measurements in the supernatant. A brief review of the clinical enzymology of AST and methods used to quantify serum macro-AST activity is provided.

Macroenzyme investigation and monitoring in children with persistent increase of aspartate aminotransferase of unexplained origin

Ten children with asymptomatic persistent cryptogenic increased serum levels of aspartate aminotransferase (AST) were screened for detection and monitoring of AST macroenzyme (macroAST). MacroAST was found in 4 patients; their serum AST levels were significantly higher than in those without biochemical evidence of macroAST (mean +/- SD: 515 +/- 433 and 78 +/- 16 IU/L, respectively; P = .0095). MacroAST was a persistent, benign phenomenon and was probably not congenital.

Aspartate aminotransferase-linked immunoglobulin complexes in serum of a patient with primary biliary cirrhosis

A 51-year-old woman who had been treated for primary biliary cirrhosis (PBC) was admitted to our hospital for evaluation of unexplained, isolated, persistently increased aspartate aminotransferase (AST) activity. Results of laboratory tests on admission showed: AST 171 KU, alanine aminotransferase 28 KU, and anti-mitochondrial titer 1/1280. Results of hepatitis B surface antigen (HBs Ag) and hepatitis C virus antibody (HCV Ab; C100-3) assays were negative. Histology of a liver biopsy specimen was compatible with a diagnosis of PBC (stage III of Scheuer's classification). The molecular size of serum AST was estimated to be more than 500,000 by high-performance size-exclusion liquid chromatography. Electrophoretic analysis showed an abnormal band of AST between supernatant AST (sAST) and mitochondrial AST (mAST), which band was characteristic of AST-immunoglobulin complexes (AST-Ig). Ouchterlony double-diffusion and immunoprecipitation tests identified the immunoglobulin component as IgM. The presence of AST-Ig appeared to be responsible for the elevated serum AST.

Investigation of a persistently raised serum AST

The AST responsible for a raised enzyme activity, with otherwise normal biochemistry, in a single individual over a 16-month period has been characterized as an IgG (lambda)-AST complex by (i) estimation of the molecular size by gel exclusion chromatography on Sephadex G200, (ii) agarose gel electrophoresis, (iii) immunoprecipitation by anti-immunoglobulin antisera and (iv) adsorption on to protein A-agarose.