Macrotransaminase of aspartate aminotransferase (AST): a benign cause of elevated AST activity

Prevalence and long-term course of macro-aspartate aminotransferase in children

OBJECTIVES

To investigate the prevalence, association with clinical conditions, and long-term course of macro-aspartate aminotransferase (macro-AST).

STUDY DESIGN

Forty-four children with an isolated elevation of serum AST were screened for macro-AST with electrophoresis and % polyethylene glycol (PEG) precipitable activity (PPA).

RESULTS

All children were healthy, except they had elevated AST values. Seventeen children (38.6%) were macro-AST-positive. They had higher AST values than the 27 children who were macro-AST-negative (P = .001). Values <67.1% PPA and >82.2% PPA were associated with a very low probability of being macro-AST-positive and macro-AST-negative, respectively. Thirty-eight children underwent clinical and laboratory follow-up (mean, 4.7 +/- 3.8; range, 1-16 years). All remained symptom-free. AST levels decreased significantly only in children who were macro-AST-negative (P = .006). Macroenzyme persisted in 6 of the 9 children who were macro-AST-positive after 6.0 +/- 4.1 years.

CONCLUSIONS

Macro-AST was present in more than one-third of children with an isolated increase of AST levels. The lack of pathological correlates in a long period argues for the benign nature of this phenomenon in childhood. We suggest that our %PPA thresholds can be used as a screening test and that electrophoresis be reserved for confirming positive screen test results and cases in which %PPA levels are of intermediate discriminant accuracy.

Macro-creatine kinase and macro-lactate dehydrogenase in a girl with ulcerative colitis

We report the case of a girl affected by ulcerative colitis with high serum levels of creatine kinase and lactate dehydrogenase due to the presence of macroenzymes. Our observation suggests that the knowledge of this association may be helpful when evaluating ulcerative colitis patients with unexplained isolated elevation of one or more serum enzyme activities.

Macro-aspartate aminotransferase (macro-AST). A 12-year follow-up study in a young female

We describe a case of chronic elevation of serum aspartate aminotransferase (AST) activity due to the presence of a macro-enzyme form of AST (macro-AST) in a young female followed up for 12 years. This biochemical abnormality, although generally detected in acute and chronic hepatitis, malignancies and autoimmune disease, was not associated with any particular illness and did not seem to be congenital, as normal AST concentrations were reported in the patient's family members. Moreover, the normal or quasi-normal values of AST associated with peak levels observed in our case suggest that this phenomenon has a fluctuating behaviour rather than persisting for many months or years. In conclusion, we believe that it is important: 1) to reassure the patient with macro-AST, as this condition has a benign evolution and does not require any specific treatment; 2) to keep in mind this biochemical abnormality in all cases of unexplained AST elevation in order to avoid unnecessary invasive diagnostic procedures.

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.

[Hypertransaminasemia in an adolescent]

CASE REPORT

An adolescent admitted to hospital because of an obvious convulsion seizure presented with a high level of serum macroaspartate aminotransferase. This macroaspartate aminotransferase was discovered by chance when blood tests were made.

DISCUSSION

Macroaspartate aminotransferase is a persistent, benign phenomenon, probably not congenital, discovered either in healthy patients, or in adults suffering from malignancies or autoimmune diseases. Macroenzymes have been identified as a cause of benign increase in a number of serum enzymes, like macroamylase serum levels. The macroenzyme is often an immunoglobulin G-complexed enzyme.

CONCLUSION

It is important for clinicians to be aware of their existence in order to avoid unnecessary procedures. It is important that the patient is informed of the macroaspartate aminotransferase and that the same is stated in his health record.

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.