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Background: Macro-aspartate aminotransferase (macro-AST), a high-molecular-weight complex formed by AST binding to immunoglobulins or plasma components, causes persistent enzyme elevation due to delayed renal clearance. Its diagnosis remains challenging due to rarity and nonspecific presentation.
Methods: We report two cases of asymptomatic isolated AST elevation: a 25-year-old pregnant woman (AST: 204 - 315 U/L) and an 83-year-old male (AST: 113 - 140 U/L). Both underwent PEG precipitation and refrigeration stability tests to confirm macro-AST.
Results: Polyethylene glycol (PEG) precipitation activity (PPA) values for Case 1 and Case 2 were 95.2% and 85.7%, respectively, exceeding the diagnostic cutoff (> 73%). Refrigeration testing revealed a 78.7% AST decline in Case 1 after 7 days, while Case 2 showed stable AST levels, consistent with macro-AST characteristics. Other hepatic and autoimmune markers were normal.
Conclusions: Macro-AST should be considered in asymptomatic patients with isolated AST elevation. PEG precipitation is a simple, reliable diagnostic tool. Effective communication between clinicians and laboratories is crucial to avoid unnecessary investigations.
DOI: 10.7754/Clin.Lab.2025.250608
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