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A comparison of methods for evaluation of a case of suspected macro-aspartate aminotransferase
Xander M R van Wijk1, Catherine A Magee2, Alan H B Wu1
1Department of Laboratory Medicine, University of California, San Francisco, Zuckerberg San Francisco General, San Francisco, CA, USA.
Background:
Macro-aspartate aminotransferase (macroAST) is a high molecular weight form of AST that is usually formed through association with immunoglobulin (Ig) in the circulation. As a result of reduced inactivation, clearance or excretion, AST values are persistently increased. This can lead to problems interpreting these values and diagnosing the patient, especially if clinicians are not aware of this phenomenon.
Methods:
For a case of suspected macroAST, we compared three simple methods: polyethylene glycol precipitation, ultrafiltration, and Ig depletion using protein A and G.
Results:
All three methods were consistent with a diagnosis of macroAST.
Conclusions:
The protein A and G method was straightforward and provided unambiguous results. However, given the affinity of protein A and protein G, it likely only detects AST-IgG macrocomplexes.
Insights
Diagnosing macro-aspartate aminotransferase (macroAST), a high molecular weight form of AST, can be challenging. Three simple methods—polyethylene glycol precipitation, ultrafiltration, and Ig depletion—reliably detected macroAST in a case study.
Area of Science:
- Clinical enzymology
- Protein biochemistry
Background:
- Macro-aspartate aminotransferase (macroAST) is a complex of aspartate aminotransferase (AST) with immunoglobulins (Ig).
- Persistent elevation of AST levels due to macroAST can complicate clinical diagnosis.
- Awareness of macroAST is crucial for accurate patient assessment.
Observation:
- This study investigated three simple methods for macroAST detection: polyethylene glycol (PEG) precipitation, ultrafiltration, and immunoglobulin (Ig) depletion using Protein A and G.
- These methods were applied to a clinical case with suspected macroAST.
Findings:
- All three tested methods consistently indicated the presence of macroAST.
- The Protein A and G method offered a straightforward approach with clear results.
- The Protein A and G method specifically identifies AST-IgG macrocomplexes due to the affinity of Protein A and G for IgG.
Implications:
- Simple laboratory methods can aid in the diagnosis of macroAST.
- Distinguishing macroAST from other causes of elevated AST is important for appropriate patient management.
- Further research may be needed to characterize macroAST variants not detected by Protein A/G methods.
