Macroenzymes in Isolated Hyperenzymemia: Detection Methods and Decision Thresholds for Polyethylene Glycol-Precipitable Activity

Macroenzymes, such as macroamylase, macro-aspartate aminotransferase (macro-AST), and macro-creatine kinase (macro-CK), are high-molecular-weight complexes formed when serum enzymes bind to immunoglobulins or other plasma components, or undergo self-polymerization. These complexes can artificially inflate results in routine activity assays, producing a picture of isolated hyperenzymemia, such as isolated AST elevation, and are sometimes the reason for costly, occasionally invasive diagnostic workup. A common screening method is polyethylene glycol (PEG) precipitation, where the result is reported as PEG-precipitable activity, with the percentage of activity precipitated by PEG (%PPA), and evaluated against a decision threshold. This review examines the heterogeneity of %PPA decision thresholds and of the alternative detection methods and assesses how consistently these criteria are applied in practice. The analysis covers the literature published from March 2021 onward, supplemented by iterative backward citation searching, which brought in the earlier studies that established the %PPA thresholds, and by forward citation searching of those studies. The thresholds compared here vary substantially for the same enzyme, with the widest discrepancies in CK. The differences stem from variations in assay platforms, reference populations, the statistical cut-offs adopted, and the precipitation protocol itself, so the thresholds are not transferable between laboratories. Within that protocol, polymer concentrations remain relatively uniform, while incubation times, centrifugation conditions, and reference materials differ substantially from report to report. Storage at 4°C, used as a lower-cost alternative, is not reliable either, since enzyme activity sometimes remains unchanged despite the presence of a macroenzyme. Reported detection rates vary by several orders of magnitude, reflecting the degree of preselection of the study group rather than the frequency of the macroenzyme itself. A negative result from PEG precipitation or from storage at 4°C therefore does not rule out a macroenzyme. Because a %PPA value depends on the protocol, the platform, and the control sample assayed in parallel, standardized reporting of these variables is needed before the results of macroamylase, macro-AST, and macro-CK can be compared between laboratories.