Macrocomplexes: An establishing critical limits of post-PEG serum enzymes and proteins in adults and children

Exclusion of serum macroform presence is essential to avoid potential misdiagnosis. The aim of this study was to determine critical limits (CL) for enzymes (total and pancreatic amylase, AMY and pAMY; aminotransferases, AST and ALT; alkaline phosphatase, ALP; creatine kinase, CK; lipase, LIP; gamma-glutamyl transferase, GGT; lactate dehydrogenase, LDH) after polyethylene glycol (PEG) precipitation in children and adults.

A total of 126 sera of patients suspected for macroenzyme presence (adults or children) was matched by serum enzyme activity of controls and all these sera were precipitated by PEG. PEG-precipitable activity ( %PPA) and CLs of %PPA were calculated for adults, children, and controls.

CLs of %PPA were substantially lower than common 60 % for ALP and CK in all subjects. Significant differences between adults and children were found for ALT and ALP (lower in children), and LIP and CK (higher in children). No meaningful correlation was found between initial enzyme activity and %PPA.

Age specific CLs should be used for ALP, ALT, CK, and LIP. Generally accepted value of %PPA of 60 % may be used with caution for AMY, pAMY, AST, GGT, and LDH. A careful selection of CLs is needed for timely detection of macrocomplexes.