[alpha 2-Macroglobulin in serum and plasma: reference values with carbobenzoxy-valyl-glycyl-arginine-p-nitroanilide,...

alpha 2-Macroglobulin can be determined using the amidolytic activity of the alpha 2-macroglobulin-trypsin-complex. Reference values are reported using a commercially available kit for continuous assay at 25 degrees C. Reference ranges obtained in a population of 235 children and adults aged between 1 day and 61 years were found to be age-dependent. Reference ranges established for the different age groups of children were grouped together in order to obtain useful guide values. The following values were obtained for serum: 1 to 10 days: 5-11 kU/l 11 days to 18 years: 8-16 kU/l The reference values (5th to 95th percentile) determined for juveniles and adults were as follows: 19 to 25 years: 4.1-12.2 kU/l (serum); 4.0-11.2 kU/l (citrated plasma) greater than or equal to 25 to 61 years: 4.1-8.1 kU/l (serum); 3.7-7.4 kU/l (citrated plasma) No variation according to sex was observed, nor was any difference noted between preprandial and postprandial catalytic concentrations, or between values in smokers and non-smokers or between values in the group of women taking hormonal contraceptives and the group not taking such drugs. If the dilution of the blood sample with citrate solution is taken into account when calculating the catalytic concentrations in citrated plasma, the values in plasma are higher than those in serum (median 11%). Measurement of the alpha 2-macroglobulin-trypsin complex in plasma is assumed to give a more realistic reflection of the in vivo activity than measurement in serum. Comparison with two immunological methods (radial immunodiffusion and kinetic nephelometry) revealed that there is a linear relationship between the measurement of the catalytic concentration of the alpha 2-macroglobulin-trypsin complex and the immunological concentration of alpha 2-macroglobulin. Therefore mutual conversion is possible for the described concentration range.