WITHIN-SUBJECT VARIATION OF ELASTASE ALPHA(1)-PROTEASE INHIBITOR COMPLEXES AND LACTOFERRIN IN PLASMA

Several studies have shown increased plasma concentrations of neutroph il elastase in complex with alpha1-protease inhibitor and/or lactoferr in in inflammatory conditions, and serial measurements have been advoc ated in order to follow disease activity. However, data on the magnitu de of the within-subject variation are necessary for evaluation of the significance of changes in results obtained on analysis of serial sam ples. Within-subject variation of elastase/alpha1-protease inhibitor c omplexes and lactoferrin over a short time was studied in six young me n who had blood samples drawn every 4 h over 2 days. Within-subject va riation over a longer time was investigated in 12 healthy adults, 6 fe males and 6 males, who had blood samples drawn in the morning once a w eek for 10 weeks. From five of the females and five of the males, bloo d samples were also drawn every morning on 5 consecutive days during 1 week. Within-subject variations over hours, days, and weeks were esti mated as 0.050, 0.124, and 0.148 for elastase/alpha-protease inhibitor complexes and as 0.101, 0.119, and 0.143 for lactoferrin. A tendency towards variation of LAC with menstrual cycle in fertile females was n oticed. From within-subject variation, between-subject variation and a nalytical variation, indices of individuality were calculated as 1.1 a nd 1.8 for elastase/alpha-protease inhibitor complexes and lactoferrin , respectively. This means that within-subject variation for lactoferr in is quite small compared to between-subject variation, and the usefu lness of reference limits is very limited, when interpreting results f rom individual patients. For elastase/alpha1-protease inhibitor comple xes, the use of reference limits might be more appropriate, although s till not optimal.