S. Antonsen, WITHIN-SUBJECT VARIATION OF ELASTASE ALPHA(1)-PROTEASE INHIBITOR COMPLEXES AND LACTOFERRIN IN PLASMA, Scandinavian journal of clinical & laboratory investigation, 53(6), 1993, pp. 611-616
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.