COMPONENTS OF BIOLOGICAL VARIATION IN SERUM-SOLUBLE TRANSFERRIN RECEPTOR - RELATIONSHIPS TO SERUM IRON, TRANSFERRIN AND FERRITIN CONCENTRATIONS, AND IMMUNE AND HEMATOLOGICAL VARIABLES

We investigated the components of biological variation in serum solubl e transferrin receptor (TfR) in relation to serum iron, transferrin (T f), ferritin, soluble interleukin-2 receptor (sIL-2R), sIL-6R, and num ber of erythrocytes, haemoglobin (Hb), haematocrit (Ht), mean corpuscu lar volume (MCV), mean cell haemoglobin (MCH), and erythrocyte distrib ution width (RDW). We took monthly blood samples during 1 calendar yea r from 26 healthy subjects for assay of the above variables. The estim ated CVs for TfR were interindividual CVg=20.8%, and intra-individual CVi=13.6%; for Tf, CVg=14.4% and CVi=6.7%; for iron, CVg=16.8% and CVi =29.2%; and for ferritin, CVg=71.1% and CVi=26.5%. There was a statist ically significant seasonal pattern in the four variables with signifi cant annual, biannual and/or trimonthly rhythms, which were expressed as a group phenomenon. The peak-trough differences in the yearly varia tions, expressed as a percentage of the mean, were: for TfR, 11.7%; fo r iron, 39.2%; for Tf, 11.7%; and for ferritin, 29.3%. Up to 34.2% of the within-subject variability in TfR (which reflects changes over tim e) could be explained by the regression on iron, ferritin, Tf, sIL-2R, sIL-6R and MCH values. Up to 67.2% of the between-subject variability in TfR (which reflects differences in the homeostatic setpoint during the study year) could be explained by the regression on gender, iron, Tf, and ferritin values.