Relationship of day-to-day variation of serum iron concentrations to iron-binding capacity in healthy young women.

Biologic intra-individual variations in concentrations of serum iron and serum iron-binding capacity were determined for nine healthy young women in a double experiment. In each of two series approximately one month in duration, venipunctures were performed three times per week. All serum specimens were assayed for iron concentration and iron-binding capacity. The average intra-subject day-to-day biologic variations for the group in terms of coefficient of variation (CV) were 29.3% for serum iron and 8.8% for iron-binding capacity. No significant difference in variances was found for any subject in serum iron concentrations from series I to series II. Only one subject had a significant positive correlation between iron concentrations and iron-binding capacity values. Percentage iron saturation was computed for each iron and iron-binding capacity combination, and the average intra-subject CV was of the same order of magnitude as the CV for serum iron. The clinical significance of an isolated serum iron result in view of the dramatic intra-subject day-to-day variability is discussed.