Variability of plasma proteins according to molecular size. Long-term and short-term intra-individual variation.

The intra-individual variations in serum concentrations of alpha 1-antitrypsin, albumin and alpha 2-macroglobulin were determined using high precision analytical methods. The long-term (3 months) variations were 8.2% for alpha 1-antitrypsin and 2.9% for alpha 2-macroglobulin in five males and five females. The coefficients of variation for albumin were 1.5 and 3.4% for males and females, respectively. In males the long-term variations of albumin and alpha 2-macroglobulin were highly correlated. The short-term (2 days) intra-individual variations in six males were 2.5, 3.8 and 3.4% for alpha 1-antitrypsin, albumin and alpha 2-macroglobulin respectively (coefficients of variation). A diurnal variation was found for albumin with maximal concentrations at 18.00 hours. At 6.00 and 10.00 hours the fractional concentrations of alpha 1-antitrypsin and albumin were lower than for alpha 2-macroglobulin. The variations of the three proteins were positively correlated.