[Centrifugal ultrafiltration method for determining the percent of free testosterone in serum]

Serum free testosterone (T) % in the follicular phase of 11 normal women, 11 normal men and 30 pregnant women of 5 to 39 weeks of gestation were determined by the centrifugal ultrafiltration method (CUF), which was performed at the centrifugation of 5 minutes, 1000 g and 37 degrees C, using the Amicon MPS-3 and YMT membrane. These conditions were shown to be appropriate for measuring the free T. There was a significant correlation between the percentage of free T due to the CUF and the equilibrium dialysis method (ED) (r = 0.88, p less than 0.01). Serum free T % and free T concentrations by the CUF method were, respectively, 2.89 +/- 0.09 (SE) % and 166.3 +/- 9.8 pg/ml in normal men, 1.76 +/- 0.09% and 9.4 +/- 0.7 pg/ml in non-pregnant women and 1.14 +/- 0.03%, 22.4 +/- 1.4 pg/ml in pregnant women. Serum free T % in non-pregnant women was significantly lower than in men (p less than 0.001) and higher than in pregnant women (p less than 0.001). In the CUF method the intra-assay CV was 4.9% in women, 6.0% in men and the inter-assay CV was 5.1% in women, 6.2% in men. The CUF method was more simple, rapid and accurate on the determination of the free T in serum than the ED method.