Rapid measurement of an index of testosterone binding to serum binding globulin using ion exchange columns

DEAE cellulose "mini" columns at pH 7.4 retain testosterone (T) bound to testosterone binding globulin (TeBG), which can be eluted at pH 2. Small 1:2 diluted serum or plasma samples are incubated with a tracer dose of tritiated T in pH 7.4 Tris buffer at 37 C then chilled and placed on columns at 4 C. Free and albumin bound T are washed off columns with pH 7.4 Tris buffer and columns are eluted with pH 2 Tris into vials for scintillation counting. After a simple mathematical correction for the small residual fraction of albumin bound T eluted at pH 2, we obtain a measure of TeBG binding of T which is highly correlated (r = .945) with that determined by dialysis. The method is quick, reproducible and applicable to serum or plasma volumes of 50 to 200 microliter. A single operator can process 100 samples in approximately 4 h.