Uncertainties in the determination of the `cortisol-binding capacity' of plasma and their removal

The determination of the `cortisol-binding capacity' by gel filtration of a small plasma sample at low temperature after the addition of cortisol results in an arbitrary measurement dependent upon experimental conditions. It is unsatisfactory also because it misleads as to conditions at 37°C. Steady-state gel filtration of cortisol in plasma can be done at 37°C, at which temperature it overcomes known variables in present methods. It should prove of clinical value in showing abnormalities of cortisol binding in disease.