SUMMARY Extracts of human plasma in ethanolic sulphuric acid contain two groups of fluorogens. The fluorescence of one of these increases linearly with time, while the other gives a constant fluorescence between 8 and 20 min. after extraction into the acid mixture. Measurement of the rate of increase in fluorescence of the plasma extracts permits the proportion of the total fluorescence due to the stable component to be calculated. The component with constant fluorescence probably consists entirely of cortisol and corticosterone. This finding has been used to improve the specificity of a simple method for the determination of adrenal corticosteroids in human plasma. This improved method is described and assessed, and a range of normal values is reported.

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A simple, inexpensive, and rapid method for the determination of pregnanediol in pregnancy urine by gas liquid chromatography is described. Automatic injection of the samples into the gas chromatograph allows up to 36 samples to be run overnight thus saving valuable technical time.The method described can easily be adopted for use in a routine steroid laboratory. The results obtained by this method have been compared with values obtained by the method of Klopper, Michie, and Brown (1955).

Many laboratories are now using fluorescence assay for the measurement of corticosteroids in urine and plasma but there has been little published work on the reliability of some of the techniques used. The automated method used in these studies is that of Townsend and James (1968) and the manual methods used are fully described elsewhere (Mattingly, 1962; Spencer-Peet et al., 1965;Mattingly and Tyler, 1967;and Townsend and James, 1968). For the automated procedure, the analytical rate is twenty samples per hour, and the between batch precision is ± 0.51 p.g. per 100 ml. (S.D.) for a range of 2-9 p.g. per 100 ml.In this paper five aspects of reliability are considered:-1. Activation source for fluorimeter. Many laboratories use a mercury lamp as an activation source. In a comparison of duplicate plasma samples analysed on the automated technique first with a zinc lamp and then with a mercury lamp, the mercury lamp values showed a range of increases of 1-6 p.g./100 ml. with a mean increase of 3.9 p.g./IOO ml. The slope of the regression line is 0.95, implying that the difference is absolute and not proportional so that even samples of low concentration may show this difference if a mercury lamp is used. This difference might be of importance in between laboratory comparisons on the same patient's plasma.2. Determination of plasma cortisol concentration using small volumes of plasma. Requests for plasma cortisol estimation are often accompanied by a sample of plasma, the volume of which is less than the customary 2.0 ml. This generally occurs with paediatric samples and the purpose of this study is to determine whether it is necessary to employ a 2.0 ml. sample. Plasma samples were analysed using where possible 2.0, 1.5, 1.0 and 0.5 ml. of plasma from the same sample without diluting the sample but adding proportionately less base to the plasma prior to extraction. The levels obtained with a 0.5 ml. aliquot of plasma showed a mean increase of 22 % over the value obtained with a 2.0 ml. aliquot of plasma. This increase suggests that one must be cautious interpreting the result of a test in which some of the samples are less than 2 ml. in volume. cortisol measurement after terminating treatment. It is now widely appreciated that plasma from patients receiving the spirolactone, Aldactone A, show spuriously high levels of fluorescence, which interfere with plasma cortisol measurement, but there is no published work on the duration of the interference. The plasma fluorescence levels in two patients who had been receiving Aldactone A were followed after they had been taken off the drug. The first had been receiving 50 mg. t.d.s. for three days. After treatment was stopped it took five days for the plasma fluorescence to reach a steady level within the normal range for plasma cortisol. The second patient had been receiving 100 mg. t.d.s. and it took nine days for the plasma fluorescence to fall to within the normal range, and a further two days to reach a steady level. These results were obtained using the manual techniqu...