A modified cumulative sum technique has been applied to radioimmunoassay quality control data. The method is approximately 50% more efficient in detecting systematic changes in the mean and variance of quality control values for plasma samples than more widely used conventional methods. The salient features of the technique have been restricted to changes in the mean quality control value of a plasma pool, but potential applications to changes in variance and as a diagnostic aid to problems in radioimmunoassay have been evaluated. The method is independent of computing facilities and statistical expertise since all computations have been presented in the form of a nomogram and thus can be used by technicians at the bench.
A cumulative sum technique has been specially designed to monitor the error between replicate determinations made on quality control plasma for consecutive batches of assays. This procedure has played a vital role in assessing assay performance. Special consideration has been given to small sample sizes (n = 2 or 3) which is generally the rule rather than the exception in many situations. This technique has been applied to numerous steroid radioimmunoassays and has ensured that both the mean value and the standard error of hormone levels of a quality control pool were under control. Data from routine assays of oestriol and testosterone in plasma from women are presented. Since this technique provides a sensitive measure of monitoring error, it assists the endocrinologist in elucidating statistical inferences which are a manifestation of assay performance.
A method is described for the resolution and individual quantitation of cortisol, cortisone, 11-deoxycortisol and corticosterone in foetal sheep plasma. The steroids were extracted by solvent partition and separated by LH-20 Sephadex column chromatography. Radioimmunoassay was used for the measurement of 11-deoxycortisol and cortisone and competitive protein-binding for corticosterone and cortisol. The relative levels of these steroids in the plasma of chronically catheterized sheep foetuses from 12 days before birth to term and then in the newborn lamb until 2 days of age are recorded. Cortisol gradually increased from a basal concentration of between 0 - 5 and 3 - 0 mug/100 ml plasma between days 12 and 5 pre partum, and then rose rapidly to 10 mug/100 ml plasma during the last 5 days of pregnancy to reach a maximum during or just after birth. Two days post partum the levels had fallen to approximately 3 mug/100 ml plasma. The mean value for 11-deoxycortisol between days 8 and 3 pre partum was 0 - 4 mug/100 ml plasma and increased in the final days before delivery to 1 - 0 mug/100 ml. Corticosterone initially showed slightly higher levels (approximately 1 - 5 mug/100 ml) in the earlier period of investigation but then fell during the immediate pre-partum period to 0 - 8 mug/100 ml. Cortisone was not detected at any stage of the investigations. The relationship between levels of cortisol and 11-deoxycortisol in foetal plasma and myometrial contractility is shown. An increase in uterine activity was seen to occur at the time that cortisol levels were at their maximum. The 11-deoxycortisol values throughout this particular study remained low. The results are discussed in relation to recorded levels in the adult and to previous studies in vitro with regard to changing steroid biosynthetic enzyme activity.
Communications to the Editor 2251 lected in (J). Ice water-baths were then placed around (B) and (C) and a hot water-bath around (A). Distillation of the bromide began accompanied by darkening and film formation in (A). The distillate collected mostly in (B). When distillation was finished, the bath around (B) was heated almost to boiling and an ice water-bath placed around (G). When this distillation was over, the bath around (C) was raised to boiling and an ice-bath placed under (H). This was the final distillation, the colorless bromide distilling into (G) while the temperature remained at 32.5 to 34.5°. A very small amount of dis-
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