A comparison of automated and manual radioimmunoassays for the estimation of serum digoxin.

Digoxin was assayed manually (SPAC kit) and by an automated radioimmunoassay instrument (ARIA II). There was good correlation between the methods (r = 0.964; n = 120). Carryover by the automated method was marginally significant from low to high level samples (5.2%), but insignificant from high to low level samples (1.4%). The precision on the ARIA II was far better in spite of the fact that assays were performed only in singlets compared with duplicates on the manual procedure. Best precision was obtained at the high level (3.76 nmol/l; between-batch CV: 2.4% ARIA; 5.5% SPAC). All values for control samples (manual and automated) fell within 6% of the all-method means. Using the ARIA II is marginally quicker and significantly cheaper. However, some back-up procedure is required for 'down time' with the machine, for what can be an urgent investigation. Patient results correlated well with clinical data.

Thyroid function in oral contraception: is there cyclic variation?

PIP: A study was carried out to determine whether there was any overall pattern of variation of thyroid parameters in women using oral contraceptives (OCs) throughout the menstrual cycle. Early morning blood samples were obtained from 7 women aged 25-45 on day 1, 7, 9, 14, 16, and 21 of their cycle while taking OCs and also on day 23 during menstruation. OCs used in this study included medium dose (6 subjects): Eugynon 50, Minilyn 50, Minovlar 50, Ovran 50, and Ovulen 50, and low dose (19 subjects): Brevinor, Eugynon 30, Microgynon 30, Norimyn 35, Ovran 30, and Ovranette 30. Out of 47 samples, 21 total thyroxine (TT4) and 23 total triiodothyronine (TT3) values were at the upper limit of normal or above, compared with 5 for free thyroxine index (FT4I) and 6 for free triiodothyronine index (FT3I). None of the free thyroid hormone levels were above the upper limit. While TT4 and FT4I are significantly raised (p0.001) in women on OCs compared to control women, there is no significant difference in free thyroxine levels between the 2 groups (p0.10) and this is true whether the estrogen dose of the OC was low (30 or 35 mcg, n = 19), or medium (50 mcg, n = 6). Each woman showed some slight variations but the pattern was different for each one; this suggests that these preparations do not interfere with thyroid metabolism per se. It has also been shown that with women taking OCs, the T3-uptake corrects insufficiently for TBG levels so that FT4I and FT3I values are near the upper limit of normal whereas the free hormones, FT4 and FT3 are in the mid-range. Where hypothyroidism is suspected, the FT4 should be followed up by a TSH measurement.^ieng

Further experience with free thyroxine assays with particular reference to pregnancy.

The Amerlex FT4 radioimmunoassay has been assessed. It is simple, quick, and precise. The assay is as good as the FTI or the Immo Phase FT4 assay in hyperthyroid, hypothyroid, or elderly subjects and in women on oral contraceptives. In acute illness and pregnancy, however, over half the values lie below the euthyroid reference range. Further work on blood samples obtained from pregnant subjects demonstrated that while FT4 values given by the Immo Phase and Liquisol kits remain constant, those given by the GammaCoat, Amerlex, and Lisophase kits show a significant decrease with gestation. What the 'true' FT4 is in acute illness and in pregnancy remains an open question.

A comparison of free thyroxine concentration and the free thyroxine index as diagnostic tests of thyroid function.

Serum free thyroxine concentrations, measured by the Immo Phase kit, and free thyroxine index values were compared in 200 subjects classified according to age, sex, and clinical diagnosis. The free thyroxine concentration was as good as the free thyroxine index in hyperthyroid, hypothyroid, elderly, and acutely ill patients and a better diagnostic index of thyroid status in pregnancy and in oral contraception.

Evaluation of a serum/plasma separator: suitability of samples for radioimmunoassay and competitive protein binding techniques.

A new method of separating serum or plasma from whole blood (Sure-Sep, W.R. Warner) has been evaluated with particular regard to the suitability of the serum/plasma samples for radioimmunoassay (R.I.A.) and competitive protein binding (C.P.B.) techniques. Sure-Sep did not affect the results obtained for the following assays: cortisol, thyroxine, triidothyronine, insulin, and growth hormone. In addition it was also found that contact of the serum or plasma samples with Sure-Sep for 24 hours at 4 degrees C was without effect on the results obtained.

Is glucagon important in stable insulin-dependent diabetics?

The role of glucagon has been evaluated in the everyday regulation of carbohydrate and lipid metabolism in insulin-dependent diabetic patients. Plasma concentrations of glucagon, growth hormone, cortisol, glucose, and free fatty acids and blood concentrations of glycerol, 3-hydroxybutyrate, acetoacetate, alanine, pyruvate, and lactate were measured in 38 fasting diabetic subjects deprived of their usual morning dose of insulin. The measurements were repeated in 25 of these patients after a further 3 hours of insulin deprivation and in 6 patients again at 6 hours. There was no correlation between the initial fasting levels of plasma-glucagon and those of the other biochemical measurements including glucose and ketone bodies. Furthermore, no correlation was found between changes in these measurements and in plasma-glucagon over a period of 3 or 6 hours. These findings suggest that glucagon is unlikely to play a role of primary importance in blood-glucose homoeostasis or ketone-body metabolism in ambulant insulin-dependent diabetic patients.

Assessment of a simple competitive protein-binding technique for plasma cortisol assay.

The Cortipac kit for cortisol assay by a competitive protein-binding technique (CPB) which utilizes 75Se cortisol has been evaluated. Results obtained by it agree well with those by the Mattingly fluorimetric method. Assays can be carried out on either plasma or serum and haemolysis does not interfere. The specificity of the assay was checked in blood samples from patients receiving synthetic steroids. Prednisone and prednisolone therapy caused significant interference with the assay; fluorocortisol and dexamethasone therapy did not. The increased progesterone in late pregnancy blood samples had only a small effect on the assay. Plasma samples for cortisol assay could be stored for at least 4 weeks at 4 degrees C and for at least 12 weeks at -20 degrees C.