Interassay variability of immunometric methods for thyrotropin in an external quality assessment survey: evidence that functional sensitivity is not always adequate for clinical decisions

We investigated the ability of current immunometric methods for thyrotropin (TSH; thyroid-stimulating hormone) to distinguish between low-normal and subnormal hormone concentrations by using the data from an external quality assessment (EQA) survey in 1990. We computed the interassay (between-run) precision profiles from results from 101 laboratories, which used the five most popular kits in the survey; during the control period (one year) each laboratory assayed 4 EQA pools distributed (as hidden replicates) in five occasions. The interassay CV was relatively low (9-13%) for three pools in the normal TSH range (greater than 0.8 milli-int. unit/L) but markedly higher (30-40%, except for one more precise kit) in the subnormal range (0.2 milli-int. unit/L). We calculated the effect of the between-run variability on the diagnostic accuracy (discrimination between normal and subnormal values) for three representative TSH concentrations: 0.2, 0.4, and 0.5 milli-int. unit/L (0.3 milli-int. unit/L was considered the lower normal limit). The three concentrations were reasonably discriminated (P less than or equal to 5%), and only one kit showed a between-run CV less than 18% at 0.2 milli-int. unit/L. For the other four less-precise kits, only the higher TSH value (0.5 milli-int. unit/L) could be classified with an acceptable diagnostic reliability. With the most precise kit, one can distinguish two TSH concentrations in the 0.3-0.5 milli-int. unit/L range that differ by at least 30%; with the other kits, differences greater than 50-60% are needed for reliable discrimination. Thus many laboratories fail to achieve the functional sensitivity of a second-generation assay, even if they use immunometric methods. TSH assays with a better interassay precision in the low concentration range are needed.

Interassay Variability of Immunometric Methods for Thyrotropin in an External Quality Assessment Survey: Evidence that Functional Sensitivity is not Always Adequate for Clinical Decisions

We investigated the ability of current immunometric methods for thyrotropin (TSH; thyroid-stimulating hormone) to distinguish between low-normal and subnormal hormone concentrations by using the data from an external quality assessment (EQA) survey in 1990. We computed the interassay (between-run) precision profiles from results from 101 laboratories, which used the five most popular kits in the survey; during the control period (one year) each laboratory assayed 4 EQA pools distributed (as hidden replicates) in five occasions. The interassay CV was relatively low (9-13%) for three pools in the normal TSH range (greater than 0.8 milli-int. unit/L) but markedly higher (30-40%, except for one more precise kit) in the subnormal range (0.2 milli-int. unit/L). We calculated the effect of the between-run variability on the diagnostic accuracy (discrimination between normal and subnormal values) for three representative TSH concentrations: 0.2, 0.4, and 0.5 milli-int. unit/L (0.3 milli-int. unit/L was considered the lower normal limit). The three concentrations were reasonably discriminated (P less than or equal to 5%), and only one kit showed a between-run CV less than 18% at 0.2 milli-int. unit/L. For the other four less-precise kits, only the higher TSH value (0.5 milli-int. unit/L) could be classified with an acceptable diagnostic reliability. With the most precise kit, one can distinguish two TSH concentrations in the 0.3-0.5 milli-int. unit/L range that differ by at least 30%; with the other kits, differences greater than 50-60% are needed for reliable discrimination. Thus many laboratories fail to achieve the functional sensitivity of a second-generation assay, even if they use immunometric methods. TSH assays with a better interassay precision in the low concentration range are needed.

Iron release and membrane damage in erythrocytes exposed to oxidizing agents, phenylhydrazine, divicine and isouramil

Mouse erythrocytes were incubated with oxidizing agents, phenylhydrazine, divicine and isouramil. With all the oxidants a rapid release of iron in a desferrioxamine (DFO)-chelatable form was seen and it was accompanied by methaemoglobin formation. If the erythrocytes were depleted of GSH by a short preincubation with diethyl maleate, the release of iron was accompanied by lipid peroxidation and, subsequently, haemolysis. GSH depletion by itself did not induce iron release, methaemoglobin formation, lipid peroxidation or haemolysis. Rather, the fate of the cell in which iron is released depended on the intracellular availability of GSH. In addition, iron release was higher in depleted cells than in native ones, suggesting a role for GSH in preventing iron release when oxidative stress is imposed by the oxidants. Iron release preceded lipid peroxidation. The latter was prevented when the erythrocytes were preloaded with DFO in such a way (preincubation with 10 mM-DFO) that the intracellular concentration was equivalent to that of the released iron, but not when the intracellular DFO was lower (preincubation with 0.1 mM-DFO). Extracellular DFO did not affect lipid peroxidation and haemolysis, suggesting again that the observed events occur intracellularly (intracellular chelation of released iron). The relevance of iron release from iron complexes in the mechanisms of cellular damage induced by oxidative stress is discussed.

Heart rate variability during the acute phase of myocardial infarction

BACKGROUND

After acute myocardial infarction (AMI), several abnormalities of the autonomic control to the heart have been described. Heart rate (HR) variability has been used to explore the neural control to the heart. A low HR variability count measured 7-13 days after AMI is significantly related to a poor outcome. Little information is available on HR variability early after AMI and its relation to clinical and hemodynamic data.

METHODS AND RESULTS

We studied 54 consecutive patients (42 men and 12 women; mean age, 60.4 +/- 11 years) with evidence of AMI by collecting the 24-hour HR SD from Holter tapes recorded on day 2 or 3. We also measured HR variability in 15 patients with unstable angina and in 35 age-matched normal subjects. HR variability was lower in AMI than in unstable angina patients (57.6 +/- 21.3 versus 92 +/- 19 msec; p less than 0.001) and controls (105 +/- 12 msec; p less than 0.001). Also, HR variability was greater in non-Q-wave than in Q-wave AMI (p less than 0.0001) and in recombinant tissue-type plasminogen activator-treated patients with respect to the rest of the group (p less than 0.02). No difference was found for infarct site. HR variability was significantly related to mean 24-hour HR, peak creatine kinase-MB, and left ventricular ejection fraction (all p less than 0.0001). Patients belonging to Killip class greater than I or who required the use of diuretics or digitalis had lower counts (p less than 0.004, p less than 0.001, and p less than 0.024, respectively). Six patients died within 20 days after admission to the hospital. In these patients, HR variability was lower than in survivors (31.2 +/- 12 versus 60.9 +/- 20 msec; p less than 0.001), and a value less than 50 msec was significantly associated with mortality (p less than 0.025).

CONCLUSIONS

HR variability during the early phase of AMI is decreased and is significantly related to clinical and hemodynamic indexes of severity. The causes for the observed changes in HR variability during AMI may be reduced vagal and/or increased sympathetic outflow to the heart. It is suggested that early measurements of HR variability during AMI may offer important clinical information and contribute to the early risk stratification of patients.

Iron release and erythrocyte damage in allyl alcohol intoxication in mice

Allyl alcohol administration in a toxic dose (1.5 mmol/kg) to starved mice causes the development of hemolysis in nearly 50% of the animals. Malonic dialdehyde (MDA) appears in plasma of the animals showing hemolysis. The treatment of mice with desferrioxamine after allyl alcohol intoxication completely prevents lipid peroxidation and hemolysis, suggesting the involvement of iron in the allyl alcohol-induced erythrocyte damage. Erythrocytes obtained from intoxicated mice before the development of hemolysis show, upon incubation, release of iron, lipid peroxidation and lysis. Studies carried out with reconstituted systems of erythrocyte lysates, containing ghosts and different fractions of erythrocyte cytosol and incubated in the presence of acrolein (the major metabolite of allyl alcohol), strongly suggest that iron is released from hemoglobin. This iron appears to promote lipid peroxidation which is accompanied by erythrocyte lysis. Thus, the allyl alcohol-induced hemolysis appears to be a model for iron delocalization from iron stores.

Positive inotropic effects of an ACTH analogue (ACTH 1-17) on myocardial performance

The aim of the present investigation was to study the effects of a single 100-micrograms i.v. administration of the synthetic heptadecapeptide [beta-Ala1-Lys17]ACTH1-17-4-amino-N-butylamide (ACTH 1-17) on the left ventricular performance. The systolic time intervals (STI) were recorded in 20 healthy adult young subjects (10 treated with ACTH 1-17 and 10 receiving placebo) before as well as 20, 40, 60 and 80 min after the i.v. ACTH 1-17 or placebo infusion. The STI were recorded immediately after blood withdrawal for measuring cortisol, aldosterone, adrenaline and noradrenaline plasma levels. A highly significant statistical difference was demonstrated for preejection period (PEP) and preejection period/left ventricular ejection time (PEP/LVET) ratio between subjects treated with ACTH 1-17 and subjects receiving placebo. As expected, a significant increase of cortisol and aldosterone plasma levels was observed in subjects treated with ACTH 1-17. The difference of adrenaline and noradrenaline plasma levels was statistically highly significant between subjects treated with ACTH 1-17 and those receiving placebo. The lack of increase in PEP and PEP/LVET ratio recorded in subjects treated with ACTH 1-17 is consistent with an increased left ventricular contractile performance. An increased plasma catecholamine release is postulated as the mechanism of this improvement.

Evaluation of valproic acid fluoroimmunoassay and comparison with a gas liquid chromatographic method

A method for monitoring valproic acid in serum with a fluoroimmunoassay is described. The evaluation was performed with run-to-run and within-run reproducibility, dilution, and recovery tests. The interferences of hemoglobin, bilirubin, and triglycerides were checked, and a comparison with a gas liquid chromatographic method was also performed. The between-run and within-run coefficients of variation were less than 5.2 and 2.6%, respectively. The method gave satisfactory results in dilution tests and a high correlation with a gas liquid chromatographic method (r = 0.98). The percentage of recovery was greater than 97%. No interference from hemolysis, bilirubin, or triglycerides was observed. The accuracy and simplicity of this method make it suitable for routine laboratory use.

Plasma catecholamines assay: comparison between fluorimetric and radioenzymatic methods

Plasma catecholamines were simultaneously measured in duplicate plasma samples by the fluorimetric method of Renzini et al. (1970) Clin. Chim. Acta 39, 587-594) and by the radioenzymatic method of Da Prada & Zurcher ((1976) Life Sci. 19, 1161-1174). The correlation of noradrenaline and adrenaline plasma concentrations determined by the two methods were, respectively, r = 0.95 (p less than 0.001) and r = 0.75 (p less than 0.01). The fluorimetric method was less sensitive, but more economical and less time-consuming than the radioenzymatic method. The fluorimetric method is still of value for measuring plasma catecholamines in man.

[Human chorionic somatommamotropins (HCS or HPL) : radioimmunologic determination and clinical significance]

The AA. have studied a new standardized radioimmunologic method for the routine determination of HCS. All the steps of the analysis have been studied, in particular those concerning the reability test and the precipitation of the complex with PEG. The best conditions were found when PEG 6000 is used at a concentration between 14-16 g in 100 ml (v/w), dissolved in veronal buffer, pH 7.4--9.4, with a dilution of protein (bovine serum) 1:4 in the incubation mixture. The reability test have given very good results. The c.p.m. of the analysis are plotted with a logit plot by computer which directly gives the values in ng/ml of the hormone in the plasma sample. The results obtained with this method are compared with those of the literature; the most striking difference in the present method appears in the last trimester of pregnancy in which the result have a low S.D. and can give a good help in clinical management of pregnant patients.

[Diazoxide test in the diagnosis of arterial hypertension: modifications in the levels of renin and aldosterone in blood of patients with various restrains of the renal function]

The AA. have applied the diazoxide test for the screening of primary hiperaldosteronism to 22 nephropatic patients suffering from hypertension and with different degrees of renal function. In 22 patients an increase in PRA and aldosterone values always followed the diazoxide infusion. Only one patient, likely suffering from primary aldosteronism, showed no increase in PRA and aldosterone values. The diazoxide infusion had no influence on renal, pancreatic and cardiovascular function. Therefore, this can be considered as a valid test easy to be performed in a short time, also in nephropatic patients who are very sensitive to pharmacological noxae.