Low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol and apolipoprotein B: relationships among the different measurements.

Serum low-density lipoprotein cholesterol (LDLC) value is a recognized target for atherosclerotic risk management, and is generally calculated using the "Friedewald formula". Alternative risk markers include directly measured LDLC, non-high-density lipoprotein cholesterol (non-HDLC) and apolipoprotein B (ApoB). The relationships among such various measured or calculated quantities in medium-sized sets of patient results were investigated. Results from two sets of patients were retrieved from our laboratory information systems. One group (n=8436) included results of cholesterol, HDLC, triglyceride (TG) and glucose measurements. A second group (n = 902) included, in addition, results of ApoB measurement. The results confirmed the unreliability of the Friedewald formula at TG >350 mg/dL (3.96 mmol/L), but also indicated TG-linked underestimation of LDLC below such a TG level. By contrast, non-HDLC values were shown to be independent of TG, and better correlated to ApoB than LDLC values. Mathematically, the difference between non-HDLC and LDLC is TG x 0.458 (values in mmol/L): therefore, the latter cannot be compared to (or converted into) the former by simply adding a constant amount. The ratio LDLC/ApoB was shown continuously to decrease with increasing TG concentrations, while the ratio non-HDLC/ApoB did not. The TG-dependent underestimation of LDLC may be the reason for the reported better cardiovascular risk predictivity of non-HDLC in diseases associated with TG increase, such as in diabetes. Non-HDLC values are not influenced by TG levels, and are better correlated with ApoB.

Accuracy of cholesterol measurements in Italian clinical laboratories. Joint project GISSI prevention--Italian Society of Clinical Biochemistry. SIBioC GISSI Prevenzione Group.

We report the results of an external quality assessment scheme for serum total cholesterol measurement involving about 100 Italian laboratories participating in an epidemiological study of post myocardial infarction. Two frozen human serum pools with Abell-Kendall assigned values are distributed quarterly at the laboratories (up to now seven events occurred); the obtained results are evaluated and discussed. In one exercise (# 5) duplicated measurements were repeated on three different days. Eighty-five to 98% of the laboratories obtained results within the total error limits (+/- 8.9%). But, while precision (calculated on the six replicates of exercise # 5) is good (90% of the laboratories obtained CV < 3%), inaccuracy problems are evident in every event. Indeed the mean bias from the reference method value ranged from 1.54 and 3.49% in the various events.

Commutability of control materials in cholesterol measurement.

The 'commutability' is the property of a material to show inter-assay changes comparable to those of patients' sera. In order to assess the commutability, the cholesterol concentration was measured in 107 patients' sera and in 24 lyophilized control materials by a direct enzymatic method and by a reference-class procedure. The distance from the regression line of patients' sera results, expressed in SD units (normalized residual), was calculated and used to assess the commutability of each material. Out of 24 materials tested one had a normalized residual outside the +/- 3 interval (-4.4), and was considered as non-commutable. However, the distribution of the normalized residuals from the remaining 23 materials suggested a different behaviour in comparison with patients' sera, in the specific pair of methods. The relevance of this finding to the control of accuracy is discussed.

An extraction/enzymatic procedure for serum cholesterol measurement: evaluation of performance characteristics.

The performance characteristics of an extraction/enzymatic procedure for serum cholesterol measurement were evaluated. The procedure is substantially derived from the accepted reference method as standardized by the Centers for Disease Control, substituting the enzymatic reaction for the Liebermann-Burchard reaction. Imprecision (CV) was consistently less than 1.5%, and accuracy was comparable to that of the definitive isotope dilution mass spectrometry method and the accepted reference method. Direct comparison of the enzymatic with the Liebermann-Burchard reaction, using a set of 50 human sera, revealed about -0.05 mmol/l constant bias of the former versus the latter, this being possibly due to higher specificity of the enzymatic reaction. As compared with the accepted reference method, the method described is characterized by higher practicability, the reagent being easier to prepare and to handle, and generating a more stable, chemically defined end-product.

Importance of using soluble derivatives in assessing bilirubin interference: the example of gamma-glutamyltransferase.

In assessing possible in vitro interference from bilirubin on analytical methods, different results are to be expected from using either unconjugated (uB) or conjugated (cB) bilirubin as test materials, because of their different solubilities. In vitro interference of a synthetic soluble bilirubin derivative (ditauro-bilirubin, dtB) on gamma-glutamyltransferase activity measurement has been studied, in comparison with uB. In three out of five analytical methods/systems for the measurement of the enzyme activity, significantly higher (negative) interference was observed in the presence of the soluble derivative. Whichever the mechanism for the observed effect, the opportuneness of using soluble derivatives in order to assess bilirubin interference is pointed out: pathological serum specimens, submitted for laboratory investigations, are indeed frequently loaded with soluble bilirubin conjugates.

[The medical team and the campaign for primary prevention of cardiovascular diseases in the Tessin canton]. / Corps médical et campagne de prévention primaire des maladies cardio-vasculaires dans le canton du Tessin.

This study presents the results of a questionnaire research into the subjective perception of the free-practicing doctors in Ticino concerning the primary prevention programme against cardiovascular risk factors, directed to the whole cantonal population by the Social Welfare Department. 93% of the doctors (82% of the population) are aware of the programme and 82% of those interviewed judged it to be useful or very useful. Furthermore, the single initiatives of the programme (TV-advertisements and information-Leaflets) were also evaluated, as well as the frequency of preventive practices during medical visits (information on tobacco risks, blood pressure measurement, treatment of hypercholesterolemia). This study was also analyzed on the basis of questionnaire received before (response rate 41%) and after having sent out a further reminder (final response rate 61%). The results and conclusions did not differ with an increase in the reply rate.

Effect of information campaign by the mass media on hysterectomy rates.

The annual frequency of hysterectomy was monitored in the Canton Ticino, Switzerland, from 1977 to 1986. From February to October, 1984, there was a public information campaign in the mass media about rates of and need for hysterectomy. After the start of the campaign and during the following year the annual rate of operations per 100,000 women of all ages dropped by 25.8%, whereas in the reference area (Canton Bern), where no information was given to the public, hysterectomy rates increased by 1%. In the same period the hysterectomy rate per 100,000 women aged 35-49 declined by 33.2%, and the number of hysterectomies performed annually per gynaecologist decreased by 33.3%. In Canton Bern these rates were unchanged. The decline began 2 months after the start of the information campaign. The reduction in the number of hysterectomies was greater (p less than 0.001) in non-teaching hospitals (31.9%) than in teaching hospitals (18.1%). Information on regional rates and on the need for hysterectomy given through the mass media to the general population can change professional practices.

[Cardiovascular prevention in the community: the plurisectorial program of the canton of Tessin]. / Prévention cardio-vasculaire dans la collectivité: le programme plurisectoriel du canton du Tessin.

It describes the primary prevention of cardiovascular diseases carried out in Tessin (Italian-speaking Switzerland). Every single action is addressed to the entire population, actively involving professional associations (doctors, pharmacists, nurses, shop-keepers, etc.) and making use in particular of the collaboration of the mass-media (daily press, radio, television). The described actions concern the struggle against the cardiovascular risk factors through the daily diffusion of tv advertisements, free measurement of arterial pressure, and the possibility of disposing in the majority of regional restaurants of a "Health menu" with a low content of saturated fats and cholesterol. In 1984 every citizen of Tessin has been reached by an average of 24 "preventive messages".

[Prevalence of hysterectomy and cancer of the uterus in the population of Tessin canton]. / Prévalence de l'hystérectomie et cancer de l'utérus dans la population du canton du Tessin.

The study presents an analysis of the prevalence of hysterectomy during the year 1982 in Canton Ticino, where the rate (507) per 100'000 women is double that found in the West Midlands area of Great Britain (P less than 0,001). No statisticaly significant difference is found in the mortality rate or morbidity rate for tumour of the cervix and body of the uterus.