Effect of moderate improvement in metabolic control on magnesium and lipid concentrations in patients with type 1 diabetes.

OBJECTIVE: To evaluate the effect of clinically obtainable improvements in metabolic control in patients with type 1 diabetes on biochemical cardiovascular risk factors. RESEARCH DESIGN AND METHODS: Blood and 24-h urinary samples were obtained from 49 patients with type 1 diabetes before and after a run-in period and after 3 months of intervention, with frequent adjustment of insulin dosage according to measured blood glucose concentrations. RESULTS: The intervention caused a mean insulin dosage increment of 10%, a 20% decrease in fasting plasma glucose concentration, a 10% decrease in albumin corrected serum fructosamine, and a somewhat lesser decrease in HbAlc.A 14% decrease in the renal excretion of magnesium (Mg) was observed, but without a change in average serum Mg concentration. Serum HDL cholesterol increased 4%, and serum triglycerides decreased 10% as an average. Looking at individual patients, the decrease in serum triglycerides correlated with both the change in serum total Mg concentration and with the increase in insulin dosage. Using the change in serum total Mg concentration and in insulin dosage as independent variables in a multiple regression analysis, the coefficient of correlation with the decrease in serum triglycerides was 0.52. CONCLUSIONS: Moderate but clinically obtainable improvement of metabolic control in patients with type 1 diabetes seems to reduce the loss of Mg, increase serum HDL cholesterol, and decrease serum triglycerides. The decrease in serum triglycerides was associated with the change in serum total Mg concentration. These reductions in Mg loss and serum triglycerides might reduce the risk of developing cardiovascular disease in patients with type 1 diabetes.

Serum lactate dehydrogenase isoenzyme 1 and tumour volume are indicators of response to treatment and predictors of prognosis in metastatic testicular germ cell tumours.

44 patients with metastatic testicular germ cell tumours treated with cisplatin-based chemotherapy were evaluated for prognostic implications of clinical characteristics. 22 obtained complete remission by the initial chemotherapy, and 30 are disease-free. S-LDH-1 had an overall predictive value regarding the response of 80%, S-LDH of 64%, S-AFP of 62%, and S-hCG of 62%. In multivariate analysis regarding response, only tumour volume classified according to the Royal Marsden system (P = 0.0036) and S-LDH-1 (P = 0.0069) yielded information. Regarding survival, S-LDH-1 (P = 0.0141) and an estimate of total tumour mass (P = 0.0171) had most impact with additional information from S-hCG only (P = 0.0536). We conclude that S-LDH-1 may be used as a tumour marker in addition to S-hCG and S-AFP in patients with metastatic testicular germ cell tumour.

Magnesium reduces insulin-stimulated glucose uptake and serum lipid concentrations in type 1 diabetes.

A magnesium (Mg) deficit has been described in patients with type 1 diabetes, and it has been related to the development of cardiovascular disease. We tested the hypothesis that type 1 diabetic patients have deficits in dietary Mg intake and that proper long-term (24 weeks) oral Mg supplementation would reduce cardiovascular risk factors. Therefore, the Mg status, dietary Mg intake, and the effect of Mg supplementation were evaluated in 10 type 1 diabetic patients and 5 control subjects. Muscle Mg content was decreased by 7% in the type 1 diabetic patients, and it increased by 5% after 24 weeks of oral MgO supplementation. Acute and chronic Mg supplementation decreased serum total cholesterol, serum low-density lipoprotein (LDL)-cholesterol, and apolipoprotein B. Insulin-stimulated glucose uptake decreased by 35% after 24 weeks of oral MgO supplementation. Eight of 10 patients with type 1 diabetes had a daily intake of Mg below 90% of the recommended daily allowance. In conclusion, a Mg deficit was found in type 1 diabetic patients. The deficit might be due partly to a relatively Mg-deficient diet. Mg repletion was associated with a decrease in atherogenic lipid fractions and a reduced insulin-stimulated glucose uptake.

The influence of analytical bias on diagnostic misclassifications.

Quality specifications for analytical imprecision and bias based on the state of the art; 'biology' and 'analysis of clinical situations' have been proposed by several scientists. Most interesting is the assessment of 'diagnostic misclassifications' based on direct evaluation of the consequences of analytical bias on the percentage of false positives and false negatives from a clinical decision situation, or based on the percentage of healthy individuals outside each reference limit when common reference intervals are used. With use of graphical or computer simulations assuming increasing (positive or negative) analytical bias, the expected percentage of misclassifications can be estimated- and, for the error for which the outcome (the fraction of misclassifications) is considered unacceptable, the maximum allowable analytical bias can be defined. An overview is given of previous proposals for specification of allowable analytical bias, and new examples are presented: (i) for S-transferrin. an analytical bias of +10% will increase the percentage of healthy individuals with measured concentration values above the upper reference limit from 2.5 to 10% (ii) the percentage of healthy men with concentration values for S-cholesterol above 6.2 mmol/l (240 mg/dl) will vary between 25 and 85% for analytical bias from - 1.0 to +1.0 mmol/l (+/- 16%): (iii) for glycated haemoglobin, two examples are given which illustrate the effect of analytical bias on the risk of retinopathy and so-called 'microalbuminuria' for measured values identical to the target 7.5% and 10.1% glycated haemoglobin, respectively. It is concluded that analytical bias may have significant impact on diagnostic performance, better standardization is needed, and quality specifications for allowable analytical bias should be based on medical usefulness criteria or, if such data are not available, on biological criteria.

External analytical quality assurance for proteins.

In the Nordic Protein Project an external control scheme (external quality assessment) was combined with the two other indispensable aspects of analytical quality, i.e. standardization (with a common high quality calibrator) and specification of needed analytical quality for sharing common reference intervals for nine serum proteins in the Nordic countries. The quality specifications are reliable for the purpose and given in clinical chemical terms--ready for application to the control systems. Further, a control design for disclosing external and internal errors, separately, is designed with respect to calibration and robustness towards analytical interference from turbid patient samples.

Discrepancy in HbA1c measurements performed at different local laboratories and at a selected central reference laboratory.

As participants in a general practice intervention study, 66 patients had their HbA1c measured both at a local and at a selected central reference laboratory. A discrepancy in the results was observed, as 97% of the results measured locally were lower than the centrally determined results. Bias (as calculated from mean value of measured HbA1c) between local laboratories and the central laboratory was measured to -1.47% HbA1c. A bias of this magnitude gave "problems" both to the general practitioners, patients and laboratories. To reduce the "problems" a bias of 0.5% HbA1c is estimated to be acceptable. But, to avoid these "problems" totally, a bias of 0.25% HbA1c is estimated to be the highest allowed bias. For HbA1c, a control system for both control of method standardisation and for specificity is described.

Analytical bias by contamination from hemolysis in determination of serum lactate dehydrogenase isoenzyme 1 in patients with testis germ cell tumors.

We investigated the impact of correction for contamination from hemolysis on serum lactate dehydrogenase isoenzyme 1 (S-LD-1) determinations. A study of hemolysates from 7 control patients showed a mean correction factor for the contamination of 0.1 U/L S-LD-1 for each 1 mg/L serum hemoglobin (S-Hb). S-LD-1 in a series of blood samples from 44 patients (EJC 1992;28:410-5) would decrease median 24 U/L (range 8-70 U/L) if the measurements were corrected with this factor. So we advice to correct S-LD-1 determinations for the contamination with a common correction based on the S-Hb concentrations in the samples.

A Nordic reference serum suitable for use as trueness control in the clinical routine laboratory.

The described reference serum is characterized by: liquid human serum at "normal" level stored in frozen state at -80 degrees C; minimum damage of proteins; aseptic preparation; cryoprecipitate and excess fibrin removed; serum cleared by ultracentrifugation; pH at 7.2-7.6; available in sealed glass ampoules with inert gas (one ml serum in each); specified components among most frequently analyzed analytes; homogeneity assured and stability monitored; produced under strict rules for good manufacturing practices (GMP). The assigned values are traceable to reference measurement procedures and reference materials of highest achievable metrological level; according to the present proposal the maximum allowable uncertainty of the assigned value is based on biological variation (shared common reference intervals); the uncertainty should ideally not exceed 1/5 of the maximum allowable bias of results obtained on patients samples (even 1/2 would theoretically be acceptable and, for a practical guide approximately < 1% may suffice). The present document provides some guidance of how the reference serum could be established in practice. The document also indicates the use of the material and further extension of the concept. The present work is done as a NORDKEM project.

The impact of quality control materials on the performance of an internal quality control system: 1. General considerations.

Quality assurance in clinical chemistry is based on statistical control procedures designed to maintain a certain level of quality. Decisions about acceptance or rejection of analytical series are made primarily from measurements of quality control materials. Such materials are most often of non-human origin; this may lead to false decisions due to non-identity of patient samples and quality control material. We have investigated the significance of non-identity between patient and control materials by running two separate quality control systems in parallel. A regular system used for acceptance or rejection of series, and a parallel system used for registration of the actual quality of the analytical routine work. The results from the latter system have not been available for the operator handling the control system used in routine work. Our study has confirmed the validity of an internal quality control system to achieve a certain level of analytical stability as expressed by the short-term and long-term precision. However, because ideal control materials are not always available, additional procedures to control accuracy, specificity, and detectability may be necessary. The usefulness of such procedures to properly handle error signals from quality control systems has been demonstrated.

Influence of analytical quality and preanalytical variations on measurements of cholesterol in screening programmes.

In screening programmes one should distinguish between the traditional bimodal distributions of results and a unimodal distribution as the basis for interpretation. A model for evaluation of the effects of biological within-subject and preanalytical variation as well as analytical variation is described. It is concluded that bias from blood sampling and analytical performance influences the outcome of screening programs significantly. At least three blood specimens are needed for estimating the homeostatic set point of cholesterol in individuals.

A model for quality achievement--the NORDKEM protein project.

UNLABELLED: The Nordic protein project demonstrates a model for the process of achieving analytical quality. GOAL: based on use of common reference intervals leading to the quality specifications. Creation of quality: through common high quality calibrator (with IFCC-values) (external factor) and individual trouble-shooting and guidelines (internal factor). Control of quality: with specially designed set of control samples and problem-related evaluation of control data. Establishing common reference intervals: through associated projects.

Appropriate sera for calibration and control of specific protein assays.

An ultracentrifugation technique is described which makes it possible to prepare protein calibrators and control sera which (i) are stable (more than 8 years documented for nine proteins), (ii) are clear (remains clear for more than 8 years at -80 degrees C), (iii) contain genuine proteins (documented electrophoretically and immunologically), and (iv) are reproducible to prepare (collection and preparation).

The impact of quality control materials on the performance of an internal quality control system: 2. Experiences from S-calcium analysis.

In this subproject the analysis of S-calcium was used for evaluation of the specified system of internal quality control. Decisions on acceptance or rejection of series were based on a non-human pool with a calcium concentration near the upper reference limit. In the parallel system, specimens from patients and healthy individuals were used together with other non-human pools to disclose changes in accuracy. The results were examined for false rejections and false acceptances. In all the rejections based on a mean rule with 9 controls and a pfr of 0.01, the parallel system supported the decisions. On 18 occasions the series were rejected based on a range rule with a pfr of 0.05. Ten of the rejections were confirmed by the parallel system, and the remaining eight times of the 165 series were close to the expected five per cent of false rejections. The matrix effect estimated from the human and non-human serum pools was less than 15 per cent of the total variation. This supported the convenient use of non-human control materials in the analysis of S-calcium. The total variation, CVt, was estimated to be in the range of 0.027-0.030. The median of the patient results could be a valuable tool in quality control, whereas the mean of patient results within the reference limits is of no value. In conclusion, the investigation confirmed the validity of a system for internal control of a specified quality.

The impact of quality control materials on the performance of an internal quality control system: 3. Experiences from S-triiodothyronine analysis.

In this subproject a method for S-triiodothyronine was used for evaluation of the specified system of internal quality control. Decisions on acceptance and rejection of series were based on results from a human pool with triiodothyronine concentration at the upper reference limit. In the parallel system specimens from patients and from healthy individuals were used in combination with artificial materials so that changes in accuracy, specificity, and detectability could be disclosed. The results were examined for false rejections and false acceptances. For all the seven rejections in 117 series due to a mean rule of 8 controls with a pfr of 0.01, the parallel system supported the decisions. In eight occasions the series were rejected due to a range rule with a pfr of 0.05; one rejection was confirmed by the parallel system and the remaining seven times out of the 117 series were close to the expected five percent of false rejections. A small systematic change in standardization of about eight percent was too small to be recognized by the quality control system. The specificity was not changed during the investigation period; all of the systematic changes were caused by variations in the standard materials. In conclusion the investigation confirmed the validity of the specified system of internal quality control.

A programme for assigning target values for external quality assessment schemes in countries with no authorized reference laboratories. Annex. Experiences with deviating results on Ektachem 700 XR.

The use of consensus values in external quality assessment schemes (EQAS) involves several problems and should preferably be replaced with target values obtained by methods of high metrological level. However, such values are difficult to obtain. In the present study we transferred values from the NIST (former NBS) certified reference serum SRM 909 to lyophilized and frozen test sera for various inorganic components using flame absorption or flame emission spectrometry. Enzyme values were assigned by laboratories of members of the former Scandinavian Enzyme Committee. The assignment was based on 2-4 determinations each day through 3 days of experiment. A total of 10 laboratories participated in the work. The results were utilized in a Danish EQAS. One practical concern is the fairly long time (9 months) which was needed for production, collection and compiling all data. To get an impression of how much dry chemistry analysers, e.g, could influence consensus values a Kodak Ektachem 700 XR was studied using lyophilized and frozen sera. The results are reported in the annex. On NIST SRM 909 the values found for sodium(I) were 6% too high even though the findings on frozen human sera were accurate. For aspartate aminotransferase a result three times the target values was found on a human lyophilized serum, while the values on the frozen sera only were slightly too high.