Multi-center epidemiological studies must ascertain that their measurements are accurate and reliable. For laboratory measurements, reliability can be assessed through investigation of reproducibility of measurements in the same individual. In this paper, we present results from the quality control analysis of the baseline laboratory measurements from the ELSA-Brasil study. The study enrolled 15,105 civil servants at 6 research centers in 3 regions of Brazil between 2008–2010, with multiple biochemical analytes being measured at a central laboratory. Quality control was ascertained through standard laboratory evaluation of intra- and inter-assay variability and test-retest analysis in a subset of randomly chosen participants. An additional sample of urine or blood was collected from these participants, and these samples were handled in the same manner as the original ones, locally and at the central laboratory. Reliability was assessed with the intraclass correlation coefficient (ICC), estimated through a random effects model. Coefficients of variation (CV) and Bland-Altman plots were additionally used to assess measurement variability. Laboratory intra and inter-assay CVs varied from 0.86% to 7.77%. From test-retest analyses, the ICCs were high for the majority of the analytes. Notably lower ICCs were observed for serum sodium (ICC=0.50; 95%CI=0.31–0.65) and serum potassium (ICC=0.73; 95%CI=0.60–0.83), due to the small biological range of these analytes. The CVs ranged from 1 to 14%. The Bland-Altman plots confirmed these results. The quality control analyses showed that the collection, processing and measurement protocols utilized in the ELSA-Brasil produced reliable biochemical measurements.

To efficiently examine the association of glutamic acid decarboxylase antibody (GADA) positivity with the onset and progression of diabetes in middle-aged adults, we performed a case-cohort study representing the ~9-year experience of 10,275 Atherosclerosis Risk in Communities Study participants, initially aged 45-64 years. Antibodies to glutamic acid decarboxylase (GAD65) were measured by radioimmunoassay in 580 incident diabetes cases and 544 non-cases. The overall weighted prevalence of GADA positivity (³1 U/mL) was 7.3%. Baseline risk factors, with the exception of smoking and interleukin-6 (P £ 0.02), were generally similar between GADA-positive and -negative individuals. GADA positivity did not predict incident diabetes in multiply adjusted (HR = 1.04; 95%CI = 0.55, 1.96) proportional hazard analyses. However, a small non-significant adjusted risk (HR = 1.29; 95%CI = 0.58, 2.88) was seen for those in the highest tertile (³2.38 U/mL) of positivity. GADA-positive and GADA-negative non-diabetic individuals had similar risk profiles for diabetes, with central obesity and elevated inflammation markers, aside from glucose, being the main predictors. Among diabetes cases at study's end, progression to insulin treatment increased monotonically as a function of baseline GADA level. Overall, being GADA positive increased risk of progression to insulin use almost 10 times (HR = 9.9; 95%CI = 3.4, 28.5). In conclusion, in initially non-diabetic middle-aged adults, GADA positivity did not increase diabetes risk, and the overall baseline profile of risk factors was similar for positive and negative individuals. Among middle-aged adults, with the possible exception of those with the highest GADA levels, autoimmune pathophysiology reflected by GADA may become clinically relevant only after diabetes onset.

O aumento crescente das opções diagnósticas e terapêuticas cria a necessidade de avaliar sua efetividade, o que pode ser feito, por exemplo, com o ensaio clínico randomizado. A difusão deste e de outros métodos da epidemiologia clínica na prática médica propicia o paradigma da "medicina embasada em evidências". Ao enfatizar a necessidade de evidências clínico-epidemiológicas sólidas para as decisões clínicas, a medicina embasada em evidências forma a estrutura para a integração dos resultados de pesquisas na prática clínica. A evidência é graduada pelo delineamento de pesquisa, fornecendo normas que estabelecem qual o grau adequado para a tomada de decisão médica. A combinação desse novo paradigma com o poder das telecomunicações modernas está causando uma revolução no modo em que a medicina é praticada. O processo é facilitado pelo acesso dos clínicos às revisões quantitativas e aos guidelines (posicionamentos clínicos) delas derivados. As limitações das fontes tradicionais de evidências médicas e as vantagens das novas fontes de evidências, como o ACP Journal Club e a Cochrane Collaboration, são descritas. É importante que o médico se familiarize com os conceitos e técnicas do paradigma de medicina embasada em evidências.

The growing array of diagnostic and therapeutic options available to the clinician has created the necessity of techniques, such as the randomized clinical trial, to evaluate their effectiveness. Recently, with the increasing penetration of the methods of clinical epidemiology into medical practice, the concept of an evidence-based medicine has arisen. Emphasizing the necessity of solid clinical evidence for clinical decision-making, evidence-based medicine provides a framework for the integration of research results into clinical practice. The evidence is graded, principally on the basis of study design, and norms are established as to what constitutes adequate evidence for clinical decision-making. The combination of this new paradigm of medical practice with the power of modern telecommunications is causing a revolution in the way medicine is practiced. Its integration into clinical practice is being facilitated by quantitative overviews of the literature, and the creation of clinical guidelines based on these reviews. Shortcomings of the traditional sources of evidence have been documented. New sources of evidence, such as the ACP Journal Club, and the Cochrane Collaboration, diminish dramatically the time required of clinicians to obtain the best avaliable evidence. All health professionals should familiarize themselves with evidence-based medicine.