Ken Sikaris

Serum 25-hydroxyvitamin D, calcium intake, and risk of type 2 diabetes after 5 years: results from a national, population-based prospective study (the Australian Diabetes, Obesity and Lifestyle study).

OBJECTIVE To examine whether serum 25-hydroxyvitamin D (25OHD) and dietary calcium predict incident type 2 diabetes and insulin sensitivity. RESEARCH DESIGN AND METHODS A total of 6,537 of the 11,247 adults evaluated in 1999–2000 in the Australian Diabetes, Obesity and Lifestyle (AusDiab) study, returned for oral glucose tolerance test (OGTT) in 2004–2005. We studied those without diabetes who had complete data at baseline (n = 5,200; mean age 51 years; 55% were women; 92% were Europids). Serum 25OHD and energy-adjusted calcium intake (food frequency questionnaire) were assessed at baseline. Logistic regression was used to evaluate associations between serum 25OHD and dietary calcium on 5-year incidence of diabetes (diagnosed by OGTT) and insulin sensitivity (homeostasis model assessment of insulin sensitivity [HOMA-S]), adjusted for multiple potential confounders, including fasting plasma glucose (FPG). RESULTS During the 5-year follow-up, 199 incident cases of diabetes were diagnosed. Those who developed diabetes had lower serum 25OHD (mean 58 vs. 65 nmol/L; P < 0.001) and calcium intake (mean 881 vs. 923 mg/day; P = 0.03) compared with those who remained free of diabetes. Each 25 nmol/L increment in serum 25OHD was associated with a 24% reduced risk of diabetes (odds ratio 0.76 [95% CI 0.63–0.92]) after adjusting for age, waist circumference, ethnicity, season, latitude, smoking, physical activity, family history of diabetes, dietary magnesium, hypertension, serum triglycerides, and FPG. Dietary calcium intake was not associated with reduced diabetes risk. Only serum 25OHD was positively and independently associated with HOMA-S at 5 years. CONCLUSIONS Higher serum 25OHD levels, but not higher dietary calcium, were associated with a significantly reduced risk of diabetes in Australian adult men and women.

Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population‐based study

Objective  Vitamin D deficiency is recognized as a global public health problem, but the population‐based prevalence of deficiency and its determinants in Australian adults is not known. This study evaluated the vitamin D status of Australian adults aged ≥25 years and risk factors associated with vitamin D deficiency in this population.

Defining analytical performance specifications: Consensus Statement from the 1st Strategic Conference of the European Federation of Clinical Chemistry and Laboratory Medicine.

*Corresponding author: Sverre Sandberg, Norwegian Quality Improvement of Primary Care Laboratories (Noklus), Institute of Global Public Health and Primary Health Care, University of Bergen and Laboratory of Clinical Biochemistry, Bergen, Norway, E-mail: sverre.sandberg@isf.uib.no Callum G. Fraser: Centre for Research into Cancer Prevention and Screening, University of Dundee, Ninewells Hospital and Medical School, Dundee, Scotland, UK Andrea Rita Horvath: SEALS Department of Clinical Chemistry, Prince of Wales Hospital, Screening and Test Evaluation Program, School of Public Health, University of Sydney, and School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia Rob Jansen: Netherlands Foundation for Quality Assessment of Medical Laboratories (SKML), Radboud University, Nijmegen, The Netherlands Graham Jones: SydPath, St Vincent’s Hospital, Sydney, NSW, Australia Wytze Oosterhuis: Atrium-Orbis, Department of Clinical Chemistry and Haematology, Heerlen, The Netherlands Per Hyltoft Petersen: Norwegian Quality Improvement of Primary Care Laboratories (Noklus), Institute of Global Public Health and Primary Health Care, University of Bergen, Norway Heinz Schimmel: European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (IRMM), Geel, Belgium Ken Sikaris: Sonic Healthcare and Melbourne University, Melbourne, Vic, Australia Mauro Panteghini: Centre for Metrological Traceability in Laboratory Medicine (CIRME), University of Milan, Milan, Italy Consensus Statement

Low serum 25-hydroxyvitamin D is associated with increased risk of the development of the metabolic syndrome at five years: results from a national, population-based prospective study (The Australian Diabetes, Obesity and Lifestyle Study: AusDiab).

CONTEXT Serum 25-hydroxyvitamin D [25(OH)D] concentration has been inversely associated with the prevalence of metabolic syndrome (MetS), but the relationship between 25(OH)D and incident MetS remains unclear. OBJECTIVE We evaluated the prospective association between 25(OH)D, MetS, and its components in a large population-based cohort of adults aged 25 yr or older. DESIGN We used baseline (1999-2000) and 5-yr follow-up data of the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab). PARTICIPANTS Of the 11,247 adults evaluated at baseline, 6,537 returned for follow-up. We studied those without MetS at baseline and with complete data (n = 4164; mean age 50 yr; 58% women; 92% Europids). OUTCOME MEASURES We report the associations between baseline 25(OH)D and 5-yr MetS incidence and its components, adjusted for age, sex, ethnicity, season, latitude, smoking, family history of type 2 diabetes, physical activity, education, kidney function, waist circumference (WC), and baseline MetS components. RESULTS A total of 528 incident cases (12.7%) of MetS developed over 5 yr. Compared with those in the highest quintile of 25(OH)D (≥34 ng/ml), MetS risk was significantly higher in people with 25(OH)D in the first (<18 ng/ml) and second (18-23 ng/ml) quintiles; odds ratio (95% confidence interval) = 1.41 (1.02-1.95) and 1.74 (1.28-2.37), respectively. Serum 25(OH)D was inversely associated with 5-yr WC (P < 0.001), triglycerides (P < 0.01), fasting glucose (P < 0.01), and homeostasis model assessment for insulin resistance (P < 0.001) but not with 2-h plasma glucose (P = 0.29), high-density lipoprotein cholesterol (P = 0.70), or blood pressure (P = 0.46). CONCLUSIONS In Australian adults, lower 25(OH)D concentrations were associated with increased MetS risk and higher WC, serum triglyceride, fasting glucose, and insulin resistance at 5 yr. Vitamin D supplementation studies are required to establish whether the link between vitamin D deficiency and MetS is causal.

Preanalytical quality improvement: from dream to reality

Abstract Laboratory diagnostics (i.e., the total testing process) develops conventionally through a virtual loop, originally referred to as “the brain to brain cycle” by George Lundberg. Throughout this complex cycle, there is an inherent possibility that a mistake might occur. According to reliable data, preanalytical errors still account for nearly 60%–70% of all problems occurring in laboratory diagnostics, most of them attributable to mishandling procedures during collection, handling, preparing or storing the specimens. Although most of these would be “intercepted” before inappropriate reactions are taken, in nearly one fifth of the cases they can produce inappropriate investigations and unjustifiable increase in costs, while generating inappropriate clinical decisions and causing some unfortunate circumstances. Several steps have already been undertaken to increase awareness and establish a governance of this frequently overlooked aspect of the total testing process. Standardization and monitoring preanalytical variables is of foremost importance and is associated with the most efficient and well-organized laboratories, resulting in reduced operational costs and increased revenues. As such, this article is aimed at providing readers with significant updates on the total quality management of the preanalytical phase to endeavour further improvement for patient safety throughout this phase of the total testing process.

Predictive accuracy and sources of variability in calculated free testosterone estimates

Background Serum free testosterone (FT) concentrations are commonly requested, but because reference FT methods are too laborious various calculational algorithms for FT based on total testosterone (TT) and sex hormone-binding globulin (SHBG) are frequently used. This study provides the first large-scale evaluation of the predictive accuracy and sources of variability for different FT formulae compared with direct laboratory measurements. Methods Using a large data-set of direct FT measurements by centrifugal ultrafiltration, the predictive accuracy of five different formulas for cFT (four existing plus a new formula) is evaluated in 3975 consecutive blood samples. In a second data-set of 124 samples from a reference panel of healthy eugonadal young men, we estimate the relative influence of the five algorithms and eight different TT and two SHBG assays including all available commercial total TT and SHBG assays together with a gas chromatography/mass spectrometry T reference method. Results cFT formulae show wide discrepancies with equilibrium-binding algorithms showing systematic overestimation relative to direct FT measurements, whereas two empirical cFT methods were more concordant. Variations between commercially available TT immunoassays have a strong impact on calculation of FT with TT assays contributing 82.2% of overall variance compared with 13.7% for the cFT algorithms and 4.1% for the SHBG assays. Conclusions If FT measurements are requested and direct measurement impractical, cFT formulae using TT and SHBG immunoassays provide an approximation to direct FT measurement that is strongly dependent on the TT, cFT formula used and, to a lesser extent, SHBG immunoassays.

A comparative study of the efficacy of simvastatin and gemfibrozil in combined hyperlipoproteinemia: prediction of response by baseline lipids, apo E genotype, lipoprotein(a) and insulin

Combined hyperlipoproteinemia (CHL) can be difficult to treat because of the heterogeneous nature of the lipoprotein abnormalities. We compared the relative efficacies of simvastatin and gemfibrozil and sought predictors of responsiveness in terms of the baseline lipids and other potential metabolic determinants (plasma insulin, Lp(a) and apo E genotype). Sixty-six subjects entered a cross-over, randomized trial involving 12 weeks on each drug. Efficacy was assessed after 6 and 12 weeks on each treatment. Simvastatin lowered total cholesterol 24%, triglycerides 12%, LDL cholesterol 33%, raised HDL cholesterol 13% and substantially reduced the cholesterol:triglyceride ratio in VLDL and IDL. Gemfibrozil lowered total cholesterol 5%, triglycerides 44%, raised HDL 26% and reduced VLDL and IDL lipids more than simvastatin did. LDL size increased with both treatments and HDL size increased with simvastatin. Responsiveness (25% fall in cholesterol or 40% fall in triglycerides) was shown by 31/61 subjects when taking simvastatin (cholesterol-lowering) and by 44/60 taking gemfibrozil (triglyceride-lowering). Responsiveness was greatest in those with apo E2 genotype with both drugs (P < 0.05). Unexpectedly, responders to simvastatin tended to have lower baseline total cholesterol but higher triglyceride levels than those whose cholesterol or triglyceride was lowered by gemfibrozil. Nevertheless, more hypercholesterolemic subjects responded to simvastatin and more hypertriglyceridemic subjects to gemfibrozil. Lp(a) (P = 0.04) and plasma insulin concentrations (P = 0.03) were negative predictors of percentage triglyceride-lowering with gemfibrozil. The difference between the two drugs in triglyceride-lowering lessened with rising insulin and falling HDL cholesterol. Thus, the responsiveness to the two major classes of lipid lowering drugs can be partly predicted from baseline lipids and related metabolic parameters.

A1C for Screening and Diagnosis of Type 2 Diabetes in Routine Clinical Practice

OBJECTIVE To evaluate A1C for screening and diagnosis of undiagnosed type 2 diabetes defined by oral glucose tolerance testing in clinical and general populations. RESEARCH DESIGN AND METHODS A1C cut offs (≤5.5% to rule out diabetes; ≥7.0% to rule in diabetes) were derived from a clinical group (Melbourne Pathology [MP] group: n = 2,494; undiagnosed diabetes 34.6%) and then evaluated in a population-based sample (AusDiab group: n = 6,015; undiagnosed diabetes 4.6%). RESULTS For diabetes in the MP and AusDiab groups, A1C at 5.5% gave sensitivities of 98.7 and 83.5%, while A1C at 7.0% gave specificities of 98.2 and 100%, respectively. Many (61.9–69.3%) with impaired A1C (5.6–6.9%) in both populations had abnormal glucose status. CONCLUSIONS A1C ≤5.5% and ≥7.0% predicts absence or presence of type 2 diabetes, respectively, while at A1C 6.5–6.9% diabetes is highly probable in clinical and population settings. A high proportion of people with impaired A1C have abnormal glucose status requiring follow-up.

Effects of combined calcium and vitamin D supplementation on insulin secretion, insulin sensitivity and β-cell function in multi-ethnic vitamin D-deficient adults at risk for type 2 diabetes: a pilot randomized, placebo-controlled trial.

Objectives To examine whether combined vitamin D and calcium supplementation improves insulin sensitivity, insulin secretion, β-cell function, inflammation and metabolic markers. Design 6-month randomized, placebo-controlled trial. Participants Ninety-five adults with serum 25-hydroxyvitamin D [25(OH)D] ≤55 nmol/L at risk of type 2 diabetes (with prediabetes or an AUSDRISK score ≥15) were randomized. Analyses included participants who completed the baseline and final visits (treatment n = 35; placebo n = 45). Intervention Daily calcium carbonate (1,200 mg) and cholecalciferol [2,000–6,000 IU to target 25(OH)D >75 nmol/L] or matching placebos for 6 months. Measurements Insulin sensitivity (HOMA2%S, Matsuda index), insulin secretion (insulinogenic index, area under the curve (AUC) for C-peptide) and β-cell function (Matsuda index x AUC for C-peptide) derived from a 75 g 2-h OGTT; anthropometry; blood pressure; lipid profile; hs-CRP; TNF-α; IL-6; adiponectin; total and undercarboxylated osteocalcin. Results Participants were middle-aged adults (mean age 54 years; 69% Europid) at risk of type 2 diabetes (48% with prediabetes). Compliance was >80% for calcium and vitamin D. Mean serum 25(OH)D concentration increased from 48 to 95 nmol/L in the treatment group (91% achieved >75 nmol/L), but remained unchanged in controls. There were no significant changes in insulin sensitivity, insulin secretion and β-cell function, or in inflammatory and metabolic markers between or within the groups, before or after adjustment for potential confounders including waist circumference and season of recruitment. In a post hoc analysis restricted to participants with prediabetes, a significant beneficial effect of vitamin D and calcium supplementation on insulin sensitivity (HOMA%S and Matsuda) was observed. Conclusions Daily vitamin D and calcium supplementation for 6 months may not change OGTT-derived measures of insulin sensitivity, insulin secretion and β-cell function in multi-ethnic adults with low vitamin D status at risk of type 2 diabetes. However, in participants with prediabetes, supplementation with vitamin D and calcium may improve insulin sensitivity. Trial Registration Australian New Zealand Clinical Trials Registry ACTRN12609000043235

Resolution of partition coefficients in the transverse plane of the lipid bilayer

Abstract The distribution of a small lipid soluble molecule across a lipid bilayer has been determined using fluorescence quenching techniques. The neutral form of the amine, N , N -dimethylaniline (DMA) quenches the fluorescence of a series of n -(9-anthroyloxy) fatty acids ( n = 2,6,9,12,16) which place a fluorophore at a graded series of positions from the surface to the centre of the lipid bilayer. A method is described for determining the partition coefficient of a quencher at each transverse position. The results show that DMA is located at all depths within the bilayer leaflet but that it is concentrated at the bilayer centre and to a lesser extent at the bilayer surface.