Systematic review of the biological variation data for diabetes related analytes.

BACKGROUND: Objective interpretation of laboratory test results used to diagnose and monitor diabetes mellitus in part requires the application of biological variation data (BVD). The quality of published BVD has been questioned. The aim of this study was to quality assess publications reporting BVD for diabetes-related analytes using the Biological Variation Data Critical Appraisal Checklist (BIVAC); to assess whether published BVD are fit for purpose and whether the study design and population attributes influence BVD estimates and to undertake a meta-analysis of the BVD from BIVAC-assessed publications. METHODS: Publications reporting data for glucose, HbA1c, adiponectin, C-peptide, fructosamine, insulin like growth factor 1 (IGF-1), insulin like growth factor binding protein 3 (IGFBP-3), insulin, lactate and pyruvate were identified using a systematic literature search. These publications were assessed using the BIVAC, receiving grades A, B, C or D, where A is of highest quality. A meta-analysis of the BVD from the assessed studies utilised weightings based upon BIVAC grades and the width of the data confidence intervals to generate global BVD estimates. RESULTS: BIVAC assessment of 47 publications delivered 1 A, 3 B, 39C and 4 D gradings. Publications relating to adiponectin, C-peptide, IGF-1, IGFBP-3, lactate and pyruvate were all assessed as grade C. Meta-analysis enabled global BV estimates for all analytes except pyruvate, lactate and fructosamine. CONCLUSIONS: This study delivers updated and evidence-based BV estimates for diabetes-related analytes. There remains a need for delivery of new high-quality BV studies for several clinically important analytes.

Dose regimens of human growth hormone: effects of continuous infusion and of a gelatin vehicle on growth in rats and rate of absorption in rabbits.

Different methods for administration of human growth hormone (hGH) have been examined with a view to efficient use of the limited amounts of hGH at present available for clinical use. We found that in hypophysectomized rats (1) hGH administered by continuous subcutaneous infusion induced a greater increase in body weight (referred to throughout as growth) than hGH administered by intermittent (daily) injection and (2) intermittent injections of hGH dissolved in 16% gelatin induced more growth than hGH dissolved in a glycine buffer. It was further found that (1) hGH dissolved in 16% gelatin compared with hGH dissolved in a glycine buffer induced lower maximal levels of immunoreactive plasma hGH and between 7 and 9 h after treatment higher plasma levels when injected subcutaneously in rabbits, (2) 125I-labelled hGH added as a tracer to hGH in gelatin was removed more slowly from subcutaneous injection sites in rabbits than 125I-labelled hGH given with hGH in glycine buffer and (3) changes in the ratio of hGH to gelatin had little effect on the time-course of plasma levels of hGH in the rabbit. Addition of the protease inhibitors aprotinin or 6-aminohexanoic acid, to injection of hGH in gelatin or glycine did not induce any consistent increase in plasma levels of hGH.

Glomerular filtration rate determination in diabetic patients using iohexol clearance--comparison of single and multiple plasma sampling methods.

Use of iohexol clearance has been described as the gold standard for the measurement of glomerular filtration rate (GFR). It is suggested that multiple plasma sampling following iohexol injection is required to accurately determine GFR by area under plasma clearance curve. The aim of this study was to determine whether single plasma sampling 4 h after injection of iohexol could accurately determine GFR in diabetic patients with mild to moderate renal failure, compared to multiple plasma sampling. A total of 120 GFR determinations in 36 patients with non-insulin dependent diabetic renal disease were done over 1 year. No acute deterioration was seen in renal function following injection of contrast in any patient. Strong correlation in GFR measurement was observed between the multiple plasma sampling method and the single plasma sampling method (r2 = 0.975). Single plasma sampling 4 h after bolus injection of iohexol is a safe and accurate method of determining GFR and change in GFR in diabetic subjects with mild to moderate renal impairment.

Effects of dietary sodium substitution with potassium and magnesium in hypertensive type II diabetics: a randomised blind controlled parallel study.

We have previously demonstrated that modest sodium restriction has a hypotensive effect in hypertensive diabetic subjects. A randomised blind controlled study has therefore been performed to study the effect of replacement of added salt intake using a salt substitute (50% NaCl, 40% KCL, 10% Mg2+, supplied by Cederroth, Sweden), compared to added whole salt intake over a 9 month period of 40 hypertensive Type II diabetic subjects (mean age 62.5 +/- 7.8 years; 24 males and 16 females). After 3 months, there was a significant reduction in systolic blood pressure (SBP) in the salt substitution group (163.2 +/- 24.2 to 153.6 +/- 20.8 mm Hg; P < 0.03) which was maintained at 9 months, when compared to the whole salt group (151.5 +/- 20.6 vs 173 +/- 18.9 mm Hg; P < 0.05). No significant changes were observed in mean weight, fasting lipid or insulin levels or diabetic control (measured by glycosylated haemoglobin). A greater number of patients were withdrawn during the study period owing to consistent BP > 160/95 in the whole salt group (n = 10) compared to salt substitute (n = 4). No significant changes were observed in diastolic pressure, 24-h urine sodium or magnesium excretion, but urine potassium was significantly increased in the salt substitute group (58.8 to 77.3: P < 0.05). The results of this study suggest that substitution of sodium, by potassium and magnesium, produces a clinically significant reduction in SBP in hypertensive Type II diabetic patients, and should be a useful antihypertensive therapy in this patient group.

Cardiovascular risk assessment in patients with retinal vein occlusion.

AIM: Patients with retinal vein occlusions (RVO) are at increased risk of cardiovascular disease (CVD). The risk of future CVD was determined using the Framingham algorithm and this risk estimate was used to guide decisions about preventative treatment for CVD in RVO patients. METHODS: 107 unselected RVO patients were studied. After excluding 18 patients because of age, missing data, or pre-existing cardiovascular disease, the calculated coronary heart disease risks (cCHDR) and calculated cardiovascular disease risks (cCVDR) were calculated on the 89 remaining and compared with both the standardised risk and the published incidence of CHD in England by t test or chi(2) test. RESULTS: The mean 10 year cCVDR was significantly higher than the Framingham standardised risk for all RVOs (20.6% (1.2%) v 15.7% (1.1%), p = 0.009) and female RVOs (17.8% (1.2%) v 12.7% (1.0%), p = 0.022) in particular. The 10 year cCHDR, compared to the actual incidence of CHD in England between the ages of 30 and 74 years, was > 15% in twice as many males than expected (62% v 28%, p <0.0001). This rose to almost six times when cCHDRs greater than 30% were compared (17% v 3%, p = 0.002). There was a fourfold increase in the proportion of female RVO patients with a cCHDR above 15% (40% v 9%, p <0.0001) and at a cCHDR of 30% and above (10% v 0%, p = 0.004). There were also significant differences in the cCHDR between central and branch RVO (both sexes). The branch form of RVO (BRVO) having higher cCHDRs because of systolic hypertension (164.1 (21.6) mm Hg v 149.5 (23.5) mm Hg, p = 0.003) and age (61.7 (8.3) years v 56.7 (10.6) years, p = 0.017). CONCLUSIONS: RVO is the presenting complaint in a group of patients at increased risk of CVD and is in agreement with the long term follow up data demonstrating an increased mortality from CVD in patients with RVO. The Framingham algorithm can accurately determine the cCHDR (or cCVDR) to assist the clinician in deciding who to treat in accordance with the Joint British Societies' guidelines, with particular regard to hypertension, lipid lowering, and the use of aspirin therapy.

A non-isotopic method for estimating 11 beta hydroxysteroid dehydrogenase activity in vivo.

11 beta-hydroxysteroid dehydrogenase (11 beta HSD) has both dehydrogenase (11 beta DH) and reductase (11 beta R) activities, which catalyse the interconversion of cortisol and cortisone, and prednisolone and prednisone. This enzyme confers specificity on the mineralocorticoid receptor by local oxidation of cortisol to cortisone. Using radiolabelled cortisol 11 beta HSD activity has been shown to be lower in some cases of essential hypertension. This study investigated a novel approach to estimating 11 beta HSD activity in vivo. Plasma steroid kinetics were investigated following oral hydrocortisone (a substrate for 11 beta DH) and prednisone (a substrate for 11 beta R) in five normotensive volunteers after dexamethasone suppression of endogenous steroid production. This approach was evaluated by inducing partial deficiency of 11 beta HSD in the volunteers who took liquorice (to inhibit 11 beta DH) and then carbenoxolone (to inhibit both 11 beta DH and 11 beta R). The ratio of cortisol to prednisolone (formed from prednisone) provided a measure of the activity of both 11 beta DH and 11 beta R. At 75 min after the steroid bolus the ratio increased from 1.1 (0.6-1.3) (median, range) under control conditions to 1.2 (0.8-1.7) after liquorice (P = 0.01, n = 5), and 2.0 (1.3-5.9) after carbenoxolone (P = 0.02, n = 5). It may therefore be applied to the measurement of 11 beta HSD activity in vivo in large numbers of hypertensive patients without the use of radioisotopes.

Effects of mobile phase composition on the chromatographic and electrochemical behaviour of catecholamines and selected metabolites. Reversed-phase ion-paired high-performance liquid chromatography using multiple-electrode detection.

The effects of pH, ionic strength, organic modifier, heptanesulphonic acid and citric acid content of a high-performance liquid chromatography mobile phase on the chromatographic and electrochemical behaviour of norepinephrine, epinephrine, dopamine, 3,4-dihydroxybenzylamine, 3,4-dihydroxyphenylethylene glycol, 3,4-dihydroxyphenylalanine and 3,4-dihydroxyphenylacetic acid in a reversed-phase system have been systematically studied. Optimal mobile phase conditions have been derived allowing the separation and reductive-mode detection of these compounds, applicable to both alumina and ion-paired solvent extracts of plasma. It is demonstrated that mobile phase composition significantly affects the sensitivity of a triple-electrode electrochemical detection system, in reductive and oxidative modes, and that electrochemical pre-treatment of mobile phase is required to attain maximum detector sensitivity in the reductive mode.

Artefactual increase in serum thyrotropin concentration caused by heterophilic antibodies with specificity for IgG of the family Bovidea.

A 19-year-old white woman presented with symptoms compatible with mild hyperthyroidism and biochemical evidence suggestive of autonomous thyrotropin (TSH) secretion. Intensive investigation of the pituitary-thyroid axis suggested that the basal concentrations of TSH were artefactually increased owing to heterophilic antibodies in the patient's serum with a broad specificity for immunoglobulin class G of the family Bovidea. These heterophilic antibodies complexed with the ovine antisera to human thyrotropin that are used in the RIA system, in particular blocking the binding of TSH but also partly blocking interaction with the second antibody. When TSH was measured immunometrically or by an RIA with TSH-specific antisera of rabbit origin, the concentrations measured were within the appropriate reference intervals. The blocking effect can be overcome by including large quantities of non-TSH-specific ovine IgG in assay incubation mixtures. Interference of this type is generally not appreciated and its incidence is poorly characterized, but it may have implications for any method in which antibodies are used as reagents.

Comparative accuracy of cardiovascular risk prediction methods in patients with diabetes mellitus.

OBJECTIVE: To compare the accuracy of cardiovascular risk prediction methods based on equations derived from the Framingham Heart Study in a cohort of patients with diabetes mellitus. RESEARCH DESIGN AND METHODS: Risk factor data was collected prospectively from 906 patients with diabetes mellitus. Absolute cardiovascular risks were calculated using the Framingham equation, and estimated with the currently available Framingham-based risk tables and charts. The sensitivity, specificity, positive and negative predictive values of the tables and charts to assess cardiovascular risk were assessed using calculation of risk from the full Framingham equation as the reference method. RESULTS: In all, 146 subjects (16.1%) had calculated 10-year coronary heart disease (CHD) risks > or = 30%, and 585 (64.6%) had risks > or = 15%. For identification of those at 10-year CHD risk > or = 30%, the original Sheffield tables had a sensitivity of 43% (95% confidence intervals (CI) 19.9-61.7%) and specificity of 94% (CI 90.8-96.7%). Modifications of the Sheffield tables improve sensitivity (95% CI 93.9-97%) but reduce specificity (90% CI 85.6-95.7%). The Joint British Guidelines' charts have a moderate sensitivity (69.5% CI 51.8-81.9%) and high specificity (99.7% CI 98.9-100%). For identification of individuals at a 10-year CHD risk > or = 27%, the Framingham categorical tables had a sensitivity of 95% (CI 91.6-97.8%), but a specificity of only 83% (95% CI 79.1-85.5%). CONCLUSIONS: The Joint British charts appear to have the best performance in a cohort of patients with diabetes mellitus, however, calculation of CHD/CVD (cardiovascular disease) risks with personal or laboratory computers using the full Framingham equation remains the most accurate way to assess cardiovascular risk in a primary prevention setting.

The acute effects of corticotropin-releasing factor on energy expenditure in lean and obese women.

Corticotropin-releasing factor (CRF) has been implicated in the development of obesity in genetically obese rodents. We have investigated the effect of 100 micrograms of intravenous CRF on energy expenditure in women, comparing the response in obese and lean volunteers. In response to CRF, energy expenditure as measured by indirect calorimetry increased rapidly with a peak response in both groups reached by two minutes with a ten minute post-CRF response averaging 9.0% in the lean and 11.0% in the obese. Subsequently, energy expenditure remained elevated for a longer duration in the lean compared to the obese. Overall, the total 30 min cumulative metabolic rise was similar in the lean and obese. The increments in energy expenditure were associated with elevation of plasma noradrenaline levels, suggesting the possible involvement of the sympathetic nervous system. The adrenocorticotrophic (ACTH) and cortisol responses to CRF were similar in obese and lean. Intravenous administration of CRF therefore acutely increases energy expenditure in both lean and obese healthy subjects.

Re-evaluation of the captopril test for the diagnosis of primary hyperaldosteronism.

OBJECTIVE: We aimed to re-evaluate the captopril test in the diagnosis of primary hyperaldosteronism. DESIGN: Serum aldosterone and plasma renin activity were measured supine prior to and 60, 90, 120 minutes after oral captopril, 25 mg. PATIENTS: We have performed this test in ten patients with primary hyperaldosteronism, two with hypertension and secondary hyperaldosteronism and in ten normokalaemic patients with essential hypertension. MEASUREMENTS: Validity was assessed by mathematical prediction methods. RESULTS: Using a ratio of aldosterone to plasma renin activity greater than or equal to 1400 pmol/l per microgram/ml/h as a predictor of primary hyperaldosteronism, the captopril test had a sensitivity of 100%, a specificity of 83% and a predictive value of 82% with a 60-minute post captopril evaluation being sufficient. Nevertheless, this test was only marginally superior to a careful analysis of the supine values where a similar ratio in the presence of a normal or suppressed plasma renin activity predicted primary hyperaldosteronism with a sensitivity also of 100% but a slightly lower specificity of 75% and predictive value of 77%. CONCLUSION: Application of the captopril test to patients identified as abnormal by screening confirms all cases of primary hyperaldosteronism but false positive or equivocal results, necessitating further investigation, may occur in some patients with essential hypertension.

Plasma total homocysteine measurement by ion-paired reversed-phase HPLC with electrochemical detection.

Homocysteine is thought to be a risk factor for vascular disease and this has led to an increase in demand for its assay in clinical laboratories. An HPLC method, incorporating electrochemical detection, for measurement of plasma total homocysteine is presented. The method is simple to perform, precise and suitable for clinical applications.

The sleep apnoea/hypopnoea syndrome depresses waking vagal tone independent of sympathetic activation.

The modest daytime hypertension and sympathetic upregulation associated with the sleep apnoea/hypopnoea syndrome (SAHS), does not explain the relatively large increased risk of cardiac morbidity and mortality in the SAHS patients population. Therefore, efferent vagal and sympathetic activity was evaluated during wakefulness in SAHS subjects and matched healthy controls, in order to determine if vagal downregulation may play a role in the aetiology of cardiac disease in the SAHS. The awake autonomic nervous system function of 15 male subjects, with mild-to-moderate SAHS was compared to that of 14 healthy controls matched for age, body mass index, gender and blood pressure. All subjects were free from comorbidity. Vagal activity was estimated from measurements of heart rate variability high frequency power (HF) and sympathetic activity was measured from urine catecholamine excretion. The %HF power was significantly (p < 0.03) reduced in SAHS patients (10+/-1.6 (mean+/-SEM)) as compared to controls (17 +/- 3). In addition, HF power correlated with the apnoea/hypopnoea index in the SAHS subjects (R = -0.592, p = 0.02). There was no statistically significant difference in the daytime excretion of nonadrenaline between control (242 +/- 30 nmol x collection(-1)) and SAHS (316 +/- 46 nmol x collection(-1)) subjects (p = 0.38). In these sleep apnoea/hypopnoea syndrome patients there was limited evidence of increased waking levels of urine catecholamines. The principal component altering waking autonomic nervous system function, in the sleep apnoea/hypopnoea syndrome subjects, was a reduced daytime efferent vagal tone.

Comparative accuracy of cardiovascular risk prediction methods in primary care patients.

OBJECTIVE: To compare the relative accuracy of cardiovascular disease risk prediction methods based on equations derived from the Framingham heart study. DESIGN: Risk factor data were collected prospectively from subjects being evaluated by their primary care physicians for prevention of cardiovascular disease. Projected cardiovascular risks were calculated for each patient with the Framingham equations, and also estimated from the risk tables and charts based on the same equations. SETTING: 12 primary care practices (46 doctors) in Birmingham. PATIENTS: 691 subjects aged 30-70 years. MAIN OUTCOME MEASURES: Sensitivity, specificity, and positive and negative predictive values of the Framingham based risk tables and charts for treatment thresholds based on projected cardiovascular disease or coronary heart disease risk. RESULTS: 59 subjects (8.5%) had projected 10 year coronary heart disease risks >/= 30%, and 291 (42.1%) had risks >/= 15%. At equivalent projected risk levels (10 year coronary heart disease >/= 30% and five year cardiovascular disease >/= 20%), the original Sheffield tables and those from New Zealand have the same sensitivities (40.0%, 95% confidence interval (CI) 26.6% to 57.8% v 41.2%, 95% CI 28.7% to 57. 3%) and specificities (98.6%, 95% CI 97.2% to 99.3% v 99.7%, 95% CI 98.8% to 100%). Modifications to the Sheffield tables improve sensitivity (91.4%, 95% CI 81.3% to 96.9%) but reduce specificity (95.8%, 95% CI 93.9% to 97.3%). The revised joint British recommendations' charts have high specificity (98.7%, 95% CI 97.5% to 99.5%) and good sensitivity (84.7%, 95% CI 71.0% to 93.0%). CONCLUSIONS: The revised joint British recommendations charts appear to have the best combination of sensitivity and specificity for use in primary care patients.

Serum leptin is elevated in Saudi Arabian patients with metabolic syndrome and coronary artery disease.

AIMS: To compare plasma leptin in Saudi subjects with Type 2 diabetes and coronary heart disease (CHD) with non-diabetic control subjects and to examine the relationship of plasma leptin to other CHD risk factors. RESEARCH DESIGN AND METHOD: Serum leptin concentrations were measured in 144 Saudi men. Subjects studied included 59 with Type 2 diabetes mellitus [BMI 27.5 (3.7) kg/m2 mean (sd)], 34 with coronary heart disease [BMI 29.6 (1.8) kg/m2], and 51 non-diabetic controls [BMI 28.0 (3.5) kg/m2]. There was no significant difference in BMI between the groups. Fasting serum leptin, lipids, insulin, apolipoproteins and glucose were measured. BMI, blood pressure; smoking habit and age were also recorded. Insulin resistance was assessed using the HOMA model. RESULTS: Leptin concentrations were significantly higher in diabetic and CHD patients than in controls (P = 0.024 and 0.016, respectively). Multiple regression analysis showed that body weight (P < 0.0006), serum triglyceride concentration (P = 0.046) and systolic blood pressure (P = 0.013) were all significantly related to the logarithm of the serum leptin concentration (R2 = 0.549) in CHD patients. A subgroup analysis, comparing those patients who had the metabolic syndrome, as defined by WHO, with controls, showed higher serum leptin in those with metabolic syndrome (P = 0.05). CONCLUSIONS: Serum leptin is increased in Saudi subjects with diabetes mellitus, metabolic syndrome and CHD. Leptin may be a marker of risk of CHD, at least in men, and contribute to the CHD risk profile in subjects with insulin resistance. Further studies are needed to evaluate this relationship prospectively.