Annals of Clinical Biochemistry: International Journal of Laboratory Medicine

There is a negative glucose gradient between the capillary and venous systems, produced by glucose uptake into peripheral tissues. This gradient is augmented by oral glucose ingestion in healthy volunteers; thus prandial status may impact on capillary glucose meter performance. Our primary aim was to investigate whether the (capillary-venous plasma) glucose difference changed in relation to prandial status, in healthy volunteers.

Glucose was measured fasting and also one hour after an ad libitum breakfast, in 103 healthy volunteers. Duplicate capillary (finger stick) measurements were undertaken at both time points, using both the FreeStyle Lite and AccuChek Performa meters. Simultaneous venous (antecubital fossa) samples were centrifuged immediately after collection and plasma glucose was measured using the laboratory hexokinase method. Results were compared by Bland-Altman difference analysis.

The mean (95% CI) pre- and postprandial (capillary-plasma) glucose differences (mmol/L) were calculated for each meter. For the Freestyle Lite, the preprandial difference was 20.51 (20.58 to 20.45) and postprandial difference was 0.81 (0.69-0.94). Corresponding differences for the Performa were 20.13 (20.20 to 20.06) and 1.19 (1.07-1.31), respectively. T-test comparison of participants’ paired pre- and postprandial (capillary-plasma) glucose differences confirmed a significant meal-related change in glucose estimation for both meters (P < 0.0001). Also, both meters read highest at lower glucose concentrations.

In healthy volunteers, both glucose meters showed a systematic positive bias one hour after breakfast. The significance of this finding in diabetes remains to be determined.

Low-density lipoprotein cholesterol (LDL-c) is the major measured parameter for cardiovascular risk assessment. The generally accepted formula (LDL-F) for estimating LDL-c developed by Friedewald and colleagues in 1972 using data from 448 individuals suffers from known inaccuracies at extremes of triglyceride (TG) and total cholesterol (TC) values.

We generated new formulas based on a large Brazilian database containing directly measured lipid values from 10,664 fasted individuals. This database LDL-c was measured by the LDL-C Select FS (DiaSys) system, a homogeneous method without centrifugation. The formulas were generated using linear and non-linear approaches, and the formula with the highest accuracy and simplicity for general clinical use was selected.

The simple formula LDL-c = 3/4 (TC - HDL-c) provided an accurate estimate of LDL-c, a higher correlation with directly measured LDL (r = 0.93) compared with LDL-F (r = 0.87), and also a higher accuracy.

The new formula outperformed several other LDL-c formulas over a wide range of TC, HDL-c and TG values. The validation and application of this formula in other populations is warranted.

The worldwide epidemic of obesity is a major public health concern and is persuasively linked to the rising prevalence of diabetes and cardiovascular disease. Obesity is often associated with an abnormal lipoprotein profile, which may be partly negated by pioglitazone intervention, as this can influence the composition and oxidation characteristics of low-density lipoprotein (LDL). However, as pioglitazone's impact on these parameters within high-density lipoprotein (HDL), specifically HDL_2&3, is absent from the literature, this study was performed to address this shortcoming.

Twenty men were randomized to placebo or pioglitazone (30 mg/day) for 12 weeks. HDL_2&3 were isolated by rapidultracentrifugation. HDL_2&3-cholesterol and phospholipid content were assessed by enzymatic assays and apolipoprotein AI (apoAI) content by single-radial immunodiffusion. HDL_2&3 oxidation characteristics were assessed by monitoring conjugated diene production and paraoxonase-1 activity by spectrophotometric assays.

Compared with the placebo group, pioglitazone influenced the composition and oxidation potential of HDL_2&3. Specifically, total cholesterol (P < 0.05), phospholipid (P < 0.001) and apoAI (P < 0.001) were enriched within HDL2. Furthermore, the resistance of HDL_2&3 to oxidation (P < 0.05) and the activity of paroxonase-1 were also increased (P < 0.001).

Overall, these findings indicate that pioglitazone treatment induced antiatherogenic changes within HDL2& ³ , which may help reduce the incidence of premature cardiovascular disease linked with obesity.

High-dose vitamin A influences glucose and lipid profile; however, the possible effects of moderate doses (25,000 IU/d) are conflicting. We aimed to compare the effect of vitamin A supplementation on several anthropometric and biochemical variables between obese and non-obese women.

This study was performed on 84 women among whom 56 were obese (body mass index [BMI] 30-35 kg/m2) and 28 were non-obese (BMI 18.5-24.9 kg/m2). Obese women were randomly divided into two groups: one group received 25,000 IU/d retinyl palmitate and another group received placebo. The third group was age-matched non-obese women who received 25,000 IU/d retinyl palmitate. At baseline and four months after intervention, fasting blood glucose (FBG), lipid profile, C-reactive protein (CRP) and liver enzymes were evaluated.

Baseline concentrations of serum FBG and triglyceride in the obese vitamin A-treated group were significantly higher compared with the other groups (P = 0.004 and 0.⁰⁰⁷, respectively). A significant increase in serum FBG (P = 0.026), total cholesterol (TC) (P = 0.004) and low-density lipoprotein cholesterol (LDL-C) (P = 0.016) in the non-obese group and a significant decrease in serum high-density lipoprotein cholesterol (HDL-C) (P = 0.001) in the obese group was observed. Serum CRP increased significantly in the obese vitamin A-treated group (P = 0.03) and serum aspartate transaminase increased significantly in the obese and non-obese groups after vitamin A supplementation (P = 0.008 and 0.⁰⁰¹, respectively).

Treatment with 25,000 IU/d vitamin A induced a mild elevation in serum lipids, CRP and liver enzymes in obese and non-obese women. Considering the other information about possible side-effects of excess vitamin A, use of vitamin A in this dose and duration should be considered with caution.

Vitamin D deficiency appears to be widespread and associated with ethnicity and economic status. Geography is the key to virtually all national statistics. It provides a structure for collecting, processing, storing and aggregating data. Linking geographic data to laboratory data allows analysis of the association of laboratory data with economic indicators.

The laboratory information system was searched to create a data-set of total 25-OH vitamin D concentrations, which was then linked to economic (Indices of Multiple Deprivation [IMD]) and ethnicity data using postcodes geocoded to Lower Super Output Areas (LSOAs).

A total of 12422 25-OH vitamin D requests were received during the time period searched. A total of 12167 of these had associated postcodes that would allow georeferencing to LSOAs. The median total 25-OH vitamin D was 24.5 nmol/L (5.3-99.0; 2.5-97.5th percentile). Statistically significant (Spearman rank) correlations were found between median 25-OH vitamin D (nmol/L) and percentage of non-White population and percentage of non-White population and IMD. No statistically significant correlation between median 25-OH vitamin D concentration and IMD was found; however, a statistically significant correlation between percentage of population classified as severely deficient and IMD was found.

In summary, vitamin D deficiency is widespread and is related to ethnicity; it does not appear to be related to economic status except in cases of severe vitamin D deficiency.

It is well known that plasma creatinine concentration is affected by muscle mass, while some studies have suggested cystatin C is affected by body mass index (BMI). Our aim was to assess the effects of lean versus fat mass on cystatin C and creatinine derivative equations in estimating glomerular filtration rate (GFR) in healthy young men.

Three groups of participants were studied: those classified as normal (BMI 18-25 kg/m 2 with body fat, 30%); muscular subjects (BMI .30 kg/m 2 and body fat, 20%); and obese subjects (BMI .30 kg/m 2 and body fat .30%). All underwent diethylenetriamine pentaacetic acid GFR, bio-electrical impedance and dual-energy X-ray absorptiometry body composition analysis, measurement of plasma cystatin C, creatinine and high-sensitivity C-reactive protein and completed a diet record.

Cystatin C was highest in the obese group (0.77 mg/L; 95% confidence intervals [CI] 0.69-0.77) and creatinine was highest in the muscular group (90.1 μmol/L; 95% CI 84.3-96.0). On multivariate analysis, body fat and GFR (P = 0.003) were significant determinants of cystatin C; muscle mass and age affected creatinine significantly (P = 0.02). Using cystatin C equations, Le Bricon and Hoek showed significantly lower estimated GFR in the obese group but performed reasonably well within 50%, 30% and 20% of GFR. Creatinine equations showed significant underestimations of GFR for the muscular group.

Body fat is a significant determinant of cystatin C while creatinine concentration is highly affected by muscle mass and age. Body composition plays an important role in the interpretation of renal function. Cystatin C equations are still accurate in predicting GFR in our healthy male group without chronic kidney disease.

Availability of whole blood creatinine estimation for patients scheduled to undergo radiological contrast investigations can provide information to aid patient care by reducing adverse effects and improving departmental efficiencies.

We performed imprecision studies, different patient sample type comparison in 40 participants, and a limited interference study with dopamine and dobutamine on the i-Stat and StatStrip point-of-care enzymatic analysers with the Beckman DxC800 Jaffe assay.

Imprecision results showed that the i-Stat performed better. Patient comparison data indicated that the i-Stat provided better correlation than the StatStrip for all the different sample types with correlation coefficients (r2) being 0.995-0.996 and 0.918-0.⁹⁹⁵, respectively. The i-Stat results had a small positive bias of 6-9% for the three different sample types, which required different reference intervals. The StatStrip method showed greater scatter and overall small negative bias of 26% for the whole blood samples and a 10% positive bias with the plasma samples. Dopamine caused significant positive interference with the i-Stat only while dobutamine caused a small negative bias with the StatStrip method only.

The findings indicated there are differences offered by the two systems. The StatStrip requires a very small finger prick capillary sample, calculates estimation of the glomerular filtration rate and has an adjustment option to improve correlation with the local method. The i-Stat offers better analytical imprecision and patient comparison with the laboratory method with the three sample types but showed significant interference from dopamine. A final consideration was the availability of middleware to capture patient results with the i-Stat. Based on all the study data, the i-Stat was recommended.

Faecal calprotectin (f-Cp), a marker of intestinal inflammation, can be used to distinguish between functional and organic bowel disease. F-Cp, following extraction, is commonly quantified using enzyme-linked immunosorbent assays (ELISAs) but there are no data comparing the different f-Cp assays or sample extraction devices. We, therefore, evaluated and compared the performance of the Immunodiagnostik, Bühlmann and Eurospital f-Cp ELISA assays as well as the Roche, Immunodiagnostik and ScheBo Biotech commercial faecal extraction devices. We also briefly report results from a pilot f-Cp external quality assurance (EQA) scheme.

Imprecision, linearity, recovery, drift and limit of quantitation of the f-Cp assays were evaluated and between-assay variability assessed. The three commercial sample extraction devices were compared with the manual weighing method. Four faecal samples were distributed as part of a pilot EQA scheme to 15 laboratories using quantitative ELISA f-Cp assays.

The three f-Cp assays demonstrated adequate intra-/interbatch imprecision, linearity and recovery. The crosscomparison study and EQA data demonstrated that, for the same sample, the Bühlmann assay reports up to 3.8 times higher f-Cp concentrations than the Immunodiagnostik and Eurospital assays. On average, the commercial extraction devices led to a 7.8-28.1% under-recovery of f-Cp in comparison to the manual weighing method.

Laboratories should be aware of the lack of the assay standardization, as demonstrated by the between-assay variability. A comparison between f-Cp concentrations reported by these assays and clinical markers of disease severity is required in order to determine their diagnostic accuracy. The EQA scheme represents the first available programme for f-Cp.

Measurements of plasma normetanephrine and metanephrine provide a useful diagnostic test for phaeochro-mocytoma, but this depends on appropriate reference intervals. Upper cut-offs set too high compromise diagnostic sensitivity, whereas set too low, false-positives are a problem. This study aimed to establish optimal reference intervals for plasma normetanephrine and metanephrine.

Blood samples were collected in the supine position from 1226 subjects, aged 5-84 y, including 116 children, 575 normotensive and hypertensive adults and 535 patients in whom phaeochromocytoma was ruled out. Reference intervals were examined according to age and gender. Various models were examined to optimize upper cut-offs according to estimates of diagnostic sensitivity and specificity in a separate validation group of 3888 patients tested for phaeochromocytoma, including 558 with confirmed disease.

Plasma metanephrine, but not normetanephrine, was higher (P < 0.001) in men than in women, but reference intervals did not differ. Age showed a positive relationship (P < 0.0001) with plasma normetanephrine and a weaker relationship (P = 0.021) with metanephrine. Upper cut-offs of reference intervals for normetanephrine increased from 0.47 nmol/L in children to 1.05 nmol/L in subjects over 60 y. A curvilinear model for age-adjusted compared with fixed upper cut-offs for normetanephrine, together with a higher cut-off for metanephrine (0.45 versus 0.32 nmol/L), resulted in a substantial gain in diagnostic specificity from 88.3% to 96.0% with minimal loss in diagnostic sensitivity from 93.9% to 93.6%.

These data establish age-adjusted cut-offs of reference intervals for plasma normetanephrine and optimized cut-offs for metanephrine useful for minimizing false-positive results.

Metabolites of ethylene glycol (EG) can cross-react in L-lactate assays, leading to falsely elevated serum lactate levels in case of EG intoxication. In this study, we evaluated the effects of EG and its metabolites on routinely used lactate measuring methods.

Serum aliquots were spiked with either L-lactate, EG or one of its metabolites (all 12.5 mmol/L): glyoxal, glycolate, glyoxylic acid or oxalate. An unspiked sample (L-lactate 2.6 mmol/L) served as a control. L-Lactate levels in these samples were measured in 31 national hospitals on 20 different analysers from nine manufacturers.

The L-lactate concentrations in the control sample and in the samples spiked with L-lactate, EG, glyoxal and oxalate provided correct results by all routinely used methods. However, the glycolate and glyoxylic acid spiked samples resulted in falsely elevated L-lactate concentration with all blood gas methods and with the majority of general chemistry methods using L-lactate oxidase.

The EG metabolites glycolate and glyoxylic acid were shown to falsely elevate L-lactate results with most of the currently used methods due to cross-reactivity with the oxidase enzyme. Falsely elevated L-lactate results can lead to misdiagnosis and inappropriate management of patients with EG intoxication.

Measurement of fractionated plasma or urine metadrenalines is the recommended screening test in the diagnosis of phaeochromocytoma, with clinical cut-offs geared towards diagnostic sensitivity. Current practice at Salford Royal Hospital is to add urine catecholamines onto samples with raised urine metadrenalines, with the aim of adding specificity to a diagnosis of phaeochromocytoma.

This practice was reviewed by identifying a series of patients with raised urine metadrenalines who had catecholamines reflectively added. A total of 358 samples were identified from 242 patients, of which 228 had urine catecholamines measured.

A diagnosis of ‘phaeochromocytoma‘ (n = 41) or ‘no phaeochromocytoma‘ (n = 90) was obtained in 131 of 228 patients, giving raised urine metadrenalines a positive predictive value for phaeochromocytoma of 31%. The finding of increased urine catecholamines in samples with raised urine metadrenalines increased specificity for phaeochromocytoma to 70%. However, 95% diagnostic specificity for phaeochromocytoma could be achieved by the introduction of a second cut-off for urine metadrenalines geared towards maximizing specificity.

Consideration of the degree of increase in urine metadrenalines is a superior method of determining the likelihood of phaeochromocytoma than measurement of urine catecholamines.