Martin R. Holland

Evidence for Consistency of the Glycation Gap in Diabetes

OBJECTIVE Discordance between HbA1c and fructosamine estimations in the assessment of glycemia is often encountered. A number of mechanisms might explain such discordance, but whether it is consistent is uncertain. This study aims to coanalyze paired glycosylated hemoglobin (HbA1c)-fructosamine estimations by using fructosamine to determine a predicted HbA1c, to calculate a glycation gap (G-gap) and to determine whether the G-gap is consistent over time. RESEARCH DESIGN AND METHODS We included 2,263 individuals with diabetes who had at least two paired HbA1c-fructosamine estimations that were separated by 10 ± 8 months. Of these, 1,217 individuals had a third pair. The G-gap was calculated as G-gap = HbA1c minus the standardized fructosamine-derived HbA1c equivalent (FHbA1c). The hypothesis that the G-gap would remain consistent in individuals over time was tested. RESULTS The G-gaps were similar in the first, second, and third paired samples (0.0 ± 1.2, 0.0 ± 1.3, and 0.0 ± 1.3, respectively). Despite significant changes in the HbA1c and fructosamine, the G-gap did not differ in absolute or relative terms and showed no significant within-subject variability. The direction of the G-gap remained consistent. CONCLUSIONS The G-gap appears consistent over time; thus, by inference any key underlying mechanisms are likely to be consistent. G-gap calculation may be a method of exploring and evaluating any such underlying mechanisms.

Clinical impact of variability in HbA1c as assessed by simultaneously measuring fructosamine and use of error grid analysis.

Abstract Background Haemoglobin A1c (HbA1c) is the only measure of glycaemic control used for many patients with diabetes, but it has limitations and might sometimes be misleading. HbA1c concentrations are influenced by conditions that alter red-cell life and there is evidence that biochemical variation in intracellular glycation rates also influence HbA1c concentrations. This paper is the first to propose a method of using simultaneously measured HbA1c and fructosamine, and error grid analysis, in the clinical setting, to gain a better understanding of glycaemic control. Methods Cross-sectional analytical study using HbA1c and fructosamine measures on the same blood sample from 1744 patients having blood taken for hospital diabetes clinic appointments. No other selection or exclusion criteria were applied. Results The fructosamine results were converted to a HbA1c equivalent which was then compared with the HbA1c. In an Altman-Bland plot, the paired result differences ranged between −6.9% and +5.5% HbA1c with 1139 (65%), 438 (25%), 130 (8%) and 37 (2%) being ≤1%, 1–2%, 2–3% or >3% of HbA1c difference, respectively. In clinical error grid analysis, 864 (50%) results had tight concordance for clinical interpretation, 761 (43%) had one block disunity of probably little clinical significance, but 105 (6%) were two blocks and 14 (1%) were three blocks discordant. Conclusion HbA1c may not accurately reflect glucose control. Our method, utilizing co-assessment with serum fructosamine, evaluates the possible clinical impact of this. We suggest the analysis used in this paper should be used routinely in diabetes practice.

Effect of a protease inhibitor on in vitro stability of intact parathyroid hormone

Background: We investigated whether increased protease activity explains the increased in vitro degradation of intact parathyroid hormone (iPTH) observed in serum when compared to EDTA plasma. Methods: Pre-dialysis blood samples for iPTH were taken from 11 patients with chronic renal failure and collected into plain glass tubes, tubes containing 200 KIU/mL aprotinin (a protease inhibitor) and EDTA tubes. All sample aliquots were separated at 20 min, 1 h, 2 h, 4 h, 8 h and 24 h post collection. Results: Over 24 h, iPTH concentrations remained unchanged in EDTA tubes. iPTH concentrations were significantly lower in both plain tubes (P < 0·01) and aprotinin tubes (P < 0·001) at 24 h when compared to the baseline sample (20 min). At 24 h, iPTH concentrations in EDTA tubes were higher than in plain tubes (P < 0·001) and aprotinin tubes (P < 0·01). The addition of aprotinin to plain tubes significantly reduced the degradation of iPTH (P < 0·05) at 24 h. Conclusion: Aprotinin significantly reduces the in vitro degradation of iPTH in plain tubes at 24 h from 24·7% to 9·6%. We suggest that increased protease activity contributes to the decline in serum iPTH over time. As this is observed in serum and not plasma it suggests that the increased protease activity may be due to the clotting process.

Clinical utility of estimated glomerular filtration rates in predicting renal risk in a district diabetes population

Aims  To determine the utility of estimated glomerular filtration rates (eGFR) in predicting renal risk over and above currently available strategies that incorporate serum creatinine and microalbuminuria in a diabetes population.

On the Transportability of Linear Discriminant Functions

Different methods can give different results for the same analyte, and inconsistent answers may be obtained if such results are used in linear discriminant functions. This is an important factor to consider when transporting linear discriminant functions from one laboratory to another; the example of alkaline phosphatase activity and the differential diagnosis of hypercalcaemia has recently been given. This study shows that results obtained by the method recommended by the Scandinavian Committee on Enzymes for alkaline phosphatase may be used in the calculation of the discriminant functions used for the differential diagnosis of hypercalcaemia and considers other factors that may affect the discrimination. It is concluded that, with care, linear discriminant functions may be transported from one laboratory to another.

Uncertain clinical utility of contemporary strategies for microalbuminuria testing.

Aims:  To determine whether conventional dipstick tests for proteinuria accurately identified patients with diabetic nephropathy and whether repeat testing for elevated albumin excretion and screening for urinary tract infection was required as part of the screening process for microalbuminuria.

Lipaemia: an overrated interference?

Abstract Reagent method sheets for analysis of common serum analytes often highlight the possibility of interference from lipaemia but the information given is often brief and may not be instrument-specific. Thus study assesses the degree of interference from lipaemia in a range of common serum analytes on the Bayer Opera (with a serum blank) using a commercial polymer, LipoClear, as a lipid-clearing agent. Serum samples (mean serum triglyceride 6.89 [range 0.58–28.4] mmol/L) are analysed for 14 common chemistry analytes and the results compared before and after treatment with LipoClear. Results showed no significant critical differences in analyte values before and after treatment, except for an expected fall in total protein, phosphate, cholesterol and triglyceride concentrations. Most of the common analytes in use on the Bayer Opera are not subject to interference from lipaemia; however, we recommend that where method sheets indicate interference from lipaemia then this should be quantified for the analyte in question.

Effect of sample tube type and time to separation on in vitro levels of C-reactive protein.

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The sweat test: effect of elution time on chloride and sodium concentrations

Background: The National Committee for Clinical Laboratory Standards guidelines and Guidelines for the Performance of the Sweat Test for the Diagnosis of Cystic Fibrosis in the United Kingdom recommend that sweat be eluted from filter paper for a minimum of 40 min. In the absence of published data, this recommendation is based on expert opinion. We therefore investigated the effect of elution time on chloride and sodium concentrations. Methods: The effect of elution time (up to three hours) on chloride and sodium concentrations was studied as recommended for measurement of quality control samples using external quality assessment solutions. Results: There were no significant differences in eluted chloride and sodium concentrations with time of elution up to 3 h. Conclusion: Elution time within 3 h had no effect on chloride and sodium concentrations when eluted from filter paper.