Robbert Slingerland

Although measurement of haemoglobin A1c has become the cornerstone for diagnosing diabetes mellitus in routine clinical practice, the role of this biomarker in reflecting long-term glycaemic control in patients with chronic kidney disease has been questioned. Consensus review paper based on narrative literature review. As a different association between glycaemic control and morbidity/mortality might be observed in patients with and without renal insufficiency, the European Renal Best Practice, the official guideline body of the European Renal Association-European Dialysis and Transplant Association, presents the current knowledge and evidence of the use of alternative glycaemic markers (glycated albumin, fructosamine, 1,5-anhydroglucitol and continuous glucose monitoring). Although reference values of HbA1C might be different in patients with chronic kidney disease, it still remains the cornerstone as follow-up of longer term glycaemic control, as most clinical trials have used it as reference.

Inaccurate blood glucsoe monitoring systems (BGMSs) can lead to adverse health effects. The Diabetes Technology Society (DTS) Surveillance Program for cleared BGMSs is intended to protect people with diabetes from inaccurate, unreliable BGMS products that are currently on the market in the United States. The Surveillance Program will provide an independent assessment of the analytical performance of cleared BGMSs. The DTS BGMS Surveillance Program Steering Committee included experts in glucose monitoring, surveillance testing, and regulatory science. Over one year, the committee engaged in meetings and teleconferences aiming to describe how to conduct BGMS surveillance studies in a scientifically sound manner that is in compliance with good clinical practice and all relevant regulations. A clinical surveillance protocol was created that contains performance targets and analytical accuracy-testing studies with marketed BGMS products conducted by qualified clinical and laboratory site...

Cytidine deaminase can cause the deamination of cytotoxic analogues of cytidine or rescue cells from the cytotoxicity of uracil analogues. Therefore, cytidine deaminase influences the cytotoxicity exerted by these compounds. We investigated the activity of this enzyme in situ in neuroblastoma cell-line cells. The in-situ cytidine deaminase activity in human neuroblastoma cell-line SK-N-SH cells appeared to be two-fold higher than in the human neuroblastoma N-myc amplified cell-line SK-N-BE(2)-C cells. The observed activity correlated with the presence of both alleles in SK-N-SH cells versus one allele of cytidine deaminase in SK-N-BE(2)-C cells. This observation may be exploited for the treatment of neuroblastoma patients having a tumour with a chromosome Ip deletion including the domain containing the gene encoding cytidine deaminase.

A highly sensitive method is presented for the automatic quantitative detection of DOPA metabolites in low concentrations in cells derived from the neural crest using reversed-phase HPLC in combination with fluorescence and electrochemical detection. The HPLC system was combined with on-line dialysis and on-line trace enrichment for the detection of small quantities of DOPA metabolites in culture media. Parameters like

A detailed quantitative study of pyrimidine metabolism in exponentially growing rat pheochromocytoma PC-12 cells has been performed. The sizes of ribonucleotide pools have been analysed and the pathways and the rates of metabolism of uridine, cytidine and aspartic acid have been determined, based on the incorporation of radioactive label. The fluxes of radioactive label through uridine-cytidine kinase, cytidine deaminase. CTP synthetase, nucleoside monophosphate kinase and nucleoside diphosphate kinase were obtained, as well as the flux through the pyrimidine de novo pathway. Also, the fluxes of radioactive label towards UDP-sugars, CDP-compounds, DNA and RNA were quantified in situ under steady-state conditions in intact PC-12 cells. From these fluxes of radioactivity, distribution ratios at the branch points of the metabolism were obtained. The pyrimidines synthesised via the de novo pathway were preferentially used for the synthesis of UDP-N-acetylhexosamines and UDP-hexoses, whe...

ABSTRACT In dit artikel wordt ingegaan op de verandering in rapportage-eenheden van HbA1c. Glucose wordt gebonden aan hemoglobine tot uiteindelijk een stabiel glycohemoglobine (HbA1c) gevormd wordt. De hoeveelheid glycohemoglobine vormt een afspiegeling van de cumulatieve waarde van glucose over de afgelopen 8-12 weken. De huidige HbA1c-bepalingen worden in sommige landen op verschillende wijzen uitgevoerd, gebaseerd op verschillende referentiemethoden. In 2007 is er door verschillende internationale organisaties van diabetologen (IFCC-ADA-EASD-IDF) consensus bereikt hoe HbA1c wereldwijd gerapporteerd moet gaan worden te weten: als HbA1c in nieuwe IFCC-getallen (mmol/mol). Vanaf 6 april 2010 zullen beide getallen dus gerapporteerd worden in mmol/mol en in procenten. Vanaf 1 januari 2011 zullen alleen nog de nieuwe mmol/mol-getallen gerapporteerd worden in Nederland (www.nieuwediabeteswaarde.nl). De waarde van HbA1c wordt beïnvloed door de levensduur van een rode bloedcel. Zodra die verandert, dan verandert de glyceringstijd van het hemoglobinemolecuul. Bij een verkorte levensduur van een rode bloedcel, zoals deze onder meer gevonden kan worden bij hemolytische anemie, HbSS en HbSC, kan een normale HbA1c-uitslag dus toch een verhoging betekenen. Als gevolg van een aanzienlijk bloedverlies kan het percentage reticulocyten omhoog gaan; ook dan is een verlaging in de HbA1c-uitslagen te verwachten. Bij een ferriprieve anemie en splenectomie zal het percentage oude rode bloedcellen toenemen waardoor relatieve verhoging van de HbA1c-uitslag te verwachten is. Op dit moment is er internationaal een discussie gaande of HbA1c gebruikt kan worden of mogelijk aanvullend gebruikt kan worden om de diagnose diabetes mellitus te stellen.

Human neuroblastoma SK-N-BE(2)-C cell-line cells were cultured in the presence of various concentrations of cyclopentenyl cytosine (CPEC). In the absence of cytidine, the IC50 value of CPEC for SK-N-BE(2)-C cells was 100 nM after 72 hr drug exposure. The IC20 value was 1 microM after 24 hr of exposure to CPEC in the presence of 10 microM cytidine, whereas in the absence of cytidine, CPEC at 1 microM resulted in an IC40 value after 24 hr. Therefore, cytidine partially prevented the cytostatic effect of CPEC. Cells cultured with 1 microM CPEC for 72 hr were enriched by approximately 410% with mono- and oligonucleosomes in comparison with cells cultured without CPEC. This enrichment was partially prevented with 10 microM deoxycytidine and completely prevented with 10 microM cytidine.

Ascomycetous yeasts produce extracellular antigens that are almost specific for the species. The antigen production by Hansenula wickerhamii and Stephanoascus ciferrii was independent of the carbon source and was proportional to the final cell density of the cultures. The same was true of chemostat cultures of Stephanoascus ciferrii, irrespective of the dilution rate and whether glucose or ammonia was the limiting nutrient. In cultures of Saccharomyces cerevisiae, however, antigen excretion mainly took place in the late exponential growth phase. Large amounts of antigen were extracted from the cell wall of Saccharomyces cerevisiae. A small amount was detected in the cytoplasm.

Iron and (stainless) steel are potent platelet aggregation activators, and may be involved in stent thrombosis, a serious complication after intracoronary stenting. Current platelet function tests are suboptimal, because of inappropriate agonists and/or lack of reproducibility. We tested the feasibility and reproducibility of a novel platelet function test using stainless steel as an agonist and compared it with other platelet function tests. In 111 patients with acute ST segment elevation myocardial infarction (STEMI), duplo measurements of iron (Fe)-induced platelet aggregation (FIPA) were performed after clopidogrel, acetylsalicylic acid and/or tirofiban treatment. Within 1 h, citrated blood samples drawn from the femoral sheath before primary percutaneous coronary intervention were added to 100 mg of low carbon steel and after 5 s mixing with vortex, the samples were incubated for 15 min. The ratio between the non-aggregated platelets in the agonist sample and platelets in a ref...

To assess the expected precision of HbA1c measurements and the magnitude of HbA1c changes eliciting the advice to change treatment among diabetes care professionals. A seven-item questionnaire was sent to participants through a website. The survey focused on physicians and nurses involved in diabetes care. In total, 104 physicians, 177 diabetes specialist nurses, and 248 primary care nurses responded to the survey. A large number of the nurses (44%) and only a small number of the physicians (4%) were not aware of the inherent uncertainty of HbA1c results. Nurses considered adjusting therapy based on very small changes in HbA1c whereas physicians in general adhere to 0.5% (5.5 mmol÷mol) as a clinically meaningful cut-off point. After therapy adjustment, a very small (0.1%) or no increase in HbA1c was considered to be significant enough to conclude that glucose regulation has worsened by 49% of the nurses and only 13% of the physicians. Significant differences exist in the interpretat...

In 2009, we investigated the conformance of 8 hemoglobin A(1c) (Hb A(1c)) point-of-care (POC) instruments. Since then, instruments have improved and new devices are available on the market. In this second study, we evaluated the performance of DCA Vantage, Afinion, InnovaStar, Quo-Lab, Quo-Test, Cobas B101, and B-analyst Hb A(1c) POC instruments. Clinical and Laboratory Standards Institute protocols EP-5 and EP-9 were applied to investigate imprecision, accuracy, and bias. We assessed bias using the mean of 3 certified secondary reference measurement procedures (SRMPs). Assay conformance with the National Glycohemoglobin Standardization Program (NGSP) certification criteria was also evaluated. Interference of common Hb variants was investigated for methods that could work with hemolysed material. The total CVs for all instruments, except for the DCA Vantage at a high Hb A(1c) value, were ≤3.1% in SI units and ≤2.1% in Diabetes Control and Complications Trial (DCCT) units. Afinion, D...

Whether self-monitoring of blood glucose (SMBG) improves glycaemic control in patients with type 2 diabetes mellitus (T2DM) not using insulin is questionable. Our aim was to investigate the effects of SMBG in patients with T2DM who were in persistent moderate glycaemic control whilst not using insulin. Patients were eligible when between 18 and 70 years of age, with an HbA1c between 7 and 8.5%, using one or two oral blood glucose lowering agents. Forty-one of the anticipated 52 patients were randomly assigned to receive either SMBG added to usual care, or to continue with usual care for one year. A fasting glucose value and three postprandial glucose values were measured twice weekly (including a Saturday or a Sunday). The primary efficacy parameter was HbA1c. Furthermore, health-related quality of life and treatment satisfaction were assessed using the Short-form 36 Health Survey Questionnaire (SF-36), the Type 2 Diabetes Symptom Checklist (DSC-r), the Diabetes Treatment Satisfacti...

Our objective was to evaluate the accuracy and safety of a real-time (RT) continuous glucose monitoring system (CGMS) in patients before and after cardiothoracic surgery and to investigate whether activation of the alarm function of the RT-CGMS had an effect on glucose control. Patients scheduled for elective cardiothoracic procedures, without a history of insulin-requiring diabetes, were perioperatively monitored with RT-CGMS for 72 h and were randomized into two groups: with or without the alarm function (set at 4 and 10 mmol/L) of the device activated. Sensor values were compared with capillary, arterial, and venous blood glucose values. Percentages of time spent in various glucose ranges were compared between groups. There were no adverse effects of the RT-CGMS. Of the 1,001 sensor value comparisons with capillary or arterial measurements, 96.6% fell within Clarke Error Grid zones A and B, with relative absolute differences ranging from 15% (preoperative period) to 12% (intensive care unit period) to 14% (postoperative period on the ward). Seventeen (7.9%) arterial and 16 (2.0%) capillary comparisons fell within zone D or E. Whether or not the alarm function, as used in this pilot study, was activated did not affect time spent in different glucose ranges. Although the RT-CGMS is safe and accurate according to accepted standards, there are still small aberrations, which in our opinion preclude unlimited use in its present form in a clinical setting. The effect of the alarm function at different glucose levels remains to be investigated.

We assessed the reference change value (RCV) of currently available hemoglobin A(1c) (HbA(1c)) laboratory assays, which is defined as the critical difference between two consecutive HbA(1c) measurements representing a significant change in health status. We examined the individual laboratory coefficients of variation (CVs) in the Dutch/Belgian quality scheme based on 24 lyophilized samples and calculated the RCV per laboratory (n = 220) and per assay method. In addition, two pooled whole blood samples were sent to the participating laboratories. The individual laboratory results were compared to the assigned value ± an allowable total error (TE(a)) of 6%. At HbA(1c) values of 41.0 mmol/mol (5.9%-Diabetes Control and Complications Trial [DCCT]) and 61.8 mmol/mol (7.8%-DCCT), 99% and 98%, respectively, of the laboratories reported a value within a TE(a) limit of 6%. The analytical CV of the HbA(1c) method used in 78% of the laboratories is <2.4%. The mean RCV at an HbA(1c) value of 53 mmol/mol (7.0%-DCCT) for methods of Bio-Rad is 5.9 mmol/mol (0.59%-DCCT); for Arkray/Menarini, 4.3 mmol/mol (0.43%-DCCT); for Roche, 6.5 mmol/mol (0.65%-DCCT); for Tosoh, 3.3 mmol/mol (0.33%-DCCT); and for other methods, 6.3 mmol/mol (0.63%-DCCT). The analytical performance of the majority of laboratory HbA(1c) methods is within the clinical requirements. However, based on the calculated RCV, 21.8% of the laboratories using different HbA(1c) methods are not able to distinguish an HbA(1c) result of 59 mmol/mol (7.5%-DCCT) from a previous HbA(1c) result of 53 mmol/mol (7.0%-DCCT). It can be presumed that differences in HbA(1c) results of 5 mmol/mol (0.5%-DCCT) do influence treatment decisions.

A new technique termed centrifugal affinity chromatography (CAC) is presented in this paper. CAC combines a high flow-rate, created by centrifugal force, with the specificity of affinity chromatography. This technique has been used for the purification of human immunoglobulin G. Furthermore this technique has been used to remove human albumin from serum and the effect of centrifugal force, ionic strength and pH has been studied. A test for determining the percentage of glycosylated hemoglobin in hemolysates has also been developed. This test, employing centrifugal chromatography, is more than three times faster than commonly used gravity flow methods.

To assess whether prehospital initiation of high-dose tirofiban in addition to high-dose clopidogrel results in more adequate inhibition of platelet aggregation (IPA) and better clinical outcome after primary percutaneous coronary intervention (PCI). Prespecified two-centre substudy of the prospective, international, multicentre, placebo controlled Ongoing Tirofiban in Myocardial Infarction Evaluation trial 2 (On-TIME-2 trial). 648 of 964 (67%) patients in the On-TIME-2 trial with ST elevation myocardial infarction undergoing primary PCI were studied. Pre-PCI IPA after early prehospital initiation of high-bolus dose (25 μg/kg) tirofiban was compared to placebo in addition to acetylsalicylic acid, unfractionated heparin and 600 mg clopidogrel. IPA was measured at a median of 60 min after study medication administration. In all four tests: Fe induced platelet aggregation, ADP induced platelet aggregation, platelet function analyser (PFA)-100 (collagen-epinephrine and collagen-ADP cartridge) IPA was higher in patients pretreated with high-dose tirofiban (p<0.001 for all tests), even after >74 min of pretreatment. Patients in the highest quartile of IPA had less residual ST segment deviation 1 h post-PCI (p value for trend: p=0.001, 0.004, 0.001, 0.002 respectively). There was a significant relationship between PFA-100 (both cartridges) and major adverse cardiovascular events (MACE, p=0.028, p=0.035) and early thrombosis (p=0.009, p=0.007). 60 min of prehospital initiated antiplatelet treatment including high-dose tirofiban resulted in higher levels of IPA compared to pretreatment with acetylsalicylic acid and high-dose clopidogrel alone, even after longer pretreatment times. Levels of IPA were significantly related to ST resolution and MACE, including stent thrombosis. This substudy confirms the main findings of the On-TIME2 trial that clopidogrel alone is suboptimal, even at high dose and administered well in advance of primary PCI.

Since the discovery of the relation between increased concentrations of fast haemoglobin fractions in patients with diabetes mellitus compared to concentrations in subjects without diabetes mellitus by Samuel Rahbar and co-workers in 1969, glycated haemoglobin A1c (HbA1c) has become a "gold standard" for glucose management in patients with diabetes mellitus. Recently, HbA1c has been advocated as a diagnostic marker for diabetes mellitus, which further underlines the importance of HbA1c. There are currently more than 30 methods available on the market with an analytical performance ranging from poor to state of the art. This review describes the biochemistry of HbA1c and the concepts of analytical and biological variation with respect to the measurement of HbA1c. Subsequently, aspects regarding the discovery of HbA1c are described. In addition, an overview is given on the assays methods that are currently available for the measurement of HbA1c. Finally, recommendations for the minimally required analytical performance characteristics of the current HbA1c assays are presented.

The A1C-Derived Average Glucose (ADAG) study was commenced to gain a better understanding of the relationship between HbA1c and average blood glucose and to investigate if HbA1c could be expressed in the same units as day-to-day glucose monitoring. Owing to the impact of the outcome of this study it was very important to determine HbA1c values with a minimum of uncertainty and as close as possible to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) primary reference method, which is the only valid anchor of HbA1c standardization. Approximately 2300 samples were analyzed with four IFCC secondary reference methods. Additional off-line calibration with IFCC secondary reference material with assigned IFCC values was performed to improve the uncertainty in the HbA1c value determination. Additional off-line calibration improved the 95% confidence interval between the four different HbA1c methods at HbA1c of 6.00% from +/-0.28% (5.72%-6.28%) to +/-0.20% (5.80%-6.20%) and at HbA(1c) of 9.00% from +/-0.43% (8.57%-9.43%) to +/-0.24% (8.76%-9.24%). The HbA1c results used in the ADAG study were determined with the lowest uncertainty technically feasible by using four certified IFCC secondary reference methods and additional off-line calibration with IFCC secondary reference material.

Various guidelines are in use for validating blood glucose meters. There are currently no analytical guidelines for validating procedures available for non-invasive or minimally invasive blood glucose meters. As a result manufacturers of these meters need to comply with different regulations in different countries with concomitant high costs. Some of the differences between different guidelines will be discussed in this article and recommendations for improvement will be presented.

We report an evaluation of the Menarini/ARKRAY ADAMS A1c HA-8180V analyser (HA-8180V), the fifth generation Menarini/ARKRAY ion-exchange HPLC for the measurement of HbA(1c). We evaluated the analytical performance, the measurement of haemoglobin variants and the performance in comparison to major analytical methods. Within-run, between-run and total CV were 0.2%, 0.4% and 0.7% at low HbA(1c) concentrations and 0.2%, 0.2% and 0.4% at high HbA(1c) concentrations, respectively. Trueness revealed a maximum deviation of 0.8 mmol/mol (IFCC units) or 0.1% (NGSP units) over the relevant analytical range. Linearity, carry-over and linear drift were excellent. Labile-HbA(1c), carbamylated haemoglobin, icteric samples and variation in hematocrit did not affect HbA(1c) outcome. Haemoglobin variants AS, AC and F do not affect HbA(1c) outcome and are explicitly identified and correctly quantified. HbA(1c) can not be measured in samples with AE and AD, but these variants are identified correctly. In comparison to other methods used at present, the HA-8180V shows excellent performance. The HA-8180V performs at a high level and is fit for any clinical application.