Associations between glycaemic control and activation of the renin-angiotensin-aldosterone system in participants with type 2 diabetes mellitus and hypertension

Introduction

Hyperglycaemia increases succinate concentrations and succinate receptor activation in the kidney resulting in renin release. The aim of our study was to determine if there is an association between glycaemic control as evidenced by glycated haemoglobin values and activation of the renin-angiotensin-aldosterone system in patients with type 2 diabetes mellitus and hypertension.

Methods

A cross-sectional study was conducted at Galway University Hospitals between December 2014 and March 2015. Participants ( n = 66) were identified following interrogation of the electronic database for patients with type 2 diabetes mellitus. Baseline clinical demographics, aldosterone, plasma renin activity, direct renin concentration, urea and electrolytes, glycated haemoglobin, cholesterol, urine sodium and albumin creatinine ratio were recorded.

Results

There was a significant positive linear correlation between glycated haemoglobin and renin (both plasma renin activity [ P = 0.002] and direct renin concentration [ P = 0.008]) and between serum creatinine and aldosterone measured using both radioimmunoassay ( P = 0.008) and immunochemiluminometric assay ( P = 0.008). A significant negative linear correlation was demonstrated between serum sodium and plasma renin activity ( P = 0.005) and direct renin concentration ( P = 0.015) and between estimated glomerular filtration rate and aldosterone measured using radioimmunoassay ( P = 0.02) and immunochemiluminometric assay ( P = 0.016). A significant negative linear correlation existed between urine sodium and plasma renin activity ( P = 0.04) and aldosterone measured using radioimmunoassay ( P = 0.045).

Conclusions

There is a direct positive association between glycaemic control and renin. We advocate for renin measurement to be part of the diabetologist's armamentarium to assess, guide and optimize therapeutic strategies in patients with diabetes.

Increased blood glycohemoglobin A1c levels lead to overestimation of arterial oxygen saturation by pulse oximetry in patients with type 2 diabetes

BACKGROUND

Non-enzymatic glycation increases hemoglobin-oxygen affinity and reduces oxygen delivery to tissues by altering the structure and function of hemoglobin.

OBJECTIVES

We investigated whether an elevated blood concentration of glycosylated hemoglobin (HbA1c) could induce falsely high pulse oximeter oxygen saturation (SpO2) in type 2 diabetic patients during mechanical ventilation or oxygen therapy.

METHODS

Arterial oxygen saturation (SaO2) and partial pressure of oxygen (PO2) were determined with simultaneous monitoring of SpO2 in 261 type 2 diabetic patients during ventilation or oxygen inhalation.

RESULTS

Blood concentration of HbA1c was >7% in 114 patients and ≤ 7% in 147 patients. Both SaO2 (96.2 ± 2.9%, 95% confidence interval [CI] 95.7-96.7% vs. 95.1 ± 2.8%, 95% CI 94.7-95.6%) and SpO2 (98.0 ± 2.6%, 95% CI 97.6-98.5% vs. 95.3 ± 2.8%, 95% CI 94.9-95.8%) were significantly higher in patients with HbA1c >7% than in those with HbA1c ≤ 7% (Data are mean ± SD, all p < 0.01), but PO2 did not significantly differ between the two groups. Bland-Altman analysis demonstrated a significant bias between SpO2 and SaO2 (1.83 ±0.55%, 95% CI 1.73% -1.94%) and limits of agreement (0.76% and 2.92%) in patients with HbA1c >7%. The differences between SpO2 and SaO2 correlated closely with blood HbA1c levels (Pearson's r = 0.307, p < 0.01).

CONCLUSIONS

Elevated blood HbA1c levels lead to an overestimation of SaO2 by SpO2, suggesting that arterial blood gas analysis may be needed for type 2 diabetic patients with poor glycemic control during the treatment of hypoxemia.

Common hemoglobin variants in southern Taiwan and their effect on the determination of HbA1c by ion-exchange high-performance liquid chromatography

BACKGROUND

Patients with hemoglobin (Hb) variants may produce false HbA1c measurement. This study aimed to detect the common Hb variants in southern Taiwan and to evaluate their effect on the determination of HbA1c.

METHODS

A total of 1,434 samples collected for HbA1c measurement at Kaohsiung Veterans General Hospital in southern Taiwan in March 2008 were submitted for Hb variant analysis by Primus CLC-385. HbA1c measurements were obtained using ion-exchange high-performance liquid chromatography (HPLC) (Tosoh HLC-723 G7) for routine analysis. Patients identified with Hb variants were recalled for boronate-affinity HPLC analysis. The values of estimated average glucose (eAG) were converted from HbA1c. Values of eAG-FPG, calculated by eAG minus fasting plasma glucose (FPG), were compared to estimate the accuracy of HbA1c measurement in patients with Hb variants.

RESULTS

Among the 1,434 patients, the mean standard deviation of FPG was 162.8 +/- 60.5 mg/dL, HbA1c was 8.28 +/- 1.97%, and eAG was 190.9 +/- 56.6 mg/dL. Five Hb variants were detected in 11 patients, the incidence being 0.76%. Hb J was identified in 4 patients, Hb G in 2 patients, Hb E in 1 patient, Hb owari in 3 patients, and high fetal hemoglobin (HbF) in 1 patient. Abnormal HPLC chromatograms were seen among the patients with Hb J, E, G and HbF, but not in the patients with Hb owari. In patients with Hb variants, FPG was 149.5 +/- 39.9 mg/dL, HbA1c was 7.29 +/- 2.01%, and eAG was 162.5 +/- 57.7 mg/dL. Lower values of eAG-FPG may have occurred in the patients with Hb J and E, and in those with high HbF. On scattergrams of the relationship between HbA1c and FPG, the plots of Hb J, E and high HbF lay below the regression line of non-Hb variants. Inconsistent Hb values between both methods were only observed among some samples of patients with Hb variants.

CONCLUSION

The existence of Hb variants may result in false HbA1c measurement. The possible presence of spuriously low HbA1c levels or abnormal HPLC chromatograms by using ion-exchange methods should be kept in mind.

Hemoglobin variant HbE found in two South Asian diabetic patients

Glycohemoglobin, also known as hemoglobin (Hb) A(1c), is a marker of long-term glycemic control in patients with diabetes. We present two South-Asian diabetic patients whose HbA(1c) peaks were not measurable using high performance liquid chromatography (HPLC). Further investigations showed that these patients were homozygous for a hemoglobin variant, HbE (beta26 Glu-->Lys). Because of the increasing numbers of immigrants in Japan, area-specific hemoglobinopathies are now encountered more frequently than before. Thus, if discrepant results are found on an HbA(1c) assay or if the HbA(1c) value cannot be measured, such patients should be screened for hemoglobinopathies and alternative measurements for monitoring diabetes should be considered.

Performance evaluation of ion exchange and affinity chromatography for HbA1c estimation in diabetic patients with HbD: a study of 129 samples

OBJECTIVES

To compare ion exchange and boronate affinity chromatography for HbA(1c) estimation in patients with type I and II diabetes having hemoglobin D.

DESIGN AND METHODS

Systems based on ion exchange and boronate affinity chromatography were evaluated and compared for their performance for HbA(1c) estimation in patients with homozygous and heterozygous D disease.

RESULTS

Boronate affinity chromatography shows least interference by HbD in heterozygous as well as homozygous diabetic patients for HbA(1c) estimation.

CONCLUSIONS

The use of boronate affinity chromatography was found to be helpful in evaluating glycemic control in diabetic subjects with HbD.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the detection of hemoglobins as the protein biomarkers for fecal occult blood

In this study, we discover that hemoglobins (Hb), highly water-soluble globular proteins that are the most predominant proteins detected by matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry in blood, can be used as protein biomarkers for fecal occult blood (FOB). Hemoglobins were extracted from the feces with pure water and separated from the solids in feces through centrifugation. Singly charged molecular ions of Hb-related alpha chains (theoretical MW: 15 126) and beta chains (theoretical MW: 15 867) were detected by MALDI-TOF operated in linear mode using 4-hydroxy-alpha-cyanocinnamic acid (alpha-CHC) as the matrix (with a volumetric ratio of 1:1). The detection limit of FOB using this method is estimated to be lower than 0.1 microg blood per mg of feces, which is approximately 10 to 100 times lower than that of the conventional chemical approaches. The foods and dietary supplements that commonly interfere with the conventional chemical assays of FOB - such as animal blood food products and tablets containing iron and vitamin C - do not interfere with the detection of Hb biomarkers during MALDI-TOF analysis.

[Glycohemoglobin (GHb): clinical and analytical aspects]

Glycohemoglobin (GHb) has a key role in the assessment of glycemic control in diabetic patients. Several studies have clearly shown that improved glycemic control is strongly associated with decreased development and/or progression of diabetic complications in both type 1 and 2 diabetes mellitus. Therefore, accurate determination of GHb concentration is an important issue for clinical laboratories. Several factors may affect and lead to erroneous results. We discuss the problems of standardization of GHb measurements for monitoring glycemic control and also consider the potential interfering factors on GHb measurements. Moreover, GHb assays may be affected by interference in different ways. The effect of interference may be more clinically relevant with poor metabolic control. Laboratory staff must be aware of all pitfalls to avoid adding more confusion to the clinical interpretation of HbA1c values and physicians should contact laboratories if discrepancies between clinical impressions and laboratory data are observed.

Unreliable estimation of HbA due to the presence of Camperdown haemoglobin [beta 104 (G6) Arg --> Ser]

AIMS

To suggest the possible unreliability of HbA(1c) determination in presence of haemoglobin variants during routine metabolic evaluation.

METHODS

We present a case of Camperdown haemoglobin, accidentally detected in a middle-aged Italian man during routine metabolic evaluation for newly diagnosed diabetes. The haemoglobin variant has been identified by exchange high performance liquid chromatography (CE-HPLC) (VARIANT trade mark HbA(1c) Program, Bio-Rad Laboratories, Hercules, CA, USA), and characterized at molecular level by direct sequencing.

RESULTS

A 56-year-old male of Northern Italian origin, presented to our centre for a Type 2 diabetes mellitus of recent diagnosis. HbA(1c) determination was routinely determinated. The patient's chromatogram showed an inappropriate peak of 38.5% in the HbA(1c) position suggestive for the presence of abnormal haemoglobin. Further evaluation identified an abnormal haemoglobin peak even higher (49.5%) eluting at 1.34 minutes in P2-window. Molecular characterization of the mutation showed a nucleotide replacement, AGG --> AGC at codon 104, causing the amino acid replacement Arg --> Ser at position 104 (G6) that give rise to Hb Camperdown.

CONCLUSIONS

Haemoglobinopathies can lead to inaccurate glycated haemoglobin level determination. In patients carrying haemoglobin variants, the different methods for determinations of glycated haemoglobin could result in different errors, showing either higher or lower values than expected.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

Background: Multiple laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

Approach: An expert committee drafted evidence-based recommendations for the use of laboratory analysis in patients with diabetes. An external panel of experts reviewed a draft of the guidelines, which were modified in response to the reviewers’ suggestions. A revised draft was posted on the Internet and was presented at the AACC Annual Meeting in July, 2000. The recommendations were modified again in response to oral and written comments. The guidelines were reviewed by the Professional Practice Committee of the American Diabetes Association.

Content: Measurement of plasma glucose remains the sole diagnostic criterion for diabetes. Monitoring of glycemic control is performed by the patients, who measure their own plasma or blood glucose with meters, and by laboratory analysis of glycated hemoglobin. The potential roles of noninvasive glucose monitoring, genetic testing, autoantibodies, microalbumin, proinsulin, C-peptide, and other analytes are addressed.

Summary: The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are of minimal clinical value at the present time, and measurement of them is not recommended.

Effects of Hemoglobin Variants and Chemically Modified Derivatives on Assays for Glycohemoglobin

Background: Glycohemoglobin (gHb), measured as hemoglobin (Hb) A1c or as total gHb, provides a common means for assessing long-term glycemic control in individuals with diabetes mellitus. Genetic variants and chemically modified derivatives of Hb can profoundly affect the accuracy of these measurements, although effects vary considerably among commercially available methods. The prevalence of genetic variants such as HbS, HbC, and HbE, and chemically modified derivatives such as carbamyl-Hb among patient populations undergoing testing is not insignificant. Clinical laboratories and sites responsible for point-of-care testing of gHb need to be aware of the interferences produced in assays by these Hbs.

Approach: We conducted a review of the literature describing the effects of variant Hbs on gHb assay methods commonly used in clinical laboratories.

Content: This review summarizes the documented effects of both common and uncommon Hb variants and derivatives on the measurement of gHb. Where known, we discuss mechanisms of interference on specific assays and methodologies. We specifically address effects of commonly encountered Hbs, such as carbamyl-Hb, HbS, HbC, HbE, and HbF, on assays that use cation-exchange chromatography, immunoassays, or boronate affinity methods for measuring gHb.

Summary: A variety of patient- and laboratory-related factors can adversely affect the measurement of gHb in patients harboring Hb variants or derivatives. Identification of the variant or derivative Hb before or during testing may allow accurate measurement of gHb by the selection of a method unaffected by the given variant or derivative. However, laboratories should make available alternative, non-Hb-based methods for assessing long-term glycemic control in individuals with HbCC, HbSS, or HbSC disease, or with other underlying disorders where the concentration of gHb does not accurately reflect long-term glycemic control.

Long-Term Evaluation of Electrospray Ionization Mass Spectrometric Analysis of Glycated Hemoglobin

Background: Electrospray ionization mass spectrometry (ESIMS) has been successfully applied to the identification of hemoglobin (Hb) variants and the presence of glucose adducts (mass difference of 162 Da) on the separate Hb α and β chains. To establish the potential of ESIMS as a routine and/or a reference method for the quantification of glycohemoglobin (HbA1c), we carried out a detailed evaluation over a 4-month period in a routine laboratory environment.

Methods: We optimized a procedure using ESIMS suitable for the routine quantitative analysis of HbA1c. We determined reliability and reproducibility over 4 months and assessed the potential for automated sample injection. We then compared values of 1022 blood samples from diabetic patients with a routine HPLC-based ion-exchange procedure (HA-8140; Menarini).

Results: Results of HbA1c measurement by ESIMS were available within 3 min. The analytical imprecision (CV) was 1.6–5.0% for both manual and automated injections. Data collection over the m/z 980-1400 range confirmed lower glycation of the α chain relative to the β chain (0.66:1). Only one glycation was observed per globin chain. The overall glycohemoglobin (i.e., the average of α- and β-chain glycations) measured by ESIMS (x) on 1022 blood samples was lower than by HPLC (y): y = 1.0432x + 0.4815. However, the β-chain glycation measured by ESIMS was up to 20% higher than the value measured by ion-exchange HPLC and showed a close conformity, particularly at 5–10% HbA1c, with the ion-exchange Diabetes Control and Complications Trial (DCCT)-corrected and the United Kingdom National External Quality Assessment Scheme DCCT mean return values.

Conclusions: ESIMS provides a precise measurement of HbA1c and, in particular, glycation of the β chain. The method is robust and could be proposed as a procedure to substantiate HbA1c measurement and/or calibration.

Direct evaluation of glycated and glyco-oxidized globins by matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been applied to achieve a qualitative and quantitative evaluation of glycated globins on a wide number of healthy and diabetic subjects. The method allowed us to establish that both alpha- and beta-globins are glycated and that, in addition to simply glycated products, other species are detected. Investigations by different sample treatments and by analysis of the glycated beta-globin fraction obtained by preparative chromatography indicated that these species correspond to glyco-oxidized globins. Consequently MALDI-MS can be validly employed to evaluate not only the glycation level, but also the degree of oxidative stress. The percentages of glycated and glycooxidized species were calculated from the related MALDI spectra by the measurement of the related peak areas, without any other treatment of data. A linear relationship between HbA1c values and the total percentage of glycated and glyco-oxidized globins has been found, and its slope (< 1) has been rationalized by the uncorrected evaluation of glycated globins content in the standard samples employed for HbA1c measurements.

Accuracy of conversion formulae for estimation of glycohaemoglobin

To analyse the accuracy of the conversion formulae for estimation of glycohaemoglobin (GHb) measured by different methods, we analysed 210 samples for HbA1c using HPLC. Fifty of these specimens were analysed by micro-column chromatography (MC), 43 by electrophoresis (EP), 50 by IMX system (Abbott Laboratories), 38 by Primus HPLC and 29 by Diamat HPLC. Regression analyses were performed and the equations were used to estimate HbA1c values (HbA1c calc) for the five methods. The 95% limits of agreement between HPLC and the converted results were -1.77 to 1.71%, -1.54 to 1.54%, -0.92 to 0.88%, -0.46 to 0.56%, and -0.39 to 0.41% for MC, EP, IMX, Primus and Diamat equations, respectively. The mean relative errors were 3.4 (-28.2 to 35%), 1.3 (-22.9 to 25.5%), 0.4 (-14.6 to 15.0%), 0.51 (-6.55 to 7.57%), -0.20 (-5.8 to 5.4%), for MC, EP, IMX, Primus and Diamat, respectively. These results show that conversion formulae based on methods that do not measure HbA1c (MC, EP and IMX) are inaccurate and can mask a clinically relevant variation of HbA1c. However, GHb results obtained by HPLC methods could be interchangeably converted with an absolute variation of less than 1%. Converted HbA1c results from non-standardized methods should be interpreted with caution.

What is hemoglobin A1c? An analysis of glycated hemoglobins by electrospray ionization mass spectrometry

Hemoglobin A1c (HbA1c) is a stable minor Hb variant formed in vivo by posttranslational modification by glucose, originally identified by using cation exchange chromatography, and containing primarily glycated N-terminal β-chains. However, the structure(s) of the quantified species has not been elucidated, and the available methods lack a reference standard. We used electrospray ionization mass spectrometry to determine the extent of glycation of samples separated by boronate affinity and/or cation exchange chromatography. Analyses of clinical samples were consistent with the curvilinear relationship of patient glucose and HbA1c. As glycation increased, the ratio of β-chain to α-chain glycation increased, and the number of glycation sites on the β-chain increased, although these were relatively minor components. We found several glycated species that cochromatographed with HbA1c on cation exchange, including species with both glycated α- and β-chains, nonglycated α- and glycated β-chains, and multiply glycated β-chains. The combined use of affinity and cation exchange chromatography with structural confirmation by electrospray ionization mass spectrometry was found to be useful in producing samples of sufficient purity for the standardization of glycohemoglobin clinical assays.

Commutability of control materials in glycohemoglobin determinations

The intermethod variabilities of control materials and patient blood samples for the measurement of glycohemoglobin were compared. Sets of 50 blood samples and 15 control materials were analyzed by HPLC and affinity and immunochemical methods. For each pair of methods, the distances of the materials from the regression line of patient blood results (expressed as normalized residuals) were calculated. Only two of 15 controls had normalized residuals exceeding 3 standard deviations from the regression line. Total hemoglobin (Hb) content, Hb derivatives, and cellulose acetate electrophoresis demonstrated that only a minority of controls could be considered similar to patients’ blood samples. We selected Menarini’s and our home-prepared controls to simulate calibration of the different techniques by these materials. Intermethod calibration succeeded mostly in harmonizing results obtained by HPLC methods. On the contrary, calibration of the immunochemical techniques (Boehringer and Roche) did not improve intermethod agreement to a clinically useful level.