Glycosylated hemoglobin and mortality in patients with nondiabetic chronic kidney disease

In the general population, hyperglycemia in the absence of diabetes may be associated with increased risk for mortality. Hyperglycemia is prevalent in chronic kidney disease; however, the relationship between glycosylated hemoglobin (HbA(1c)) as a marker of chronic hyperglycemia and outcomes has not been studied in nondiabetic chronic kidney disease. HbA(1c) was measured at baseline in the randomized cohort of the Modification of Diet in Renal Disease Study (n = 840). Participants with diabetes (n = 43), fasting glucose levels >126 mg/dl (n = 20), or missing HbA(1c) levels (n = 9) were excluded. Survival status until December 2000 was obtained from the National Death Index. Death was classified as cardiovascular (CVD) when the primary cause was International Classification of Disease, Ninth Revision codes 390 to 459. Cox models were performed to assess the relationship of HbA(1c) with all-cause and CVD mortality. Mean (SD) age was 52 (12) years, and mean (SD) GFR was 32 (12) ml/min per 1.73 m(2). Eighty-six percent of participants were white, and 61% were male. Mean (SD) HbA(1c) was 5.6% (0.5). A total of 169 (22%) patients died, 96 (13%) from CVD. After adjustment for randomization assignments and demographic, CVD, and kidney disease factors, HbA(1c) was a predictor of all-cause mortality (hazard ratio per 1% increase 1.73; 95% confidence interval 1.24 to 2.41; P = 0.001). There was a trend toward statistical significance in the relationship between HbA(1c) and CVD mortality (hazard ratio per 1% increase 1.53; 95% confidence interval 0.96 to 2.43; P = 0.07). HbA(1c) is associated with increased mortality in nondiabetic kidney disease. Hyperglycemia may be a potential therapeutic target and HbA(1c) may be important as a risk stratification tool in this high-risk population.

Influence of in vivo hemoglobin carbamylation on HbA1c measurements by various methods

Increased carbamylated hemoglobin formed in erythrocytes during uremia may interfere with HbA1c assays, but few studies compared directly both parameters. We measured carbamylated hemoglobin by HPLC in 45 non-diabetic uremic patients (16 with acute and two with chronic renal failure, 27 with transplant recipients) as 57.8 +/- 22.3 microg carbamylvaline/g Hb (mean +/- standard deviation) vs. 31.6 +/- 5.1 in 15 controls (+83%, p < 0.001). In these samples, HbA1c was evaluated by three ion-exchange HPLC methods, 1: Diamat (BioRad), 2: A1c2.2 (Tosoh) and 3: HA8140 (Menarini), and one immunoassay method (Tinaquant II Roche). Whichever the method, mean HbA1c values obtained increased in patients with high (> 60 microg carbamylvaline/g Hb) vs. low (< 45) carbamylated hemoglobin values (+0.08 to 0.25% of total Hb), but differences were not significant. Minor peaks on the chromatograms were however increased in parallel to carbamylated hemoglobin. HbA1c values over 6% were found in 4, 1, 2 and 0 samples, with HPLC 1, 2, 3 and immunoassay, respectively. Fructosamine values were not significantly altered. Our results show that Hb adducts, whether due to carbamylation or to other chemical reactions, interfere to a variable extent with different HbA1c assay methods, and confirm that HbA1c values should be interpreted with caution in uremic patients.

Evaluation of a fully automated high-performance liquid chromatography assay for hemoglobin A1c

INTRODUCTION

Measurement of hemoglobin A1c (HbA1c) is used as an objective measure of long-term blood glucose control in diabetic patients. Recent improvements in automation combined with new recommendations for precision and accuracy have caused us to reevaluate our methods for measuring HbA1c.

OBJECTIVE

We evaluated a newly automated high-performance liquid chromatography (HPLC) instrument for measurement of HbA1c (Tosoh A1c 2.2 Plus Glycohemoglobin Analyzer, Tosoh Medics, Foster City, Calif) and compared the results obtained by HPLC to those obtained with an immunoassay (Hitachi 911, Boehringer Mannheim Corporation, Indianapolis, Ind).

RESULTS

The Tosoh analyzer was found to be linear in a range of 5.3% to 17% and had a throughput of 20 samples per hour. HbA1c results for 102 patient samples by the 2 techniques showed good correlation, with a slope of 0.87 and an intercept at 1.27% +/- 0.15%. Both the total and within-run coefficients of variation were consistently lower for the HPLC method compared with the immunoassay method. The HPLC method produces a chromatogram that shows the different hemoglobin fractions, allowing identification of abnormal hemoglobin variants. In heterozygous individuals, HbA1c measurements are made with no interference from the hemoglobin variant. In the case of homozygous or doubly heterozygous hemoglobin variants, the Tosoh HPLC identifies the hemoglobin variants as such and correctly does not report a HbA1c value in the presence of a markedly decreased amount of hemoglobin A.

CONCLUSIONS

The Tosoh HPLC provides adequate throughput and improved precision, and the method is traceable to the Diabetes Control and Complications Trial.

Effect of acetaldehyde and acetylsalicylic acid on HbA1c chromatography in the FPLC method with Mono S cation exchanger

The effects of alcohol and aspirin on HbA1c chromatography in the Mono S method were studied in vitro and in vivo. A modified chromatography with enhanced resolution was used, making possible detailed examination of minor interfering peaks included in the routine HbA1c value. Incubation with acetylsalicylic acid increased a hemoglobin fraction separate from HbA1c. In vivo this fraction was elevated by 0.1% of the total hemoglobin during therapeutic aspirin ingestion for one month. In vitro acetaldehyde generated two labile hemoglobin fractions and slightly increased a minor stable fraction which was also elevated in vivo in both alcoholics and heavy drinkers. In relation to the HbA1c concentration, this stable fraction was equal in both alcoholic groups. We conclude that the in vivo effects of both aspirin and alcohol are negligible in routine HbA1c determination. Factors other than acetaldehyde might account for the unexpected HbA1c values in alcoholics.

Progress in immunoassay technology

Immunoassay is now the most widely used analytical technique in laboratory medicine embracing a vast repertoire of analytes and delivered through an increasingly diverse range of devices. This explosion of analytical techniques is complemented by an increasing knowledge base on the antigen antibody reaction that is being used to explore new and improved methodologies. Our knowledge of the molecular chemistry of the antigen antibody reaction coupled with the molecular biology of immunoglobulin expression has led to the development of antibody and antibody-like molecules with enhanced specificity, and reaction kinetics. These developments include novel fusion proteins, antibody mimics and antibodies that recognise antigen antibody complexes. The advances in the chemistry of the analytical systems are matched by the design of delivery vehicles: on the one hand the automated analyser that facilitates the analysis of large numbers of samples and on the other, the encapsulated, miniaturised device that enables an immunoassay to be performed at the point of care.

Does uremia interfere with HbA1c results in the FPLC method with Mono S cation exchanger?

To study the effect of uremia on hemoglobin A1c determination by the Mono S FPLC method, samples from uremic patients, with and without diabetes, and controls, were analysed with a modified chromatography with enhanced resolution. Besides specific HbA1c, four minor peaks could be seen, included in routine HbA1c values. Two of these differed in concentration in the patient groups studied: a shoulder-like peak close to the specific HbA1c (S fraction) and a slightly less cationic minor peak (M fraction). Both S and M peaks were higher in uremic than in nonuremic subjects, but the M peak was associated more with diabetes. In the nondiabetic group, the mean routine HbA1c value was 0.8% units higher in uremic than nonuremic individuals. The specific HbA1c was nondependent on uremia. Thus, in uremic patients, there seems to be falsely elevated HbA1c values, mainly because of small interfering hemoglobin fractions, not specific HbA1c.

Monitoring diabetic control in developing countries: a review of glycated haemoglobin and fructosamine assays

Measurement of glycated proteins, especially haemoglobins, is now a routine procedure for monitoring previous glycaemic control in diabetic patients in the developed world. Until recently, however, the assays were sophisticated and costly and, therefore, were only rarely used in developing countries. With easier and cheaper tests now available, the measurement of glycaemic control could be also introduced into regional hospitals in developing countries. This paper reviews feasible methods for clinical laboratories with limited resources. Recent experiences from African countries are included.

Evaluation of an immunoturbidimetric assay for haemoglobin A1c on a Cobas Mira S analyser

We evaluated a homogenous immunoturbidimetric assay for haemoglobin A1c (Tina-quant Haemog bin A1c, Boehringer Mannheim, GmbH, Mannheim, Germany) adapted to a Cobas Mira S analyser (F. Hoffmann-La Roche & Co., Basel, Switzerland) and not requiring sample pretreatment. Between-day CV's determined over a 6 week period were 5.9% and 5.3% for mean haemoglobin A1c values of 5.4% and 17.0% of total haemoglobin respectively. The imprecision was higher than with an in-house ion-exchange high performance liquid chromatographic method. Bilirubin, triacylglycerols and the labile fraction of haemoglobin A1c did not interfere with the assay of haemoglobin A1c. Fetal haemoglobin is not recognized by the antibodies used. Results correlated well with those obtained by high performance liquid chromatography. In conclusion, the Tina-quant assay is not prone to common interferences and allows the rapid and automated determination of haemoglobin A1c on open photometric analysers.

Night blood pressure: relation to organ lesions in microalbuminuric type 1 diabetic patients

Ambulatory blood pressure was measured in 23 microalbuminuric Type 1 diabetic patients without hypertension. Nine patients had a reduction in mean arterial blood (MAP) pressure at night < 10% of their day-time value (non-dippers). The following parameters were measured: glomerular filtration rate (GFR), overnight urinary excretion of albumin (UAE), sodium and potassium, left ventricular dimensions, extracellular volume (ECV), plasma aldosterone, and arginine vasopressin (AVP). Night-time MAP was 11 mmHg lower in patients designated as dippers than in non-dippers. Day-time MAP was similar in dippers (98 +/- 5 mmHg) and non-dippers (99 +/- 8 mmHg, NS). No statistical significant difference was found for UAE in dippers (geometric mean, x/- tolerance factor, microgram min-1) (72 x/- 2.1) vs non-dippers (63 x/- 2.1), for left ventricular mass index (63 +/- 12 vs 59 +/- 10 g m-2), or for GFR (134 +/- 19 vs 148 +/- 22 ml min-1). Aldosterone and AVP were lower in non-dippers (p < 0.05) and a negative correlation in all patients was noticed between ECV and aldosterone (rho = -0.50, p < 0.05). Sodium and potassium excretion and ECV were indistinguishable between the groups. We conclude (1) that impaired reduction of night blood pressure does not seem to be associated with more signs of renal or cardiac lesions and (2) that the lower aldosterone and AVP in non-dippers may counteract volume expansion.

Night blood pressure and cigarette smoking: disparate association in healthy subjects and diabetic patients

Cigarette smoking and diabetes are well known risk factors for cardiovascular disease. The relation of nocturnal blood pressure (BP) to cigarette smoking is unclarified. We examined ambulatory BP in 18 healthy smokers matched for sex and age to 18 non-smokers. Sixteen smoking type 1 diabetic patients matching 16 non-smoking patients with normal urinary albumin excretion were also investigated. None of the healthy subjects or diabetic patients had a clinic BP > 160/95 mmHg. Night BP (systolic/diastolic mmHg) in healthy smokers (mean +/- SD) 102 +/- 9/57 +/- 5 was lower than in healthy non-smokers 108 +/- 10/61 +/- 6 (p = 0.06/p < 0.05). The difference between smokers and non-smokers was most prominent in the 3 h period just before rising (99 +/- 9/57 +/- 6 versus 108 +/- 8/62 +/- 7, p < 0.01/p < 0.05). Daytime BP was similar between groups. The night/day ratio (%) of systolic (84 +/- 7) and diastolic (74 +/- 7) BP in healthy smokers was lower than in non-smokers (88 +/- 5 versus 80 +/- 5, p < 0.05 and p < 0.01) indicating an altered diurnal rhythm of blood pressure. No statistical significant difference was found for night or day BP in diabetic smokers versus non-smokers. The finding of a significantly lower BP in healthy (supine) smokers at night speaks against dysautonomia explaining the lower clinic BP found in epidemiological studies, as recently proposed. Alternatively a rebound effect or the existence of a substance with vasodilating properties in non-diabetic smokers is suggested.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal blood pressure variations in normoalbuminuric type 1 diabetic patients

OBJECTIVE

To test the hypothesis that normoalbuminuric type 1 diabetic patients segregate into groups with normal and elevated ambulatory blood pressure. To evaluate diurnal variation of blood pressure assessed by individual or fixed night-time periods.

DESIGN

Cross-sectional study.

SETTING

Tertiary referral centre.

SUBJECTS

Inclusion criteria for type 1 diabetic patients (n = 33): normal urinary albumin excretion (UAE age < 45 < 20 micrograms min-1), diabetes duration < or = 20 years, age 45 years. Healthy controls (n = 33) were matched for sex and age.

MAIN OUTCOME MEASURE

Twenty-four hour, day-time, night-time and night/day ratio of ambulatory blood pressure.

RESULTS

Twenty-four-hour blood pressure in diabetic patients did not differ significantly from a normal distribution. The 24-h systolic blood pressure was higher in diabetic patients than in healthy controls (difference: 6 mmHg, 95% confidence interval (CI) from 1 to 10 mmHg, P < 0.05), while no significant differences were found for diastolic values. The 24-h systolic blood pressure in diabetic patients with UAE above the median value (5.8 micrograms min-1) was higher than for those with lower UAE (difference: 7 mmHg, 95% CI from 0.5 to 13 mmHg, P < 0.05). The night/day ratio of diastolic blood pressure based on individual informations of the night period was (mean +/- SD) 80 +/- 6% in diabetic patients and 78 +/- 8% in controls (difference: 2%, 95% CI from -1 to 5%, not significant [NS]). This ratio increase significantly (P < 0.00001) to 90 +/- 5% in diabetes and to 84 +/- 7% in controls if a fixed night period from 22.30 hours to 06.30 hours was assumed.

CONCLUSIONS

It was not possible to identify a well-separated group of normoalbuminuric type 1 diabetic patients with elevated ambulatory blood pressure. Values of UAE above the median in diabetic patients are associated with higher ambulatory blood pressure. Assessment of the night/day variation from fixed time-points should be abandoned because this leads to a serious underestimation of the nocturnal reduction in blood pressure.

Acute renal effects of angiotensin converting enzyme inhibition in microalbuminuric type 1 diabetic patients

The renal effects of intravenous injection of 10 mg enalapril were investigated in 16 normotensive microalbuminuric type 1 (insulin-dependent) diabetic patients. After enalapril the following changes were observed: fractional albumin clearance (theta Alb) decreased from 9.9 (3.0-23.8) to 8.2 (2.0-18.3) x 10(-6) (2 P < 0.01); filtration fraction (FF) decreased from 0.260 (0.225-0.312) to 0.253 (0.190-0.297) (2 P < 0.01); renal plasma flow (RPF) increased from 565 (411-690) to 623 (449-785) (2 P < 0.01); and glomerular filtration rate (GFR) remained stable at 149 (128-181) versus 150 (124-185) ml.min-1 (NS). These values were unchanged after placebo (n = 8), except for RFP which decreased from 606 (401-701) to 559 (381-677) ml.min-1 (2 P < 0.05) and GFR which was reduced from 148 (111-173) to 138 (111-167) (2 P < 0.05). A reduction in mean blood pressure from 94 (87-103) to 89 (79-101) mmHg (2 P < 0.05) was found in the enalapril group and a minor reduction in the placebo group from 97 (83-106) to 96 (81-104) mmHg (2 P < 0.05) was also noted. The relative changes in systolic blood pressure in the enalapril group correlated with changes in theta Alb (Spearman's r = 0.66, 2 P < 0.02) and FF (r = 0.53, 2 P < 0.05). Acute inhibition of angiotensin converting enzyme does not reduce the pathological hyperfiltration in these patients and a reduction in theta Alb and FF can not be dissociated from the reduction in blood pressure.

Circadian variation of blood pressure in patients with diabetic nephropathy

The association between diurnal blood pressure variation and diabetic nephropathy was assessed in four groups of Type 1 (insulin-dependent) diabetic patients who underwent 24-h ambulatory blood pressure monitoring using an oscillometric technique. Patients with nephropathy, who had never been treated for hypertension (group D3, n = 13), were individually matched for age, sex and diabetes duration to a group of microalbuminuric patients (D2, n = 26), to normoalbuminuric patients (D1, n = 26) and to healthy control subjects (C, n = 26). Group D3 was also compared to patients with advanced nephropathy receiving treatment for hypertension, mainly a combination of angiotensin converting enzyme inhibitors, metoprolol and diuretics (D4, n = 11). In group D3 24-h diastolic blood pressure (85 +/- 8 mm Hg) was comparable to the results obtained in D4 (85 +/- 8 mm Hg) but significantly higher than in D2 (78 +/- 7 mm Hg), D1 (73 +/- 7 mm Hg) and C (73 +/- 7 mm Hg, p < 0.05, Tukey's test). The night/day ratio of diastolic blood pressure was higher in D3 (86 +/- 5%) and D2 (85 +/- 7%) than in C (80 +/- 7%, p < 0.02). This ratio was also elevated in group D4 (94 +/- 8%) compared to D3 (p < 0.05) corresponding to a marked smoothing of the diurnal blood pressure curve. The 24-h heart rate (beats per min) was significantly elevated in D3 (84 +/- 8) and D2 (80 +/- 10) compared with C (73 +/- 11, p < 0.05 Tukey's test), suggesting the presence of parasympathetic neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycated haemoglobin: an assessment of high capacity liquid chromatographic and immunoassay methods

We have assessed five high-throughput systems for the measurement of glycated haemoglobin and have reviewed published evaluations of individual analysers. All systems offered better precision than a widely used electroendosmosis method. The low pressure chromatography and immunoassay systems demonstrated greater between-batch imprecision than the high performance liquid chromatography analysers, the latter achieving the proposed analytical goal of between-batch coefficients of variation less than 5%. Agreement between all systems measuring HbA1 was good but there was variability amongst observed HbA1c values. The systems were also assessed for their quality of chromatographic separation, simplicity of operation, flexibility, cost and potential for interference by other haemoglobins.

Ambulatory blood pressure in microalbuminuric type 1 diabetic patients

Twenty-four-hour ambulatory blood pressure (AMBP) was performed in microalbuminuric (micro.) type 1 diabetic patients, with the aim of comparison with a matched group of normoalbuminuric patients (normo.) and healthy controls. Thirty-four patients without antihypertensive medication were investigated in each group. Urinary albumin excretion (UAE) for micro. was (geometric mean, tolerance factor microgram/min) 51.7 x/divided by 1.94, 5.1 x/divided by 1.88 for normo. and 5.2 x/divided by 1.75 for controls. Twenty-four-hour AMBP (mean systolic/diastolic mm Hg +/- SD) was significantly higher in micro. (131 +/- 10/78 +/- 7) than in normo. (122 +/- 8/73 +/- 6; P less than 0.001/P less than 0.01). No 24-hour AMBP difference between normo. and controls (120 +/- 9/71 +/- 7) was found. No difference in the night/day ratio of blood pressure was found between the diabetic groups. Coefficient of variation for day time systolic measurements did not show any intergroup difference. Systolic day time blood pressure for the pooled diabetic group correlated significantly with UAE (r = 0.45, P less than 0.001), whereas no significant correlation with auscultatory systolic values in the clinic was found (r = 0.21; P = 0.09). In conclusion, blood pressure in micro. as compared to normo. is not more labile but is elevated day and night without significant alteration of the diurnal rhythm. AMBP reflects the association between UAE and blood pressure more precisely than clinical measurements and may be preferable for identifying candidates for antihypertensive treatment.

Effects of ACE inhibition supplementary to beta blockers and diuretics in early diabetic nephropathy

Angiotensin converting enzyme (ACE) inhibition has shown promising results in diabetic nephropathy, but long-term results on survival are not available. In a cohort of patients receiving antihypertensive treatment predominantly consisting of beta blockers in combination with diuretics, support for an improved survival has been presented. Addition of ACE inhibition to such a combination treatment may be favorable both due to the suggested renoprotective effects of ACE inhibitors and because diuretics activate the renin-angiotensin system. In 10 insulin-dependent diabetic patients with early diabetic nephropathy [urinary albumin excretion rate (UAE) less than 100o micrograms/min], who were receiving continuous therapy with metoprolol and bendroflumethiazide, a double-blind crossover study with four months addition of ramipril 5 mg (Ramace) and placebo was conducted. UAE (radioimmunoassay) and fractional albumin excretion were significantly reduced after the four months of ramipril administration [UAE: 114.1 x/divided by 1.3 (geometric mean x/divided by confidence factor] versus 174.6 x/divided by 1.2 micrograms/min, 2P less than 0.005). Renal plasma flow (clearance of 131I-hippuran) tended to increase [497 +/- 25 (mean +/- SE) vs. 464 +/- 28 ml/min/1.73 m2, 2P = 0.08], while GFR (125I-iothalamate) stayed unchanged (121 +/- 8 vs. 120 +/- 9 ml/min/1.73 m2). Mean arterial pressure during clearance studies fell moderately (95 +/- 3 vs. 101 +/- 1 mm Hg, 2P less than 0.05) and renal resistance was decreased (2P less than 0.03). ACE activity was suppressed in all patients. Twenty-four-hour ambulatory blood pressure measurements were not significantly different after the two periods (daytime averages: 91 +/- 2 vs. 93 +/- 2, nighttime 80 +/- 2 vs. 84 +/- 3 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)