A multisite physician's office laboratory evaluation of an immunological method for the measurement of HbA1c

Evaluation of glycated hemoglobin and fetal hemoglobin-adjusted HbA1c measurements in infants

BACKGROUND

As the presence of fetal hemoglobin (HbF) affects the accuracy of hemoglobin A1c (HbA1c) analysis methods, HbA1c measurement may not be a good indicator for patients with neonatal diabetes mellitus, whereas glycated albumin (GA) may be a good indicator.

OBJECTIVE

To investigate whether total glycated hemoglobin (GHb) or HbF-adjusted HbA1c (adj-HbA1c) can act as a glycemic control marker in infants.

SUBJECTS AND METHODS

Plasma glucose (PG), GA, HbF, GHb measured using the affinity method, and HbA1c measured using the latex-immunoturbidimetry (LA) or the high-performance liquid chromatography (HPLC) methods were determined in 26 full-term newborn infants aged 4-234 d. Adj-HbA1c was calculated as HbA1c/(total Hb - HbF).

RESULTS

GHb, adj-HbA1c measured using the LA and the HPLC methods were 4.8 ± 0.5%, 4.5 ± 0.5%, and 4.7 ± 0.6%, respectively. GA was most positively correlated with PG (r = 0.696, p < 0.0001). GHb was positively correlated with both PG (r = 0.479, p = 0.013) and GA (r = 0.727, p < 0.0001). Adj-HbA1c measured using the LA method was positively correlated with GA (r = 0.465, p = 0.017), but not PG (r = 0.304, p = 0.132). Adj-HbA1c measured using the HPLC method was correlated with neither PG (r = -0.077, p = 0.710) nor GA (r = 0.360, p = 0.071).

CONCLUSIONS

GHb measured using the affinity method may be a useful glycemic control marker in infants. Although adj-HbA1c measured using the LA method was correlated with GA, it may not be a practical measure because it was not correlated with PG and determining HbF levels using HPLC method can be troublesome. Adj-HbA1c measured using the HPLC method should not be used as a glycemic marker in infants.

Measurement of glycated hemoglobin and glycated albumin in umbilical cord: evaluation of the glycemic control indicators in neonates

OBJECTIVE

As neonatal blood contains a high proportion of fetal hemoglobin (HbF), it is difficult to use high-performance liquid chromatography (HPLC) method, latex-immunoturbidimetry (LA) method and enzymatic methods, which determine hemoglobin A(1C) (HbA(1C)) in order to provide the glycemic control indicators of neonates. In this study, we evaluated glycated hemoglobin (GHb) and glycated albumin (GA) as appropriate indicators of the glycemic control in the neonatal period.

STUDY DESIGN

Umbilical cord blood samples collected during delivery were subjected to measurements of GHb (HPLC methods using two different instruments, LA method, enzymatic method and affinity method) and serum GA.

RESULT

HbA(1C) levels determined by the HPLC method, the LA method and the enzymatic method were as low as <3.0% in all the cases. Although GHb determined by the affinity method was 3.6 ± 0.2%, this method may not measure accurately the values of glycated HbF plus glycated HbA. Serum GA was 9.4 ± 1.1%.

CONCLUSION

We speculate that serum GA, but not GHb, could be used as glycemic control indicators in neonates.

A preliminary report on an assessment of a community-based intervention for diabetes control in adults with type 2 diabetes

OBJECTIVE

The aim of this study was to evaluate the effectiveness of lay diabetes facilitators (LDFs) to increase knowledge and improve control among persons with diabetes. Methodology. A prospective cohort study was conducted among persons with diabetes in 16 health care centres in Jamaica to evaluate the effect of LDFs on glycaemia [haemoglobin A1c (HbA1c)] and body mass index (BMI). One hundred and fifty-nine persons with diabetes were recruited for the intervention from eight clinical settings in which LDFs had been recruited and trained. A matched group of 159 were recruited as a comparison sample from eight clinical settings without LDFs. HbA1c and BMI were measured at baseline and 6 months.

RESULTS

Mean HbA1c at baseline for the intervention and comparison groups were 7.9% and 8%, respectively. After 6 months, the intervention group showed a mean decrease of 0.6% while the comparison group showed an increase of 0.6%, significant after control for potential confounders (P < 0.05). There was no statistically significant change in BMI between groups.

CONCLUSION

Patients educated by LDFs showed improved metabolic control over the first 6 months of observation.

Nurse-based evaluation of point-of-care assays for glycated haemoglobin

BACKGROUND

Various devices are now available to measure glycated haemoglobin (HbA1c) outside of the laboratory. The aim of this study was to assess the performance of these point-of-care instruments in the hands of non-laboratory trained personnel.

METHODS

Two nursing staff tested samples from patients attending a diabetes research clinic using the following point-of-care devices for HbA1c-Metrica A1C Now, Bayer DCA 2000, Cholestech GDX and Axis-Shield Nycocard HbA1c. In addition they performed regular analysis of quality control samples. The effects on analytical performance of multiple operators as well as laboratory-trained staff, were also assessed. All measurements were compared to a boronate-affinity HPLC method in the central laboratory.

RESULTS

The mean HbA1c difference of the point-of-care devices compared to the laboratory reference method ranged from -0.31% to +0.39%. Only the DCA device had a between batch imprecision of less than 5%. The analytical performance obtained by laboratory staff was similar to nursing staff for 3 devices and better for the Nycocard device.

CONCLUSIONS

On the basis of the results obtained by nursing staff, only the DCA of the devices tested, can be recommended for measurement of HbA1c outside of the laboratory.

Evaluation of a new diabetes screening method at the Derbarl Yerrigan Health Service

BACKGROUND AND OBJECTIVES

Diabetes is a major health problem for the Aboriginal population of Australia. Early detection is a key strategy to reduce the burden of diabetes. The aim of this study was to assess the acceptability, sensitivity and specificity, effectiveness and cost of a new method of screening for diabetes at Derbarl Yerrigan, the Aboriginal health service in Perth.

METHODS

Between January and May 1999, all clients over the age of 30 years and not known to have diabetes were approached for HbA1c testing using the DCA 2000 analyser. Those whose HbA1c results indicated the need for follow-up were asked to return for confirmatory testing using the gold standard oral glucose tolerance test (OGTT). A questionnaire was administered to participants who did not return. A file audit was conducted over 15 non-consecutive days to determine screening, follow-up and the number of new cases diagnosed using the previous ad hoc approach to screening with a glucometer.

RESULT

238 clients were approached and all agreed to participate and undertook the test. Of these, 37 were referred for follow-up diagnostic testing. Of these, only 14 had an OGTT. Among these 14, five were found to have diabetes and three were found to have impaired glucose tolerance. Of the remaining 23 participants, we were able to contact only six and administer the questionnaire to four. Poor follow-up meant that the sensitivity, specificity and cost-effectiveness of the test could not be assessed.

CONCLUSIONS AND IMPLICATIONS

The reasons for poor follow-up need to be investigated if Aboriginal health services are to be more successful at screening for diabetes.

Agreement between HbA1c measured by DCA 2000 and by HPLC: Effects of fetal hemoglobin concentrations

BACKGROUND

In subjects with type 1 diabetes, persisting elevations of fetal hemoglobin (HbF) have been demonstrated. This study evaluated whether HbF levels typically seen in type 1 diabetes (up to 3%) interfere with glycohemoglobin determinations using a common immunologic method (DCA 2000).

METHODS

HbA(1c) was measured by high-performance liquid chromatography (HPLC) using a Diamat analyzer in 90 type 1 diabetics with parallel determinations of HbF. Results were compared with HbA(1c) concentrations obtained using DCA 2000.

RESULTS

Reproducibility was good for both methods with coefficients of variation <5% and correlation between the two methods was good (r(2)=0.939, p<0.0001). Mean difference between the two methods was small (0.007%). Limits of agreement varied between -0.92% and +0.93% (95% confidence interval [95% CI]) and constant bias (intercept: 0.73 95% CI 0.28-1.18) as well as a proportional bias (slope: 0.92 95% CI 0.87-0.97) were detected. At low concentrations of HbF, the DCA 2000 immunologic method tended to underestimate and at higher concentrations tended to overestimate HbA(1c) when compared with Diamat. Stepwise linear regression with HbA(1c) (DCA 2000) as dependent variable included HbA(1c) (Diamat) and HbF in the model (r(2)=0.946, p<0.0001), explaining 94.6% of the variability of HbA(1c) (DCA 2000). Partial correlation coefficient between HbA(1c) (DCA 2000) and HbF corrected for HbA(1c) (Diamat) was 0.337 (p=0.0012).

CONCLUSIONS

DCA 2000 allowed measurements of HbA(1c) rapidly and with precision adequate for clinical purposes. However, agreement with Diamat results was comparatively weak with both constant as well as proportional biases. The 95% limits of agreement between Diamat and DCA 2000 fell within a range that significantly limited traceability between these two methods; therefore, the two methods should not be used interchangeably. Small but persistent elevations of HbF concentrations were identified as a significant cofactor, which may be relevant for limited traceability between the two methods.

Body size and shape and glycemic control among Maya women in rural Yucatán

Studies on relationships between aspects of physique and glucose physiology generally focus on clinical glucose tolerance or on fasting glucose or insulin assays showing glycemic status at the time of testing. Little work has examined the associations between body variables and glycemic control, or average past glucose levels in regular living conditions. The aim of this research was to investigate connections between body size and shape and glycemic control. The sample consists of 60 nondiabetic Maya women, ages 40-85 years, residing in 16 rural villages around Mérida, Yucatán. Body morphology was assessed through anthropometric and derived measures of size and shape, including indicators of fat distribution and general adiposity. Glycemic control was measured through microvenous samples analyzed for glycated blood proteins HbA(1c) and fructosamine to demonstrate average circulating glucose under customary living conditions during the previous several months and weeks. Four-variable regression models explain 17% of the variance in HbA(1c) and 25% of the variance in fructosamine. Arm circumference has the largest positive effect on HbA(1c), while weight has the greatest positive impact on fructosamine. The predictor with the largest negative effect on both glycated blood proteins is calf circumference. In general, variables reflecting overall adiposity and central adiposity demonstrate positive associations with HbA(1c) and fructosamine, whereas lean body measures exhibit negative associations. Findings support the value of glycated blood proteins and of less common anthropometric measures, such as calf circumference, in population research on morphological relations with glycemia.

Interpretation of Hemoglobin A1c (HbA1c) Values among Diabetic Patients

Background: Few studies have examined patients’ views, knowledge, and understanding of glycohemoglobin A1c (HbA1c) testing. We explored such issues in patients with type 1 diabetes and used their statements to estimate analytical quality specifications for HbA1c testing.

Methods: We recruited 201 patients from a hospital outpatient clinic. A questionnaire was used to collect information on diabetes characteristics, perceived knowledge of HbA1c, last HbA1c value, HbA1c target value, and thresholds for action. Patients were asked to indicate the magnitude of change in HbA1c from 9.4% that they would consider to be a true (real) change; from their responses, we calculated patient-derived quality specifications for HbA1c.

Results: Fifty-eight percent of the patients felt they had “high” knowledge about HbA1c, and &gt;80% of responders knew their last HbA1c value, their target HbA1c, and the threshold value of HbA1c for treatment intensification. The mean acceptable HbA1c value was 7.5%. Patients with lower values on their most recent tests reported lower target values for HbA1c and lower values for the upper HbA1c threshold for treatment intensification. An analytical CV (CVa) of 3.1% would be satisfactory for 75% of patients when HbA1c is increasing (80% confidence), and a CVa of 3.2% would be satisfactory for 75% when HbA1c is decreasing (95% confidence).

Conclusions: Type 1 patients’ perceived knowledge about HbA1c testing is high. They are well informed about their own personal results and about target values and the upper HbA1c threshold for action. The patient-derived analytical quality specification for imprecision (CV) is 3.1%.

Effect of immediate hemoglobin A1c results on treatment decisions in office practice

OBJECTIVE

To assess the effect of an immediately available hemoglobin A1c (HbA1c) result on glycemic control and physician decisions about pharmacologic therapy in an office practice.

METHODS

In a 1-year retrospective review of medical records, HbA1c results were analyzed in 115 patients beyond the age of 65 years, who had type 2 diabetes and were referred for the first time to a private endocrinology practice between April 1, 1997, and March 31, 1998. These patients were classified into two groups: group A (N = 93, insured by standard Medicare) had immediate HbA1c results (during the patient encounter) and group B (N = 22, insured by Medicare health maintenance organization [HMO]) had commercial laboratory HbA1c results available within 2 to 3 days. We reviewed the changes in the HbA1c level during the 12-month period and the presence or absence of a change in therapy at each visit. HbA1c levels were measured by ion-exchange low-pressure liquid chromatography in group A and by one of three capitated commercial laboratories (depending on HMO contracts) in group B.

RESULTS

At the end of the 12 months, the mean HbA1c decrease was 1.03 +/- 0.33% in group A and 0.33 +/- 0.83% in group B. During the first visit, 52% of the patients in group A had pharmacologic treatment interventions, whereas only 27% in group B had such interventions.

CONCLUSION

Rapid availability of the HbA1c results during the clinical encounter improves the ability of the physician to make appropriate therapeutic decisions and results in improved glycemic control.

Use and interpretation of HbA1c testing in general practice. Implications for quality of care

We evaluate the interpretation and use of HbA1c results in general practice in relation to diabetes follow-up and case-finding. As part of an external quality assurance scheme for laboratory analyses, two case histories were mailed to all Norwegian GPs with equipment for HbA1c analysis in their office laboratory (n=566) and to a random sample of GPs without such instruments (n=419). Patient A represented a monitoring situation and the GPs were asked to state changes in HbA1c signifying any improvement or deterioration of metabolic control. The initial HbA1c value stemmed from analysis of quality control material in the instrument group and was a preset value for the other group. In patient B, we focused on the use of HbA1c and other laboratory tests in diabetes case-finding. In the monitoring situation, 22% of GPs in the instrument group misclassified changes in HbA1c values, since these were less than the analytical uncertainty. Further, when interpreting HbA1c results, 64-93% of GPs (i) assumed that analytical quality was better than it really was, (ii) did not appreciate biological variation of HbA1c, or (iii) acted on small differences to be on the safe side. In case-finding, HbA1c was deemed important by 29% of GPs; doctors choosing not to perform a glucose tolerance test relied more on HbA1c. GPs have to be aware of analytical quality and biological variation when interpreting HbA1c results. The present limitations of HbA1c in the diagnosis of diabetes are not properly understood.

24-hour ambulatory blood pressure and renal disease in young subjects with type I diabetes

Twenty-four hour ambulatory blood pressure (ABP) was evaluated in 150 teenage and young adults with insulin-dependent diabetes mellitus (IDDM) to define high-risk subjects who are likely to develop early diabetic nephropathy. Their age range was 16-28 years with diabetes of 3.5-25.8 years duration. All subjects had office blood pressure (BP) measured, wore an ABP monitor for 24 h, and collected two or more timed urine samples for albumin excretion rates (AERs). Eighty-six subjects had no elevation of AER (< 7.6 micrograms/min), 29 subjects had borderline elevations (7.6-20 micrograms/min), 24 subjects had microalbuminuria (20.1-200 micrograms/min), and 11 had macroalbuminuria (> 200 micrograms/min). Age, gender, duration of diabetes, and single office BP readings were similar in the four groups (p > 0.05, logistic regression). All 24-h ABP parameters were significantly higher in subjects with diabetes having AER values greater than 7.6 micrograms/min when compared with healthy age- and gender-matched nondiabetic controls (p < 0.05, Dunnett's t test). The percent of nighttime systolic and diastolic ABP readings above the 90th percentile of normal for age, gender, and race and the percent of readings in the hypertensive range (> 140/90) were significantly related with AERs (p < 0.01; logistic regression). A higher percentage of ABP values above the 90th percentile for age, gender, and ethnic group or of ABP readings above hypertensive levels (> or = 140/90) are associated with diabetic renal disease.

Comparison between a rapid glycohaemoglobin (HbA1c) immunoassay and other indices of glycaemic control

The aims of the study were to compare glycohaemoglobin (HbA1c) values measured by DCA (a benchtop analyzer primarily designed for within-clinic rapid HbA1c determination) to a reference HbA1c method and home blood glucose monitoring, and to explore the possibility of an uniform expression of data. A total of 103 blood samples and the corresponding mean capillary glucose values (4.4 +/- 1.2 tests/day) of the preceding 2 months were collected from 34 insulin-dependent diabetic adults. We measured the correlations and agreements using the residual plots method and regression equations between HbA1c measured by DCA and high-pressure liquid chromatography (HPLC), and between DCA and capillary glucose values. A highly significant correlation (r2 = 0.85, P < 0.001) and an acceptable agreement (97% of values within 2 SD of the mean difference of 0.9% +/- 0.4%) was found between DCA and HPLC values. The regression equation calculated on the first half of the cases was: DCA (%) = 0.72 HPLC (%) +1.38. Of DCA values expressed in HPLC terms using this equation 87% fell within a clinically acceptable confidence interval when compared with measured HPLC data. A significant correlation (r2 = 0.40, P < 0.01) was found between DCA and capillary glucose values, and the regression equation was: DCA (%) = 0.34 capillary glucose (mM) +4.44. Of glycaemic levels calculated from DCA values using this formula 82% fell within a clinically acceptable error range when compared with measured glycaemic values. We conclude that the three methods of assessment of diabetes control are well correlated and that it is possible, with a degree of precision acceptable for the clinical setting, to express all data in uniform units, e.g. mM of capillary glucose or percentage of HPLC-HbA1c, though a simple correspondence table based on our transfer equations may be clinically sufficient and more handy.