Standardization of glycated haemoglobin assays throughout the Northern region of England: a pilot study

Glycemic Control in the 12 Months following a Change to SI Hemoglobin A1c Reporting Units

BACKGROUND

Many countries have implemented, or are considering, a change in hemoglobin A1c (Hb A1c) units from traditional percentage values [Diabetes Control and Complications Trial (DCCT)] to the new Système International d'Unités (SI) unit in millimoles per mole. Concern exists that such a large alteration in numeric values might lead, through confusion, to a deterioration in patients' glycemia. This study has assessed Hb A1c in the year before and after the change of units in a UK diabetes population.

METHODS

The Hb A1c in the 12 months immediately before the unit change (October 2010 to September 2011) was compared with the 12 months after (October 2011 to September 2012). Also, the subsequent change in Hb A1c in patients who had poor glycemic control [Hb A1c >8% (64 mmol/mol)], either before or after the unit change, was compared.

RESULTS

Over the 2 years, 44 721 Hb A1c measurements were requested on 13 197 (7247 male, 5950 female) known diabetes patients. The population Hb A1c was no different between years, with a median [interquartile range (IQR)] value of 7.5% (6.6%–8.7%) after the change and 7.5% (6.5–8.7) before (P = 0.34). The subsequent change in Hb A1c following a raised (>8%) result was the same regardless of whether the initial value reported was in DCCT or SI units [median (IQR) change in Hb A1c −0.2% (−0.9% to 0.3%), n = 4316, following a DCCT result, vs −0.2% (−0.8% to 0.3%), n = 4396, following SI; P = 0.44].

CONCLUSIONS

In this UK diabetes population, a move to SI Hb A1c reporting did not lead to any marked short-term deterioration in glycemia or a different Hb A1c outcome in patients with initial poor glucose control.

Intrauterine growth rate in pregnancies complicated by type 1, type 2 and gestational diabetes

Fetal macrosomia is a feature of all subtypes of maternal diabetes. The intrauterine time course of development of macrosomia in type 1, type 2 and gestational diabetes (GDM) could identify the times of more rapid growth, which differ as a result of different influences in subtypes of diabetes. Higher maternal weight in type 2 and GDM may be expected to contribute to macrosomia and the blood glucose control will exert an additional influence. Information was collected prospectively on 217 pregnancies in insulin-treated women at a single centre over a six-year period. All women were managed by a single team of obstetricians and diabetologists at a Joint Obstetric Medical Clinic. The rate of increase in abdominal circumference from 28 weeks was identical in each subtype of diabetes and there were no differences between subtypes at the earliest gestation assessed. Use of customized growth centiles showed rates of macrosomia to be similar in type 1, type 2 and GDM (43.0%, 50.0% and 41.8%, respectively). The intrauterine time course to macrosomia is similar in type 1, type 2 and GDM. The relationship of macrosomia to extent of elevation of mean blood glucose control is weak, implying a low threshold for maximal effect on the rate of fetal growth.

[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.

[Diagnosing type 2 diabetes mellitus: in primary care, fasting plasma glucose and glycosylated haemoglobin do the job]

OBJECTIVE

To determine the validity of glycosylated hemoglobin (HbA1c) values as a method to diagnose type 2 diabetes mellitus (DM2) in a population at risk seen in primary care.

DESIGN

Cross-sectional analytical study.

SETTING

Data were obtained for the Raval Sud study population (epidemiologic study of alterations in glucose metabolism in a population at risk).

PARTICIPANTS

454 subjects from this population (mean age, 65 +/- 3 years; 52% male) at high risk for DM2, seen at a primary care center, were included in the study.

MAIN MEASURES

We recorded demographic data and laboratory values for fasting plasma glucose (FPG), oral glucose tolerance test (OGTT), and HbA1c. The diagnostic criteria used for DM2 were those published by the WHO in 1999. Values for HbA1c were expressed as the number of standard deviations (SD) above the mean.

RESULTS

Levels of HbA1c correlated with FPG (r=0.72) and glucose levels 2 h after oral glucose overload (r=0.43). Thirty percent of the patients with FPG between 110 and 125 mg/dL had HbA1c values higher than the reference limits. A combined technique based on FPG>125 mg/dL or FPG 110-125 mg/dL with HbA1c > or = 3 SD (5.94%) showed a sensitivity of 92% and a specificity of 95%.

CONCLUSIONS

When FPG is inconclusive (110-125 mg/dL), an HbA1c value more than 3 standard deviations above the mean (>5.94%) is useful in suggesting a likely diagnosis of diabetes and identifying patients who require treatment.

Evaluation of HbA1C results in an external quality assessment scheme in South Africa

BACKGROUND

Measuring HbA1c blood levels allows us to assess average glycaemia in individuals during the preceding 6-8 weeks. There is a clear association between increasing risk of complications with higher HbA1c values and a significant risk reduction of the complications with lower HbA1c values.

METHODS

The performance of South African laboratories in an External Quality Assurance scheme for HbA1c is reported.

CONCLUSIONS

A number of laboratories and methods do not meet the required analytical standards. South African laboratories should adopt measures similar to other regional and national initiatives to significantly improve laboratory performance and bring about harmonization of HbA1c assays.

Glycated haemoglobin assays. Approaches to standardization of results

AIMS

To compare different approaches to DCCT standardization of glycated haemoglobin (HbA(1c)) results.

METHODS

In the first part of the study seven laboratories in the Mersey area participated, using a variety of methods of measurement. The approaches used were the Standardization Initiative for Glycated Haemoglobin Scheme (SIGH) using fresh blood samples and the Wales External Quality Assurance Scheme (WEQAS) using both fresh and lyophilized blood samples. Additional studies performed in the Royal Liverpool University Hospital (RLUH) laboratory involved: (i) re-calibration of the HPLC analyser using lyophilized blood samples supplied by the manufacturer and (ii) the use of fresh blood samples from the UK National External Quality Assurance Scheme (UKNEQAS).

RESULTS

Inter-laboratory analytical coefficients of variation following DCCT alignment showed little change. The effect on percentage bias was more marked and was independent of the level of HbA(1c). Comparing DCCT-aligned HbA(1c) results from 3902 diabetic patients attending the RLUH, indicated that there was a statistically significant difference (P < 0.0001) between the corrected results produced by the five schemes. The effect of DCCT alignment on reported HbA(1c) values using the different approaches was variable resulting in an apparent increase in the number of diabetic patients with poor glycaemic control (HbA(1c) values > 7.0%) in all cases.

CONCLUSION

The method of HbA1c standardization used determines the degree of correction required and a consensus approach is recommended. Implementation will assist extrapolation from research-based evidence to local practice. Associated changes to patient management must come under the jurisdiction of the physicians responsible for the diabetic service.

Episodic hyperglycaemia in pregnant women with well-controlled Type 1 diabetes mellitus: a major potential factor underlying macrosomia

AIMS

To test the common assumption that pregnant women who are sufficiently motivated to achieve very good HbA1c levels will record home blood glucose data accurately.

METHODS

A new device was used to download information from electronic blood glucose meters to assess the extent of selectivity in patient glucose diary-keeping.

RESULTS

In an index case, a woman with excellent ambient HbA1c (5.9%; upper limit of normal 6.1%) was observed to have 68% of preprandial blood glucose readings above the target range of 3.5-6.5 mmol/l and a mean (+/- SD) level of 8.9+/-3.9 mmol/l in the corresponding period. No such impression was conveyed by the home monitoring diary. Six pregnant women with well controlled Type 1 diabetes (mean HbA1c 6.6+/-0.2%) exhibited between 42 and 68% of preprandial readings above the target range.

CONCLUSIONS

The frequency of hyperglycaemia has hitherto been underestimated in well controlled pregnant women whose near-perfect home monitoring record is apparently corroborated by near-normal HbA1c levels. These observations provide a hypothesis for understanding of the disappointing continuance of macrosomia despite excellent HbA1c levels throughout pregnancy.