HB1AC DIABETES PDF
HbA1c is a term commonly used in relation to diabetes. This guide explains what HbA1c is, how it differs from blood glucose levels and how it’s used for. It’s often viewed as the number to rule all numbers. But hemoglobin A1c (HbA1c) test results can be misleading and don’t tell the full story. Hemoglobin A1c (HbA1c) has been a standard test of long-term average blood glucose control for patients with type 2 diabetes (T2D) for more.
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The evidence base in support of HbA 1c as a diagnostic test for diabetes mellitus is focused on predicting a clinical outcome, considered to be the pinnacle of the Stockholm Hierarchy applied to reference intervals and clinical decision limits.
hb1av In the case of diabetes, the major outcome of interest is the long term microvascular complications for which a large body of data has been accumulated, leading to the endorsement of HbA 1c for diagnosis in many countries worldwide, with some variations in cut-offs and testing strategies. HbA 1c is now hb1ad endorsed in many countries as a diagnostic test for type 2 diabetes as well as for monitoring, although some debate still continues regarding its applicability for diagnosis.
In considering the diagnosis of diabetes, viabetes are primarily concerned with defining a disease state rather than establishing a reference interval for health. In particular, the evidence base is focused on predicting a clinical outcome, considered to be the pinnacle of the Stockholm Hierarchy applied to reference intervals and clinical decision limits.
Hb1af debate surrounding the role of HbA 1c as a diagnostic test addresses the relative merits and disadvantages of glucose versus HbA 1c and brings into focus many pre-analytical, analytical and other biological hb1c as well as factors such as cost and accessibility. Type 1 diabetes usually presents with symptoms and unequivocal hyperglycaemia, thus diagnosis is usually uncomplicated.
The onset of type 2 diabetes, however, is slower with a more gradual increase in glucose levels over time. A continuum exists from health hb1ax to diabetes, from low risk through to high risk of complications. Conventionally, blood glucose levels measured either in the fasting state or following a standard glucose load have formed the basis for diagnosis of diabetes.
Some populations with a high prevalence of diabetes, such as the Pima Indians and the Micronesian population of Nauru, demonstrate a bimodal distribution doabetes glucose levels. Inan expert committee shifted the emphasis away from the bimodal distribution to focus more on clinical outcomes. They updated the diagnostic criteria based on the relationship between glycaemia, measured as fasting or 2-hour plasma glucose, and prevalent retinopathy in three studies.
These criteria are still recommended by the WHO. Firstly, HbA 1c gives an indication of chronic glycaemia rather than being a test of glycaemia at a single point in time.
Secondly, it is a relatively convenient test, not requiring the patient to fast and only using a single blood sample. Diaetes is an important consideration, in that it may enable improved uptake of testing and improved detection of diabetes, given the large proportion of diabetes cases fiabetes go undiagnosed.
For an oral glucose tolerance test OGTTmore extensive pre-test preparation is required, including an appropriate diet for 3 days before the test and a satisfactory period of overnight fasting. The OGTT is also time-consuming, taking at least 2 hours. The glucose load is poorly tolerated by a significant number of people, with nausea, vomiting, delayed gastric emptying and issues of venous access all diabees contributing to an invalid test result.
The test often needs to be repeated and has poor patient compliance. Unlike plasma glucose, HbA 1c shows minimal pre-analytical variability. Within-subject biological variation of HbA 1c is in the order of 3. This in part explains the poor correlation of 2-hour post oral glucose levels with significant prevalent diahetes retinopathy in patients with previously undiagnosed diabetes, 22 and it is therefore somewhat arbitrary that eiabetes 2-hour post glucose cut point for diabetes is currently set at Most importantly, with respect to prediction of clinical outcomes hbb1ac central tenet of the evidence baseHbA 1c has a similar relationship with prevalent diabetic retinopathy as that of both fasting and 2-hour plasma glucose, as shown in the recent DETECT-2 analysis.
This landmark study involved data pooling of nine studies from five countries, with participants aged 20—79 y with gradable retinal photographs. The study examined the relationship between diabetes-specific retinopathy defined as moderate or more severe retinopathy and three glycaemic measures: Aside from dianetes consideration of the relationship between Ciabetes 1c and microvascular complications, it should also be noted that the relationship between glycaemic parameters whether glucose or HbA 1c and cardiovascular outcomes is different from that seen for microvascular disease.
This also brings into question the validity of any single chosen cut-off and whether risk prediction may be expressed in any other way. There is also a relationship with cardiovascular outcomes associated with lower levels of HbA 1c. The case for HbA 1c for as a diagnostic test was put forward as early as the mids, but concerns regarding its availability and poor assay standardisation prevented its uptake.
HbA1c test results don’t tell the full story
Diagnostic criteria for diabetes; the American Diabetes Association Ref. In formulating the WHO recommendations Table 2a process of consultation included experts in diabetology, biochemistry, immunology, genetics, diabetse and public health. The main question to be answered for the update was agreed upon by the expert group: Applying the principles of Evidence Based Medicine, a search for existing systematic reviews in Embase did not identify any such review.
The recommendation, quality of evidence and strength of the recommendation were discussed and consensus was reached. All the experts diwbetes on the recommendation.
Additionally, the committee sought to ensure that its recommendations otherwise concur diabtes recently published National Health and Medical Research Council NHMRC guidelines for the detection and diagnosis of type 2 diabetes. Australian recommendations for HbA 1c as a diagnostic test for diabetes Ref. In an asymptomatic patient with a positive test result, the test should be repeated to confirm the diagnosis.
The use of HbA 1c measurement will simplify the diagnostic djabetes and may lead to earlier diagnosis of diaetes patients with diabetes. Part of the NZSSD rationale for rounding of HbA 1c was to make the molar units more memorable, diaabetes in addition, to maximise the specificity for the diagnosis of diabetez.
New Zealand recommendations for type 2 diabetes screening. The New Zealand position is therefore somewhat inconsistent with approaches adopted in other countries, although the rationale and arguments in support of this variance have been well presented and the approach is pragmatic and practical. There are some important caveats. If used as a diagnostic test, the HbA 1c assay needs to be reliable and consistent across different centres.
There have been problems in the past with HbA 1c results varying considerably between laboratories. When applying HbA 1c testing for the diagnosis of diabetes, some medical conditions may affect the test bb1ac cause falsely high or low readings Table 5. Red blood cell survival time is reduced in any haemolytic anaemia, and it can also be reduced in chronic renal failure, severe liver disease and anaemia of chronic disease.
Vitamin B12 and folic acid deficiencies may also shorten red blood cell survival time. A common clinical situation that shortens red blood cell survival time occurs when patients undergo regular phlebotomy for medical indications e.
Iron deficiency may also have an impact on red blood cell survival and increase the HbA duabetes level. African, Mediterranean affect the result to a variable amount, principally due to interference with the laboratory measurement of HbA 1c.
Many newer laboratory methods have measures in place to reduce this problem. The NGSP provides a summary of the effect of common haemoglobinopathies on measurement of HbA 1c levels using various methods. Some methodologies for HbA 1c measurement such as boronate affinity chromatography are less susceptible to the effects of haemoglobinopathies and such methods may be favoured for populations where a higher proportion of abnormal haemoglobins may be expected.
Otherwise, it is diabetfs to have access to HbA 1c measurement by an alternative method when a hn1ac haemoglobin variant is suspected and to follow up with further investigations such as haemoglobin electrophoresis or mass spectrometry.
Simplistically, if a haemoglobin variant is suspected, then HbA 1c is not an appropriate diagnostic test and glucose based criteria should be preferred. HbA 1c should also not be regarded as the appropriate test to confirm the diagnosis of diabetes in patients with any significant chronic medical disease, any anaemia or any abnormality of red blood cell structure. If any of these diabete exist, the diagnosis of diabetes should be based on measures of blood glucose levels.
It should also be recognised that HbA 1c is more expensive than plasma disbetes testing and this may prohibit its use in many countries worldwide. Others, however, have argued that its practical advantages may, indeed diabetew access to care in disadvantaged populations Table 5. There dibaetes also evidence which indicates that HbA 1c will detect a different population as having diabetes to that identified by plasma glucose. Alternatively, it may be that HbA 1c detects real differences in chronic glycaemia that are not represented by the fasting and 2-hour plasma glucose levels of the OGTT.
If the former explanation is true, then HbA 1c may not be appropriate for diagnosis or else it may be necessary to consider the use of ethnic-specific cut hv1ac for HbA 1c both in the management and diagnosis of diabetes.
Conversely, if the latter explanation is true, it would argue in favour of using HbA 1c to diagnose diabetes, as the observed elevations of HbA 1c are likely to be reflective of increased complication risk at the tissue level. This point also brings into consideration the presumption that the OGTT is a gold standard for diagnosis which may not necessarily be the case, and that HbA 1c is a more valid marker of tissue glycation.
It remains to be determined whether or not these supposed ethnic differences in HbA 1c are clinically consequential, although this is another factor that needs to be taken into further consideration as we move forward. Another perspective emanates from the studies of Zhong Lu et al. Other authors, rather than accepting a single cutoff have advocated for separate rule out and rule in criteria applying the same cut-offs suggested diabettes the Melbourne studies.
The case for HbA 1c as a diagnostic test for diabetes has therefore been submitted to a very rigorous examination based upon the principles of diabeets based medicine. In particular, the evidence base is focused mainly on predicting clinical outcomes particularly microvascular complications dibaetes to be the pinnacle of the Stockholm Hierarchy applied to reference intervals and clinical decision limits.
There are clear advantages for HbA 1c over glucose and in particular OGTT as a diagnostic test for diabetes, although with an important series of caveats that clinicians need to be aware of. As always, there is need for hba1c resources to be widely available and for on-going dialogue between clinicians and the laboratory.
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Introduction HbA 1c is now formally endorsed in many countries as a diagnostic test for type 2 diabetes as well as for monitoring, although some debate still continues regarding its applicability for diagnosis.
Background Type 1 diabetes usually presents with symptoms and unequivocal hyperglycaemia, thus diagnosis is usually uncomplicated.
Glucose Based Criteria for the Diagnosis of Diabetes Conventionally, blood glucose levels measured either in the fasting state or following a standard glucose load have formed the basis for diagnosis of diabetes. The Case for HbA 1c as a Diagnostic Test Firstly, HbA 1c gives an indication of chronic glycaemia rather than being a test of glycaemia at a single point in time. Open in a separate window. Recommendations for HbA 1c as a Diagnostic Test The case for HbA 1c for as a diagnostic test was put forward as early as the mids, but concerns regarding its availability and poor assay standardisation prevented its uptake.
Fasting is defined as no caloric intake for at least 8 h.
What is HbA1c? | Diabetes UK
The test should be performed as described by the World Health Organization, using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water.
HbA 1c hv1ac be used as a diagnostic test for diabetes providing that stringent quality assurance tests are in place and assays are standardised to criteria aligned to the international reference values, and there are no conditions present which preclude hbb1ac accurate measurement.
An HbA 1c of 6. A value of less than 6. Measurement of HbA 1c level can be used as diabehes diagnostic test for diabetes if analysis is performed in a facility producing acceptable performance in external quality assurance, assays are standardised to criteria aligned to international reference values, and if no conditions which preclude its accuracy are present.
It is important to note that HbA 1c testing is not currently funded by Medicare for the purpose of diagnosis of diabetes. The existing criteria based on fasting and random glucose levels, and hb1a the oral glucose tolerance test, remain valid, and are the diagnostic tests of choice for gestational diabetes, type 1 diabetes and in the presence of conditions that interfere with HbA 1c measurement.
Table 5 Arguments for and against the use of HbA 1c as a diagnostic test.