Features of Glycosylated Hemoglobin Test - Essay Example

HbA1c TEST: A project Affiliation: Introduction: The test is also known as glycosylated haemoglobin test. Haemoglobin is found in red blood cells. When glucose is present in the blood, it attaches to the haemoglobin making it glycosylated haemoglobin or HbA1c (Fig 1. a). Fig 1. a) Haemoglobin in the blood (red, rectangle) attaches with glucose in the blood (green, circle) to form glycosylated haemoglobin. This reaction occurs over a 10 week period (Source:Web ref 1). When there is more glucose in the blood more HbA1c will be formed. The amount of glucose attached to haemoglobin is measured in this test (McCool and Woodruff, 1999). The HbA1c test is performed at three month interval when glucose level is high and it needs to be brought down. In case blood glucose level is well within control and gives stable results, the test is performed every six months intervals. The long-term or chronic complications of diabetes are those that characteristically occur after years of high blood sugar levels. These are diabetic macrovascular and microvascular diseases. The long term complications correlate well with A1c levels.(Web ref 2). Wild and Bains (2004) cautioned clinical laboratories and point-of-care testing to be careful of the interferences produced in assays by variant Hbs. The majority arise from point mutations in the , , , or Hb chains. Herman et al (2007) also raised the important question of whether A1c can be used as a diagnostic test for diabetes detection and control in ethnic minorities whose mean A1c concentration vary significantly from whites. In the light of these observations the current project intends to analyse literature particularly on blood glucose tests, long term complications of high blood sugar and applicability of HbA1c test to ethnic diabetics. Importance of HbA1c test: Studies have shown that glycohaemoglobin values in the "better ranges" correlate with less incidences of diabetic complications later in life (Table 1; Fig 1 b). Type 1 diabetics will typically have hemoglobin A1c levels determined every 3 to 4 months, while Type 2 diabetics will require measurements less often (Web ref 3; Web ref 1). It so because Red blood cells are replaced in about 90 days thus test gives blood glucose levels for that period. Normal blood glucose levels are below 6 percent HbA1c however these vary laboratory to laboratory (McCool and Woodruff 1999; Web ref 1) HbA1c levels compare well with blood glucose levels as shown below: Table 1. Comparison of HbA1c test and Blood glucose levels (from McCool and Woodruff 1999) HbA1c Level of control Blood glucose (mg/dl) 5 % 6% 7% 8% 9% 10% 11% 12% Excellent Excellent Good Acceptable Poor Poor Poor Poor 90 mg/dl 120 mg/dl 150 mg/dl 180 mg/dl 210 mg/dl 240 mg/dl 270 mg/dl 300 mg/dl The rapid fluctuations in blood glucose that normally occur are smoothed out and the long-term level of glucose is now available to clinicians as a HbA1c test, because glycosylated hemoglobin has been shown to correlate with the integrated average blood consumption of glucose over the preceding six to eight weeks (Nathan 1990). Moreover, No preparation is necessary. Fig1 b) Controlled and uncontrolled diabetes conditions. (from Web ref 1) Controlled diabetes, less blood glucose results in less glycosylated haemoglobin Uncontrolled diabetes, more blood glucose results in high glycosylated haemoglobin HbA1c is also a reasonably sensitive test for gestational diabetes mellitus (GDM) which occurs in pregnant women. The test when conducted on pregnant women, it could pick up 87.1 cases of GDM successfully. The study gives a good alternative to OGTT (oral glucose tolerance test) which is inconvenient and requires fasting (Aldasouqi et al, 2008). The HbA1c test earlier done in laboratories only is now available in relatively economical home version as well (Web ref 4). The control of HbA1c and avoiding long term diabetic complications are discussed later. Diabetes: An overview The word 'diabetes' originated from Greek word for "flow through," since two of the most common warning signs are excessive thirst and need to urinate frequently. In the pancreas there are special cells known as islets of Langerhans. Nearly 75% cells of these islets produce hormone insulin which decreases blood glucose level and rest 25% produce another hormone, glucagon which increases blood sugar level. In normal persons blood has glucose after food intake. As a result the insulin is secreted to convert blood glucose into glycogen and fat for storage. In diabetes, there is a trouble with insulin (Web ref 2). Delahanty (2006) states that diabetes is a type of abnormal metabolism. There are two types of diabetes, type I & II. In type I body does not make insulin as the pancreatic cells responsible for insulin are damaged. In type II, body does not have increased insulin because of insulin resistance. As a result, in both the conditions blood sugar levels become very high causing hyperglycemia. Most of the symptoms of diabetes are similar for type I and type 2 diabetes. These symptoms include: Excessive thirst and urination, fatigue, weight loss, nausea, irritability, blurred vision, delayed healing of wounds, frequent infections , mood fluctuations (Web ref 2. Long term complications: Hyperglycemia is most common after meals when sugar from digested food reaches the blood stream. Many complications can develop if there are high sugar levels in the blood for a long period of time. Larrabee, (2006) suggested that HbA1c levels validate daily home blood sugar monitoring results. They pose the threat for diabetic complications. The higher the haemoglobin A1c percentage, more are the chances of developing diabetic eye, kidney, cardiovascular, and nervous system diseases. Both types of diabetes cause such long term complications. Type I diabetes occurs in children and young adults. The immune system starts attacking the beta cells a condition known as autoimmune disease. Type II diabetes occurs later in life and is influenced by lifestyle. Conditions that trigger Type II Diabetes are overweight, sedentary life style, polycystic ovary, advancing age etc. The cases of this are much higher as almost 90% diabetics have type II diabetes The high circulating blood glucose causes blindness, kidney failure, foot ulcers and amputations. Besides, the risk of heart diseases and stroke is also substantially increased.( Delahanty 2006). Possibly the most important reason for good blood sugar control in people with diabetes is that the longer the blood sugar remains elevated, the greater the chances of developing one or more of the complications of diabetes (Web ref 2). Dunning (2003) explains the long term complications of diabetes as : Macrovascular disease, these are more frequent in Type II diabetes. These are cardiovascular, cerebrovascular and peripheral vascular diseases.Heart and blood-vessel disease can develop because of poor circulation caused by damage to the blood vessels. This can increase the chances of a heart attack or stroke. High blood pressure often cause a strain on the kidneys, which may make it more likely for nephropathy to develop (Web ref 2; Dunning, 2003). The high A1c level is an independent risk factor for heart disease and stroke and keeping it to near normal will reduce the risk of heart disease and stroke in people with diabetes (Web ref 5) Microvascular diabetic diseases include retinopathy, Neuropathy and nephropathy. These are particularly of great concern in type I. Blurry vision occurS if the blood sugar level is too high. Vision usually returns to normal when the blood sugar level returns to normal. Retinopathy is damage to retina of eye causing vision problems and even blindness. Nephropathy or kidney damage is diabetic damage of small blood vessels in the kidneys as a result the kidneys cannot filter waste products out of blood through urine. Neuropathy or nerve damage occurs after years of poor blood sugar control because the small blood vessels feeding the nerves become blocked. Peripheral neuropathy results in numbness, tingling, or pain in the feet, legs, hands and arms due to poor circulation from diabetes (Web ref 2; Dunning, 2003). The DCCT (Diabetes Complications and Trials Study) also showed that if blood glucose levels are kept as close to normal as possible, long term complications of eye disease reduce by almost 80%, kidney disease by more then 50% and nerve disease by more then 60% (Web ref 2). With tight control of blood sugar, diabetes related damage to the eyes, kidneys, nervous system and cardiovascular system occur much less. Today, people with Type I diabetes have many more tools to achieve this goal. insulin is now available in rapid-, short-, intermediate- and long-acting formulations. Moreover, Insulin analogues mimic insulin produced naturally by the human body and are better able to act as close as the natural human insulin (Merkin et al 2008 ). Dunning (2003) emphasises necessity of glycaemic control stating it most important determinant of long term complication. It affects mitochondrial function. As a result oxidative stress increases on mitochondria.causing both macro and microvascular diseases. Increases in HbA1c from normal to 9.5 % causes 10 fold increase in microvascular diseases. The relationship between hyperglycemia and macrovascular complication is not clear as about 2 fold increase was seen by UKPDS (p206). Hyper glycaemia affects metabolic pathway that generates energy in mitochondria. Most cells reduce glucose transport to plasma during hyperglycemia and maintain homeostasis. However some cells can not reduce glucose transport such as cells of retinas, kidneys and neurons. Hyperglycemia results in cell death ,thickened material in basement membranes besides the vessels become stiff( Dunning 2003). Similar emphasis is raised by Felig and Frohman (2001), who observed that intensive glycaemic control reduces retinopathy by 76% and in persons already with retinopathy the progression was reduced by 54% percent. The reduction in kidney and nerve damage was also impressive. Thus tight glycaemic control prevented the incidents and progression of micro vascular diseases in type I diabetes. Risk of developing complications was dramatically increased when A1c was 2 points above the upper limit of normal i.e. above 8% (in DCCT) For every 1% rise in A1c over 8% level there was 40 to 50 % more chances of developing retinopathy. Moreover, the quality of life of those with glycaemic control was very good. Good control requires changes in life style and adhering to these changes. It may be achieved through meal planning, exercise, prescribed medications, and regular medical care. If the blood sugar level gets too low, accidents and even a loss of consciousness may occur. Also, raising the insulin dose to lower the blood sugar may contribute to weight gain, which can cause additional problems (Web ref 6). The control of glucose levels is of great importance in surgical would healing and infection prevantion. Zerr et al (1997) found that the incidence of deep wound infection in diabetic patients was reduced after careful maintenance of mean blood glucose level less than 200 mg/dL in the immediate postoperative period. , Ethnic minority and HbA1c: Wild and Bain (2004) discovered more than 800 abnormal or variant haemoglobins besides the six types of haemoglobins that occur at various stages of development,. The significant clinical consequences of many of these variant haemoglobins are not known apart from causing confusion to clinicians and in laboratories though, some of the variant haemoglobins result in major morbidity or mortality. Bry et al (2001) cautioned that the occurrence 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. Genetic variants and chemically modified derivatives of Hb can profoundly affect the accuracy of Hb A1c and Glycohemoglobin (gHb) measurements. Manley et al (2006) also reported that variant haemoglobins may not give a reliable HbA1c result for clinical purpose. HbA1c results from laboratory/point of care testing analysers can be affected by variant haemoglobins including elevated HbF; only ion exchange HPLC (and LPLC) detects their presence. HbA1c reported from immunochemistry or affinity chromatography in case of variant haemoglobins may not be suitable for medical monitoring. Highest HbA1c levels are found in the non-Hispanic blacks, followed by Mexican-Americans and whites, and these differences were not accounted for by other demographic or clinical factors. Such differences in HbA1c levels, which are generally within a normal range, can be interpreted in several ways. On one hand, such differences may reflect physiological differences in HbA1c metabolism that could be related to genetic or other factors (Saaddine et al 2002). Herman et al (2007) raised the possibility that A1c may not be valid for assessing and comparing glycaemic control across racial and ethnic groups or as an indicator of health care disparities.. They found that A1c levels are higher among adults with Impaired Glucose Tolerance (IGT) enrolled in the DPP. glucose AUC, -cell function, and insulin resistance. Thus, the racial and ethnic differences in A1c are not explained by differences in these factors. The mean A1c levels were 5.78% for whites, 5.93% for Hispanics, 6.00% for Asians, 6.12% for American Indians, and 6.18% for blacks. Besides caution while reporting HbA1c results scientists are looking for more sensitive techniques to overcome variant Hb problem. Lahousen et al (2002) developed a modified automated HPLC method to aid the identification of interference caused by the clinically silent haemoglobin variants in HbA1c determination. They found that silent haemoglobin variants, namely: Hb Graz, Hb Sherwood Forest, Hb O Padova, and Hb D. results OOF HbA1c for patients with Hb O Padova were acceptable.while other variants did not give clinically significant results. PART - II Blood glucose tests Alternatives to HbA1c Fasting Blood Glucose or Sugar (FBS) levels: The Fasting Blood Glucose measure has been a "gold standard" for diagnosing diabetes. The blood sugar (glucose) is checked after an overnight fast or after you have not eaten for at least 8 hours. It often is the first test done to check for diabetes. A value above 140 mg/dl on at least two occasions typically means a person has diabetes. Normal people have fasting sugar levels that generally range between 70-110 mg/dl. (Web ref 3;Web ref 7). 2-hour postprandial blood sugar measures blood glucose exactly 2 hours after one ate a meal. Random blood sugar (RBS) measures blood glucose regardless of one last ate. Several random measurements may be taken throughout the day. Random testing is useful because glucose levels in healthy people do not vary widely throughout the day. Blood glucose levels that vary widely may indicate a problem. This test is also called a casual blood glucose test (Web ref 9) Table 2. The normal values of blood sugar in the three tests (Web ref 7) Blood glucose Fasting blood glucose: 70-99 mg/dl or less than 5.5 mmol/L 2 hours after eating (postprandial): 70-145 mg/dl (less than 7.9 mmol/L) Random (casual): 70-125 mg/dl (less than 7.0 mmol/L) The Oral Glucose Tolerance Test (OGTT) The test starts in fasting state. The person being tested should not have eaten or drank anything except water for 10 hrs prior to the test.. The initial blood sample is taken. Thereafter, the person is given a high glucose drink containing 75 g glucose usually but increased to 100g glucose for pregnant women. The blood is drawn at intervals of 30 min, 1, 2 and 3 hrs and tested to check body's ability to use given glucose. If the blood glucose does not get utilised, the person is diabetic. Prior to test the person should not be confined to bed due to illness, should be normally active and not taking medication affecting blood sugar levels. While during the test person should either sit or lie down (Web ref 3). GSP and GSA In situations where the A1C test cannot be measured or may not be useful (e.g., hemolytic anemia), the Glycated serum protein (GSP) assay may be used. Mostly it is albumin, as glycated serum albumin (GSA) test, providing level of glycaemia for a 1-2 weeks period. In that case The reason for shorter period than HbA1c is that half life of serum albumin is shorter. Both GSP and GSA compare well with one another and A1c. Fructosamine assay is the method of choice for quantification of GSP and GSA. The serum protein levels are affected in diseases of liver resulting in variation of GSP. Simultaneous measurements of GSP and the A1c test might complement one another and disclose much more useful clinical information than the A1c test alone. However as stated, GSP needs to be done every 1-2 weeks unlike A1c which is required only 4-5 times a year. Moreover, The long term complication of high GSP are not as well available as for A1c levels (ADA 2003). The epidemic proportions of diabetic populations have encouraged researchers for look for faster and more informative methods about blood sugar levels. Paredi et al (1999) found that diabetes related oxidative stress induces a stress protein heme oxygenase (HO)-1. Since carbon monoxide (CO) is a product of HO activity they correlated between exhaled CO and glycemic levels. However the test did not correlate well with A1c levels. Though there was significant correlation between OGTT and exhaled CO. A further research could give another simple test for blood glucose monitoring along with level of oxidative stress. Conclusion: The following points were noticed during the course of literature survey for intended project: 1. One of the advantages of HbA1c test is that one does not need to fast before taking it neither needs to drink an excessively sweet drink as in OGTT. A small amount of blood is taken from the arm with a needle. The blood is collected in tubes and sent to a lab (Larrabee, 2006). The other tests, though measures short term blood glucose level, are GSA and GSP which complement HbA1c well. 2. The A1c correlated well with long term macro and microvascular diabetic complications and its control was found to be extremely important in avoiding these. 3. Herman et al (2007) found that ethnic minority group in US , blacks, Hispanics, American Indians, and Asians had higher A1c levels than whites. This effect continued after adjusting for factors likely to affect glycaemia viz. age, sex, education, marital status, blood pressure, BMI, hematocrit, fasting and post-glucose load glucose levels etc. They suggest that differences are genetic. Lahousen et al (2002) found interference by variant hemoglobin significant and suggested more sensitive detection of these variants. Manley et al (2006) warned, If chromatographic separation is conclusive in heterozygous patients, laboratories should either avoid reporting HbA1c or recommend another method for monitoring glycaemia, or report HbA1c and with a caution that it may not be appropriate for guidelines. Thus for ethnic minority likely to possess variant haemoglobing and give ambiguous results more than one blood glucose test should be conducted. . . References Aldasouqi , S. A., Solomon, D. J., Bokhari, S. A., Khan, P. A., Muneera, S., and Gossain, V. V. (2008) Glycohemoglobin A1c: A promising screening tool in gestational diabetes mellitus. International Journal of Diabetes in Developing countries 28 (4), 121-124. American Diabetes Association (2003) Tests of Glycemia in Diabetes , Diabetes Care 26:S106-S108, 2003, Available from: http://care.diabetesjournals.org/cgi/content/full/26/suppl_1/s106 Bry, L., Chen, P. C., and Sacks, D. B. (2001) Effects of Hemoglobin Variants and Chemically Modified Derivatives on Assays for Glycohemoglobin, Clinical Chemistry 47,153-163. Delahanty, L. M. (2006) Beating Diabetes: Lower Your Blood Sugar, Lose Weight, and Stop Diabetes and Its Complications in Their Tracks, McGraw-Hill Professional Dunning, T. (2003) Care of people with diabetes: a manual of nursing practice, 2nd ed, Wiley-Blackwell Felig, P., and Frohman, L. A. (2001) Endocrinology & metabolism, 4th ed, McGraw-Hill Professiona. Herman, W. H., MA, Yong, Uwaifo, G., Haffner, S., Kahn, S. E., Horton, E. S. et al (2007) Differences in A1C by Race and Ethnicity Among Patients With Impaired Glucose Tolerance in the Diabetes Prevention Program, Diabetes Care 30 (10), 2453-2457. Lahousen, T., Roller, R. E., Lipp, R. W. and Schnedl, W. J. (2002) Silent haemoglobin variants and determination of HbA1c with the HPLC Bio-Rad Variant II Journal of Clinical Pathology 55:699-703. Larrabee, R . (2006) Diabetes and the Hemoglobin A1C Test. http://www.lancastergeneral.org/content/Diabetes_Hemoglobin_Test_Physician_ Chronicles.htm Manley , S. E., Round, R. A., and Smith, J. M. (2006) Calibration of HbA1c and its measurement in the presence of variant haemoglobins: report on questionnaire to manufacturers, Ann Clin Biochem 43,135-145. McCool, M. H. and Woodruff, S. (1999) My doctor says I have a little diabetes, Avery, Merkin, S., Movsas, S., and Zonszein. (2008) The Fight against Diabetes. Available from: http://www.thedoctorwillseeyounow.com/articles/diabetes/type1_8/ [ Apr 6 2009] Nathan, David M. (1990) Hemoglobin A(1c) - infatuation or the real thing http://www.faqs.org/abstracts/Health/Hemoglobin-A1c-infatuation-or-the-real-thing-Glycosylated-hemoglobin-and-the-risk-of-microalbuminuri.html Paredi, P., Biernacki, W., Invernizzi, G., Kharitonov, S. A., and Barnes, P. J. (1999) Exhaled Carbon Monoxide Levels Elevated in Diabetes and Correlated With Glucose Concentration in Blood-A New Test for Monitoring the Disease CHEST 116(4), 1007-1011 Saaddine, J. B., Fagot-Campagna, A., Rolka, D., Narayan, K.M.V., Geiss, L., Eberhardt, M., and Flegal, K. M. (2002)Distribution of HbA1c Levels For Children and Young Adults in the U.S. :Third National Health and Nutrition Examination Survey , Diabetes Care 25,1326-1330. Web ref 1.What is the HbA1C http://medweb.bham.ac.uk/easdec/prevention/what_is_the_hba1c.htm Web ref 2.Diabetes in control.com http://www.diabetesincontrol.com/results.phpstoryarticle=1286 Web ref 3 . http://www.endocrineweb.com/diabetes/diagnosis.html, The two primary tests Web Ref 4. Life lesson for Diabetics, http://www.diabetesreviews.com/lifethreateningdangerslifelesson.doc Web ref 5. NEEDED TO HELP PEOPLE WITH DIABETES MANAGE THE "ABCS OF DIABETES", http://www.ndep.nih.gov/diabetes/pubs/ABCs_press.pdf Web ref 6. 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