Canine HbA1c
Canine HbA1c LIN, WEN-YANG (WESLEY), Ph.D HbA1c is a type of hemoglobin on which several monosaccharides such as glucose, galactose and fructose tend to bind with and exist in the bloodstream. The chemical linking process between sugar and hemoglobin is named glycation. HbA1c is actually an indicator of the beta-N-1-deoxy fructosyl on hemoglobin, which has been used as diagnostic measurement of long-term glycemic control for patients with diabetes mellitus. The increasing number of HbA1c in bloodstream represent the elevated plasma glucose level that usually indicating a poor diabetic management may lead to severer conditions. Due to the lifecycle of red blood cells is average four months, the HbA1c test could effectively present the real blood sugar degree in latest three months. In 1980, Wood and Smith first demonstrated the applicable method of examining canine diabetes with monitoring glycosylated haemoglobin. Later, Smith et al 1982, Mahaffey and Cornelius 1982, Dennis 1989, Jensen 1995 all confirmed this method is workable on diagnosing diabetic dogs. Molecular structure of HbA1c Figure 1 showed an aldimine linkage between glucose and hemoglobin (Figure1). Figure 1. Glycation process between Hemoglobin and glucose https://www.sciencedirect.com/science/article/pii/S0956566318304500 As we previously discussed that different monosaccharide would form different chemical structure with blood cells. Thus, while using cation exchange chromatography to separate Hemoglobin type A, different fractions would be separate out like HbA0, HbA1a, HbA1a2, HbA1b, and HbA1c. Fractions were named after eluting order (Figure 2). Figure 2. Different separated fractions of Hemoglobin type A with cation exchange chromatography https://www.sciencedirect.com/science/article/abs/pii/S0003269711000753 Glycated hemoglobin forming harmful factors in human body Highly reactive free radicals promote the formation of abnormal ferryl Hb (Fe4+-Hb), which enhance macrophage accumulation in blood vessel. Both macrophage accumulation and accumulation of glycated hemoglobin would elevate blood viscosity and slow down normal blood flow. Thus, atherosclerotic plaque would gradually occur in blood vessel. History of standardized HbA1c as diagnostic tool for diabetes Diabetes has become a serious health issue in entire world, due to over 220 million patients are suffering of it. Among all cases of diabetes, type 2 diabetes take majority part (90% to 95%). Besides, worsen type 2 diabetes could also cause extra complications, such as cardiovascular diseases, peripheral neuropathy, nephropathy, optic neuropathy, diabetic foot and even unto death. Several risks factor related to diabetes including high fat diet, obesity, smoking, elevated cholesterol levels, high blood pressure and lack of regular exercise. For preventing and relieving conditions of diabetes, taking healthy diet and regular exercise are important. In addition, diabetic patients’ blood sugar condition should be monitored regularly all the time. There are many clinical methods to evaluate glycemia like urine glucose, random or fasting plasma glucose etc. However, HbA1c is considered to be one of the most accurate and efficient method for measuring long-term blood sugar level (3 to 4 months). From 1894 to 1993, Diabetes Control and Complications Trial (DCCT) established the big data of diabetic patients’ HbA1c values to mean blood glucose resulted in making HbA1c a reliable index of mean blood glucose. However, DCCT haven’t standardized the HbA1c assay methods for labs and clinics. Later, the American Association for Clinical Chemistry (AACC) Standards Committee established a HbA1c Standardization Subcommittee to develop a plan for standardizing HbA1c assay that clinical laboratories could take advantage of it to perform precise glycemic evaluation and control. Now, the National Glycohemoglobin Standardization Program (NGSP) continue to develop reliable assays of HbA1c. Diagnosing canine diabetes with HbA1c 2018 American Animal Hospital Association suggested guidelines of diagnosis and assessment for animal diabetes. Clinical evaluation of animal diabetes (cats and dogs) include hyperglycemia, physical exam, complete blood count [CBC], Elevated blood glucose (BG), glucosuria, chemistry with electrolytes, urine analysis with culture, urine protein creatinine ratio (UPC), triglycerides, blood pressure (BP), and thyroxine (T4). While the level of BG concentration elevated to 200 mg/dL in dogs and 250–300 mg/dL in cats, glucosuria will typically occur. Pets with persistent glucosuria, persistent hyperglycemia, and presence clinical signs would be judged as diabetes mellitus (DM). Furthermore, HbA1c now have become a crucial glycemic indicator for diabetic dogs. Neslihan Tascene et al. revealed that blood HbA1c levels of diabetic were found to be 3.11±0.4 %, whereas the normal dog was 1.07±0.08 % respectively. Besides, the blood serum glucose level of diabetic dogs was around 526.71±22 mg/dl, whereas blood sugar in control dogs were around 97.80±2.93 mg/dl. Hasegawa S. demonstrated 6.41% HbA1c in diabetic dogs, whereas normal dogs with 2.6% (mean HbA1c of total Hb, %). And mean HbA1 values of normal dogs and diabetic dogs were 3.58 and 7.41%. In addition, Na-Yon Kim et al. showed significantly higher HbA1c concentrations of diabetic dogs (>6.2%) than non-diabetic dogs (p < 0.001) with commercial HbA1c testing system. Furthermore, Chao-Nan Lin et al. present the stability of canine glycosylated hemoglobin sample at room (25°C) and refrigerator (4°C) temperatures over 14 days. Besides, different purified methods would cause slight variation in measuring HbA1c value. Monitoring of pets’ diabetes Monitoring options include performance of blood glucose curves (BGCs), monitoring urine glucose (UG), measuring fructosamine, and assessment of clinical signs and weight. a. Blood glucose (BG) levels： Blood glucose levels fluctuate and could be used for indicating short periods of hyperglycemia. Normal BG were 63~110mg/dL in dogs; 47~151mg/dL in cats. As we mentioned, when the BG concentration goes over approximately 200 mg/dL in dogs and 250–300 mg/dL in cats, Glucosuria will occur. Blood Glucose Curves should be established during insulin treatment. b. Threshold of urine glucose (UG): UG concentration reflects only the average BG. Thus, it’s not recommended to solely rely on UG measurements is not recommended. Regardless, UG concentration can assist in assessment of DM together with other evaluation parameters. The threshold of urine glucose (UG) would fall in 180mg/dL in dogs; 252mg/dL in cats. c. Fructosamine: Fructosamine is a glycosylated protein formed by nonenzymatic, irreversible binding of glucose to serum albumin. It able to discern normal glycemic level from diabetes with chronic hyperglycemia and won’t be affected by