Clinical chemistry

• Carbohydrates are the primary source of the brain, red blood cells and retinal cells in humans.
• Carbohydrates are stored in the liver and in the muscles as glycogen.
• Carbohydrates are classified into four properties: the size of the base carbon chain, the location of the CO (Carbonyl) group, the number of sugar units, and the stereochemistry of the compound.
• Another classification of carbohydrates is based on the number of sugar units in the chain: Monosaccharides, Disaccharides, Oligosaccharides, and Polysaccharides.
• Chaining of sugars relies on the formation of glycoside bonds that are bridges of oxygen atoms.
• When two carbohydrate molecules join, a water molecule is produced.
• When they split, one molecule of water is used to form the individual compounds.
• The reaction of hydrolysis is used when two carbohydrate molecules join or split.
• The glycoside linkages of carbon can involve any number of carbons; however, certain carbons are favored, depending on the carbohydrate.
• Simple sugars that cannot be hydrolyzed to a simpler form are known as Monosaccharides.
• These sugars can contain three, four, five, and six or more carbon atoms (known as trioses, tetroses, pentoses, and hexoses, respectively).
• The most common Monosaccharides include glucose, fructose, and galactose.
• Disaccharides are formed when two monosaccharide units are joined by a glycosidic linkage.
• On hydrolysis, disaccharides will be split into two monosaccharides by disaccharide enzymes (e.g., lactase) located on the microvilli of the intestine.
• Clinical conditions associated with insulin resistance include severe obesity and acanthosis nigricans.
• History of cardiovascular disease is a criteria for testing for diabetes.
• Testing for prediabetes and diabetes should begin at the age of 45 years.
• If results are normal, testing should be repeated at least 3 - year intervals (with consideration of more frequent testing depending on initial results and risk status).
• Due to the rise of the incidence of adolescent type 2 diabetes in the past few years, there are criteria developed for testing type 2 diabetes in asymptomatic children.
• Testing at the age 10 years or at the onset of puberty (if puberty occurs at a younger age) is a criteria for testing type 2 diabetes in children.
• Follow-up testing every 2 years is a criteria for testing type 2 diabetes in children.
• Testing should be carried out on children who display overweight (BMI >85th percentile for age and sex, weight for height >85th percentile, or weight >120% of ideal for height) and any two of the following risk factors: family history of type 2 diabetes in first- or second-degree relative, race/ethnicity (e.g., Native American, African American, Latino, Asian American, and Pacific Islander), signs of insulin resistance or conditions associated with insulin resistance (e.g., Acanthosis nigricans, hypertension, dyslipidemia, and PCOS), maternal history of diabetes or GDM.
• The criteria for testing for diabetes were revised by the International Association of Diabetes and Pregnancy Study Groups.
• Pregnant women are screened for GDM in their 24 - 28th week of gestation.
• There are two types of approaches for screening and diagnosis: One-step approach 2hr OGTT using a single dose of 75g glucose load, and Two-step approach: first step is an initial measurement with a 50g glucose load and is then measured after an hour.
• These monosaccharides are then actively absorbed.
• The most common disaccharides are: Maltose = Glucose + Glucose, Lactose = Glucose + Galactose, and Sucrose = Glucose + Fructose.
• Oligosaccharides are formed by the chaining of 2 to 10 sugar units.
• Ketone bodies are produced by the liver through the metabolism of fatty acids to provide an energy source from stored lipids at times of low carbohydrate availability.
• Ketone bodies are normally low in the body but elevated in cases of carbohydrate deprivation such as DM (type 1), fasting/starvation, high-fat diets, prolonged vomiting, and Glycogen storage disease.
• The three ketone bodies are Acetone (2%), A cetoacetic acid (20%), and β-hydroxybutyric acid (78%).
• Ketonemia is the presence of ketone in blood.
• Ketonuria is the presence of ketones in urine.
• Measurement of ketone is recommended for patients with Type 1 DM, during acute illness, stress, pregnancy, or elevated blood glucose level (>300 mg/dL) or if patients have signs of ketoacidosis.
• The specimen requirement for ketone measurement is fresh serum or urine.
• The historical test for ketone measurement is Gerhardt’s, where ferric chloride reacts with acetoacetic acid, resulting in a red color.
• The presence of autoantibodies to the β-islet of the pancreas is the characteristic of Type 1 diabetes.
• Albuminuria is a sign of diabetic nephropathy and its measurements aid in diagnosis at an early stage and before the development of proteinuria.
• Factors that affect elevated albumin include exercise within 24 hr, infection, fever, congestive heart failure, marked hyperglycemia, and marked hypertension.
• Random Spot Collection is a method for self-monitoring of blood glucose.