Glucose Measurements Clinical Chemistry 1Prepared by Jommel C. Amar

Specimen considerationsSerum or plasma must be separated from the cells within 30 minutesAt room temperature, glycolysis is metabolized at 7 mg/dl/hrAt refrigerated temperature, loss is approximately 2 mg/dl/hr

Glucose MethodsIt can be divided into two: Chemical and Enzymatic

Chemical MethodUnder chemical method there are two:Oxidation-reduction method

Condensation method

Oxidation reduction methodAlkaline copper reductionReduction of cupric ions to cuprous oxide by hot alkaline solution by glucoseFolin wu method MethodNelson Samongyi MethodNeocuproine MethodBenedicts Method

Oxidation reduction methodAlkaline Ferric Reduction MethodHagedorn Jensen Reduction of ferricyanide to ferrocyanide by glucose

Condensation MethodOrtho-toluidine (Dubowski Method)Only chemical method still widely used and it is based on the condensation of aldosaccharides such as glucose with an aromatic amine and glacial acetic acidCan be used for plasma, urine, CSF without any protein precipitation

Enzymatic MethodYields higher specificity than chemical methodsBecause of its specificity, it only acts on glucose but not on other sugars and not on other reducing substances.Glucose can be measured by its reaction with glucose oxidase in which gluconic acid and hydrogen peroxide are generated

Enzymatic MethodGlucose Oxidase MethodMeasures -D glucoseAlpha form of glucose must be converted to beta D glucose before reacting

Enzymatic MethodHexokinase MethodMost specific glucose methodReference methodReduced NADPH is the measured end product of the method

Glucose measurementsRBSFBS2 hour PPBSGTTGlycosylated hemoglobinFructosamine

RBS (Random Blood Sugar)Fasting is not neededRequested during insulin shock, hyperglycaemic ketonic comaNV: 45-130 mg/dl

FBS (Fasting Blood Sugar)NPO (Non-per-Orem) atleast 8 hours before the testUsed to diagnose hyperglycemia and hypoglycemia

2 hour Post Prandial Blood SugarUsed to screen, monitor and diagnose diabetes mellitusMost sensitive of the values of GTT for diagnosing diabetes

GTT (Glucose tolerance test)Multiple blood sugar testMeasures impaired glucose toleranceSensitive but less specificEither oral or intravenous

Kinds of GTTOGTT(Oral-GTT)Intravenous GTT

OGTT(Oral-GTT)Janney Method

Exton rose method

Requirements for OGTTFasting of 8-14 hoursDiet of 150g of carbohydrate per day for 3 days prior to testingPatient should not smoke or drink alcoholGlucose load is 75grams and 1.75 g/kg body weight for children

Added plasma glucose after OGTT30 mins = 30-60mg/dl above fasting1 hour = 20-50 mg/dl above fasting2 hour = 5-15mg/dl above fasting3 hour = fasting level or below

Intravenous GTTUsed for diabetes with gastro intestinal disorder0.5g of glucose/kg body weight is administered within 3 minutesFasting sample is also requiredBlood is collected after 5 minutes of administration of glucose

Glycosylated Hemoglobin (HBA1c)Largest subfraction of normal hemoglobin A in both diabetic and non diabetic patients.Method for monitoriong long term glucose control3%-6% HbA1c is normal18-20% is prolonged hyperglycemia

FructosamineGlycated albumin

Short term glucose control

RV: 205-285 umol/L

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