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Role of the Laboratory in Differential Diagnosis of Diabetes Mellitus - PowerPoint PPT Presentation


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Role of the Laboratory in Differential Diagnosis of Diabetes Mellitus. Dr. Essam H. Jiffri. INTRODUCTION. -The demonstration of hyperglycemia or hypoglycemia under specific conditions is used to diagnose diabetes mellitus and hypoglycemic conditions.

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introduction
INTRODUCTION
  • -The demonstration of hyperglycemia or hypoglycemia under specific conditions is
  • used to diagnose diabetes mellitus and hypoglycemic conditions.
  • -Other laboratory tests have been developed to identify insulinomas and to monitor
  • glycaemic control and the development of renal complications.
glucose estimation
Glucose Estimation
  • -Glucose may be estimated in either plasma or whole blood.
  • -The glucose concentration in whole blood is approximately 15% lower than the glucose
  • concentration in serum or plasma, because the volume of distribution of glucose is lower, as erythrocytes contain less free water than plasma.
  • -Samples for glucose can be obtained either by veinpuncture or by a fingerprick technique (collected in capillary tubes).
glucose estimation1
Glucose Estimation
  • -Blood cells continue to metabolize glucose after veinpuncture and serum or plasma must be refrigerated and separated from the cells within 1 hour to prevent substantial losses of glucose by the cellular fraction.
  • -A preservative that inhibits glycolysis should be used (sodium fluoride, together with potassium oxalate as an anticoagulant, is used for this purpose).
glucose estimation2
Glucose Estimation
  • -Test strips which measure blood glucose can be useful in obtaining an indication of
  • blood glucose concentrations, but diagnosis should be based on laboratory measurements.
fasting plasma glucose
Fasting Plasma Glucose
  • -A more important measurement is the fasting glucose concentration, which is drawn after an overnight fast (10-16 h).
  • -A fasting glucose concentration greater than 140 mg/dL (7.8 mmol/L) is considered diagnostic for diabetes mellitus by the National Diabetes Data Group.
two hour postprandial plasma glucose
Two-Hour Postprandial Plasma Glucose
  • -The two-hour postprandial glucose measurement is often used in conjunction with the fasting plasma glucose.
  • -The patient is advised to consume a meal that contains approximately 75 grams of
  • carbohydrates.
two hour postprandial plasma glucose1
Two-Hour Postprandial Plasma Glucose
  • -Two hours after eating, a blood sample is drawn for plasma glucose measurement.
  • -A glucose value greater than 200 mg/ dl (11.1 mmol/L) indicates diabetes mellitus.
oral glucose tolerance test ogtt
Oral Glucose Tolerance Test (OGTT)
  • -The OGTT is the most sensitive test for the diagnosis of diabetes.
  • -A sample of the patient's blood is drawn after an over night fast.
  • -The patient then consumes 75g of a glucose solution and blood is drawn every 30 minutes for two hours.
oral glucose tolerance test ogtt1
Oral Glucose Tolerance Test (OGTT)
  • -For children, glucose is administered at 1.75 9 glucose/kg body weight to a 75 g
  • maximum.
  • -A plasma glucose greater than or equal to 200 mg/dL (11.1 mmol/L) at the 2-hour
  • time point indicates diabetes mellitus.
oral glucose tolerance test ogtt2
Oral Glucose Tolerance Test (OGTT)
  • -Impaired glucose tolerance is diagnosed with a plasma glucose between 140 and 200 mg/dL (7.8 and 11.1 mmo1/L) at 2 hours time point in the test.
  • -Gestational diabetes is considered present when the values of the OGTT are greater than the following; fasting, 105 mg/dL (5.8 mmo1/L); 1 h, 190 mg/dl (10.6 mmo1/L),
  • and 2 h, 165 mg/dL (9.2 mmo1/L).
urinary glucose
Urinary Glucose
  • -Glucose can be detected in urine using the specific test strips that contain glucose
  • oxidase, peroxidase, and a chromagen.
  • -Other carbohydrates using Benedict's and Febling's reagents.
urinary ketones
Urinary Ketones
  • -Acetone and acetoacetic acid can be detected in urine using the AcetesTM or
  • KetostixTM systems.
  • -These tablets or strips use nitroprusside (sodium nitroferricyanide) to detect ketones.
urinary ketones1
Urinary Ketones
  • -Because beta-hydroxybutyric acid lacks a ketone group is not detected by this assay.
  • -Quantitative assays for acetoacetate and beta-hydroxybutyric acid are available using beta-hydroxybutyrate dehydrogenase and either NADH or NAD.
urinary ketones2
Urinary Ketones
  • -If NAD is used as the cofactor and the reaction is buffered at around pH 9.0, beta-hydroxyburyric acid is measured.
  • -On the other hand, a separate reaction using NADH and buffered around pH 7.0 would measure acetoacetic acid.
glycosylated proteins and hba 1c
Glycosylated Proteins and HbA1c
  • -Long-term blood glucose regulation can be followed by measurement of glycosylated
  • haemoglobins, this provides the clinician with a time average picture of the patient's
  • blood glucose concentration.
glycosylated proteins and hba 1c1
Glycosylated Proteins and HbA1c
  • -Many proteins are known
  • to react with carbohydrates at the peptide N-terminus forming glycosylated peptides.
  • -Glucose can rapidly
  • react with hemoglobin
  • to form a labile
  • aldimine (Schiff base).
glycosylated proteins and hba 1c2
Glycosylated Proteins and HbA1c
  • -The keto amine product is stable and cannot revert back to hemoglobin and glucose.
  • -HbA1cis the largest subfraction of normal HbA in both diabetic and non-diabetic
  • subjects and is formed by the reaction of the-beta chain of HbA With glucose.
glycosylated proteins and hba 1c3
Glycosylated Proteins and HbA1c
  • -The ketoamine (HbA1c) fraction reflects the concentration of glucose present in the
  • body over a prolonged time period .
  • -The measurement of glycated haemoglobin therefore gives an indication of the overall
  • degree of blood glycaemic control, in contrast to glucose measurements which give information for a single time-point.
microalbuminuria
Microalbuminuria
  • -Diabetes mellitus causes progressive changes to the kidneys and ultimately results in diabetic renal nephropathy.
  • -This complication progresses over a period of years and may be delayed by aggressive glycaemic control.
  • -An early sign that nephropathy is occurring is an increase in urinary albumin.
microalbuminuria1
Microalbuminuria
  • -Microalbumin measurements are useful to assist in diagnosis at an early stage and
  • prior to the development of proteinuria.
  • -Microalbumin concentrations are between 20 to 300 mg/d.
  • -Proteinuria is typically greater than 0.5 g/d.
proteinuria in diabetes
Proteinuria in Diabetes
  • - Many people excrete small quantities of protein in urine, typically around 10
  • mg/day of mainly low molecular weight proteins such as albumin.
  • -Some diabetic patients develop albumin excretion rates 30 µg/min this range
  • classed as microalbuminuria.
methods for the determination of glucose
METHODS FOR THE DETERMINATION OF GLUCOSE
  • The most used
  • methods of glucose analysis employ the enzymes glucose oxidase or hexokinas.
  • A) Glucose Oxidase
  • B) Hexokinase