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BLOOD GLUCOSE

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Methods of measurement

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  • Procedures in common use include:
  • Enzymatic (glucose oxidase)
  • Colourimetric (O – toluidine)
  • Oxidation reaction (copper sulphate).

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Samples used for measurement

  • Values for glucose in whole blood are less than in plasma
  • Red blood cells contain 80% water, compared with 93% in plasma,

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  • Glucose concentration in plasma is about 12% higher than in whole blood

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Collection and handling of specimens

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The average rate of decrease in serum glucose is approximately 7% in each hour

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Equal to (0.28 – 0.56 mmol/L) = (5-10 mg/dl).

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This decrease is the result of glycolysis

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To gain accurate result

  • Glucose values within 0.5 mmol/L (10 mg/dl) of the original values are to be obtained.
  • Centrifugation
  • Sodium Fluoride ions prevent glycolysis by inhibiting enolase enzyme.

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  • Oxalate, on the other hand, inhibits coagulation by binding calcium.

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Clinical significance�

  • Normal range (using enzymatic method) :

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  • Plasma glucose = 3.0 – 5.6 mmol/L (55-100 mg/dl)
  • CSF glucose = 2.2 – 4.2 mmol/L (40-75 mg/dl)

or 60% of plasma value

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Hyperglycaemia

  • Raised blood or plasma glucose is the hallmark of diabetes mellitus.
  • The common underlying defect is:
  • Deficiency of insulin action which may be absolute (as in type 1 diabetes)
  • or relative with resistance to insulin action (as in type 2 diabetes).

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The WHO classification

  • Classified diabetes in 1980-1985 as follows:-
  • A- Clinical Classes
  • Diabetes mellitus
  • IDDM or Type 1.
  • NIDDM or Type 2.
  • Other types associated with certain diseases e.g.
  • Pancreatic disease,
  • Endocrine disease,
  • Drug induced,
  • Insulin receptor abnormalities,
  • Malnutrition related and others.
  • Impaired glucose tolerance
  • Gestational diabetes. (DM developing during pregnancy).

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  • B- Statistical risk classes (subjects with normal glucose tolerance but with substantially increased risk of developing diabetes).

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  • Previous abnormality of glucose intolerance.

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  • Potential abnormality of glucose intolerance.

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The ADA Diagnostic criteria of Diabetes (2010)

Parameter

normal

prediabetic

Diabetic

FPG(mg)

<100

100-125

≥126

2-hr P G on

OGTT(mg)

<140

140-199

≥200

Random

P G(mg)

<140

---------------------

≥200

HA1c %

<5.7

5.7-6.4

≥6.5

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Oral Glucose Tolerance Test (OGTT)

  • 75 g oral glucose dissolved in 250 – 300 ml water.
  • Fasting blood samples and 2 hr.
  • 2 hPG level:
  • < 7.8 mmol/L ( < 140 mg/dl) is normal
  • ≥ 11.1 mmol/L ( ≥ 200 mg/dl) is DM.
  • 2hPG between 7.8 – 11.1 mmol/L (140 – 199 mg/dl) is indicative of impaired glucose tolerance (IGT).

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�Glycated Hemoglobin (HbA1c)�

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Binding of glucose to the N terminal valine of the beta chains of HbA

Normally about 4-6% of the circulating haemoglobin is in this form HbA1C.�

Reflect the average plasma glucose concentration over the preceding 12 Weeks

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Hemoglobin consists of : 97% HbA, 2.5%HbA2 and 0.5% of HbF 

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. HbA consists of : HbA1a, HbA1b and HbA1c

. Collectively, these are referred to as HbA1c

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Hypoglycemia

Defined as plasma glucose less than 2.5 mmol/L (45 mg/dl).

  • Insulinoma
  • Pancreatic tumors
  • Hepatoma,
  • Adrenal carcinoma
  • Hypopitutarism
  • Addison’s disease
  • Inborn error of metabolism

a. Glycogen storage disease

b. Galactossemia

c. Fructose intolerance

  • Essential reactive hypoglycaemia