BLOOD OR PLASMA GLUCOSE

Glucose concentration in plasma is about 12% higher than in whole blood (depending on the haematocrit). It is preferred to prevent reduction in blood glucose as a result of glycolysis by collecting blood into sodium fluoride containing tubes. Fluoride ions prevent glycolysis by inhibiting enolase enzyme. Oxalate, on the other hand, inhibits coagulation by binding calcium.

Cerebrospinal fluid (CSF) is frequently contaminated with bacteria or cellular constituents and should be analysed for glucose without delay or, otherwise, the sample should be preserved with sodium fluoride. Normal range (using enzymatic method) 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

The WHO Expert Committee on Diabetes Mellitus has classified diabetes as follows:- 1. Diabetes mellitus a- Insulin – dependent (IDDM) or type 1. b- Non – insulin dependent (NIDDM) or type 2. c- Other types associated with certain diseases e.g. pancreatic disease, endocrine disease, drug induced, insulin receptor abnormalities, malnutrition related and others.

2- Impaired glucose tolerance 3- Gestational diabetes 2- Impaired glucose tolerance 3- Gestational diabetes. (DM developing during pregnancy).

The ADA Diagnostic criteria of Diabetes (2010) E:\كتاب العملي للصف الثاني.pdf p.57

Oral glucose tolerance test (OGTT) is performed by giving the patient 75 g oral glucose dissolved in 250 – 300 ml water. Blood samples are taken before (fasting) and 2 hr. following the load for the measurement of glucose. A 2 hr. post glucose plasma glucose (2 hPG) level below 7.8 mmol/L ( < 140 mg/dl) is considered as normal, higher than 11.1 mmol/L ( 200 mg/dl) is diagnostic of diabetes, while 2hPG between 7.8 – 11.1 mmol/L (140 – 199 mg/dl) is indicative of impaired glucose tolerance (IGT).

Glycated Hemoglobin (HbA1c) Within the circulation sugars can bind non enzymically to haemoglobin. Binding of glucose to the N terminal valine of the beta chains of HbA (the normal adult haemoglobin) forms a glycated haemoglobin called HbA1c. Normally about 4-6% of the circulating haemoglobin is in this form. The life span of a red blood cell is about 12 weeks. Assuming normal red cell life span, HbA1c thus reflects the average plasma glucose concentration over the preceding 12 weeks.

Hypoglycaemia hypoglycaemia is defined as plasma glucose less than 2.5 mmol/L (45 mg/dl). It is less common than hyperglycaemia, and it is eventuated in practice in cases including insulinoma, pancreatic tumors, hepatoma, adrenal carcinoma, hypopitutarism, addison’s disease, inborn error of metabolism of glycogen storage disease.

Enzymatic Method for Measurement of Glucose E:\كتاب العملي للصف الثاني.pdf p.59