Practical 3: Investigation of plasma glucose
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Diabetes is the failure of insulin function due to what two reasons?
• catastrophic immune destruction of the B-islet cells of the pancreas which produce insulin = Type 1 • Development of tissue resistance to insulin leading eventually to pancreatic exhaustion = Type 2
Why is diabetes rising?
Obesity and dietary abuse
What tests are used to diagnose diabetes? (3)
Fasting serum [glucose] is elevated and/or Post prandial serum [glucose] is abnormally high following an oral glucose tolerance test Or when glucose exceeds the renal threshold and appears in the urine
How does a patient prepare for an oral glucose tolerance test? (4)
Patient should follow an unrestricted diet containing at least 150g carbohydrate daily Patient should undergo usual physical activity for at least 3 days before the test Patients must fast for 10-16 hours before the test Water must be drunk during the fast
How is an oral glucose tolerance test carried out (3)
A blood sample is collected for measurement of fasting glucose before the test is undertaken A glucose load of 75g anhydrous glucose is given in a total fluid volume of 250-300mls and this should be consumed over 5 minutes A further blood sample should be collected two hours after the glucose load has been given and the glucose concentration measured
What does it mean if the patient’s fasting glucose is 1 mmol/L greater than the WHO fasting diagnostic value i.e. a value of 8.0 mmol/L?
The patient is diabetic
For how long does a patient need to fast before an oral glucose test?
eight hours
How much glucose should a child be given in an oral glucose tolerance test
1.75g anhydrous glucose per kg of body weight up to a total of 75g glucose
What would deem an oral glucose tolerance test invalid
If the patient vomits If the timer isn’t starter at the beginning of ingestion If the patient doesn’t drink the sample within 5 minutes
How long after ingesting the glucose should another blood sample be taken?
2 hours after
What method is used to determine the concentration of glucose in serum or plasma?
GOD/PAP method
What is the principle behind the GOD-PAP method (6)
Glucose oxidase converts glucose into gluconate Hydrogenperoxide (H2O2) is produced in the reaction Peroxidase degrades H2O2 to produce phenol and 4-aminoantipyrine Phenol and 4-aminoantipyrine is measurable using Trinder indicator at 505nm i.e. phenol and 4-aminoantipyrine react to produce red quinone and water The increase in absorbance correlates with the glucose concentration of the sample
At what wavelength is the GOD-PAP assay read
505nm
At what temperature should the glucose assay be read
Between 15 and 25 degrees Celsius
What blank should you use for the GOD-PAP assay
Reagent blank
For how long should you incubate the GOD-PAP assay?
Incubate for 20 minutes at room temperature Or incubate for 15 minutes at 37 degrees Celsius
How do you determine the concentration of glucose from the absorbance
Unitary method
What is the reference range for fasting glucose?
3.5-6.1 mmol/L
What three diagnosis can be made from your glucose tolerance test and GOD-PAP test?
Diabetes Mellitus Impaired glucose tolerance Impaired fasting glycaemia
What results from your glucose tolerance test and GOD-PAP test indicate diabetes mellitus?
Fasting of >7.0/=7.0 AND/OR 2hrs post glucose load >11.1/=11.1
What results from your glucose tolerance test and GOD-PAP test indicate impaired glucose tolerance?
Fasting of <7.0 AND 2hrs post glucose load >7.8/=7.8 and <11.1
What results from your glucose tolerance test and GOD-PAP test indicate impaired fasting glycaemia (IFG)?
Fasting between >= 6.1 and <7.0
What should be done if a patient’s tests come back as positive for diabetes
Patient should be retested on another day
When would a patient not be retested after a positive diabetes result
If there is unequivocal hyperglycaemia with acute metabolic decompensation e.g. coma or obvious symptoms