Practical 3: Investigation of plasma glucose

Question 1

Diabetes is the failure of insulin function due to what two reasons?

Answer 1

1. catastrophic immune destruction of the B-islet cells of the pancreas which produce insulin = Type 1
2. Development of tissue resistance to insulin leading eventually to pancreatic exhaustion = Type 2

Question 2

Why is diabetes rising?

Answer 2

Obesity and dietary abuse

Question 3

What tests are used to diagnose diabetes?
(3)

Answer 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

Question 4

How does a patient prepare for an oral glucose tolerance test?
(4)

Answer 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

Question 5

How is an oral glucose tolerance test carried out
(3)

Answer 5

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

Question 6

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?

Answer 6

The patient is diabetic

Question 7

For how long does a patient need to fast before an oral glucose test?

Answer 7

eight hours

Question 8

How much glucose should a child be given in an oral glucose tolerance test

Answer 8

1.75g anhydrous glucose per kg of body weight up to a total of 75g glucose

Question 9

What would deem an oral glucose tolerance test invalid

Answer 9

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

Question 10

How long after ingesting the glucose should another blood sample be taken?

Answer 10

2 hours after

Question 11

What method is used to determine the concentration of glucose in serum or plasma?

Answer 11

GOD/PAP method

Question 12

What is the principle behind the GOD-PAP method
(6)

Answer 12

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

Question 13

At what wavelength is the GOD-PAP assay read

Answer 13

505nm

Question 14

At what temperature should the glucose assay be read

Answer 14

Between 15 and 25 degrees Celsius

Question 15

What blank should you use for the GOD-PAP assay

Answer 15

Reagent blank

Question 16

For how long should you incubate the GOD-PAP assay?

Answer 16

Incubate for 20 minutes at room temperature

Or incubate for 15 minutes at 37 degrees Celsius

Question 17

How do you determine the concentration of glucose from the absorbance

Answer 17

Unitary method

Question 18

What is the reference range for fasting glucose?

Answer 18

3.5-6.1 mmol/L

Question 19

What three diagnosis can be made from your glucose tolerance test and GOD-PAP test?

Answer 19

Diabetes Mellitus

Impaired glucose tolerance

Impaired fasting glycaemia

Question 20

What results from your glucose tolerance test and GOD-PAP test indicate diabetes mellitus?

Answer 20

Fasting of >7.0/=7.0

AND/OR

2hrs post glucose load >11.1/=11.1

Question 21

What results from your glucose tolerance test and GOD-PAP test indicate impaired glucose tolerance?

Answer 21

Fasting of <7.0

AND

2hrs post glucose load >7.8/=7.8 and <11.1

Question 22

What results from your glucose tolerance test and GOD-PAP test indicate impaired fasting glycaemia (IFG)?

Answer 22

Fasting between >= 6.1 and <7.0

Question 23

What should be done if a patient’s tests come back as positive for diabetes

Answer 23

Patient should be retested on another day

Question 24

When would a patient not be retested after a positive diabetes result

Answer 24

If there is unequivocal hyperglycaemia with acute metabolic decompensation e.g. coma or obvious symptoms

Question 25

List the three common symptoms of diabetes needed for a diagnosis

Answer 25

Polydipsia (excessive thirst)

Polyuria

Polyphagia (excessive hunger)

Question 26

Why should glucose concentration not be determined on serum?

Answer 26

Glycolysis will result in an unpredictable under estimation

Question 27

What are the only acceptable ways of using serum to test for glucose?

Answer 27

If red cells are immediately removed

If samples are taken in a collection tube containing a glycolysis inhibitor