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Present a table of results of the blood glucose samples from all the subjects in your practical group. Calculate the mean and standard deviation of the blood glucose measurements for each of the three groups at each time point, and give these values to two decimal places.
One of the subjects i.e. subject 9 had a surprisingly low blood glucose levels when checked during the fasting state i.e. 2.2. The reason for this could have been either a prolonged fast which could have led to such low levels or some strenuous activity before the test.
The other subject to have abnormally low blood glucose levels is subject 6. The subject had a normal fasting level glucose which should have gone up after ingesting 200 ml Lucozade. The reading at 30 minutes did not show any evidence of glucose levels rising. The measurement at 60 minutes is also in sync with the other subjects. However the sudden dip in the reading at 120 minutes is suggestive of a few things. There could either have been a human error while testing; it could have been low blood sample volume for test at 120 minutes or the patient could have been hypoglycaemic.
One of the subjects Sara had abnormal results as she had a thyroid problem which led to abnormal blood sugar pattern after ingesting lucozade drink.
b) What are the two major sources of variation in the results?
The graphs give a clear indication that drinking Lucozade has a greater effect on the plasma glucose level than eating the diabetic chocolate bar. If we analyse the mean blood glucose level values after 30minutes of taking the meal, it is evident that those subjects who drank Lucozade had an increase in plasma glucose to about 6.5 mmol/L, while those subjects who ingested the diabetic chocolate bar only had a slight increase in plasma glucose levels to about 4mmol/L. This can clearly be attributed to the varying glucose contents in the two test meals.
The diabetic chocolate bar consists of xylitol which is sugar substituent which is a low-calorie alternative to table sugar. It is absorbed at a much slower rate as it has a low glycemic index than normal sugar so it does not contribute to hyperglycaemia caused by insufficient insulin response while Lucozade contains glucose syrup and has a very high Glycemic index and is thus absorbed rapidly showing a sudden increase in plasma concentration.
There could also have been inaccuracies while measuring results
It could have been the:
Strip factors e.g. outdated strips, improper storage of strips etc
Physical factors e.g. temperature etc also can cause variations
Patient factors e.g. hand washing, contamination can alter results
Pharmacological factors e.g. medications etc
Or also genetic factors, age sex etc could have played a role in varying results.
4. Are the changes in blood glucose concentration what you expected for each test meal? Did the volunteers who ingested lucozade pass the OGTT? (8 marks)
The changes are as per expectation except for a few subjects.
As the graph shows, after ingestion of Lucozade the levels of blood glucose rise when checked at the 30 minute interval and when checked again at 60 minutes. The levels come down as insulin levels shoot up and they lower the glucose levels by a variety of pathways.
If after a 2 hour period the subject has plasma glucose concentration < 7.8 mmol/L then he is considered to have normal glucose tolerance. The glucose tolerance is impaired if after a 2 hour period the value is between 7.8 - 11.1mmol/L
As shown graphically the glucose levels are within the defined range when checked at those particular time intervals and this indicates that all the subjects have passed the Oral glucose tolerance test with one subject showing abnormally low levels of glucose which could have been caused due to various other factors.
5. For each test meal, perform a paired t-test on blood glucose values at each time point (30, 60, 120 minutes) and compare it to the resting values (0 minutes).
a) Present the p values from each t-test in a new table (do not give the values of t or other statistics.
b) Explain what the p value means?
c) A p value of <0.05 is commonly taken to represent a statistically significant difference. Look at your data and comment on its significance.
Paired T-test values (pre-test vs. 30, 60, and 120mins)
Lucozade P =
Diabetic Chocolate P =
P-value is the probability value ranging from 0 -1. P-value in this experiment identifies the significance of the results obtained at 95% confidence limit. If the p value is less than the threshold value then that difference is statistically significant. If the p value is higher than the value it is compared to then the null hypothesis is not rejected and the difference is not statistically significant
For the t-test results to have a significant statistical difference, they must have a value below 0.05. The table above shows that only the Lucozade values at 30 and 60mins had a significant statistical difference. This is because the Lucozade increased the levels of glucose in the blood considerably, so the results were significantly different compared to the values obtained at fasting. However after 2 hours the levels of glucose go down as insulin is released in response and it conducts a variety of pathways to metabolise glucose levels and hence the results not statistically significant.
The results for chocolate do not show any significant difference at any point of time as they are quite similar to the pre-test values and didn't have as big an increase as with the Lucozade as they are not meant to elevate blood sugar levels. They contain polyols (as sugar replacement) which do not interact much with the blood sugar levels and hence do not elevate the sugar levels.
The results for water too do not show any significant difference as water was not meant to interfere with the blood glucose levels.
6. Design an experiment to test the precision and accuracy of the glucometers. Answer the following:
a) define accuracy and precision.
b) explain how you would actually perform the experiment.
(c) describe how you would present your results of accuracy and precision.
Accuracy of a blood glucometer is the measure of the closeness of the mean value of the series of values against the reference value. The mean value of a series can be perfectly accurate whilst none of the individual values might represent the reference.
Precision is the reproducibility of a series of values independent of the closeness of any values against the reference.
An experiment can be designed to test the accuracy and precision of glucometers. Different types of glucometers can be assigned to different students. They are to be provided with glucose standards and unknown aqueous samples. They then measure the glucose standard and the unknown mixture several number of times. The students will then be required to perform t-test, F-test and Q-test to evaluate the data obtained.
The experiment can then be designed on the factors below:
Calibration of glucometers
Method of preparation of samples
Dynamic range of the glucometers
Volume of the sample applied
Preparation of samples and if the sample composition affects results.
If the outdated strips give the same results.
We will have data taken from varying glucometers using same aqueous glucose samples. Each set of values will represent the precision and accuracy of the particular glucometer.
7. Research and describe a test of long term glucose control suitable for patients with diabetes. What does the test measure, why is it used, and what are the target values? (5 marks)
One of the tests suitable for long term glucose control for patients with diabetes involves monitoring the levels of glycated haemoglobin or glycosylated haemoglobin.
Haemoglobin A1c is a form of haemoglobin which is majorly used for identification of average plasma glucose levels over prolonged periods of time. Normal exposure of haemoglobin to high plasma glucose leads to the formation of HbA1c in a non enzymatic way. This attachment of sugar to Hb is called glycosylation. This monitoring HbA1c levels may be helpful in treating the symptoms on long term basis.
This process of glycation occurs over a 120 day life span of the red blood cell. But recent glycaemia has major influence on HbA1c levels. Measuring the level of glycated haemoglobin (by measuring serum glucose levels) determines the amount of sugar attached to the haemoglobin. .
This test should be done at least twice a year. It should be done a little more often for people already diagnosed of diabetes.
Glycation of haemoglobin has been linked with nephropathy and retinopathy in diabetes mellitus, lowering the haemoglobin A1c number can reduce the development of serious kidney, eye and nerve disease in people with diabetes
This test is used to diagnose the blood sugar levels in a patient over a 3 months period.
The current UK guidelines suggest a target between 6.5% and 7.5% (depending on the presence of any type of complications or high arterial risk) 7 and in the USA a value of 7% is now recommended in all situations.
Findings have shown that people who manage to keep their Hba2c levels below 7 have a greater chance of keeping healthy and cutting out on diabetes linked kidney and eye problems etc
Target values of below 6.5% are being eyed as per the new draft guidelines for UK for Type 2.