Monitoring diabetic control
Basic principles: Monitor;
- Wellbeing and weight
- Urine glucose
- Imprecise, but useful as a ‘traffic light’
- Blood glucose
- For self regulation. However, its only really people on insulin who can benefit from this.
- Haemoglobin A1c (HbA1c)
- For risk assessment. Everyone with diabetes should have this measured at least twice a year!
- Blood glucose monitoring – this can be done quickly and easily by measuring a tiny amount of blood. It is an essential skill for all involved in diabetic care, and for many diabetic patients themselves. The testing equipment contains glucose oxidase which catalyses the reaction of glucose to gluconic acid, and a detection system that detects the products of this reaction. The detection is either done electrochemically, or colorimetrically (using dyes). Then this signal is either read electrically or by a reflective material, and this signal converted to a number corresponding to glucose concentration. Some more basic tests may involve a colour strip that changes colour.
- The sample is obtained by pricking the sides of the finger (not the pad – which is more sensitive)
- Blood must cover the whole of the test area, and the result must be taken after an exact amount of time – many modern kits do this by themselves now – however in cases where they don’t inaccurate readings are common.
- These tests are accurate enough for the purposes of self monitoring, but are not accurate enough for diagnosis.
Monitoring schedules
These will depend on the treatment. Type 2
diabetes treated by diet and oral agents can get away with measuring their levels once or twice a week. These patients should check their fasting glucose levels.
Patients on insulin need to monitor much more carefully, in order to adjust the dose of insulin. There are two types of insulin – short acting and long acting. Long acting insulin has be monitored typically 12 hours after it was administrated, whilst short acting insulin should be monitored 90 to 120 minutes after administration. Patients should check their glucose levels regularly. This could consist of checking twice every day, or it ay be that they check 4 times a day, but only on a couple of days each week.
- Patients should be encouraged to record their glucose levels, as this makes it easier to spot any abnormalities. They should also be encouraged to check their glucose frequently when they feel unwell.
- Patients on insulin are encouraged to alter their own regimen from their glucose level results, although a clinician should always be available via telephone for advice.
- These home testing kits also require that the patient has been taught how to use them properly!
As a doctor, it is also important to check the patients monitoring technique, and make sure they have an action plan for what to do if they get readings outside of the normal level.
HbA1C and fructose amide
HbA1c is glycosylated haemoglobin. It is formed when haemoglobin comes into contact with glucose, and is formed via a non-enzymatic pathway. When glycosylation occurs via a non-enzymatic pathway, we call it glycation. This process occurs all the time, but the rate of the reaction is proportional to the concentration of glucose.
During its 120 day lifecycle, a red blood cell comes into contact with glucose. Some of this glucose will become joined to haemoglobin within the red cell through glycation. In individuals with poorly controlled glucose, the haemoglobin is more likely to come into contact with a glucose molecule, and thus more HbA1c is formed!
- Once a haemoglobin is glycated it stays like that forever.
- Therefore, this method of monitoring shows us the level of glucose in the blood over the last 4-12 weeks. Many experts believe that the value is weighted towards glucose levels of the last 2-4 weeks.
- A good target rate is 4-7%. This percentage value is a percentage of the total amount of Hb. The levels in a normal individual are 4-6.5%.
- The value can be misleading if there is thalassaemia, or reduced red cell lifespan, or something affecting haemoglobin.
Fructosamide can be used in similar tests – in this case fructose reacts with albumin to produce fructosamide. This is generally used in situations where HbA1c cannot be tested, such as:
Glycation is the process by which a protein or lipid molecule will bind to a sugar molecule (such as glucose or fructose) without enzymatic control. Glycation is usually an unwanted process in the body because it impairs the functioning of normal molecules. At certain specific sites in the body, glycation occurs under the control of enzymes for a specific purpose, and under these circumstances it is called glycosylation.
AGEs – advanced glycation end products. Some AGE’s are benign whilst the production of some others can predispose to certain conditions such as;
- cardiovascular diseases (fibrinogen, collagen and endotherlium are all damaged by AGE’s). Collagen will be stiffened and weakened. This results in increased blood pressure (due to stiffening) and increased risk of aneurysms (due to weakening). These aneurysms can result in stroke. Glycation products can also be the basis of the formation of atherosclerotic plaques.
- Alzheimer’s disease (amyloid plaques are side products in the production of AGE’s)
- cancer (acylamide and other AGE side products are released)
- peripheral neuropathy (myelin is affected), blindness (due to microvascular damage to the retina).
This damage results from the production of highly oxidising products such as hydrogen peroxide.
Glycated products are removed very slowly from the body – they are removed by the kidney. Glycated products take about twice as long to remove from the body as the average red blood cell life cycle.
Long lasting cells of the body – such as nerve cells, beta cells and retinal cells are most likely to be affected by the damage of AGE’s.
Monitoring urine glucose and ketones
You can measure glucose leves in the urine, but this isn’t much use, because it is affected by the renal threshold (which can be anywhere between 7 and 11mmol/L – note also that the renal threshold rises with age. The mean level is 10 mmol/L), urine output and time since the bladder was last emptied. Hypoglycaemia cannot be detected – because urine glucose gives no idea ofglucose levels once they are below the renal threshold.
Therefore in patients where this is used as the main monitoring method, consistent negative results, and no symptoms of hypoglycaemia will usually confirm that the disease is being well controlled.
In some circumstances urinary glucose may be acceptable – this is in type 2
diabetic patients who refuse to prick their fingers, who have a normal renal threshold, and who are not on hypoglycaemic medications (insulin or suulphonylureas).
Changes in urine glucose are also slow to appear after changes in blood glucose have occurred.
Ketone monitoring may be useful for those with
diabetes in times of illness, when glucose levels may become higher than normal. This test will then predict when ketoacidosis may be about to take place.
Monitoring risk factors
To reduce the risk of complications, there are several risk factors that should be monitored and brought under control. These are summarised below. Some patients will achieve these levels but many will not. Achievable targets should be discussed and encouraged with individual patients. The longer the disease goes on, the harder it is to get these levels under control. Eating, lifestyle, and reducing weight are the main ways theses value can be brought under control. Obviously, for many patients, there will also be specific treatments, such as insulin or metformin. The benefits of attaining these values are the same, irrespective of the method used to attain them (i.e which treatment they are on)
These levels are the same irrespective of which type of diabetes you have.
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Test
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Ideal
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HbA1c
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<7%
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BP (mmHg)
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