Type 1 diabetes mellitus

T1DM is characterised by complete, or near-complete, deficiency of insulin production from the pancreatic beta cells due to auto-immune destruction of pancreatic islets. Diagnosis is usually clinical but is supported by finding high titres of anti-islet cell, or anti-glutamic acid decarboxylase antibodies, and low levels of C-peptide in the face of hyperglycaemia. Treatment is mandatory insulin therapy.

Insulin therapy

What are the advantages of a basal bolus regimen?

Most newly diagnosed adult T1DM cases will be started on a QDS (basal bolus) insulin regimen consisting of a once daily long acting insulin. This will normally be an analogue such as insulin-glargine (Lantus) or insulin detemir (Levemir) and three injections of prandial insulin such as insulin aspart (Novorapid), insulin glulisine (Apidra) or insulin lispro (Humalog).

In the first instance, an approximate guide to insulin dose can be calculated follows: the patient’s weight in Kg is halved, this is the total daily number of units that will be required and this amount is given as 40% in the form of the basal insulin and 20% as rapid acting insulin with each meal.

Thus a 60 kg patient will require 30 units of insulin, given as approximately 12 units of basal insulin at bed time and six units of rapid acting insulin with each meal.

Are there circumstances where twice daily biphasic insulin may be more appropriate?

Twice daily biphasic insulin regimens - with insulins such as biphasic human isophane insulin (e.g. Humulin M3), biphasic insulin aspart (Novomix 30), biphasic insulin lispro (Humalog Mix 25) - have the advantage of fewer injections. They require two per day as compared to four a day for a basal bolus regimen and may therefore be preferred in paediatric practice, in the elderly and in those who are very reluctant to inject insulin at all.

The major draw back of twice daily mixed insulin regimens is that the longer acting component tends to 'peak' five to six hours after injection. This mandates eating a midday meal within a relatively narrow time window and at night leads to increased risk of nocturnal hypoglycaemia and often mandates a pre-bed time snack to reduce this risk.

For these reasons, it is often more difficult to achieve a good HbA1c without unacceptably high frequency of hypoglycaemia with twice daily mixed insulin regimens.

New insulins

Recently we have seen the addition of two new insulin glargine products to the market which may cause confusion. Abasaglar is a bio-similar version (100 units/ml), which has an identical license to the original product, Lantus. Toujeo, however, is a more concentrated product (300 units/ml) allowing smaller volume injections and it is promoted as a longer-acting product.

Any switch from Lantus to Toujeo will therefore require dose adjustment and glucose monitoring. Dose adjustment may also be required from Lantus to Abasaglar and glucose monitoring will certainly still be required. Switching, therefore, should only be performed by specialists.

There have also been updates to the short-acting market, with a recent launch of Humalog (insulin lispro) in a more concentrated form (200 units/ml). No dose conversion is required, as the Kwik pens dial in the same one unit increment, but a smaller volume is delivered.

When is continuous subcutaneous insulin infusion (CSII) therapy indicated?

CSII therapy involves the patient wearing a pump device connected to a permanently indwelling subcutaneous needle.

Soluble insulin is continually delivered at a pre-set basal rate which can be programmed to vary at different times of day. The patient then triggers a bolus each time they eat. The size of the prandial bolus being selected by the patient.

CSII is expensive and its availability on the NHS, in adult practice, is tightly restricted and patients must fulfil a number of criteria specified by NICE. 

What other treatment modalities may be available?

A range of other insulin delivery options are available, including: 

1. Needle-less injection devices which utilise high pressure air to 'inject' an aerosol of insulin through the skin.

2. Inhaled insulin has briefly been available and, although it was subsequently withdrawn by the manufacturers, other companies are still working on bringing other formulations of inhaled insulin to the market.

3. Simultaneous kidney pancreas transplantation. In patients who require renal grafting for diabetic nephropathy, and thus will be taking immunosuppressant drugs anyway, it is possible to perform simultaneous pancreatic transplantation. When this is successful, it effects a surgical 'cure' for diabetes. The procedure is not without technical challenges and in those who not due to receive a renal graft, an isolated pancreatic transplant is much more difficult to justify.

4. Islet cell transplantation is an alternative to conventional pancreatic transplantation and has the advantage of requiring no actual surgery (the islet cells are delivered intravenously and they seed into the liver). But, it still requires immunosuppression and should be regarded as a procedure that is largely research-oriented and currently under development.

Patient education

Who should be taught self-monitoring of glucose levels?

All newly diagnosed patients with T1DM need to be taught home blood glucose monitoring, encouraged to do so two to four times a day and keep records of the results in order to inform discussion with their diabetic team. 

What topics should be covered in general diabetes education at presentation?

This is a large and important subject and it is important that the diabetes specialist nurses spend considerable time with newly diagnosed T1DM covering several important topics.

These include hypoglycaemia recognition and self management, sick day rules, injection sites, driving, diet, adjusting insulin doses, use of insulin injection devices (including storage of insulin), changing cartridges and needles, recognising potential injection device failure and, for female patients, contraception and pre-pregnancy planning.

How are patients taught to adjust their insulin doses?

Adjusting insulin doses is an essential part of self-management for patients with T1DM.

While a minority of patients take fixed doses of insulin regardless of dietary intake and variations of physical activity this approach rarely produces good glycaemic control and, especially for patients on basal bolus regimens, it means that the patient is not realising much of the potential benefit of the flexibility of such a regimen.

It is usual for the dose of basal insulin to be kept fairly constant and most of the adjustments to be made on the prandial insulin. Some experienced patients learn empirically how much rapid acting insulin they need with meals of varying size and composition. Other patients develop a habit of testing their blood sugar and reacting to the result by adjusting the size of the next dose of rapid acting insulin, sometimes giving extra doses in between meals.

However, many would discourage this approach as it tends to promote a relatively unstable blood sugar oscillating between low and high blood sugars.

Formal systems for dose adjustment include carbohydrate counting, DAFNE which, although based in carbohydrate counting, is a much more sophisticated approach.

Another approach used by some patients is to record blood sugars and dietary intake and to regularly consult with their DSN who will advise on future adjustments to insulin doses based on the results. This system has the advantage of being both educational and therapeutic but is quite labour-intensive.

What are the recommended precautions around driving?

The mainstay of safe driving in people with diabetes is the avoidance, recognition and appropriate management of hypoglycaemia.

Thus, patients are advised to check their BM before getting in the car and to not set off if it is low until this has been rectified, to stop and check BM periodically during long journeys and to keep a source of rapidly absorbable carbohydrate, such as dextrose tablets, in the car.

If the patient does feel hypoglycaemia coming on they should pull over at the side of the road as soon as it is safe to do so, check their BM, ingest rapidly absorbed carbohydrate followed by a source of longer-acting carbohydrate and not proceed until their BM is back to a safe level and they feel well enough to continue.

The DVLA regularly re-assess the driving-safety of insulin-treated patients with diabetes by questionnaire to the patient and their doctor. The medical questionnaire includes an assessment of the patient's knowledge of the above guidance.

Patients with significant hypoglycaemia un-awareness may have their licence suspended by the DVLA for a period until some awareness has been restored.

What is the standard advice around ethanol consumption?

Somewhat counter-intuitively to many patients, alcohol tends to lower rather than raise blood sugar levels.

This effect is largely due to inhibition of hepatic gluconeogenesis. Thus patients should be educated about this effect, should check their blood sugar after imbibing alcohol and may even need to reduce the dose of prandial insulin taken with food before an evening in the pub.

What should pre-pregnancy counselling cover?

The most important message for pre-pregnancy counselling in diabetes is that unplanned pregnancies should be avoided as far as possible.

While the foetal and maternal risks of pregnancy in diabetes are elevated in comparison with the background population risks, these can be significantly reduced by scrupulous glycaemic control, especially around the time of conception, and thus unplanned conception should be avoided.

It is therefore essential that young women with diabetes have these considerations explained to them and that they are encouraged to use effective contraception until such time as they are ready to conceive.

Prior to attempting to conceive they need to lower the HbA1c to around 7% (53.0mmol/mol) and aim to achieve fasting blood sugars in the region of 6 or less and post prandial blood sugars around 8 mmol/L or less. These are targets that should be maintained throughout pregnancy but are now thought to be most important of all around the time of conception.

Other factors to consider are the cessation of smoking, avoidance of alcohol and use of folic acid at neural-tube defect prevention doses (i.e. 5 mg/day).

What are sick day rules? 

Sick day rules are guidelines for patients with diabetes providing advice on how to manage blood sugars and insulin/tablets during times of illness, especially illnesses that lead to reduced food intake and/or vomiting.

During these times, the cardinal advice is that patients should NEVER STOP THEIR INSULIN.

Insulin requirements often actually rise during inter-current illness, even if food intake has significantly fallen. Thus, patients are advised to regularly check BMs (two to four hourly), continue their regular doses of insulin, counter any falling blood sugars with frequent small sips of a sugary drink and maintain a high fluid intake (ideally 3 litres per day).

Read more on sick day rules and T1DM.

What does good dietetic advice include?

Dietary advice for people with diabetes should be little different from general healthy eating advice.

Specifically, avoidance of refined sugars, reduction of saturated animal fats, the majority of calories coming from complex carbohydrates, five portions of fresh fruit and vegetables per day and a caloric intake aimed at maintaining steady weight (~2,000 cal per day for women and ~2,500 for men).

Much of this advice is summarised on the 'eatwell plate'. One particular aspect of relevance to patients treated with insulin is the carbohydrate content of meals as this is a major determinant of prandial insulin requirements. This can be assessed by a system known as carbohydrate counting.

What is carbohydrate counting?

Carbohydrate counting is a system for estimating the carbohydrate content of a meal by eye. It requires skill and takes time to learn. However, with practice, it becomes a very useful to self-management tool.

The system involves patients learning to recognise standard quantities and types of food-stuff which can be done in practical sessions with dieticians or from books containing photos of plates of food.

Examples include 1 medium size boiled potato = 10 g carbohydrate. One slice white bread (standard thickness) = 15 g carbohydrate. With experience, the patient also learns how much prandial insulin they require per 10 g carbohydrate and thus after inspecting a plate of food can then accurately estimate the required dose of prandial insulin to take with that meal.

The system is an important component of the DAFNE system.

 Annual review

What areas should be covered in the consultation?

The aim of the annual review is to screen the patient for the presence of established complications and assess their risk factors for future complications.

Areas covered in the consultation depend on the patient’s history but should normally include:

1. Review of the glucose monitoring diary and or glucometer.

2. Assessment of the frequency of hypoglycaemia; whether the patient has adequate warning symptoms; does the patient know how to treat their hypos, and are there any obvious precipitating factors?

3. What insulins and what doses are being taken.

4. What other medicines are being taken, especially focussing on primary and secondary cardiovascular prevention (statins, aspirin, ACE inhibitors).

5. Is the patient a smoker?

6. Is their weight changing? Are they overweight?

7. How is their general health?

8. For all women of child bearing age, advice on pre-pregnancy measures is necessary and a discussion of use of effective contraception and avoidance of unplanned pregnancy.

9. An opportunity for the patient to discuss specific problems and concerns.

10. For male patients: Erectile dysfunction should be discussed.

What physical examination should be performed?

As a minimum this should always include physical examination of feet (foot pulses, two-modality sensory screening including 10 g monofilament and vibration sensation), blood pressure, injection sites and retinal screening (ideally by digital retinal photography scored by an ophthalmologist or accredited retinal grader).

What biochemical investigations should be performed?

Biochemical assessment of HbA1c, ACR, renal function and fasting lipids including cholesterol and triglycerides should be undertaken.

What else?

 Patients should also be offered a review by a diabetes nurse specialist and dietician. 

What are 'correction doses'? 

A correction dose is a dose of insulin given when the patient feels their blood glucose is too high and they want to give a bolus of soluble insulin to bring it back to 'target'. A typical target value might be 8 mmol/L.

The correction factor is calculated using the 'hundred rule'. This works by dividing the patient's total daily of insulin in to 100. Thus, a patient taking 50 units of insulin per day will have a correction factor of two i.e. one unit of soluble insulin will bring their blood glucose down by 2 mmol/L.

For example, if their random blood glucose is 18 mmol/L, they want to bring it down by 10 mmol/L and thus they will need to give five units of soluble insulin.

However, we often discourage patients from using too many correction doses, preferring that they focus on getting the dose of basal insulin right for them. Ideally this should be by dose-adjustment with meals (e.g. by carbohydrate counting).

Structured education

What is structured education?

Standard 3 of the NSF states that all people with diabetes will receive a service that encourages partnership and decision-making, supports them in managing their diabetes and helps them to adopt and maintain a healthy lifestyle.

Structured education is one of the key interventions needed to achieve Standard 3. There are several structured education systems available. 

What structured education systems are available?

DAFNE (Dose adjusted for normal eating) is a system for adjusting insulin doses based on food intake and prevailing blood glucose concentrations.

It is not suitable for all patients as it requires the patient to perform several blood glucose measurements each day and requires a high degree of commitment from the patient to assiduously testing, adjusting and recording.

The system is taught on a five day long non-residential course where trained DAFNE educators work (and eat!) with the patients intensively all week long. The basic principles of DAFNE involve the patient first discovering what their basal insulin requirement is by achieving stable blood sugars across the night and across a carbohydrate-free meal time. They next learn carbohydrate counting - a system of estimating carbohydrate content of common food stuffs - and then calculate the required ratio of units of fast acting insulin to carbohydrate content which can be different for each meal.

There is also a system for correction doses of insulin for unexpectedly high blood sugar readings.

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