Ketones

Brixham harbour, August 2012

Warning to readers: more of the technical diabetes stuff coming up.

I do try to simplify the descriptions and explanations of what I'm learning about diabetes. Firstly because I want people to be able to understand what I write, and secondly because it's good to practise what I would say when there's a patient in front of me. I want them to be able to understand the information I provide, and it helps to think about it in the writing of this blog.

So this post is about what happens when things don't go quite right with diabetes. 'Ketones' are a by-product of fat metabolism, i.e. when fat rather than carbohydrate is used to generate energy, a state known as 'ketosis'. The main reasons why this would happen are a) if less carbohydrate is eaten than the body needs for fuel, which might be if someone is deliberately trying to lose weight or is on a low-carb diet, or b) if there is a lack of insulin, in which case the blood glucose just can't get into the cells to fuel carbohydrate metabolism. The two types are sometimes respectively called 'starvation ketones' and 'diabetic ketones'.

Starvation ketones don't generally build up to significant levels, and aren't a problem. Diabetic ketones, on the other hand, are an indication that all is not well.

Diabetic ketones arise when there is a deficiency or lack of insulin in relation to blood glucose. The most common scenarios are either when a person with Type 1 diabetes stops injecting insulin for one reason or another, or when they get ill, which tends to result in higher blood glucose levels. If this glucose isn't available to be used for energy - if it can't get out of the bloodstream into the cells due to the lack of insulin - it will hang around in the blood, keeping levels high, and be excreted in the urine, potentially causing dehydration.

Because the body isn't aware that the reason for lack of carbohydrate fuel is that it's all in the blood and not in the cells, this will provoke the breakdown of fat, leading to a rise in blood ketone levels. In people with Type 2 diabetes who are still producing endogenous insulin, the presence of the insulin inhibits fat breakdown, which produces a protective effect, so Type 2's generally don't become ketotic. But their livers will keep chucking more glucose into the blood, not realising that there's plenty there already, keeping blood glucose levels high as can be.

Ketones in excess are damaging to the body because they are acidic, and acidic blood is not a good thing. The body responds to raised ketones by excreting them in the urine, but also via the lungs, which is what causes ketotic diabetics and slimmers on the Atkins diet to have breath that smells of pear drops or nail varnish remover. Historically, ketones were measured in the urine, which gives an indication of ketone levels over the period that the urine has been accumulating in the bladder. It is now more routinely possible to measure blood ketones, which are a more immediate indication of the current situation.

Raised ketones with normal blood glucose suggests starvation ketones - a lack of carbohydrate - and is not immediately worrying. Raised ketones with raised blood glucose is an indication of diabetic ketosis, and depending on the level of ketones, an individual may just monitor the situation, inject extra insulin, or take themselves to the Emergency Department of the nearest hospital. If ketosis has progressed so that the blood is acidic (known as diabetic ketoacidosis or DKA), it is usually necessary to start medical intervention, often with an IV infusion of insulin. If the illness (or the DKA) has caused vomiting and dehydration as well, then glucose and re-hydration will probably be needed too. It's a life-threatening condition if left untreated.

As well as illness, there are potentially many other causes of DKA resulting from disruption to the delivery of insulin: faulty insulin pumps, blocked or kinked cannulas, bubbles in pump tubing, forgetting or neglecting to give injections, hitting 'lipohypertrophy' when injecting so the insulin is poorly absorbed, insulin that is out of date or has been inactivated through heat or cold, being an inpatient or unconscious and not being given insulin, and there are probably more reasons that I haven't immediately called to mind.

In contrast with these unintentional insulin deficiencies, 'diabulimia' is the informal name given to a type of behaviour that involves injecting less insulin than is needed, in order to excrete glucose instead of utilising it, and thereby remaining both slim and constantly on the brink of DKA.

Within all the education and empowerment and interaction we have with diabetic patients, especially those with Type 1 diabetes, 'Never Stop Taking Insulin' is probably the most important central message that we offer.