What causes gout?

Uric acid is one of the many chemicals floating around in our bloodstream. Chemicals called purines are present in all us and in many foods, and are constantly being broken down by the body; one waste product is uric acid.

Crucially, the last step involved in the production of uric acid involves a chemical called xanthine oxidase. The relevance of this will become apparent when we discuss treatment.

All animals produce uric acid; birds get rid of it as the white stuff in bird faeces. Most mammals can convert it into something which dissolves very readily in urine. The problem for man (and some apes) is that this ability to convert it into something very soluble was lost somewhere in evolution.
As a result, if the concentration in the blood rises too high, it will not dissolve and tends to form crystals like salt crystals. Perhaps fortunately, it does not tend to form crystals in the bloodstream itself, but builds up deposits in the lining (‘synovium’) of joints.

This may never cause any problems, but if the uric acid level in the blood is high for many years, the deposits build up to critical levels and can then break down, often for no apparent reason, and the crystals leave the lining and enter the joint itself. Joints are generally very sensitive to having anything unusual in them and the uric acid crystals are recognized as something which should not be there. The joint reacts to them rather as they would to a germ or bug, and send in lots of extra cells and chemicals to try and destroy the crystals. It is this reaction which causes the swelling, warmth, redness, tenderness and pain, and which together comprise inflammation. The inflammation is thus a normal and healthy reaction to the crystals in the joint, and it is very effective at dealing with them. This is why the inflammation settles down over 7 to 10 days.

In many cases, nothing further will happen, but the underlying problem persists, namely high levels of uric acid in the blood, building up in the lining of joint, and the attack could recur at any time.

Why is the level of uric acid too high?

There are many factors which influence the level of uric acid in the blood. Rather like someone’s height, in most cases the average level is set by genes and there is little that can be done about it.
However, variations in the level around the average are influenced by diet, alcohol consumption (and type of alcohol), medication, obesity and illness. Where a secondary cause of a high uric acid level can be identified it can be classified as causing overproduction of uric acid, or under excretion, both of which will cause the uric acid level in the blood to rise.

Why do attacks happen when they do?

This is very poorly understood. Attacks often appear to have no clear precipitant, but sudden changes in the level of uric acid in the blood, up or down (e.g. caused by eating certain foods, alcoholic binges, crash diets, a new medication), can precipitate an attack. They often follow trauma, surgery, starvation or dehydration.