Liver function tests measure a series of chemicals which relate to the way the liver works. They include substances that are made in the liver or affected by the health of the liver cells, chemicals which are processed or excreted by the liver, and hormones that the liver makes in order to do its work. Show
Liver function tests are aimed at giving a picture of the 'state' of your liver. They are a sensitive way of looking for liver strain or liver damage, as they often show this well before you get any symptoms or problems with your liver. This means that the cause of liver strain or damage can be diagnosed and, often, reversed. Liver function tests are also used for monitoring in cases of known liver inflammation, injury or disease. The liver is your largest internal organ. It sits in the tummy (abdomen), under your diaphragm on the right-hand side. It is usually tucked under the ribs, which protect it, although in some people the edge of the liver protrudes slightly. If the liver is swollen, through inflammation or disease, it can swell out from under the ribs and make your tummy swollen. The liver is a factory for the production and breakdown of carbohydrates, fats, proteins, hormones and other essential body chemicals, and helps dispose of waste products. This work is mainly carried out by liver cells (hepatocytes). Some of the most important functions include: Production of these substances
Breakdown of these substances
Storage of these (and other) substances
The usual liver function tests typically include the following:
Each of these is discussed below. The liver performs hundreds of different functions, so there are many other possible tests that look at its health. These would normally be done if an abnormality is found with the basic liver function tests described here, or if a specific problem is suspected. They might include:
What can cause your liver function tests to be abnormal?Your liver function tests can be abnormal because:
What does the 'normal range' mean in liver function tests?The 'normal range' is a range of values given by the local laboratory for liver function tests. The range varies slightly between laboratories according to the measurement methods that they use. The 'normal' limits are defined by laboratories as the range of levels inside which 19 of every 20 people with healthy livers will fall. This means that, for any one liver function test, around 1 in 20 people with healthy livers will have a result that is slightly abnormal. There will, in the majority of cases, be nothing wrong with their liver; having a liver function test that's just over the edge usually means nothing, as long as - crucially - there is only one slight abnormality out of the whole range of tests. You should always discuss even a slightly abnormal result with your doctor. It is important to remember that having normal liver function test results doesn't mean you aren't at risk of liver problems. For instance, if you are involved in harmful behaviour, such as drinking excess alcohol, you could have normal liver function test results but still be putting your liver under strain. You are likely to find out that your liver function tests are abnormal from your healthcare provider, who will tell you what you need to do next. However, if you obtain your liver function test results without explanation, you should contact your healthcare provider to discuss them. Doctors consider a slightly abnormal liver function test as one that is less than twice the upper limit of the 'normal' value. Doctors consider a very abnormal liver function test as one that is more than two or three the upper limit of the 'normal' value. Your doctor is also likely to be looking at the rate of change of your liver function tests - if a test has increased very rapidly, it may be of more concern even though it is not that high.
What will my doctor do if I have abnormal liver function tests?All abnormal liver function tests need explanation, even if that explanation is that you are one of the 5% who fall outside the 'normal' range. In many cases, a single, isolated, slightly abnormal liver function test in a well patient will not signify an underlying problem. However, some liver disorders, including early signs of overuse of alcohol, can produce slight changes (especially at first), so it's important to be sure. Your doctor will want to do further liver tests and to see, question and examine you, to determine the reason for the blood test abnormality. If you are otherwise well, this will initially be done in primary care. Options include:
Can my doctor make a diagnosis from my liver function test?Sometimes. Single abnormalities in the liver function tests do not give diagnoses on their own but the pattern of abnormalities can point to the most likely cause of the problem. When this is combined with speaking to and examining you, your doctor may be able to make a clear diagnosis. Once the cause of the abnormality has been determined, your doctor will discuss what you need to do next. What do unusually low levels on my liver function tests mean?Note that in most cases (except albumin and calcium) it is a raised (rather than a lowered) level in the liver function test which may indicate a problem. In the following descriptions, where low levels can be significant for your health they are also described. Bilirubin comes from the breakdown of red blood cells in the body. The liver processes (conjugates) bilirubin so that it can be excreted via the kidneys. A high bilirubin level can make you appear jaundiced (with a yellow tinge to the skin and to the whites of the eyes). The most likely cause of raised bilirubin depends on whether the rise is in bilirubin that the liver has already processed (conjugated bilirubin), in the bilirubin that the liver has not yet processed (unconjugated bilirubin), or in both. A rise in both types of bilirubinConjugated bilirubin tends to rise if the flow of bile in the tiny tubes within the liver is blocked, and unconjugated bilirubin tends to rise if the liver calls cannot do their work (or there is too much work for them to do). If the liver is both damaged (not working properly) and swollen or scarred (blocking the drainage system) then both types of bilirubin will tend to rise. An isolated rise in unconjugated bilirubinUnconjugated bilirubin may increase because the liver can't process the bilirubin, or because the body is making an excess of bilirubin by breaking down too many blood cells, and the liver is normal but can't keep up. Increased conjugated bilirubin suggests that the liver is conjugating the bilirubin properly (the job of liver cells) but not excreting it properly via the bile ducts. Causes include:
Albumin is the main protein in your serum, and its level is a good guide to long-term liver health. Albumin levels that are abnormally low have the greatest significance for the liver. Low levels of albuminThis can be due to:
High levels of albuminThis is usually due to having the tourniquet on for too long before your blood sample is taken. Sometimes it can be due to a very high-protein diet, as in bodybuilders, or to lack of fluid in the body (dehydration), when the blood is more concentrated. Total protein measures the total of albumin and globulins. It is usually normal in liver disease even if albumin levels are low, as globulin levels tend to increase as albumin levels fall.
These substances are also called transferases. They are liver hormones (proteins which help do the work of the liver) which are normally found inside liver cells rather than in the blood.
If blood levels of transaminases go up this suggests leakage from damaged liver cells due to inflammation or cell death. AST and ALT tend to be high in liver disease and very high in liver inflammation.
Causes of mild rises in transferasesThese include: Causes of marked increases in transferasesMarked increases are usually caused by acute injury to the liver by viruses, shortage of oxygen (ischaemia) or toxic substances. Causes include: Gamma-glutamyl transferase (GGT) levels increase in most liver diseases. This liver function test is very sensitive, although it also goes up in some heart, lung and kidney conditions.
Alkaline phosphatase (ALP) comes mainly from the cells lining bile ducts and from bones - particularly growing bones. It rises if there is slow or blocked flow in the bile ducts, if the bile ducts are damaged and in bone disorders. If the cause is in the liver, the GGT is also abnormal, whereas if it's the bone, the GGT is usually normal. ALP is also raised during the third trimester of pregnancy. Common causes of raised ALP with other abnormalities on your liver function tests include: Isolated raised ALP can occur in: 99% of the body's calcium is stored in the bones, with the remaining 1% stored in other tissues, including the blood plasma. The calcium test measures the total calcium in the blood plasma. About half of this is tightly attached to the protein, albumin, which forms the bulk of the protein in your plasma. The calcium level that really counts is the 'free', or unbound, calcium that floats unattached in the plasma. If you have low albumin levels, the total calcium in your blood will be lower. However, because the amount attached to the albumin is reduced (because there is less albumin), the actual free levels of calcium may be normal (or even raised). Corrected calcium corrects the figure to give the actual, free amount of calcium. Causes of low (corrected) calcium levelsCalcium levels are regulated by the kidney, thyroid and parathyroid glands, using the hormones parathyroid hormone, calcitonin and vitamin D. Low levels are uncommon. Causes include:
Causes of raised (corrected) calcium levels
Rarer causes of hypercalcaemia (raised calcium levels) include:
Prothrombin time (PT) or International Normalised Ratio (INR) are sometimes measured as a part of standard liver function tests. PT and INR are ways of measuring the ability of your blood to clot. Conditions which impair this clotting (prolonging the PT and increasing the INR) include:
There is a difference between what you need to do to keep your liver healthy most of the time and what you need to do if your liver is inflamed or damaged.
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