Having learnt last week what an amazing organ the liver is, the kind of conditions that can cause damage to it and the clinical signs you’d expect to see with liver problems; we now continue with the topic by thinking about diagnosis.
The first type of diagnostic test normally done is a blood test. It’s really important to understand that there are two types of liver blood tests and they tell us very different things. The initial screening test is looking at the liver enzymes and is often carried within the laboratory at your own vets. It is usually included in pre-anaesthetic and more comprehensive blood screening profiles they will offer. Elevated results of these enzymes tell us that liver cell damage is occurring at that point and the higher the results the greater the number of cells being damaged. However, these results tell us nothing about the liver function or whether the liver is failing.
If raised enzymes are picked up the second type of blood test, a liver function test is likely to be suggested. This involves getting a blood sample after your pet has been fasted (often not needed in cats), feeding them a meal (normally more fatty than normal) and then collecting another bloods sample a particular number of hours after the meal. How the liver responds to the food is measured by looking at the bile acids. These tests give an indication of how well the liver is functioning on a daily basis rather than just a snap shot of the damage occurring at that moment, which is much more useful when thinking about further testing and the prognosis.
To put it into perspective, in theory an animal may have very high liver enzymes one day after reacting to a poison it has come in contact with but the overall liver function be fine, and, given the correct treatment, the liver could fully recover. In contrast, another animal could hypothetically come back with normal liver enzymes but has actually, over a prolonged period, been suffering liver damage and now be in liver failure and unable to recover, which only the second test would pick up. In reality with this second example you would expect the enzymes to be at least slightly raised, but it emphasises how both tests are useful but at telling us different things.
Sometimes additional blood and urine tests are run in addition to specific liver ones, especially if a liver biopsy may end up being advised. As mentioned last week the liver produces the factors in our blood that help it to clot so if they are depleted the biopsy could cause internal bleeding.
Visualising the liver is the next step to working out what is happening. This involves X-rays, which show the general size and position of the liver, and ultrasound which can give detail as to the structure of the liver tissue itself and help pick up any shunts (abnormal bloods movement). Both imaging methods may highlight any gall bladder stones, fluid in the abdomen or show up a mass on the liver as well.
After these tests your vet may be fairly confident as to what is causing the problem but generally the only way of getting a definitive diagnosis is by taking a biopsy.
Next week we finish this series of articles on liver disease by discussing the pros and cons of biopsying and the treatment options available.