Question: Dr. Utchen My 12-year old cat has been losing weight and not eating very well for a while. The vet did some blood tests, and says my cat needs a liver biopsy. Don’t the blood tests tell us what we need to know?
Blood tests tell us which organ in the body is diseased. Sometimes this is all that is needed in order to proceed in treating a patient, but often a tissue sample of that organ is needed in order to determine precisely what is causing that organ to malfunction.
For example, sometimes there is an infection present. Other times, the organ has gotten old and is simply starting to fail due to age. Sometimes poisons have entered the system and caused damage. And sometimes one form or another of cancer has begun. In order to know how to repair things, we have to know specifically what is going on in an organ, and in some cases blood tests don’t tell us that piece of information. That’s when the issue of performing a biopsy comes up.
The best biopsy samples are obtained by doing open abdominal surgery--you can see the organ in question, check it all over, get a sizable piece of tissue from any area of the organ that looks suspect, and make sure there is no bleeding. This is also the most aggressive method of biopsying any internal organ. The trade off is that it is a bigger procedure for a dog or cat to go through than the following methods of obtaining a biopsy.
At our office we do many organ biopsies laparoscopically. This is a procedure identical to that in humans, where two small entry holes are made through the abdominal muscles and a small fiberoptic scope is used to visualize the internal organs. This allows inspection of the internal organs and helps us biopsy the right spot on an organ.
A liver biopsy can also be done using ultrasound and a rather large needle (about the size of the lead inside a pencil) called a Tru-Cut Biopsy Needle. In this procedure, there is no incision made into the abdomen. Instead, with a dog or cat under general anesthesia, the needle is inserted with aid of ultrasound to “see” the internal organs. This is easier on a dog or cat than either of the two procedures mentioned above. However, this has been shown to sometimes miss the problem due to small sample size, and the inability to visually inspect an organ before obtaining the sample and therefore possibly just biopsying a normal spot on an otherwise abnormal organ. You always go for any area of an organ that looks abnormal on ultrasound, but ultrasound images are still not as good as looking right at it during surgery.
Lastly, a fine needle aspirate could be done of the liver. For this we just use a regular syringe and a hypodermic needle. This takes only a moment--no sedation or anesthesia required. It's about like having a blood sample taken. However, all that is obtained is a few cells inside the needle, which you then squirt out onto a microscope slide and examine under a microscope. Overall, this is a very minimal sample, much less than the previous Tru-Cut method I mentioned, and has a higher likelihood of a false negative report--again due to small sample size and an inability to visually inspect an organ before obtaining the sample. Nonetheless, this is often worth doing because it is simple to do and does not require anesthesia, and if a definite result is obtained, then it is as good as having done the more invasive procedures mentioned above.
When it comes to invasive procedures like liver biopsies, it is good to know all the options. Best of luck with your kitty.