Tissue tests are the examination of tissue samples under a microscope to diagnose or assess the severity of a condition.
Some disorders disrupt the proportion of different types of cells within an organ or cause the individual cells to look abnormal. These changes can be detected by tissue tests, in which small samples of tissue are examined under a microscope. Such tests may enable doctors to make a diagnosis or to assess the severity of a disorder.
Why am I having tissue tests?
Your doctor may arrange for a tissue test if other tests have not established a diagnosis. Tissue tests are often used to distinguish between certain disorders that have similar symptoms, such as the inflammatory bowel conditions ulcerative colitis and Crohn's disease. Tests on a small sample of the inflamed colon may be able to distinguish between the two conditions.
In addition to confirming a diagnosis, tissue tests may also be used to look for a cause. For example, a tissue test on a sample of liver tissue may confirm a diagnosis of cirrhosis, in which fibrous tissue develops, and suggest possible causes.
A tissue test may also be performed to determine the extent of a disease once a diagnosis has been made. For example, if you have had an area of skin removed to treat a cancerous tumour, a tissue test may show whether the edges of the removed skin are free of abnormal cells, indicating that the entire tumour has been removed, or if cancerous cells have reached the edges of the removed tissue, suggesting that the tumour has spread beyond the margins of the sample.
Finally, tissue tests may help your doctor to decide on the most appropriate treatment. For example, if a tissue test shows that cancer has spread from the original site of the tumour, more extensive treatment may be needed.
How are tissue tests done?
Samples of tissue are often obtained by a biopsy. During this procedure, a small piece of tissue is removed specifically to make a diagnosis. In other cases, a tissue sample may have been removed as part of the treatment for a particular disorder. For example, a section of the colon may be removed during treatment for colorectal cancer.
The tissue sample is immersed in a preservative substance such as formalin. The sample is then thinly sliced and stained to highlight the different structures in the tissue. Preparation of the tissue may take several days.
Tissue samples are usually examined under a light microscope, but certain changes may be seen only using a more powerful electron microscope. For example, a sample of kidney tissue taken from a person with nephrotic syndrome may appear normal when viewed under a light microscope, but an electron microscope may reveal abnormalities.
How are the results interpreted?
A pathologist, a doctor who is specially trained to analyse tissue samples, usually examines several slides prepared from a single biopsy sample or from different areas of a surgically removed piece of tissue. He or she looks for the presence of abnormal cells or an abnormal bala nce of cells. The extent to which the tissue is different from healthy tissue indicates the severity of the disease. The slides are usually retained in case they need to be reviewed later.
Will I need further tests?
Tissue tests provide a definitive diagnosis for many conditions in which tissue is damaged. However, further tests may be necessary to determine whether other areas of the body are affected. For example, if tissue tests have confirmed that a growth in your intestine is cancerous, you may have CT scanning or MRI of your liver to look for evidence that the cancer has spread from the intestine to the liver.
Occasionally, you may need to have repeated tissue tests to monitor disease progression or response to treatment. For example, repeated tissue samples may be taken from an organ transplant to detect early signs of rejection.
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