What is cytology and how is this test utilized in the clinic?

Cytology is the examination of cells (from fluid, blood, bone marrow, or tissue) under the microscope, and can help provide essential information about various disease processes.  It is most often utilized to further characterize a mass or enlarged lymph nodes, but can also be used to evaluate abnormalities suspected on the skin or in the blood, bone marrow, body fluids (such as abnormal accumulation of fluid in the chest or abdominal cavity), or lesions detected by imaging associated with internal organs.  It is important to note that cytology does not evaluate tissue architecture, which can only be done through histopathology from a biopsy sample (ie taking a piece of tissue, not just cells acquired from a fluid suspension or fine needle aspiration of tissue).  Cytology is very useful in that it can detect inflammation, infectious agents (eg bacteria, fungi, parasites), and cancer.  It can often help your veterinarian obtain a definitive diagnosis, and is usually a good first step in the diagnostic cascade; however, this test is not 100% sensitive or specific, and evaluation of a biopsy sample may be necessary in certain situations. 

How is cytology obtained?

Samples can be acquired by using a very small needle (with or without a syringe depending on what is being evaluated), aspirating cells, and spreading them on a slide for review under a microscope.  For fluids (such as blood, urine, cerebrospinal fluid, or effusions in the chest or abdomen), samples are usually centrifuged to concentrate cells at the bottom of a tube, which can then be aspirated and spread on a slide.  Other ways to obtain a sample include impression smears (gently pressing a glass slide onto the region of interest), skin scraping (gently scraping the skin with a scalpel blade), or using a cottons swab if the lesion is moist.  Once the sample is spread on glass slides, the slides are stained with special dyes, are left to dry for 5 minutes, and are then ready for evaluation under a microscope.

Is cytology safe?

This procedure is very safe and causes minimal to no discomfort.  In most cases, cytology can be done with the patient awake and no medications, although aspiration of internal organs, body cavity fluids, or bone marrow sometimes requires sedation/light anesthesia. Side effects include bleeding (usually self-limiting), mild bruising, or short-term limping (if bone or bone marrow is aspirated); however, this is very uncommon.  

How long does cytology take?

The process of aspirating a mass or collecting fluid usually takes less than 10 minutes, although spinning down fluids and staining slides may add an extra 10-20 minutes.  In some situations the attending clinician has enough experience to evaluate the slides himself; however, most veterinarians will send them to a board certified veterinary clinical pathologist for evaluation. It usually takes 1-4 days to get a final report when slides are sent out to a diagnostic laboratory.  

Why is cytology important for cancer patients?

Cytology can be an easy and inexpensive way to gain more information about a lesion on a patient.  In some cases (particularly in patients with suspected cancer), it can help determine if a mass or other lesion is benign or malignant; in other instances, cytology will help the clinician decide if further diagnostics and/or treatment is indicated. In addition, cytology is commonly performed on regional lymph nodes or abnormalities detected in internal organs to rule in/out the presence of metastatic disease (spread of cancer to other areas of the body).