What Is Cytology?
Technically speaking, cytology is the study of individual normal cells, but it is always used in conjunction with cytopathology, which is the study of diseased cells. The human body is born with a single cell; it then divides and differentiates into tissues, organs, organ systems, and then an entire human being.
Most diseases start at the cellular level; these can be sampled and observed under a microscope to diagnose different medical conditions. Different areas of medicine use cytology for diagnostic purposes, but the most common branch is oncology (study of cancer).
What Are the Uses of Cytology?
The ultimate objectives of cytology are given below-
a. Definitive Diagnosis- Patient’s all over the world dream of healthcare where one diagnostic test gives them the reason for their suffering. Science is at a point now where different cytological examinations from different organs give sufficient evidence for an absolute diagnosis.
b. Screening Tool- Papanicolaou smears, most popularly known as pap smears, since their invention in the early 1900s, have drastically reduced cervical cancer deaths due to early screening.
c. Follow-Up for Different Diseases- Samples from affected organs are frequently collected and observed for follow-up after initial diagnosis. For example, sputum, bronchoalveolar lavage (sample from the lungs), and bronchial brushings have been used as a follow-up for patients with previous pulmonary carcinoma.
d. Establish Prognostic Factors- Cytological samples are often used in ancillary studies to determine prognostic markers (tools to assess remission and progression). For example, HER-2/Neu is a protein involved in normal cell growth; cancer cells produce this protein in large quantities for them to grow quickly. Analyzing HER-2/ Neu helps to predict the outcome of respective cancer.
Where Is the Difference Between a Pap Smear and a Fine Needle Aspiration Cytology?
Depending on the location and the device used to collect the sample, cytology can be differentiated into two types-
a. Exfoliative Cytology- The sample is taken from superficial or deep serosal or mucosal surfaces. It is further divided into-
Gynecologic Cytology- Pap smear is the gold standard for cervical cancer screening, also used to check inflammation and infections. There are two acceptable ways of collecting the pap smear- liquid-based and conventional. Both of them collect with a brush using a speculum, but the former uses a liquid preservative, whereas the latter fixes the cells on the slide with a preservative. The liquid-based technique allows for testing human papillomavirus, gonorrhea, and chlamydia and is easy to interpret.
Urinary Cytology- A urine cytology test is recommended when there is blood in the urine. An innovation called fluorescent in situ hybridization (FISH) uses cytological urine samples to detect abnormal chromosomal aberrations.
Respiratory Cytology- Commonly used to test for lung cancer and infections. The samples can be obtained by sputum, bronchoalveolar lavage, and bronchial washing.
Body Fluid Cytology- Typical samples include pericardial fluid (serous fluid surrounding the heart), cerebrospinal fluid (fluid surrounding the brain and spinal cord), and peritoneal fluid (fluid surrounding the abdominal cavity), mainly done to check for malignancies and infections.
Gastrointestinal Tract Cytology- Usually done during an endoscopy, the lining of the gastrointestinal tract is brushed to check for viral, bacterial infections, and neoplasms.
Discharge Cytology- As the name suggests, discharge from different body parts is sampled to check for cancer; a common example is breast nipple discharge.
Scrape Cytology- This is a simple technique and can be done by the clinician. Skin and mucosa are scraped to check for cancer and infections.
b. Aspiration Cytology- Commonly known as fine-needle aspiration cytology (FNAC), uses a syringe (with or without a syringe) to collect cellular material from lesions for diagnosis. It is always performed by a pathologist and is of two types based on the type of lesion-
Palpable Lesion- Lesions in this category can be actually touched and felt by the pathologist. After anesthetizing, a 21-25 French gauge needle is inserted and aspirated (withdrawn) till sufficient diagnostic cells are collected.
Non-palpable Lesion- The non-palpable lesions are aspirated with image analysis. The procedure is done with the guidance of a CT (computed tomography) scan, ultrasound, endoscopy, and fluoroscopy.
What Is a Cytology Report?
After any one of the above-mentioned procedures is done, the cellular sample is studied, and resulting observations are recorded. It is important that it expresses important components like the following-
a. Adequacy- It is important that the statement mentions the adequacy of the sample; an inadequate sample leads to re-investigation. It is paramount that a pathologist collects the sample to avoid repetition.
b. General Categorization of the Diagnosis- Although a specific diagnosis is desired, often not all diagnostic criteria are present, so a broad interpretation is given in this section. For example, a pap smear may mention “positive for malignant cells” instead of “squamous cell carcinoma of the cervix.”
c. Descriptive Diagnosis- This is more helpful for the clinician to plan the next step in the diagnosis as it is in detail. For example, for the same pap smear test mentioned above, a descriptive diagnosis will say, “high grade squamous intraepithelial lesion encompassing severe dysplasia.” In this case, the clinician will ask for a colonoscopy for further investigation.
What Are the Advantages of Using Cytology?
Compared to core biopsy (tissue sample), cytological samples taken through aspiration and exfoliation have plenty of advantages. Some of them are-
What Are False Positives and False Negatives?
Despite efforts to be accurate, sometimes the results may be wrong, resulting in false positives and false negatives.
False Positives- The test result will indicate a positive for the disease when the person does not have it. It may happen due to pregnancy (commonly increases cell size in pap smears), contamination of the sample, or hemorrhage.
False Negatives- The test result will indicate a negative for the disease when the person actually has the condition. Usually seen in desmoplasia- where certain carcinomas like a mammary, pancreatic, and biliary tree induce fibers around the tumor, misdirecting the result. It is also seen in well-differentiated tumor cells, which mimic the normal cells, like thyroid follicular carcinoma.
With recent improvements in technology, the old gold standard of tissue biopsy is rapidly changing. Teamwork and communication between the pathologist and the clinician help serve the patient better. With the aid of recently established guidelines for diagnostic utilization of cytological materials, a patient’s dream of getting a definitive diagnosis with one test will become a reality.
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