A smear refers to the collection of a few cell samples for cytodiagnostic examination. To do this, the doctor uses small spatulas, brushes, or swabs. A smear can be performed quickly and is relatively painless for the patient. The procedure is also relatively simple and does not involve high costs.
Cytological smears are used, for example, in gynecology as a routine measure for early cancer detection.
The “Pap smear,” for example, is a well-known procedure covered by health insurance and a routine measure. During the procedure, the gynecologist collects cell samples from the cervix and the cervical canal. The material is then examined under a microscope for abnormalities. This allows for the diagnosis of abnormally developed cells or infections.
Another type of cytological smear is the so-called bronchoscopic smear. In this procedure, the doctor uses an endoscope to collect cell samples from the bronchi. Based on abnormal cells, the examination can indicate, for example, the presence of bronchial carcinoma.
The swab taken from the oral mucosa for DNA analysis is also used in criminology. In this procedure, cells are collected from the inside of the oral cavity using a sterile swab. Genetic information (DNA) is extracted from these cells. It can then be used, for example, for
- paternity testing,
- creating a genetic fingerprint, or
- genetic typing
.
A doctor performs a throat swab. Racle Fotodesign | AdobeStock
The microbiological swab specifically collects material from sites of infection. It is frequently used, for example,
- in the throat (for purulent inflammations of the throat or tonsils),
- on wounds that are slow to heal,
- on the eye,
- in the urethra, and
- in the vagina.
A swab test can be used to diagnose the specific type of bacteria or fungus present. The swab and the resulting analysis serve to identify the exact cause of the infection.
This identification of the pathogen forms the basis for initiating rapid and effective treatment of the patient.
Various procedures are used to make a diagnosis.
If a bacterial or fungal infection is suspected, the sample from the swab is applied to a culture medium. Once an infection is confirmed, the cells are used to grow a fungal or bacterial culture in the laboratory. This allows the exact pathogen to be identified. Identifying the pathogen then allows for the selection of an appropriate medication to treat the infection.
In the case of a cytological smear, the primary focus is on diagnosing abnormal cells. To do this, the smear is spread onto a glass slide (microscope slide) immediately after collection. A chemical solution fixes the sample.
Next, the specimen is chemically stained. This makes the cells and any possible cellular changes visible under the microscope for an initial diagnosis.
For certain purposes, smears are also collected that are not further processed but examined fresh. These smears are then referred to as native preparations. The doctor examines them directly under the microscope to make a diagnosis.
Such unstained specimens may include, for example, smears from bodily fluids or secretions.
No significant complications usually occur during the collection of smears. Only with gynecological smears taken from the cervix may slight spotting occur. However, this is generally harmless. The spotting should stop shortly after the smear is collected.
In addition, there is a possibility that the cells collected may not be sufficient for a diagnosis. In rare cases, the processing of the sample in the laboratory may also fail.
In such cases, a repeat smear may be necessary.
Smears are
- based on the specific object of examination or diagnosis (cells, DNA, or pathogens) or
- by the site of collection
.
In gynecology, the smear test is used particularly frequently as a diagnostic tool. For women aged 20 and older, a Pap smear is recommended once a year for cancer screening. The cellular material collected from the cervix and the cervical canal is used to diagnose abnormal cells. These may indicate precancerous changes, such as those leading to cervical cancer.
If the diagnosis of abnormal cells is confirmed by a Pap smear, a colposcopy may be performed. This procedure uses a special microscope (called a colposcope). It allows abnormal cells to be visualized and examined directly at the cervix. A smear can also be taken.
The colposcopic smear is obtained by swabbing the surface of the mucous membrane. The gynecologist uses a spatula or cotton swab for this purpose.
A cheek swab consists of cells from the oral mucosa on the inside of the cheeks. This swab is collected using a sterile swab or brush. DNA can be extracted from these cells. It is used for diagnosis or further testing.
The urethral swab is usually performed to diagnose an infection. To do this, a thin, sterile cotton swab is inserted into the urethra, rotated, and then withdrawn.
If a man is being tested for pathogens from the prostate, the prostate is massaged beforehand. This helps to collect secretions from the gland.
In general, a urethral swab should be taken no sooner than three hours after the last urination. The area around the urethral opening must be carefully cleaned beforehand. This prevents contamination of the sample by other pathogens from the urine.
A throat swab is used to establish a definitive diagnosis when various diseases are suspected. These include, for example,
- tonsillitis,
- scarlet fever,
- whooping cough,
- diphtheria,
- gonorrhea, or
- fungal infections.
To perform the test, the doctor presses down on the tongue with a spatula while the patient’s mouth is open. Then, applying light pressure, the doctor swabs the relevant areas with a cotton swab. If there is a coating present, the sample should be taken from beneath it, if possible, for diagnostic purposes. When removing the swab, care must be taken to avoid touching the oral mucosa.
The swab containing the specimen is then placed in a transport medium, which is usually a liquid. It should be examined in the laboratory within the next 24 hours to enable a reliable diagnosis.
A wound swab is used to diagnose pathogens colonizing the surface of wounds. A swab is rolled over the affected wound without applying excessive pressure. This usually causes wound exudate to be released. The wound secretion is examined in the laboratory, and the pathogens are identified.
In addition to the superficial wound swab, there is also what is known as an intraoperative wound swab. In this procedure, the swab is taken from deep within the affected tissue during a surgical procedure.
Performing a wound swab © Racle Fotodesign | AdobeStock
In many cases, the bronchoscopic swab is used to diagnose
The patient is anesthetized for the procedure. A bronchoscope—a special type of endoscope—is used. It is inserted through the mouth or nose and advanced to the large or medium-sized bronchi. The sample for the swab and further diagnosis can then be collected.
In general, the smear is a quick, simple, and relatively reliable tool for an initial diagnosis. Nevertheless, uncertainties do exist regarding the various types and applications of smears. Great care is therefore required when taking a swab. In particular, it is important not to contaminate the sample and to collect sufficient material.
Often, a single swab is not sufficient to make a definitive diagnosis. This depends, among other things, on the disease and the affected organ. In such cases, further diagnostic tests are necessary.
Problems with Microbiological Swabs
The biggest problem with a microbiological smear is potential contamination of the smear sample. Bacteria or fungi that are not actually involved in the infection may have entered the sample.
These can enter the sample, for example, due to carelessness during the swab collection process. They can lead to a false diagnosis. In this case, effective and targeted treatment cannot be provided.
A false diagnosis can occur, for example, with a wound swab if
- it is not taken from the center of the wound
- or does not contain enough wound secretion.
An incorrect diagnosis can also result from improper technique during sample collection in the case of a urethral swab. Before taking the swab, the area around the urethral opening must be thoroughly cleaned. The patient must not urinate for 3 hours prior to the swab.
Even with the very commonly performed throat swab, a false or unclear diagnosis can occur. For example, the doctor may be unable to collect the sample from beneath existing deposits in the throat. Instead of the actual pathogens, components of these deposits—such as white blood cells or metabolic waste products from the infectious bacteria or fungi—could end up in the sample.
Problems with Cytological Smears
Problems can arise with cytological smears if the smear contains too little cellular material. This may be due, for example, to an incorrect or imprecise technique used by the doctor to collect the cellular material.
In some cases, the fixation or staining of the collected cells may also not work properly. In such cases, the cells to be examined may not be clearly visible under the microscope. This makes it difficult to reach a clear diagnosis.
In such cases, a repeat smear is necessary.
