A smear test refers to the taking of several cell samples for cytodiagnostic examination. The doctor uses small spatulas, brushes or swabs for this purpose. A smear test can be carried out quickly and is relatively painless for the patient. The procedure is also relatively simple and does not involve high costs.
Cytological smears are used in gynecology, for example, as a routine measure for the early detection of cancer.
The "Pap smear", for example, is a well-known health insurance benefit and routine measure. The gynecologist takes cell material from the cervix and the cervical canal. The material is then examined microscopically for changes. This enables the diagnosis of abnormally developed cells or infections.
Another cytological smear test is the so-called bronchoscopic smear test. Here, the doctor takes cell material from the bronchi using an endoscope. The examination provides information on the presence of a bronchial carcinoma, for example, based on altered cells.
The swab from the oral mucosa for DNA analysis is also used in criminology. Cells are taken from the inside of the oral cavity using a sterile swab. The genetic information (DNA) is extracted from these cells. They can then be used, for example, for
- parentage reports,
- creating a genetic fingerprint or
- typing
be used.
Doctor taking a throat swab Racle Fotodesign | AdobeStock
The microbiological swab contains specific material from sources of infection. It is frequently used, for example
- in the throat (for purulent inflammation of the throat or tonsils),
- on poorly healing wounds,
- the eye,
- in the urethra and
- the vagina.
The swab can be used to diagnose the respective type of bacteria or fungi. The smear and the examination serve to identify the exact cause of the disease.
This determination of the pathogen forms the basis for initiating rapid and effective treatment of the patient.
Various methods are used to make a diagnosis.
If an infection with bacteria or fungi is suspected, the sample from the swab is applied to a culture medium. Once an infection has been detected, the cells are used to cultivate a fungal or bacterial culture in the laboratory. This allows the exact pathogen to be identified. The diagnosis of the pathogen then makes it possible to select a suitable medication to treat the infection.
A cytological smear test is primarily concerned with the diagnosis of altered cells. For this purpose, the smear is spread on a glass plate (slide) immediately after collection. A chemical solution fixes the sample.
Next, the specimen is chemically stained. This makes the cells and possible cell changes visible under the microscope for an initial diagnosis.
For certain purposes, smears are also taken, which are not processed further and are directly examined fresh. These smears are then also referred to as native preparations. The doctor examines them directly under the microscope to make a diagnosis.
Such native preparations can be smears from body fluids or secretions, for example.
As a rule, there are no significant complications when taking smears. Only gynecological smears from the cervix can lead to slight spotting. However, this is generally harmless. They should also stop shortly after the smear has been taken.
There is also the possibility that the cells taken may not be sufficient for a diagnosis. The preparation of the material in the laboratory can also fail in rare cases.
In such a case, a new smear test may be necessary.
Smears are
- according to the respective object of examination or diagnosis (cells, DNA or pathogens) or
- according to the sampling site
categorized.
In gynecology , the smear test is used particularly frequently as a diagnostic tool. Women over the age of 20 are required to have a Pap smear once a year for cancer screening. The cell material from the cervix and cervical canal is used to diagnose altered cells. These can indicate precancerous stages of cervical cancer, for example.
If this diagnosis of altered cells is confirmed by a Pap smear, a colposcopy can be performed. This involves the use of a special microscope (known as a colposcope). This allows altered cells to be visualized and examined directly on the cervix or neck of the womb. A smear test is also possible.
The colonoscopic smear is taken by wiping the surface of the mucous membrane. The gynecologist uses a spatula or cotton swab for this.
Thebuccal swab consists of body cells from the oral mucosa on the inside of the cheeks. This swab is taken with a sterile swab or brush. The DNA of the person in question can be extracted from the cells. It is used for a corresponding diagnosis or further examination procedures.
The swab from the urethra (urethal swab) is usually taken to diagnose inflammation. For this purpose, a sterile, thin cotton swab is inserted into the urethra, twisted and withdrawn again.
If pathogens from the prostate are to be diagnosed in men, the prostate is massaged beforehand. This serves to extract secretions from this gland.
In general, a smear from the urethra should be taken no earlier than three hours after the last urination. The area around the urethral orifice must be carefully cleaned beforehand. This prevents contamination of the sample by other pathogens from the urine.
The throat swab is used to make a clear diagnosis if various diseases are suspected. These include
- Tonsillitis,
- scarlet fever,
- whooping cough,
- diphtheria,
- gonorrhea or
- fungal infections.
To carry out the test, the doctor presses the tongue down with a spatula while the mouth is open. He then swipes a cotton swab over the relevant areas with light pressure. If plaque is present, the sample should be taken from underneath it for diagnosis. When pulling out the swab, avoid touching the oral mucosa.
The swab with the swab material is then placed in a transport medium. This is usually a liquid. It should be examined in the laboratory over the next 24 hours in order to make a conclusive diagnosis.
The swab from wounds or wound swab is used to diagnose superficially colonizing pathogens in wounds. A swab is rolled over the affected wound while not applying too much pressure. Wound secretions usually emerge. The wound secretion is examined in the laboratory and the pathogens are identified.
In addition to the superficial swab from wounds, there is also the so-called intraoperative wound swab. In this case, the swab is taken from the depths of the affected tissue during a surgical procedure.
Taking a wound swab © Racle Fotodesign | AdobeStock
In many cases, the bronchoscopic swab is used for the diagnosis of
The patient is anaesthetized for the procedure. A bronchoscope, a special form of endoscope, is used. It is pushed through the mouth or nose to the large or medium-sized bronchi. The actual sample for the smear test and further diagnosis can then be taken.
In general, the swab is a quick, simple and relatively informative tool for an initial diagnosis. Nevertheless, there are also uncertainties regarding the various forms and applications of smears. Great care must therefore be taken when taking a smear. In particular, it is important not to contaminate the sample and to take sufficient material.
Often, a single smear test is not enough to make a definitive diagnosis. This depends, among other things, on the disease and the organ affected. Further diagnostic examinations are then necessary.
Problems with microbiological smears
The biggest problem with a microbiological smear is possible contamination of the smear sample. Bacteria or fungi that are not actually involved in the infection may have gotten into the sample.
These can get into the sample, for example, through inaccurate work when taking the smear. They can lead to a falsified diagnosis. In this case, efficient and targeted treatment is not possible.
A falsified 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 be made when taking a urethral swab if the sample is not taken properly. The area around the entrance to the urethra must be thoroughly cleaned before the swab is taken. The patient must not urinate in the 3 hours before the smear test.
Even if a throat swab is taken very frequently, the diagnosis may be distorted or unclear. For example, the doctor may not be able to take the sample from underneath the plaque in the throat. Instead of the actual pathogens, components of the plaque, such as white blood cells or waste products from the metabolism of the infectious bacteria or fungi, could be found.
Problems with cytological smears
Problems can occur with cytology smears if the smear contains too little cell material. This can be due, for example, to an incorrect or inaccurate technique used by the doctor to collect the cellular material.
The fixation or staining of the collected cells may also not work properly. In these cases, the cells to be examined may not be clearly visible under the microscope. This makes a clear diagnosis more difficult.
In these cases, a new smear test is then necessary.
