Blog
Urethral swab: microbiological evaluation of the urethra in the diagnosis of STIs
Urethral swab is a basic laboratory method that remains indispensable in the comprehensive assessment of inflammatory diseases of the genitourinary system. Despite the development of molecular diagnostics, it is direct microscopic analysis of a urethral smear that often allows quickly navigate the pathogen and choose a starting therapy.
Biological value of urethral swab
The urethra is the anatomical structure through which urine passes, but it can also be a reservoir of pathogenic microorganisms, especially in sexually transmitted infections. A sample taken from her mucous membrane allows you to assess:
presence of leukocyte reaction (inflammation);
morphological features of epithelial cells (signs of damage);
presence of pathogens: gonococci, trichomonads, fungal colonies, bacterial aggregates.
Laboratory approaches to urethral smear analysis
Modern laboratory diagnostics involves several stages of biomaterial processing:
1. Light microscopy (methylene blue or Gram stain)
Evaluates number of leukocytes, epithelium, presence of microflora.
Typical picture of gonorrhea — intracellular diplococci, gram-negative.
Typical picture of candidiasis — fungal hyphae or spores against the background of a pronounced inflammatory reaction.
2. Inoculation on nutrient media
Required for selection anaerobic or specific flora, which is not always detected microscopically.
Advantage: allows you to evaluate antibiotic sensitivity (antibiogram).
3. Molecular diagnostics (PCR)
Detects genetic material chlamydia, mycoplasma, ureaplasma, herpes viruses.
Sensitivity >95%, used as diagnostic standard in asymptomatic cases.
Clinical interpretation: leukocytes, flora, pathogens
A normal urethral smear (in men) contains:
up to 5 leukocytes in the field of view;
single epithelial cells;
mixed nonspecific flora (in small quantities).
More than 5 leukocytes in the field of vision - a sign urethritis, even if there are no complaints. If at the same time they find absence of gonococci, but there are mycoplasmas, chlamydia or trichomonads - we are talking about nongonococcal urethritis (NGU).
Male and female specifics of taking material
In men, a sterile probe is used to take the sample to a depth of 2–4 cm.
In women, a urethral swab is less common, but is used when genitourinary complaints without signs of vaginitis.
In both cases, the material is taken before urination, because urine washes out pathogens.
Comparison with other diagnostic methods STIs
| Method | Sensitivity | Advantages | Disadvantages |
|---|---|---|---|
| Urethral swab (microscopy) | 70–80% (for gonorrhea) | Accessibility, quick results | Low sensitivity to chlamydia |
| PCR test | >95% | Detects the pathogen in asymptomatic | More expensive, requires quality control |
| Back-sowing | High (with active flora) | Provides data on resistance | Long-lasting result (3–7 days) |
The role of urethral swab in the modern protocol
Despite the dominance of PCR in the private sector, urethral swab remains mandatory initial test in dermatovenereology offices. This is:
rapid method for detecting active urethritis;
basis for decision-making on immediate empirical therapy;
monitoring the effectiveness of treatment over time (in combination with PCR or culture).
A properly taken and analyzed urethral swab is not just a formality, but a valuable diagnostic tool, which helps maintain reproductive health, prevent chronic infections, and avoid complications.
