Many minor and superficial skin and wound infections are diagnosed by a healthcare practitioner based on a physical examination, signs and symptoms, and experience. A clinical evaluation cannot, however, definitively tell the healthcare practitioner which microbe is causing a wound infection or what treatment is likely to be effective. For that, laboratory testing is required.
Examples of common tests include:
- Bacterial culture – This is the primary test used to diagnose a bacterial infection. Results are usually available within 24-48 hours.
- Gram stain – This is usually performed in conjunction with the wound culture. It is a special staining procedure that allows bacteria to be evaluated under the microscope. The results are usually available the same day and provide preliminary information about the microbe that may be causing the infection.
- Antimicrobial susceptibility – A follow-up test to a positive wound culture, this is used to determine the bacteria's likely susceptibility to certain drugs and helps the healthcare practitioner select appropriate antibiotics for treatment. Results are typically available in about 24 hours. This testing can identify resistant bacteria such as MRSA.
Other tests may include:
- KOH prep – This is a rapid test performed to detect fungi in a sample. The sample is treated with a special solution, placed on a slide, and examined under a microscope.
- Fungal culture – This is ordered when a fungal infection is suspected. Many fungi are slow-growing and may take several weeks to identify.
- AFB testing – This is ordered when a mycobacterial infection is suspected. Most AFB are slow-growing and may take several weeks to identify.
- Blood culture – This is ordered when infection from a wound may have spread to the blood.
- Molecular testing to detect genetic material of a specific microbe
- Basic metabolic panel (BMP) or Comprehensive metabolic panel (CMP) – This may be ordered to detect underlying conditions that can affect wound healing, such as a glucose test to detect diabetes.
- Complete blood count (CBC) – An elevated white blood cell (WBC) count may be a sign of infection.
In some cases, imaging scans such as ultrasounds or x-rays may be ordered to evaluate the extent of tissue damage and to look for areas of fluid/pus.