Throat Swab

• The most common test for tonsillitis is a throat swab. For this procedure, a sterile swab is briefly rubbed over the inflamed tonsil. The secretions collected on the swab are then tested to determine if a strain of streptococcus bacteria is causing infection.
  
  

Blood Test

• Rarely, a blood test may be required to pin down the exact cause of tonsillitis. A complete blood count (CBC) may indicate whether or not a virus is causing the swollen tonsils. Viruses such as mononucleosis my cause an elevated white blood cell count, which can be discovered with a CBC.
  
  

What to Expect

• During a throat swab, the doctor will gently rub the tonsils with a sterile swab. This can be slightly uncomfortable, but shouldn't take more than 1 or 2 seconds to complete. You may experience a gag reflex, but usually this is mild. Small children may need to be comforted or gently restrained. After the tonsils are swabbed, the sample is tested for the presence of streptococcal bacteria. This is usually performed at the office in as few as 5 minutes. An overnight culture, taking 24 to 48 hours, may also be performed.
  
  

Results

• If the throat swab comes back as positive for streptococcus, your doctor will likely prescribe a course of antibiotics. If it is negative, indicating a viral infection, your doctor may choose to have you rest at home and use over-the-counter medication for throat pain. Unlike in earlier years, tonsillitis today is rarely treated by removing the tonsils.
  
  

Accuracy

• The rapid strep test correctly identifies approximately 95 to 98 percent of tonsillitis infections caused by Group A strep. It also has about a 2 percent chance of providing a false positive.