The Rapid Strep Test (RST) is a fast diagnostic method used in healthcare settings to determine if a patient’s sore throat is caused by a bacterial infection. This simple test targets specific antigens from the bacterium Streptococcus pyogenes, commonly known as Group A Streptococcus (GAS). By providing results within minutes, the RST helps clinicians make immediate decisions regarding the need for antibiotic treatment and appropriate patient care.
Group A Strep: The Target Infection
The primary reason for performing a Rapid Strep Test is to identify an infection with Group A Streptococcus (GAS), the most frequent bacterial cause of pharyngitis, or strep throat. S. pyogenes causes symptoms such as the sudden onset of a sore throat, fever, and sometimes white patches or pus on the tonsils. Differentiating strep throat from common viral infections is challenging because the symptoms often overlap.
Timely diagnosis and treatment of Group A Strep prevents potential health complications. If a GAS infection is left untreated, it can lead to serious conditions like rheumatic fever, which can cause permanent damage to the heart valves. Post-streptococcal glomerulonephritis, a type of kidney disease, is another possible complication.
Performing the Rapid Strep Test
The Rapid Strep Test is an immunoassay that uses principles of immune recognition to detect the target bacteria. The procedure begins with a healthcare professional collecting a sample using a sterile swab, gently brushed across the back of the throat and the tonsillar area. It is important to collect cells and mucus from the inflamed areas while avoiding contact with the tongue.
The collected swab is then placed into a solution containing chemical reagents that extract the specific bacterial antigens from the sample. The extracted solution is applied to a test strip or cassette containing immobilized antibodies specific to the GAS antigens. If GAS antigens are present, they bind to the labeled antibodies, resulting in a visible color change or line appearing on the test device within five to ten minutes.
Interpreting Results and Next Steps
The interpretation of the Rapid Strep Test result guides the immediate treatment decision, though the reliability of a negative result must be considered. A positive RST result is highly specific (95 to 100 percent), meaning the patient almost certainly has a Group A Strep infection. When positive, the diagnosis is confirmed, and a course of antibiotics is prescribed to shorten the illness and prevent complications.
However, the rapid test has lower sensitivity (65 to 80 percent), meaning it can produce a “false negative” result even when the bacteria are present. Since untreated strep throat in children carries a higher risk of rheumatic fever, a negative rapid test in pediatric patients often requires a follow-up test.
This confirmatory test is traditionally a throat culture, where the original swab is sent to a laboratory to see if Group A Strep bacteria will grow over 24 to 48 hours. Alternatively, some clinics utilize highly sensitive molecular tests, which detect the bacterial DNA and provide accurate results quickly, often eliminating the need for a culture.