Strep throat is a pharyngeal infection caused by the bacterium Group A Streptococcus (Streptococcus pyogenes). Symptoms typically include a sudden onset of sore throat, fever, and sometimes white patches on the tonsils. Patients often wonder if an over-the-counter strep test is available for home use. Reliable, diagnostic-grade rapid strep tests approved by the Food and Drug Administration (FDA) for use by the untrained public are generally not available in pharmacies.
The Current Status of Over-the-Counter Strep Tests
The lack of readily available over-the-counter strep tests is due to regulatory and technical challenges. Current diagnostic tests are complex instruments cleared for professional use, often designated as “point-of-care” devices. These tests require a precise swabbing technique to collect a sufficient sample from the tonsils and back of the throat.
Improper sample collection by an untrained user can lead to unreliable results, particularly an increase in false-negative outcomes. Although some companies market consumer kits, these products lack the FDA clearance required for reliable, diagnostic home use compared to professional tests. Professional settings maintain strict accuracy standards necessary for diagnosing strep infection.
How Professional Strep Testing Works
Healthcare providers rely on two main methods to diagnose strep throat, both requiring a professional throat swab. The first is the Rapid Antigen Detection Test (RADT), a quick screening tool that provides results in minutes. The RADT is a lateral flow immunoassay that detects the presence of the Group A Streptococcus carbohydrate antigen in the sample.
The RADT is highly specific, meaning a positive result is very likely accurate. However, it has lower sensitivity, meaning it might fail to detect the bacteria when a person is infected, resulting in a false-negative. Therefore, the second method, the throat culture, is often used to confirm a negative RADT result, especially in children where the risk of complications is higher.
The throat culture remains the gold standard for diagnosis due to its superior sensitivity. The specimen is taken to a laboratory and inoculated onto a 5% sheep blood agar plate, then incubated at 35–37°C. If bacteria are present, they grow for 24 to 48 hours, forming colonies examined for beta-hemolysis. This incubation period allows even a small number of bacteria to multiply for definitive identification, ensuring a highly accurate diagnosis.
Why Accurate Diagnosis Is Critical
Accurate and timely diagnosis of strep throat is important because antibiotic treatment prevents serious, delayed complications. These complications result from an aberrant immune response triggered by the infection, not the bacteria directly. Failing to treat strep can lead to Rheumatic Fever (RF), an inflammatory condition that can permanently damage the heart.
Rheumatic Fever causes a systemic autoimmune reaction where antibodies developed to fight strep mistakenly attack the heart valves and joints. This damage, known as Rheumatic Heart Disease, commonly affects the mitral valve, leading to scarring and potential heart failure years later. A second complication is Post-Streptococcal Glomerulonephritis (PSGN).
PSGN is inflammation in the kidneys that occurs when immune complexes deposit in the glomeruli, the tiny filtering units of the organ. Symptoms can include hematuria, facial puffiness (edema), and elevated blood pressure. Professional testing is necessary to confirm the presence of Group A Streptococcus and ensure appropriate antibiotic therapy is initiated promptly due to these potential long-term health consequences.