27 Mar Strep Test Results: What the Colors Mean
Editor’s note: Please remember there are other causes of a sore throat besides Strep bacteria, some of which may be serious including Mono (mononucleosis), Haemophilus, Whooping cough and others. Please consult your health care provider for specific medical advice. Information in this post is for background education only and not to be construed as specific medical advice.
A sore throat can be annoying. But if it comes with fever and swollen glands, it might be strep throat. Rapid strep throat tests give you quick results. But those color changes on the test strip can be confusing. Many people don’t know what they mean. Understanding these results is essential to knowing whether you are suffering from a viral infection or a strep throat. This guide explains strep test colors, what they mean, and what to do next.
How a Strep Throat Test Works
There are two main types of tests: the rapid antigen test and the throat culture.
- Rapid antigen tests work by detecting proteins (antigens) from the strep bacteria using a chemical reaction .
- In the throat culture method, the sample is placed in a lab to grow bacteria if present.
Both tests are reliable, but the rapid antigen test is widely used because of its speed, especially in clinics and urgent care settings.
Understanding the Color Changes on a Strep Throat Test
The color changes on a strep throat test happen due to chemical reactions with the bacteria’s antigens. All brands follow a similar reaction mechanism and pattern:
- Positive test: Two lines appear (one control line and one test line), often in shades of red or pink. This means the strep bacteria are present.
- Negative test: Only one line (the control line) appears, indicating no strep bacteria were detected.
- Invalid test: No lines or a single faint line in the wrong spot. This means that there is an error, such as an insufficient sample or a faulty test kit.
Understanding these color changes helps you to seek treatment or consider other causes for your symptoms.
What a Positive Test Means for Your Health
If your test shows two lines, you have a strep infection. Strep throat is treatable, but leaving it untreated can lead to complications like sinus infections, ear infections, or even rheumatic fever.
Your doctor will likely prescribe antibiotics to shorten the illness duration and prevent spreading it to others. You must take the full course of medication, even if you start feeling better. Strep bacteria are highly contagious, so it is better to avoid contact with anyone for the first 24 hours after medication.
Negative Results: Could It Still Be Strep?
A negative test result suggests that strep bacteria weren’t detected, but that doesn’t always mean you’re in the clear. Rapid tests can sometimes produce false negatives, meaning the bacteria are present but in low amounts that the test missed.
If your symptoms are severe or persist despite a negative test, your doctor might recommend a throat culture. Since throat cultures are more accurate, they can confirm whether you have strep or if another illness, such as a viral infection, is the cause of your symptoms.
The Importance of the Control Line
Every strep throat test includes a control line to ensure the test is working correctly. If this line doesn’t appear, your test is invalid. This could be due to:
- A defective test strip
- An improper sample collection
- Insufficient moisture for the test to process
If you receive an invalid result, it may be due to faulty kit or improper sample. In that case, you should take another test or consult a healthcare professional for further guidance.
How to Take an Accurate Strep Throat Test
Getting an accurate result depends on proper sample collection. Whether performed at home or in a clinic, here are essential steps to ensure accuracy:
- Use a sterile swab: Avoid touching the swab with your hands or other surfaces before use.
- Swab the correct area: The back of the throat and tonsils should be swabbed firmly, avoiding the tongue or inner cheeks.
- Follow test instructions carefully: Each test kit has specific steps for handling and processing samples.
If you’re unsure about the results, it’s always best to consult a doctor for a second opinion.
When to See a Doctor Even After Testing
While a strep throat test can be a helpful tool, there are situations where a doctor’s visit is necessary, even if the test is negative:
- Symptoms last longer than a few days or worsen.
- Difficulty breathing or swallowing develops.
- Fever persists despite taking medication.
- A rash appears, which could indicate scarlet fever, a related bacterial infection.
In these cases, a thorough medical evaluation is essential to determine the best course of treatment.
Interpreting strep throat test results correctly is key to managing your health effectively. The colors on the test strip indicate whether strep bacteria are present, guiding you toward the appropriate next steps. A positive test means you need antibiotics, while a negative result might still require a follow-up test if symptoms persist. Proper sample collection and an understanding of test limitations ensure accuracy. If in doubt, always consult a healthcare professional for confirmation and the right treatment plan.
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Last Updated on March 27, 2025 by Marie Benz MD FAAD