Sulfamethoxazole in Serum/Plasma (Quantitative Measurement)
This test measures the amount of the antibiotic sulfamethoxazole in your blood. It helps monitor your dose and check if the drug is working properly.
["This test helps ensure your antibiotic levels are safe and effective."]
Key facts at a glance
- LOINC
- 72947-5
- Short code
- Sulfamethoxazole (neut) IgM SerPl Ql FC
- Synonyms
- Sulfamethoxazole (neut) IgM SerPl Ql FC
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- flow-cytometry
- CPT
- 82784
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your healthcare provider may order this test if you’re taking sulfamethoxazole (often combined with trimethoprim, like in Bactrim®) to treat infections such as urinary tract infections, pneumonia, or certain parasitic diseases. It helps adjust your dose to avoid side effects or ensure the medication is working.
What to Expect Before the Test
No special preparation is needed. You may have a small needle inserted into your arm to draw blood. If you’re on a long-term medication like this, your provider may check levels periodically to optimize your treatment.
What the Results Mean
Results are typically reported as a concentration in micrograms per milliliter (mcg/mL). Low levels may indicate the drug isn’t working well, while very high levels could suggest toxicity. Your provider will interpret these results in the context of your symptoms and medical history.
Possible Side Effects or Considerations
Sulfamethoxazole can cause side effects like nausea, rash, or kidney issues. If you experience severe reactions (e.g., skin rash, difficulty breathing), seek medical attention immediately. Avoid taking this medication if you’re allergic to sulfonamides or have certain kidney/hepatic conditions.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Monitoring sulfamethoxazole levels is critical for patients with kidney disease, liver problems, or those taking other medications that interact with it. Low levels may require dose adjustments, while high levels could necessitate stopping or reducing the medication to prevent toxicity. This test is especially important for long-term therapy to balance efficacy and safety.
Short name
Sulfamethoxazole Level
Frequently asked questions
When might I need this test?
How often will I need this test?
What happens if my results are out of range?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy