Trimethoprim Concentration in Serum
This test measures the amount of the antibiotic trimethoprim in your blood serum. It may be used to monitor drug levels in people taking trimethoprim for infections.
["This test helps ensure your antibiotic dose is appropriate for your needs."]
Key facts at a glance
- LOINC
- 73101-8
- Short code
- Trimethoprim ind plt IgM SerPl Ql FC
- Synonyms
- Trimethoprim ind plt IgM SerPl Ql FC
- Category
- hematology
- 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 Might Be Ordered
Your healthcare provider may order this test if you’re taking trimethoprim (such as in combination with sulfamethoxazole) to check whether the drug is working at the right level in your blood. This is especially important if you have kidney problems or take other medications that interact with trimethoprim.
What to Expect Before the Test
No special preparation is needed. You’ll have a small needle inserted into your arm or vein to draw blood. It usually takes a few minutes, and you may feel a brief pinch. If you’re on blood thinners or have a history of bleeding issues, let your provider know.
What the Results Mean
Results are compared to a reference range specific to your medication dose, kidney function, and other health factors. Low levels may indicate the drug isn’t working effectively, while very high levels could signal toxicity or improper dosing.
Common Causes of Abnormal Results
Low trimethoprim levels might occur if you’re not taking the medication as prescribed, have poor absorption, or have kidney problems reducing its clearance. High levels could result from overuse, kidney dysfunction, or interactions with other medications.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Monitoring trimethoprim levels is critical for infections like urinary tract infections, pneumonia, or traveler’s diarrhea caused by certain bacteria. Proper dosing prevents resistance and reduces side effects like rash, nausea, or blood disorders. Your provider will adjust your treatment based on these results if needed.
Short name
Trimethoprim Level
Frequently asked questions
What does a ‘normal’ result mean for me?
Can I eat or drink before this test?
How long will it take to get my results?
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