Understanding Your Laboratory Test: A Patient's Guide to Medical Testing
This blood test measures the lowest level of acetylsalicylate (the active form of aspirin) in your blood to ensure you are receiving the correct therapeutic dose.
{"Measures the trough (lowest) level of aspirin in your blood","Helps ensure you are receiving the right dose for your condition","Blood sample is typically collected just before your next aspirin dose","Used to monitor therapy for conditions like heart disease or arthritis","Results help your doctor adjust your medication for optimal effectiveness and safety"}
Key facts at a glance
- LOINC
- 74970-5
- Short code
- ASA trough
- Synonyms
- Acetylsalicylate Trough SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plasma collection tube (potassium EDTA or sodium heparin)
- Units
- N/A
- Ref low
- 5
- Ref high
- 20
- Critical range
- — – 30 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Liquid chromatography-tandem mass spectrometry (LC-MS/MS) or High-performance liquid chromatography (HPLC) with ultraviolet (UV) detection
- CPT
- 80329 - Therapeutic drug monitoring; aspirin
- SNOMED
- 387458009 - Acetylsalicylate measurement (procedure)
- Specimen volume
- 2-5 mL serum or plasma
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Protect from light.
- Hemolysis max
- 50
- Lipemia max
- 100
- Icterus max
- 20
- TAT
- 24–72 hours
- Order
- routine
What is this test, and why has my doctor ordered it for me?
The Acetylsalicylate Trough Level test measures the amount of acetylsalicylate (the active form of aspirin) in your blood serum or plasma. The term "trough" refers to the lowest concentration of the drug in your bloodstream, which typically occurs right before you take your next scheduled dose. This test is a form of therapeutic drug monitoring (TDM) that helps ensure you are receiving the optimal dose of your medication.
Why is this test performed, and what health conditions can it help detect or monitor?
Your healthcare provider may order this test to: (1) Monitor therapeutic levels of aspirin when you are taking it for conditions like heart disease, stroke prevention, or inflammatory conditions such as rheumatoid arthritis; (2) Ensure the drug is working effectively at your current dose; (3) Prevent toxicity by making sure the drug level doesn't get too high; (4) Adjust your dosage if needed to achieve the best balance between effectiveness and side effects.
How is the test performed, and what should I expect before, during, and after the procedure?
A healthcare professional will draw a small blood sample from a vein in your arm. For accurate trough measurements, the blood is typically collected just before you take your next scheduled dose of aspirin. The sample is then sent to a laboratory where the concentration of acetylsalicylate is measured. No special preparation is usually required, but follow your healthcare provider's specific instructions about timing and medication schedules.
What do my test results mean, and how will my healthcare provider use them to guide my care?
Your test results will show the concentration of acetylsalicylate in your blood. The therapeutic range varies depending on your condition: for cardiovascular protection, typical trough levels are lower, while for inflammatory conditions like rheumatoid arthritis, higher levels may be needed. Your doctor will interpret your results based on your specific medical condition, symptoms, and overall treatment goals. Both subtherapeutic (too low) and toxic (too high) levels may require dose adjustments.
Reference range
Therapeutic trough range: 5-20 mcg/mL (50-200 mg/L). Subtherapeutic: <5 mcg/mL. Supratherapeutic: >20 mcg/mL.N/A
Collect trough specimen immediately before next scheduled dose. Inform patient not to take their morning dose until after sample collection. Record exact time of last dose and scheduled time of next dose on requisition.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The Acetylsalicylate Trough Level test is clinically significant for several reasons: (1) Therapeutic drug monitoring helps maintain drug concentrations within the therapeutic window for optimal efficacy; (2) It helps prevent aspirin toxicity, which can cause symptoms ranging from tinnitus and nausea to serious complications like bleeding or respiratory failure; (3) For patients on long-term aspirin therapy, regular monitoring ensures consistent drug exposure; (4) The test is particularly important for patients with conditions requiring precise dosing, such as those with cardiovascular diseases or inflammatory disorders; (5) It helps healthcare providers personalize medication dosages based on individual patient factors including age, kidney function, and other medications.
Frequently asked questions
How often will I need this test?
What happens if my level is too high?
What happens if my level is too low?
Do I need to fast before this test?
Can I take my regular aspirin before the blood test?
Sources
- 1
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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 10, 2026. · Read our editorial policy