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Serum/plasma mass concentration of free (unbound) salicylic acid

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of salicylic acid (a pain reliever and anti-inflammatory) that is not attached to proteins in your blood.

Quick summary

["Assesses free salicylate levels to monitor drug safety and effectiveness."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
13128-4
Short code
IAP SerPl-aCnc
Synonyms
IAP SerPl-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 doctor may order this test if you’re taking salicylate-containing medications (e.g., aspirin, some pain relievers) and want to check how much is circulating freely in your blood. It helps ensure safe dosing, especially in children or people with kidney issues.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. If you’re on salicylate medications, your doctor may ask to check levels at specific times (e.g., before or after doses).

What the Results Mean

High levels may indicate overdose or improper metabolism, while very low levels could suggest poor absorption. Your doctor will compare results to your medication regimen and overall health.

Common Uses

Used to monitor salicylate toxicity (e.g., in overdose cases), evaluate kidney function, or confirm therapeutic drug levels in certain conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Salicylate Level

Frequently asked questions

Why might my doctor want to check my free salicylate level?
Your doctor may order this test if you’re taking salicylates (e.g., aspirin) for conditions like arthritis, fever, or pain, or if you’ve had symptoms like dizziness, stomach upset, or unusual bleeding.
What happens if my free salicylate level is too high?
If levels are dangerously high, your doctor may adjust your medication, increase fluids, or recommend supportive care (e.g., activated charcoal for overdose). Symptoms like vomiting or confusion may require urgent medical attention.
Can I eat or drink before this test?
Typically, you can eat and drink normally unless instructed otherwise. If you’re on salicylates, ask your doctor about timing—some tests may require fasting or specific timing relative to your dose.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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