Unit Converter
Salicylate
(Aspirin / Acetylsalicylic Acid Metabolite - Critical Marker in NSAID Toxicity, Overdose, and Therapeutic Monitoring)
Synonyms
- Salicylate
- Salicylic acid
- Aspirin metabolite
- ASA metabolite
- Total salicylate level
- Serum salicylate
- Plasma salicylate
Units of Measurement
- mmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Unit Conversions
Molecular Weight of Salicylic Acid = 138.12 g/mol
mmol/L ↔ mg/L
1 mmol/L=138.12 mg/L1\ \text{mmol/L} = 138.12\ \text{mg/L}1 mmol/L=138.12 mg/L 1 mg/L=0.00724 mmol/L1\ \text{mg/L} = 0.00724\ \text{mmol/L}1 mg/L=0.00724 mmol/L
mg/dL ↔ mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
mg% = mg/dL
µg/mL ↔ mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
Description
Salicylates include aspirin (acetylsalicylic acid) and its active metabolite salicylic acid.
Clinical salicylate testing is used to:
- Diagnose aspirin overdose
- Monitor high-dose aspirin therapy (e.g., rheumatology)
- Assess toxicity in mixed ingestions
- Evaluate symptoms like tinnitus, metabolic acidosis, hyperventilation, confusion
Aspirin is absorbed in the stomach and small intestine, undergoes hepatic metabolism, and follows zero-order kinetics at toxic doses → leading to rapid accumulation.
Physiological Role
Salicylates do not have a normal physiological role.
They act pharmacologically as:
- COX-1/COX-2 inhibitors
- Anti-inflammatory
- Antipyretic
- Analgesic
- Antiplatelet (aspirin)
Clinical Significance
HIGH SALICYLATE LEVELS
Symptoms by Level
| Serum Salicylate | Clinical Effects |
| > 30 mg/dL | Mild toxicity: tinnitus, nausea, tachypnea |
| 40–70 mg/dL | Moderate toxicity: vomiting, diaphoresis, alkalosis |
| > 70 mg/dL | Severe toxicity: metabolic acidosis, hyperthermia, agitation |
| > 100 mg/dL | Life-threatening: coma, pulmonary edema, seizures |
Mechanisms of Toxicity
- Respiratory alkalosis (early)
- High anion-gap metabolic acidosis (late)
- Uncoupled oxidative phosphorylation → hyperthermia
- CNS toxicity
- Hypoglycemia
- Volume depletion
Major Causes
- Acute salicylate overdose
- Chronic salicylate poisoning (elderly, chronic pain therapy)
- Co-ingestion with acetaminophen, antidepressants, alcohol
LOW SALICYLATE / NORMAL
Normal in people not taking aspirin.
In therapeutic dosing, low-level values confirm compliance.
Reference Intervals
(Tietz 8E + ACMT + Mayo + ARUP)
Therapeutic Range
- 10 – 30 mg/dL
(= 100 – 300 mg/L)
(= 0.07 – 0.22 mmol/L)
Toxicity Ranges
- > 30 mg/dL → mild toxicity
- > 50 mg/dL → moderate/severe
- > 70 mg/dL → very severe
- > 100 mg/dL → potentially fatal
Peak Levels After Ingestion
Peak may be delayed up to 6 hours, or longer with enteric-coated tablets.
Diagnostic Uses
1. Suspected Aspirin Overdose
- Acute ingestion
- Chronic aspirin toxicity
- Mixed overdoses
2. Therapeutic Monitoring
High-dose salicylates in:
- Rheumatoid arthritis
- Kawasaki disease
- Juvenile idiopathic arthritis
3. Metabolic Acidosis Evaluation
Salicylates are a key cause of high anion-gap acidosis.
4. Altered Mental Status
Especially in elderly patients.
5. Tinnitus Evaluation
Classic early toxicity symptom.
Analytical Notes
- Sample: serum or plasma
- Draw serial levels every 2 hours to assess absorption curve
- Measure blood gas + electrolytes for acid–base evaluation
- Highly protein-bound at therapeutic doses → fraction saturates in overdose
- LC–MS/MS or enzymatic assays commonly used
Clinical Pearls
- Tinnitus strongly suggests salicylate toxicity.
- Salicylate causes respiratory alkalosis first, then metabolic acidosis.
- Activated charcoal is most effective if given early.
- Alkalinization of urine enhances salicylate elimination.
- Hemodialysis indicated for:
- Level >100 mg/dL (acute)
- Level >60 mg/dL (chronic)
- Severe symptoms regardless of level
- Level >100 mg/dL (acute)
Interesting Fact
Salicylic acid was originally derived from willow bark, used medicinally for thousands of years before aspirin was chemically synthesized in 1897.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Toxicology
- ACMT / AACT Aspirin Poisoning Guidelines
- Mayo Clinic Laboratories - Salicylate
- ARUP Consult - Salicylate Testing
- NIH / MedlinePlus - Aspirin Toxicity
- AAPCC Toxic Exposure Surveillance System