Blood Arsenic Levels: Clinical Thresholds
Blood arsenic levels above 1 µg/L warrant clinical concern and further investigation for exposure sources, though interpretation must account for recent seafood consumption which can transiently elevate levels without toxicity. 1, 2
Normal Reference Ranges
- Reference populations with only environmental exposure average 5.1 ± 6.9 µg/L in blood, though this older data may not reflect current standards 3
- More recent data from unexposed populations shows median blood arsenic of 0.6 µg/L (range <LOD to 3.3 µg/L) 2
- The internationally recommended guideline for blood arsenic is 1 µg/L 2
Concerning Levels by Exposure Category
Low-Level Chronic Exposure
- Blood arsenic concentrations of 0.9-2.5 µg/L indicate low-to-medium environmental exposure and correlate with drinking water arsenic levels of 0.45-6.0 µg/L 2
- Blood arsenic increases by approximately 0.034 µg/L for each 1 µg/L increase in water arsenic concentration 2
High-Level Chronic Exposure
- Blood arsenic levels of 1.6-4.2 µg/L (median 1.6 µg/L) indicate significant environmental exposure requiring source identification and remediation 2
- These levels correlate with drinking water arsenic of 1.75-81.3 µg/L and soil concentrations of 23.91-92.1 mg/kg 2
Critical Interpretation Caveats
The Seafood Confounding Problem
- Seafood consumption dramatically elevates urinary arsenic for 24-48 hours but does NOT increase blood levels of toxic inorganic arsenic or its metabolites (monomethylarsonic acid and dimethylarsinic acid) 3
- Organic arsenic from seafood does not mix with the inorganic arsenic pool in the body and can be separately detected 3
- Do not dismiss elevated blood arsenic in patients with high seafood consumption, as organic arsenic can mask concurrent toxic inorganic arsenic exposure 1, 4
Occupational Exposure Context
- For occupational lead exposure (not arsenic), removal is recommended when blood lead exceeds 30 µg/dL or two successive measurements are ≥20 µg/dL - this provides context but arsenic thresholds are much lower 5
- Blood arsenic correlates proportionally with exposure levels and specifically with urinary dimethylarsinic acid excretion 3
Clinical Action Thresholds
When to Investigate Further
- Any blood arsenic level >1 µg/L requires exposure history focusing on:
When to Test Water Sources
- Test drinking water when blood arsenic exceeds 1 µg/L and patient uses well water or lives in high-risk geographic areas 1
- Water arsenic levels >10 µg/L require alternative water sources 4
When to Consider Chelation
- Chelation therapy with DMPS or BAL is indicated for acute and subacute poisoning with symptomatic toxicity, NOT for asymptomatic individuals with low blood levels 6
- Blood arsenic monitoring during arsenic trioxide chemotherapy requires maintaining potassium >4 mEq/dL and magnesium >1.8 mg/dL, with weekly QTc monitoring when absolute QTc >500 ms 5
Long-Term Health Surveillance
- Patients with confirmed chronic exposure (blood arsenic consistently >1 µg/L) require lifelong surveillance for skin, lung, and bladder cancers 1
- Even populations with elevated blood arsenic showing no clinical symptoms (skin lesions) require monitoring, as 30-40% of exposed individuals remain asymptomatic 7