Gunshot Residue (GSR) Blood Test: Principle, Interpretation & Limitations

GSR blood test detects lead (Pb) and barium (Ba) from primer residue absorbed into circulation post-discharge.

Mechanism

Firing → aerosolized Pb/Ba particles → inhaled/dermal absorption → bind RBCs → detectable in blood.

Interpretation

• Positive: Recent exposure (shooter, bystander, contaminated environment). Not proof of firing.
• Negative: Does not exclude involvement (washing, time delay, low exposure).

Limitations

• Time-sensitive (clears in hours-days)
• Environmental Pb/Ba confounders (industrial, batteries, fireworks)
• Not universally court-admissible; contextual corroboration required.

Primarily investigative lead, not standalone forensic proof.