Understanding Potential Errors in DNA Paternity Tests

DNA paternity testing is >99.9% accurate when performed correctly. False results are rare but possible:

False Negative (Exclusion of True Father)

• Sample Contamination: Foreign DNA (handling, mixed swabs) → allele dropout or extra alleles.
• Mutation in Child: De novo mutation at tested STR locus (rate ~10^-3 per locus) → mismatch.
• Chromosomal Abnormality: Uniparental disomy, chimerism, mosaicism.
• Consanguinity: Alleged father and mother closely related → shared alleles mimic exclusion.

False Positive (Inclusion of Non-Father)

• Extremely rare with modern multiplex STR kits (20+ loci). Could occur with low-quality samples, laboratory error, or close relative of true father (brother) tested.

Quality Assurance

Accredited labs (AABB, ISO 17025) use duplicate testing, positive/negative controls, chain-of-custody, and statistical calculation (CPI > 10,000; probability of paternity >99.9%).

If Doubt Persists

Request re-test with new samples; include mother (trio testing increases certainty). Consult genetic counselor.