Modern paternity testing compares genetic markers between a child and an alleged father using buccal swabs or, prenatally, cell-free fetal DNA from maternal blood. Postnatal STR testing yields very high probabilities of paternity when inclusion occurs; exclusions are definitive. For legal matters, follow chain-of-custody and use an accredited laboratory.

What a paternity test examines

Paternity testing compares DNA to answer whether a man is the biological father of a child. DNA (deoxyribonucleic acid) is built from four nucleotides - A (adenine), C (cytosine), G (guanine) and T (thymine). In humans, DNA is packaged into 23 pairs of chromosomes; you inherit one chromosome of each pair from your mother and one from your father.

Modern paternity testing looks at specific genetic markers (short tandem repeats, STRs) across the child and the alleged father. By comparing these markers, laboratories can either exclude a man as the biological father or calculate a probability of paternity.

Sample types and how tests are done

For postnatal tests, the most common sample is a buccal (cheek) swab from the child, the alleged father, and ideally the mother. Buccal swabs are noninvasive, easy to collect, and widely accepted by testing labs. Blood can still be used, but swabs have largely replaced routine blood draws.

There are two common test pathways:

  • "Peace-of-mind" tests: Collected at home and sent to a commercial laboratory. These are suitable for personal knowledge.
  • Legal/court-admissible tests: Collected under chain-of-custody procedures by an approved collector and processed by an accredited lab. These are required for child support, custody, or immigration cases.
Noninvasive prenatal paternity (NIPP) tests have also become available. NIPP analyzes cell-free fetal DNA circulating in the pregnant person's blood to assess paternity before birth. NIPP requires a specialized lab and different analysis than postnatal STR testing.

Accuracy and interpretation

Standard postnatal autosomal STR testing can produce very high probabilities of inclusion when the tested man is the biological father; exclusions are conclusive. Courts and labs typically report a probability of paternity and a combined paternity index.

NIPP and other prenatal methods report different performance metrics and must be interpreted by the testing lab. Including the mother's sample improves margin of certainty in many analyses.

When people use paternity testing

People seek paternity testing for many reasons: confirming biological parentage, resolving custody or child-support disputes, establishing inheritance rights, or for personal peace of mind. For legal actions, use an accredited lab and follow chain-of-custody procedures to ensure results are admissible in court.

Practical considerations

Turnaround times vary from a few days to several weeks depending on the test type and whether legal documentation is required. Labs typically provide clear reports and, if requested, expert interpretation letters for legal use.

If you need results for a legal proceeding, ask the testing provider about accreditation, chain-of-custody procedures, and how they report probability metrics.

: Specific numeric accuracy figures for postnatal autosomal STR testing and NIPP (reported probabilities and earliest gestational age for reliable prenatal testing).

  1. Verify typical reported probability of paternity for postnatal autosomal STR testing (commonly cited values such as >99.99% for inclusion) and cite authoritative lab guidance.
  2. Confirm performance metrics and the earliest recommended gestational age for reliable noninvasive prenatal paternity (NIPP) testing.
  3. Confirm common accreditation bodies and standards for court-admissible relationship testing (e.g., AABB or equivalent) and current best practices for chain-of-custody procedures.

FAQs about Paternity Blood Test

What sample is usually used for a paternity test?
Most postnatal tests use a buccal (cheek) swab from the child, the alleged father, and ideally the mother. Blood is less commonly used now but remains an option.
How accurate are paternity tests?
Standard postnatal autosomal STR tests produce very high probabilities of paternity when a man is the biological father; exclusions are definitive. Exact reported percentages vary by laboratory and marker set.
Can paternity be tested before birth?
Yes. Noninvasive prenatal paternity (NIPP) analyzes cell-free fetal DNA from the pregnant person's blood. It requires specialized labs and different interpretation than postnatal testing.
Do I need a special test for court?
Yes. Courts require tests collected under chain-of-custody procedures and processed by an accredited lab. Ask the provider about accreditation and documentation before testing.