Last updated: September 17, 2025

This article explains the history of paternity testing across three stages — blood type testing, HLA typing, and DNA testing. It compares the principles, characteristics, and accuracy of each method, and shows in detail why modern DNA testing, with an accuracy of 99.99% or higher, is the most reliable way to establish paternity.

Introduction

In TV dramas and movies, scenes where DNA testing is used to answer the question "Who is the real father?" have become increasingly common. In real life too, the need to confirm the biological parent-child relationship between a father and child is very common, and the number of DNA paternity tests performed continues to rise year after year.

DNA testing is often thought of as something only carried out by law-enforcement or judicial institutions, but individuals can also accurately investigate biological parent-child relationships on their own. Today, DNA testing is the mainstream method for checking paternity, but do you know how it was determined before DNA testing existed?

This article introduces, in plain language, the older methods of paternity testing (blood type testing and HLA typing) along with the principles, characteristics, and accuracy of each. It also explains in detail how modern DNA testing works, how accurate it is, and why DNA testing is the most reliable test available. Whether you are considering confirming a parent-child relationship or are simply interested in the scientific background of DNA testing, we hope you find this content useful.

Paternity Testing Using Blood Type

One of the oldest methods used to check parent-child relationships is blood type testing. In the early 20th century, checking blood type (the ABO blood group system) was the most common method of paternity testing.[ref:1] As taught in middle school science, there are four blood types: A, B, AB, and O. Blood type is determined by inheritance, and a child's blood type is determined by the blood type genes inherited from the father and mother respectively.

In other words, a child's blood type is determined by receiving one piece of genetic information from each parent. In the ABO blood group system, there are three alleles — A, B, and O — where A and B are dominant over O. For example, a genotype of AO results in type A, BO results in type B, AB results in type AB, and OO results in type O in the observed phenotype. Understanding this rule of inheritance is fundamental to understanding paternity testing by blood type.

<Figure 1> Example Combinations of Parents' Blood Types and Children's Blood Types

In the blue column is the father's blood type, in the pink row is the mother's blood type, and the entries in the yellow cells where they intersect are the possible blood types of the resulting child. In this way, the inheritance of blood type is determined by the combination of alleles (A, B, or O) inherited from each parent.

For example, if the father is type AB, it is genetically impossible for the child to be type O.[ref:2] A person with type AB carries both the A and B alleles, and can only pass on either A or B to a child — never O. Conversely, if the father is type O, his genotype consists of two O alleles, so he cannot pass an A or B allele to a child. Therefore, if a child is type A or type B, a father who is type O can be determined not to be the biological father.

In this way, blood type testing predicts what blood type a child "should" have based on the combination of the parents' blood types, and to some extent rules out (excludes) paternity when the actual result contradicts that prediction. Although this was the most widely used method before DNA testing became available, blood type could not always be determined accurately in newborns, leading to many misjudgments, so it cannot be considered a highly reliable method.

Principles, Characteristics, and Accuracy of Blood Type Testing

Paternity Testing Using HLA Type

To overcome the limits in accuracy of blood type testing, a test emerged that reflects genetic information in much greater detail: HLA typing. HLA (human leukocyte antigen) refers to the protein type found on human white blood cells — essentially a "blood type of the white blood cells".[ref:4]

HLA involves multiple gene loci, including A, B, and DR, among many others, and each locus has dozens of possible types (alleles), so the number of possible HLA type patterns in a person is said to run into the tens of thousands. A child inherits half of their HLA type from the mother and half from the father.

Therefore, if a man does not share most of the child's HLA type with them, that man cannot be the father. Conversely, a man whose HLA type matches the child's completely is highly likely to be a blood relative. HLA is extremely diverse, and the probability that unrelated individuals would coincidentally share the same HLA type is thought to be on the order of one in several hundred to one in tens of thousands.

HLA typing became widely used for paternity testing from the 1970s through the 1980s. In cases where blood type testing alone had proven insufficient, adding HLA testing significantly improved the accuracy of excluding non-fathers. However, HLA testing requires a blood draw and the relatively complex process of isolating white blood cells for analysis, making it costly and cumbersome — not something the average person could easily access.

Principles, Characteristics, and Accuracy of HLA Typing

Modern DNA Testing for Confirming Parent-Child Relationships

DNA testing revolutionized the field of paternity testing beginning in the 1980s. It is the most accurate method for examining a biological parent-child relationship, used not only in criminal investigations by forensic science laboratories but also in family court inheritance disputes and for personal confirmation purposes.

DNA (deoxyribonucleic acid) is the substance of genes, and each person's DNA sequence (except in identical twins) is unique. In other words, DNA is personally identifying information sometimes called a "genetic fingerprint."[ref:1] The rapid spread of DNA testing in forensic science and paternity testing was triggered in 1985, when British geneticist Dr. Alec Jeffreys developed the technique of DNA fingerprinting.[ref:8]

A child's DNA contains, in equal halves, portions inherited from the biological mother and from the father. Applying this principle, comparing the DNA sequences of the child and a candidate father makes it possible to determine the parent-child relationship. In other words, when two people's DNA sequences are compared, if half matches, they are determined to be parent and child, and if it matches completely, they are determined to be the same individual.

In DNA testing, several specific regions (markers) on the DNA are typically examined. Rather than comparing a person's entire genome (the complete set of genetic information), the presence or absence of a parent-child relationship can be confirmed by checking several DNA regions with large individual variation.[ref:3] Current standard DNA paternity testing generally analyzes 16 to 24 or more STR markers simultaneously, and the more markers used, the more dramatically the accuracy of the test improves.

In practical terms, DNA is extracted from blood or oral mucosal cells (collected by swabbing the inside of the cheek), and the target regions of that DNA are amplified and analyzed using a method called PCR (polymerase chain reaction).[ref:1] The DNA regions analyzed include STRs (short tandem repeats) — repeating sequences whose length varies from person to person — and single nucleotide variants (SNVs/SNPs), which are single-letter differences.

For each of the child's DNA markers, it is checked whether the "type not derived from the mother" matches the candidate father's DNA. If all of the multiple markers match, it is judged extremely likely that the person is the biological father. On the other hand, if a certain number or more of the markers do not match, the person can be immediately determined not to be the father. The test can be performed on an extremely small amount of DNA — as little as one billionth of a gram — and results can typically be obtained in about two to four days.[ref:5]

Principles, Characteristics, and Accuracy of DNA Testing

Accuracy Comparison of Each Testing Method

The table below summarizes the accuracy and characteristics of the three paternity testing methods discussed so far. It clearly shows the historical progression from blood type testing, to HLA typing, to DNA testing.

As the comparison above shows, DNA testing offers overwhelmingly higher accuracy compared to the other methods.[ref:3] While blood type and HLA typing could only "exclude," the advent of DNA testing made it possible to reach a decisive conclusion that includes "affirmation (proof)" as well.

Points to Check When Choosing a DNA Testing Provider

When choosing an institution to perform DNA testing, not only test accuracy but also the institution's reliability and quality-control systems are important criteria. Check the following points.

• Whether it holds an international quality certification such as ISO 9001
• Whether personal information protection (such as Privacy Mark certification) is thoroughly enforced
• Whether a sufficient number of STR markers are analyzed (16 or more is preferable)
• Whether it supports legal testing that can be used in court
• Whether expert support and explanation of test results is available

General Flow of DNA Testing

A DNA paternity test generally proceeds through the following steps.

1. Apply for and purchase a test kit
2. Collect an oral mucosa sample using the dedicated swab
3. Mail the sample to the testing laboratory
4. The laboratory extracts the DNA and performs STR analysis
5. Receive notification of the test results (usually within about 2 to 4 days)

Conclusion

Blood type and HLA typing were valuable tools for checking parent-child relationships in the era before DNA testing existed. Each method made use of the principles of inheritance, but neither could provide the kind of decisive certainty that lets one say "this is definitely true." However, the spread of DNA testing has dramatically improved the accuracy of paternity testing, making it possible to determine a parent-child relationship with confidence.

The principles of DNA testing may seem difficult, but at its core is the simple idea of "directly comparing the genetic information of parent and child." Thanks to advances in science and technology, we can now obtain far more certain answers.

If you are troubled about confirming a parent-child relationship, we strongly recommend choosing scientifically established DNA testing rather than relying on guesswork based on blood type. Modern DNA testing allows samples to be collected using the very simple method of an oral mucosa swab, with no pain, so anyone can take the test with peace of mind.

\ Confirm the parent-child relationship with the highest accuracy /

Frequently Asked Questions

Q1. Can paternity be proven using blood type alone?

A. No, blood type alone cannot prove (affirm) a parent-child relationship. The only thing blood type testing can do is "deny (exclude)" paternity by finding a genetically impossible combination. Moreover, since its exclusion rate is only about 40%, the absence of a contradiction in blood type cannot be taken as confirmation that a man is the father. To accurately confirm a parent-child relationship, DNA testing with an accuracy of 99.99% or higher is recommended.

Q2. What is the difference between HLA typing and DNA testing?

A. HLA typing examines the type of protein (HLA antigen) on the surface of white blood cells, and has an exclusion rate of about 80%. DNA testing, on the other hand, directly compares the DNA base sequence itself, achieving an overwhelming accuracy of 99.99% or higher in terms of probability of paternity. In addition, HLA typing requires a blood draw, whereas DNA testing can be performed using a simple sample such as an oral mucosa swab.

Q3. What kinds of samples can be used for DNA testing?

A. The standard sample for DNA testing is collected by swabbing the inside of the cheek (oral mucosa) with a dedicated cotton swab. No blood draw is required, and there is no pain. DNA can also be extracted and tested from various other items containing a person's cells, such as blood, hair (with the root attached), nails, or a used toothbrush.

Q4. How long does it take to receive DNA test results?

A. At seeDNA, we typically report results within about 2 to 4 days after the sample arrives at our testing laboratory. This may vary somewhat depending on the type and content of the test, but we strive to provide prompt reporting of results. Please check seeDNA's testing period and pricing page for details.

Q5. Can DNA test results be used as evidence in court?

A. Yes, we also support "legal testing (forensic testing)" that can be used in court. Legal testing requires strict procedures at the time of sample collection, such as identity verification with photo ID and the presence of a third-party witness. seeDNA supports both "private testing" for personal confirmation purposes and "legal testing" for use in court, so please feel free to contact us.

Q6. Can a blood type mutation cause a paternity test to be misjudged?

A. Yes, although rare, there have been reported cases where paternity was incorrectly denied by blood type testing due to special blood type inheritance patterns, such as cis-AB type or Bombay phenotype. There are indeed cases where paternity was denied based on blood type but was later proven, through DNA testing, to be a genuine biological parent-child relationship. For this reason, DNA testing is essential for an accurate confirmation of paternity.

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