Before the 1980s, blood tests were the primary way to establish paternity when the father of a child was in question. Since that time, DNA has become prevalent tool to determine paternity, and is a popular choice because of its powerful accuracy. Blood tests are still used and, while there are differences in blood tests and DNA tests, often have results that are comparable.
Blood samples can be compared between parents and offspring and establish paternity to within 30 to 40 percent certainty, based on factors such as blood typing, serum factors or proteins. DNA samples, however, can establish paternity with nearly 100 percent accuracy because they are based on the actual genes not just blood type —which is simply a manifestation of a handful of genes.
Paternity tests based on blood require that blood samples be taken from both the parent and offspring. DNA samples are available not only in blood, but in hair and skin cells as well. Because of this, DNA samples are considered less invasive to retrieve.
Small amounts of DNA can be sampled, whereas blood samples required can be large. This makes using blood tests for young babies difficult, if not impossible. Only a few cells are necessary for a DNA test, because DNA must be replicated before it can be tested, regardless of whether the sample is large or small.
DNA tests are useful in establishing paternity, and are also useful in determining degrees of relatedness among other relatives—for instance, a suspected paternal grandmother. Blood tests are not as accurate. Because blood testing is not as exact, it is nearly impossible to establish extended relations using blood testing.
DNA for paternity testing can be collected in the privacy of your home and sent to a private laboratory, for a fee. Samples for blood testing for paternity must be taken by a medical professional, and is therefore not as discreet as a DNA test. It should be noted that DNA samples sent in from home will likely not be admissible in court, because it cannot be determined definitively to whom the samples actually belong.
Test Cost and Timing
The cost of a DNA paternity test can be as little as just under $100. However, for the results to be legally admissible, a test will average around $600. DNA test results are generally available within two weeks, but can be done in as little as two days, if necessary. Blood testing is done less frequently because the cost of DNA tests has decreased and they offer a great deal more accuracy, as well as a number of other advantages. However, the results of blood tests can be determined immediately. Kits can be purchased for under $20 that can test for ABO and Rh, factors which are limited in their accuracy as paternity tests.