In recent years, paternity testing has become easier, faster, and more reliable. However, DNA testing isn't perfect, and what you don't know can hurt you.
Courts now routinely accept paternity test results as a valid (and mostly irrefutable) means of determining the identity of a child's father for the purpose of instituting orders for child support. The acceptance of paternity tests to prevent or terminate child support orders, however, varies greatly from jurisdiction to jurisdiction at this time. Some courts will allow paternity test results to be used to prevent or terminate child support orders; some will not.
Since the results of a paternity test can have wide-ranging implications, it is crucial that the test method used be accurate and reliable, and that the laboratory performing the test be reputable and follow accepted scientific practices. A "false positive" result could have serious or even devastating consequences for all involved. What follows is a brief discussion of the paternity testing, with some recommendations you will want to consider if you are ever asked to take a paternity test.
For a DNA paternity test, samples (either cheek cells or blood) are taken from the mother, the child, and the alleged father. When the DNA is processed, attempts are made to find similarities between the samples. This involves looking at specific locations for common matches or 'markers'. The two most commonly used test methods vary in the number of possible locations available as markers, which has an effect on the overall ability of the test to differentiate between samples that match and samples that don't.
DNA Testing Methods Two different techniques are used to perform DNA typing: the Polymerase Chain Reaction (PCR) and Restriction Fragment Length Polymorphism (RFLP). There are other techniques, but PCR and RFLP are by far the most widely and frequently used.
PCR is a more recently developed type of DNA test. Its main advantage over RFLP testing is that it is relatively fast- a PCR test typically takes from 3 to 9 days to complete. PCR testing is most frequently used with cells collected from a swab of the inner cheek, referred to as a "buccal swab".
One advantage of PCR testing is that the analysis requires only a very small amount of material be collected to perform the test. For paternity testing the subjects (mother, father, and child) can easily provide adequate samples with a buccal swab.
The major drawback of PCR testing is that it looks at DNA locations that have fewer possible DNA sizes. Therefore a single DNA location using PCR does not generally provide as much information about paternity. Laboratories using the PCR method usually test only between six and nine DNA locations, which typically provides much less information than testing just four RFLP locations.
RFLP is an older DNA analysis technique that has been in use for a number of years. The main advantage of RFLP is accuracy- RFLP testing of four or more DNA locations will usually produce a much higher probability of paternity, and will be more reliable.
The RFLP method requires a larger sample than PCR to perform an accurate analysis. Because of this, blood was often used as a sample material for RFLP analysis. Advances in laboratory instrumentation and techniques now permit the use of material collected from a buccal swab to be used in RFLP analysis.
A minor disadvantage of the RFLP method is that it is slightly slower to produce results than PCR; it takes 10 to 14 days to properly process a DNA sample using RFLP analysis. The small amount of extra time is generally not an issue in paternity testing situations.
What You Don't Know Can Hurt You DNA testing is still not widely understood by the general public, including judges and attorneys- the technology simply has not been around long enough for differences between the two methods of testing to have become general knowledge. This unfamiliarity can have disastrous consequences, as demonstrated in an excerpt from the 'Question & Answer' section of the December 19, 2000 issue of the Dads Divorce Weekly Newsletter:
Q: I had a paternity test done and it came back 99.99% probability. A friend of min also had a paternity test done and his came back the same way. He went and had a blood test done and it came back at only 21.9%. Which one is more accurate? Is it possible that the people screwed up on my results. If so then where can I have a blood test done?
A: In at least one case I was involved with a few years ago, a "buccal swab test" (saliva test) came back with a 99% probability of paternity, but a subsequent blood test showed that the child was not my client's. A blood test is more accurate than a buccal swab test. It is certainly possible that the test was screwed up, and generally if you ask the court for a blood test (not a buccal swab test) and offer to pay all the expenses for it, you can frequently convince the judge to allow it.
In this example it appears that the attorney is confusing the type of sample (blood or buccal swab) with the type of test (PCR or RFLP). Properly performed tests using either method should yield the same result regardless of whether blood or a buccal swab is used. Based on the information above, we would guess that a PCR test was done on the buccal swab, while the blood test was performed using RFLP. Remember that PCR is generally less discriminating than RFLP.
The Importance Of Accreditation Private paternity laboratories in the United States are accredited by the American Association of Blood Banks (AABB). We cannot over-emphasize the importance of using a laboratory that is certified by the AABB. Accreditation with the AABB is important for two reasons:
Accreditation assures you that the test is performed by qualified staff and is done according to scientifically valid scientific practices. Note that at present, paternity testing laboratories are not required to obtain a license to perform paternity testing. Anyone can open a paternity laboratory and use any method they choose to perform tests. Accreditation is crucial to ensure that the test results will be accurate and reliable.
Laboratory accreditation may be required in order to allow the results of a paternity test to be admitted into evidence. Indeed, the trend is that an increasing number of courts require paternity tests to be performed by an accredited analysis service. Keep in mind that the most favorable test results in the world are of no use if they cannot be used in court. Depending upon the nature of your case, this could work for you or against you. If you intend to use a paternity test to your benefit, make certain that the court will accept the results of the test as valid.
Accuracy Considerations Many paternity testing laboratories guarantee their test results to an accuracy of 99.0%. Although this sounds extremely accurate, the fact is that it is not. A 99.0% "match" means that the test has identified a genetic pattern that is possessed, on average, by one in every one hundred men in the population. One out of one hundred is not sufficient to be certain of paternity, in our opinion. We strongly recommend using a laboratory that tests to a probability beyond 99.0%. The chances of receiving a false positive are 100 times greater if the test only shows a 99.0% probability of paternity compared to a 99.99% probability of paternity. A probability of 99.99% equates to one in ten thousand- sufficient for a reasonably certain determination of paternity. Unfortunately, at this time a limited number of laboratories test to levels beyond 99.0%
Paternity Testing Costs The average price for a paternity test is $450 to $500. There is a wide variance in pricing, but a properly conducted paternity test should not cost more than $600 or so. The more rigorously-controlled laboratories are likely to have higher internal costs which may in turn be passed along to their clients. Not surprisingly, it costs more to run a highly-controlled, consistent testing process than it does to perform shoddy tests with poor methodology and/or outdated, less expensive equipment. Factors like accreditation and newer, more capable laboratory instrumentation may add to the base cost of the testing process.
Some State agencies arrange for a contracted rate with testing laboratories that allows them to offer paternity tests at rates well below the standard fee. Check with the court and Office of Support Enforcement in your State to see if they can provide testing services at a reduced cost.
Results Of Paternity Testing Paternity test results are normally expressed as "0% chance of parentage" or "better than a 99.0% chance of parentage". Most of the better laboratories test to 99.9% (1 in 1000), which is the minimum percentage we recommend. Currently, only one laboratory (PTC) tests to 99.99% (1 in 10,000). A result such as "21.9%" (as in the example above) should never be seen, much less accepted. Such a result may indicate that the test was performed by an unaccredited laboratory, or performed improperly.
Chain Of Evidence Another factor to pay attention to is the "chain of custody" procedure the lab must follow. Simply put, the sample must be able to be accounted for every step of the way, from collection to testing. If at any time the movement, handling or storage of the sample cannot be documented and accounted for, the possibility exists that the sample may have been tampered with or perhaps substituted with another sample altogether. Make certain that the laboratory performing the test has procedures in place to satisfy the court's rules regarding the chain of custody for evidence.
EXERCISE CAUTION WHEN USING A PCR TEST. The PCR test is usually less discriminating (accurate) than a 4-probe RFLP test if only six or nine DNA locations are tested (especially so in 'motherless' cases). Another consideration is that because PCR analysis is a more recently developed test, PCR results may be challenged in court as "unreliable" or "unproven". The RFLP technique has been in use for a long time and is widely recognized as scientifically valid. Virtually all courts will accept RFLP test results without argument. We strongly suggest obtaining an RFLP test if at all possible (this is a must for motherless testing). If for some reason you must use the PCR method:
request a specific number of PCR locations to be tested (10 or more locations), and
make sure that you are being guaranteed a minimum of at least a 99.99% probability of paternity.
Educate your attorney. Your attorney may be a legal wizard, but chances are he doesn't know enough about DNA analysis to make an informed choice when it comes to paternity testing methods. Send him this page, then discuss it with him. This may provide him with alternative legal strategies he can use to better represent you.
Know what kind of results to expect. A properly performed test should rule the tested person in or out with virtual certainty- "0%" or "99.0%". Never accept a test result that falls somewhere in the middle- it doesn't work that way.
Test To Beyond 99.9% As mentioned above, accuracy increases radically beyond the 99.0% mark. One out of one hundred is not sufficient to conclusively determine paternity. We suggest you insist on using a laboratory that will test beyond 99.0%. Because the results of a paternity test can have serious implications, we strongly recommend that you get the most accurate test possible.