When having a genetic test it can be difficult to imagine what happens to your sample, what the scientists do with it to get your result and why it can take a long time. This section should help make this a bit clearer.
What happens to your sample when it arrives at the genetic laboratory?
When your sample arrives at the genetic laboratory a record is created on the hospital system and the sample is given a unique code. This code enables the sample to be tracked throughout the testing process. Most samples received by the laboratory arrive as blood, but sometimes they can be tissue samples, such as muscle or tumour samples, as well as saliva, cells and occasionally urine.
A scientist will check they have been given enough information about you, your family history and any symptoms that you or your family members may have. It is important for the scientist to have this information as it will help them check that the correct test has been requested and it may help them when interpreting the test results.
Your sample will then undergo a process to extract the DNA and will be assigned to a specialist laboratory technician. Once the DNA is extracted, it is ready for testing.
What is involved in the genetic testing process?
Each genetic condition is tested in a different way, depending on the gene or genes involved and the types of genetic alterations (mutations) associated with the condition. Laboratories use a lot of specialised equipment to be able to achieve this. Throughout the testing process there are many steps and checks that have to be done to ensure the correct result is given to a patient. The actual testing process itself can take many weeks to complete.
If a genetic alteration is found during testing it will always be re-tested using a separate sample from the same patient. This is to double check the result is accurate.
Once a complete set of raw results have been obtained, two different scientists will analyse them separately. If a genetic alteration found has not been seen before, it will need to be looked up on specialist databases to try and work out if it’s likely to be the cause of a patient’s symptoms. In other cases, genetic alterations will be found which have already been seen in another individual with similar symptoms, and thus it may be more straightforward to know whether or not the alteration found contributes to the condition.
If both scientists agree, the result is confirmed and a report is written. It is not unusual for additional calculations to be completed at this point to determine the risk of the condition for other family members. Sometimes this may require extra tests to be performed, or further family history information to be obtained.
Finally, the report is checked by a senior scientist and sent to your doctor or genetic counsellor. Your doctor/genetic counsellor will then need to read this report carefully and sometimes come back to the lab with questions before they see you in clinic to give you your results.
This careful process is carried out by all NHS and other accredited laboratories to ensure you get the most accurate result possible.
Why do some tests take longer than others?
Individual samples are not usually tested on their own. Before starting the testing process, the laboratory will often wait for a few samples needing the same test to arrive. This is because the testing process is complex and has many steps, so it’s more efficient for samples to be batched together.
Each genetic test has its own set reporting time, which is the number of days or weeks by which all testing should be completed and the report sent to your doctor. Scientists work hard to ensure they get the result back to your doctor as quickly as possible, but there are occasions when there may be slight delays. Occasionally samples fail and another fresh sample needs to be requested. This is all part of ensuring high quality, accurate testing.
Can any genetic lab do any genetic test?
Not all genetic labs do all genetic tests. Each laboratory has its own set list of different tests that it can provide. Some of the more common genetic conditions, such as Cystic Fibrosis, may be tested by multiple laboratories, but less common conditions may only be tested by one or two different labs. If, for instance, you live in the South East of England and your blood was sent to your local genetic centre but they did not test for that condition, your sample may need to travel to the north of the country for testing. Occasionally samples need to be sent abroad for very specialist or new types of testing.
By Keeley Monsen, Genetic Technologist and Emily Clarke, Genetic Counsellor