The length of the whole process depends on how smooth and problem-free its individual steps turn out to be. The basic steps include:
1. Taking a blood sample
A 10 ml sample of peripheral maternal blood will be taken by a female nurse, minimizing possible contamination by a male DNA, which could affect the correct determination of the sex of the fetus (if the patient is interested to know). The optimum time for taking a sample is when the woman has completed 11 weeks of pregnancy.
Stored in a 10 ml test tube containing EDTA, the blood sample must be labelled with a bar code sticker (included in a special order form), the patient’s name and birth certificate number. As soon as the test tube is filled, it must be mixed carefully (by turning it upside down 10 times over – no shaking!). The biological material must be stored at 4 °C. The sample must not be allowed to freeze.
If the transport period is expected to be longer, i.e. more than 36 hours after the blood taking, it is necessary to use the Streck Cell Free DNA BCT system.
2. Delivery of the sample to the lab
Along with a correctly completed special order form, the sample is stored in a single transport bag and thermobag (at 4 °C), which must be delivered to the Central Lab of Medirex, a. s. in Bratislava within a maximum of 36 hours after the blood was taken.
3. Payment for the test
This step is specific for every country.
4. Release of the sample for analysis
To ensure timely analysis, it is necessary to make the required payment as soon as possible following the blood taking. Due to the financial burden of the screening test, only the samples linked to a completed payment can be analyzed. In the event of a delayed payment, incorrectly entered data, or a hindered/impossible identification of the payment, the laboratory cannot guarantee that the standard examination time limit will be met.
5. In the lab: Data analysis and evaluation using special software
1. Blood Sample Processing
As soon as the test tube is delivered to the laboratory, the plasma is separated. It contains genetic fetal material in extracellular form.
2. DNA Isolation
A free circulating DNA sample is obtained through high-precision multi-step purification. The DNA comes from both the mother and the fetus. The fetal DNA represents approximately 13 % of the DNA obtained from the plasma. If the blood was not taken in compliance with the guidelines, the blood cells can be broken down and the proportion of the fetal DNA drops, which makes the detection of potential fetal trisomy impossible. Upon isolation, a sample quality check is performed in order to identify a potential breakdown of blood cells. If such a case is identified, we contact the treating doctor, asking them to take another blood sample.
3. Preparing DNA Samples for Analysis
The isolated DNA is subjected to a specialized laboratory treatment – referred to as sequencing library preparation. To analyze samples using new-generation sequencing, it is necessary to use a sequencing library. As the total DNA amount obtained from the plasma is very small, we use a polymerase chain reaction to multiply this amount. The preparation of a sequencing library suitable for the analysis takes 48 hours.
4. Sample Quality Check
The TRISOMY test is a time-consuming and costly screening test, its result heavily dependent on well- prepared samples for analysis. Using a sensitive fluorescent electrophoretic analysis, however, we can check whether the prepared sequencing library is suitable for further analysis. Well-prepared sequencing libraries are used in the subsequent phase, which is called “sequential analysis”.
5. Final Analysis - Sequencing
Reading 30 million fragments in the course of a 20-hour period of analysis performed in a special laboratory, we analyze the whole genome with low coverage (reading approximately every tenth base, not every single one there is). The sequencing yields approximately 500 MB of data, which is subsequently evaluated using special software based on a unique mathematical algorithm. Our high-performance server is capable of evaluating data obtained from a single sample in about 20 minutes.
6. Test Results
On the basis of the data obtained, using the most progressive algorithm and a sophisticated statistical and mathematical model, our lab specialist can determine the outcome of the analysis. Along with the medical report, the results are delivered directly to the hands of the patient‘s treating physician.
6. Delivery of test results
Generally, test results are available within 5 working days upon payment verification. The test results report is delivered directly to the doctor who requested the test and took the patient‘s blood.
The patient is informed about the results of her TRISOMY test by her treating physician. Information about the sex of the fetus can be provided only after the first trimester has been completed.
|Negative result||Trisomy of chromosome 21, 18 or 13 not detected.||A negative result does not have to be validated by another screening test; the treating physician, generally a gynecologist, will choose further healthcare to be provided.|
|Positive result||Trisomy of the examined chromosomes detected.||A genetic consultation at a genetic clinic is inevitable. All positive results of the TRISOMY test must be confirmed by a genetic screening test obtained using invasive sampling.|
|Noninformative result||The sample provided could not be processed in accordance with the standard laboratory practice or the result of the screening test does not answer the diagnostic question.||Another blood sample must be taken (with no additional payment).|
Patients stay informed all through the procedure
The patient receives text messages so that she is kept up-to-date with the status of the examined sample (right after her blood is taken, the required payment is made, and a Test Result Report is sent to the treating physician, who will eventually interpret the results).
The form of the screening test
Negative results only apply to the trisomy types 21, 18 and 13 that the test is designed to monitor; however, the test does not exclude the presence of other genetic disorders, or other disorders that are not part of this test. The test result can be distorted due to multiple pregnancy, vanishing twin syndrome or foreign DNA in maternal blood samples – for example, following a blood transfusion, stem cell transplantation, organ transplantation, malignant diseases of the woman or her fetus. The detection rate of chromosomal abnormalities is individually affected by placental mosaicism, vanishing twin syndrome, point mutation, gene inactivation, or other types of genetic or epigenetic mechanisms. In such cases, the test must be preceded by a consultation with the laboratory.
Despite its high sensitivity and specificity, a positive result of the TRISOMY test must be confirmed by a genetic examination of the amniotic fluid or a chorionic villi sample. A positive result of the TRISOMY test is not a relevant reason for abortion. *
Before you recommend TRISOMYtest, make sure you consider not only the purpose, advantages and potential risks involved in this type of screening, but also other alternatives to the TRISOMY test. In addition, ensure you have weighed all relevant information about your pregnant patient‘s health condition that might possibly affect your choice of the best health care procedure.
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