The development of non-invasive prenatal test cfDNA 2011 opened new perspectives to detect chromosomal abnormalities in the first trimester of pregnancy with a simple blood draw from the arm of the pregnant woman which is 100% safe!
The first four years there were only five companies that were offering this test worldwide. But over the last 12 months other companies have started to replicate the technology of the first but it is unsure if they meet very basic criteria for safe analysis of samples. One of the most important and initial data analysis one cfDNA test is the correct blood collection and transportation of the samples.
Already in 2003, Angert and colleagues had shown that if the blood sampling is done on blood collection tube with anticoagulant K3EDTA (purple cap tubes), then the analysis of the sample must be done within 6 hours after blood collection. Otherwise, the maternal blood cells are lysed as the time goes by and release additional free DNA interfering with the analysis of the free fetal DNA in blood. I myself also confirmed this research during my PhD at King’s College London.
Indeed in 2011, Barrett and colleagues reinforced these findings and added that maintaining the samples at 4 degrees Celsius is no better than the preservation at room temperature. Furthermore, they concluded that the best preservation of the sample is in special tubes with stabilizing agents.
Finally, in 2013, Norton and colleagues confirmed that free fetal DNA is kept completely unchanged for 7 days into the tubes with a special stabilizer which are globally patented by the company Streck in USA. This opened the way of shipment of samples in the USA for their analysis, which usually takes two days from our territory. Currently, the vast majority of tests performed worldwide are in cfDNA Streck tubes and their reliability has been confirmed extensively.
Therefore, when deciding upon a cfDNA test, it is advisable to verify that the blood samples are placed in the specific tubes by Streck containing a fixative material in order to make sure that your sample will remain unchanged for seven days. Other options should be avoided because the sample cannot be maintained for 24 hours and their only purpose is to reduce the cost of the examination (the Streck tubes are 100 times more expensive than regular test tubes).
References
Angert RM, LeShane ES, Lo YM, Chan LY, Delli-Bovi LC, et al. Fetal cell-free plasma DNA concentrations in maternal blood are stable 24 hrs after collection: analysis of first- and third-trimester samples. Clin Chem. 2003;49:195–198.
Barrett AN, Zimmermann BG, Darrell Wang D, Holloway A, Chitty AS. Implementing Prenatal Diagnosis Based on Cell-Free Fetal DNA: Accurate Identification of Factors Affecting Fetal DNA Yield, PLoS One. 2011; 6(10): e25202.
Norton SE, Lechner JM, Williams T, Fernando MR. A stabilizing reagent prevents cell-free DNA contamination by cellular DNA in plasma during blood sample storage and shipping as determined by digital PCR.Clin Biochem. 2013 Oct;46(15):1561-5. doi: 10.1016/j.clinbiochem.2013.06.002. Epub 2013 Jun 13.
