HAEM-Lok™, a new approach to the collection and stabilization of cell-free DNA in plasma

Introduction. Currently available blood collection tubes for cell-free DNA in plasma stabilize white blood cells either by mild fixation or precipitation. Typically, cellular DNA appears in plasma within several days. HAEM-Lok™ tubes use an entirely different principle for preserving cell-free DNA: they contain a special matrix and solution that act together to produce a physical barrier separating plasma from blood cells.

Methods. Blood samples were collected in EDTA or HAEM-Lok™ tubes from >200 pregnant women carrying a male offspring. HAEM-Lok™ tubes were centrifuged between 10 min and 4 hours after collection and then kept at room temperature. Plasma samples were removed at different times for qPCR analysis. Cell-free fetal DNA was quantified using primers for Y-chromosome specific TSPY1 gene and total DNA using primers for chromosome 18 gene TYMS.

Results. There was no distinguishable difference in total DNA levels in EDTA plasma and HAEM-Lok™ plasma at day 0 (average of about 6 ng/mL plasma). However, collection of cell-free plasma in HAEM-Lok™ was appreciably easier than EDTA tubes because of the absence of a white blood cell “buffy coat”. In HAEM-Lok™, both plasma total and fetal DNA levels were essentially unchanged from day 0 for all time points up to 21 days. In contrast, levels of total DNA in EDTA plasma began to rise after a few days and continued to rise, reaching levels by day 21 of 100-1000-fold higher than day 0 levels.

Discussion and Conclusions. HAEM-Lok™ collection tubes are unique in that they stabilize cell-free fetal DNA by introducing a physical barrier between plasma and blood cells. The levels of total DNA and fetal DNA in plasma remain essentially constant for samples stored at ambient temperature for at least 21 days, thereby allowing for considerable flexibility in scheduling and shipping. An additional benefit of HAEM-Lok™ is the absence of a buffy coat, which appreciably simplifies the collection of cell-free plasma.