A comparison of Sarstedt S-Monovette® cfDNA Exact and Streck® Cell-Free DNA blood collecting tubes in liquid biopsies

Imagine your body is a bustling city, and inside your bloodstream, tiny fragments of information are constantly drifting like paper airplanes. These aren't just any papers; they are pieces of DNA, the instruction manuals for your cells. When cells die naturally or get hurt, they drop these fragments into the river of your blood. In cancer patients, some of these paper airplanes come from the tumor itself, carrying secret codes about the disease. Scientists call this "liquid biopsy." Instead of sticking a needle into a tumor to get a sample (which can be painful and tricky), doctors can just take a vial of blood and read the tumor's secrets from these floating DNA fragments.

But here's the catch: the blood sample is a fragile thing. If you leave it sitting around, the white blood cells in the tube might burst open, spilling their own DNA all over the place. It's like trying to read a specific note in a library, but suddenly, someone dumps a truckload of old newspapers onto the floor. The signal gets drowned out by the noise, and the tumor's secret code becomes impossible to find. To stop this, scientists use special blood collection tubes filled with a "preservative potion" that keeps the white blood cells calm and intact while the DNA floats safely on top. For a long time, one brand of these tubes was the gold standard. But recently, a new contender entered the ring, promising to do the same job. The big question was: Is the new tube just as good, or does it let the chaos begin too soon?

This study set out to put two famous blood collection tubes to the test: the well-known Streck® Cell-Free DNA BCT and the newer Sarstedt S-Monovette® cfDNA Exact. The researchers gathered 30 patients who needed liquid biopsies for their cancer care. They drew blood from each patient and split it between the two types of tubes. Then, they played a game of "spot the difference" over two timeframes: immediately after collection (Day 0) and after letting the tubes sit for a week (Day 7). They wanted to see three things: how much DNA they could get out of the tubes, how "pure" that DNA was (meaning, how much of it was actually from the tumor versus just messy background noise), and whether the tubes kept the sample stable over time.

The results were a bit of a surprise for the new tube. On Day 0, the Sarstedt S-Monovette® tubes gave up significantly less DNA than the Streck® tubes. The median amount found in the Sarstedt tubes was 19.5 ng, while the Streck tubes yielded 24.2 ng. It's as if the new tube was holding back some of the treasure. However, the "purity" of the DNA—the ratio of tumor DNA to background noise—was almost identical for both tubes right away, with both hovering around 0.90 to 0.91. So, initially, the new tube wasn't "dirty," it just had less to give.

The real story, though, unfolded over the week. When the researchers checked the tubes again on Day 7, the Streck® tubes remained rock solid. The amount of DNA didn't change much, and the purity stayed the same. The white blood cells inside were still behaving themselves, keeping their own DNA locked away. But the Sarstedt S-Monovette® tubes told a different tale. Between Day 0 and Day 7, the DNA levels shifted significantly, and the purity dropped slightly. The statistical tests showed that the null hypothesis (the idea that nothing changed) was rejected for the Sarstedt tubes with a p-value of 0.0016, but not for the Streck tubes (p = 0.81).

What does this mean in plain English? It suggests that in the Sarstedt tubes, some white blood cells started to burst open (lyse) during that week. When they burst, they released their own genomic DNA into the mix. This is like those old newspapers we mentioned earlier suddenly flooding the library. While this might make it look like there is more DNA floating around, it actually dilutes the precious tumor signal with background noise, making the sample less reliable for precise testing. The researchers suspect this might be because the preservative in the Sarstedt tube is a bit harsher on the cells, or perhaps the plastic of the tube interacts differently with the blood than the glass of the Streck tube.

The authors are careful to note that while they found these differences in the lab, they didn't test whether these changes actually messed up the final cancer diagnosis in these specific patients. They also point out that the Sarstedt tube has some practical perks: it's made of plastic (so it won't shatter if dropped) and has a special piston that might be gentler on veins during the draw. But when it comes to keeping the DNA sample stable and abundant for a full week, the Streck® tube came out on top in this head-to-head battle. The study concludes that while the Sarstedt tube is a viable option, it yields less DNA and shows signs of cell breakdown after a week, suggesting that doctors and labs need to be extra careful about how they handle it compared to the established standard.