I personally prefer the Qiagen kits.

We use the qiasymphony kit, but there is a lab that uses the manual QIAamp kit. Manual kit has slightly higher yield. Our application is IVD.

the qiagen kit "QIAamp DSP Virus Kit" is very good and yield can be increased by addition of formaldehyde may increase the yield of fetal dna by stabilising the in lysed maternal cells minimising fresh release of maternal cell free dna . quote below from wiki

Addition of formaldehyde to maternal blood samples increases the yield of cffDNA. Formaldehyde stabilizes intact cells, and therefore inhibits the further release of maternal DNA. With the addition of formaldehyde, the percentage of cffDNA recovered from a maternal blood sample varies between 0.32 percent and 40 percent with a mean of 7.7 percent.[20] Without the addition of formaldehyde, the mean percentage of cffDNA recovered has been measured at 20.2 percent. However, other figures vary between 5 and 96 percen

Hello, Mr. Paul,

Thank you for your suggestions. I am not planning to isolate cell free fetal DNA, but would want to isolate circulating cell free DNA from human serum or plasma samples.

I think that the point of the formaldehyde is to stop normal maternal cells lysing on sampling and storage of the sample irrespective of what the source of the cell free dna that you are interested in comes from Sneha

MagMax cell-free DNA kit (Applied Biosystems), we used it for a good number of experiments

I will suggest using Qiagen's QIAamp Circulating Nucleic Acid Kit (Cat# 55114). I get very pure preparation of DNA which I have used for droplet digital PCR and NGS. I personally have compared extraction from 10 plasma sample using Qiagen and Zymo kits and the recovery by Zymo kit was almost 10 times less. The vacuum extraction protocol which is more convenient in dealing with such a large volume of sample was not working well with Zymo Kit (note: I used regular vacuum available in our lab). The recommended centrifugation speed by Zymo kit was also not working well so I increased it and allowed it to go for more time to finish the extraction. Adding these additional steps lead to lots of inconvenience. So I will suggest Qiagen over Zymo. One of my colleague also said that my samples are of better quality then Roche kit so it suggests preparation is good compared to Roche kit as well. I don't have any experience with other cell free DNA kits.

Sunil Kumar Can Kiessling Is there a method of using the QiAmp nucleic acid kits that do not require the vacuum pump? I did not anticipate having to purchase an instrument just to carry out an extraction? I am only exploring the possibility of using cfDNA in clinical diagnostics, so can't justify such a purchase for a small validation test.

Karen Sherwood You can use any regular vacuum system available in lab instead of buying costly vacuum pump. You can also use the vacuum system available in any regular cell culture hood. However, you need to have a vacuum manifold. That work perfectly fine. In extreme case, if you don't have vacuum manifold and still want this for some validation then you may try slow centrifugation; however you need to add sample in the column multiple times as the capacity of column is only about 750 ul and you will not have option of use reservoir during centrifugation. Please let me know if you want further explanation.