Be careful with the results, try to get samples in a popper solution like Tempus or PAX Tubes. Often unfortunately this is not possible so try to use the liquid parts only with the column you usually take. Clotted parts always stick on the membrane (they could be removed by pipette manually). You could also dilute (wash out) your clotted blood with a binding buffer. Often its helpful to increase centrifugation time and speed. Compare only clotted samples to find first ideas and improve data with better samples.

Dear Anke,

Thanks a lot for the comments, were very useful.

So, our case was the following: generally all the samples represented about 1 ml of clotted blood with very low liquid phase, thus it was not possible to use it. But I extended the time of Proteinase K treatment until 60'. Besides, I tryed to use the DNA extration protocol for the tissues, which includes the step of DNase treatment, comparativ to the protocol for blood. In the end I found that application of the protocol for blood with longer Proteinase K treatment was more efficient, as I got higher quantities of DNA (over 30 ng/mcl comparative to 7-10 ng/mcl) and A260/A280 ratio was more than 1.7. Still I am not satisfy with A260/A230 values that are under 1, but this is what I could get. Probably I will add one more step to perform ethanol purification of the DNA.

Kind regards,

Alexei