DNA Diagnostic Laboratory - Human and Clinical Genetics (LUMC) - LMDp_Protocols

DNA isolation from blood

(last modified December 30, 1999)


for the isolation of DNA from leucocytes (kindly provided by Jitske Weegenaar and Els Voorhoeve)

Target group

The technicians who are working in the clinical DNA-diagnostic department.


The technicians who perform the DNA-isolation are responsible for the blood- and DNA-samples until the samples are handed over to the technicians responsible for further DNA-diagnostic analysis.



In this protocol the isolation of DNA from leucocytes according to the salting out procedure [1] is described. The leucocytes are separated from the red blood cells by differential lysis of the red blood cells, followed by centrifugation to pellet down the intact leucocytes. The supernatant contains the lysed red cells. The DNA containing leucocytes are lysed and the protein debris is removed by the salting out procedure. For dirty samples a phenol-chloroform extraction (ALG009) can be performed. The data related to all samples and other findings/remarks are noted on the form WDNA.

See LP010 for the procedures concerning sample registration, handling, storage, etc.

At the end of this protocol a troubleshooting list is added.

The receipt of all the samples and their processing takes place in the pre-PCR lab. Storage of the DNA-samples is in the cold room. DNA-samples should never enter post-PCR rooms.


NOTE: equivalent durables may be used


NOTE: equivalent consumables may be used



For the solutions marked with a * a special form (with the protocol on it) is filled out. The other solutions are ready to use or made as described here.

Rules for the DNA-isolation shift


Safety measures

DNA isolation protocol

  1. Day 1: CELL LYSIS
    This part of the protocol is carried out in the laminar flow cabinet in the pre-PCR lab. Wear gloves and a lab-coat.
    a blood sample from a baby less than one year old, is lysed with 0.8 x bloodlysisbuffer instead of the regular 1 x bloodlysisbuffer. The relative high amount of fetal haemoglobin in the red cells gives these cells a different osmotic value. Washing of the pellet can be done with the 1 x bloodlysisbuffer.
    NOTE: see LP010 for the procedures concerning sample registration, handling, storage, etc.
    1. print the WDNA list and the labels from ORACLE (see LP010)
    2. check the name and date of birth present on the tube with WDNA, notate any discripancies on WDNA. Label the blood tubes and the empty blue cap tubes with the ‘Oracle-labels’
    3. a second person checks the correct labelling of the blood tubes and signs WDNA.
    4. the volumes in this protocol are based on tubes with 1 to 10 ml of decoagulated blood.
    5. invert the tube several times to get a homogeneous solution. See Troubleshooting if this is not the case.
    6. transfer the blood to a labelled sterile 50 ml blue cap tube and rinse the blood-tube with 1 x bloodlysisbuffer. Add 1 x bloodlysisbuffer to a final volume of 50 ml. Mix gently.
    7. put the tubes on ice for 30 to 60 minutes to lyse the red blood cells.
    8. spin the white cells down for 10 minutes at 1,800 rpm in the centrifuge, use the brake.
    9. Important: check if the lysis was complete before continuing. The pellet should be white and clearly visible, the supernatant should be clear. (see Troubleshooting 2, if this is not the case.)
    10. discard the supernatant in the plastic 1 l container.
    11. rinse the tube with bloodlysisbuffer, until the removal of the red supernatant is complete.
    12. to wash the leucocytes add 15 ml bloodlysisbuffer and put the tube back on ice until centrifugation. Resuspend the pellet just before the centrifugation step. Spin down (see step 1.5) and discard the supernatant. The pellet should be clean, white and without blood-clots. (see Troubleshooting 2)
    13. gently add 3 ml of nucleuslysisbuffer, use the dispenser (see Rules for the DNA-isolation shift, general). Resuspend the pellet with a vortex or tuberack directly before or after the addition of the nucleuslysisbuffer. Do not wait until you have finished a series, because lysis of the leucocytes will start and impair the resuspension of the cells.
    14. add 100 l of pronase (20 mg/ml) and mix gently. Keep the pronase on ice.
    15. add 300 l of 10% SDS and mix gently. Check if nothing has been forgotten by looking at the suspension. After addition of pronase and SDS the solution becomes clear and viscous.
    16. if nothing is forgotten and all the samples look well, incubate overnight at 37C in the incubator or for two days at RT, but not longer than 3 nights. Sign WDNA for completion of day 1
    This part of the protocol has to be carried out in the pre-PCR lab, outside the laminar flow cabinet.
    Check the samples, after the incubation with pronase and SDS, for homogeneity, clarity and viscosity by slowly stirring the tubes "in the light". When a sample is not well lysed, see Troubleshooting 3. If the sample is well lysed, but looks very dirty, you have to inform the technician responsible for the DNA diagnosis of this sample. He or she can than decide to take over the sample at this point and continue with a phenol-chloroform extraction (ALG009)
    1. print the WDIS (Oracle distribution list) list and the labels for the cryotubes from ORACLE (see LP010).
    2. mix the saturated NaCl (6.0 M) stock before use. Add 1 ml of saturated NaCl (6.0 M) to the samples.
    3. shake vigorously for 15 seconds.
    4. centrifuge for 15 minutes at 3.000 rpm in the centrifuge (Heraeus-Christ Varifuge GL), use the brake.
    5. transfer the supernatant to a clean, labelled blue cap tube by "pouring".
    6. repeat step 2.3 and 2.4. If the supernatant isn't clear after 2 centrifugation steps, you should try to remove the debris with a clean pipet, before precipitating the DNA.
    7. precipitate the DNA by gently adding 8 m1 of absolute ethanol (RT), use the dispenser (see par. 9, general). Mix gently and fish out the precipitated DNA with a sealed Pasteur pipet.
    8. wash the DNA in 70% ethanol. Remove traces of ethanol by pressing the DNA against the wall of the tube.
    9. transfer the DNA to a labelled cryotube with 100-350 l of TE-4 (for 8-10 ml of blood).
      Put a red cap on the cryotubes with a D1-isolationnr. and a yellow cap on the cryotubes with a D2-isolationnr. Write the last three digits of the DNA isolationnr. on the cap.
    10. incubate in the 65 C incubator for 30 minutes to get rid of any DNase contamination.
    11. put the cryotubes overnight on the roller bench (RT). Sign WDNA for completion of day 2
    This part of the protocol also has to be carried out in the pre-PCR lab.
    1. put the DNA samples on a bench in the prelab, together with the WDIS. The disease specific technicians collect the tubes there and take over the responsibility for the samples. They sign for receipt of each sample separately, by putting their name, date and initial on the list and store the DNA sample in the fridge. Samples that are not well dissolved are distributed later. The responsibility for the samples ends when they are accepted by the authorized persons. When all samples are distributed, sign WDIS for completion of day 3 and archive WDNA and WDIS in the folder.


[1] Miller SA, Dykes DD, Polesky HF (1988). A simple salting out procedure for extracting DNA from human nucleated cells. Nucl.Acids Res. 16: 1215.

[2] Maniatis, Sambrook and Fritsch: Molecular Cloning. Part 3, 2nd edition: page 9.18.


  1. if there are coagulations present in the blood or other abnormalities are observed, you should always seek advice from the person in charge (or his/her replecemant). In case of a blood clot it is best to remove it with a Pasteur pipet and isolate DNA from the non coagulated blood that is left over.
  2. if a white pellet is not visible, do not discard the supernatant. Always seek advice from the person in charge (or his/her replecemant). There are 2 possible explanations for this situation:
    1. lysis of the red blood cells is incomplete. There is a pellet, but it looks dirty. In this case, resuspend and put the tube back on ice for 15 minutes to complete the lysis
    2. the leucocytes are lysed too. In this case you see a very small pellet. Remove the supernatant carefully with a pipet, and store it until the isolation is completed. Handle the small pellet with care and proceed with the regular DNA isolation protocol.
  3. if lysis is incomplete, do not proceed with the protocol. Check if you did not forget to add SDS by shaking the tubes. If no foam formation is seen, add 100 l of pronase (20 mg/ml) and 300 l of 10% SDS. If there is foam formation, only add the 100 l of pronase. Incubate again at 37C as long as possible. Seek advice.
  4. sometimes blood arrives in tubes with glass pearls in it. Get rid of the glass pearls before spinning down the leucocytes. Use a plastic Pasteur pipet to transfer the blood (before or after the lysis) to a clean blue cap tube.

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