Minimal residual disease (MRD) testing in leukemia — what parents need to know

How MRD is measured — what happens at each stage

Here is what the process looks like from the point your child’s doctor orders an MRD test, through to receiving and acting on the result. Every step is the same whether the test is done for the minimal residual disease test at the end of induction or at a later monitoring point.

1. 1

   Bone marrow aspiration — collecting the sample

   The sample for MRD testing in leukemia almost always comes from the bone marrow, because that is where blood cells are made and where leukemia cells tend to accumulate. A bone marrow aspiration is performed: a thin needle is inserted into the back of the hip bone (posterior iliac crest) and a small amount of liquid marrow is drawn out.

   In children, this is done under general anaesthesia or deep sedation — your child will be completely asleep. The procedure takes about 15 to 20 minutes, and most children go home the same day. Mild soreness at the site for a day or two is normal.

2. 2

   Sample preparation in the laboratory

   The marrow sample is sent immediately to the laboratory, where it is processed to separate different types of cells. For flow cytometry MRD, the cells are stained with fluorescent antibodies that bind to specific proteins on cell surfaces. For PCR-based MRD, the DNA or RNA is extracted and amplified. The right method to use will have been decided at the time of diagnosis, based on what type of leukemia your child has and what genetic marker is being tracked.

3. 3

   Analysis — looking for leukemia cells

   For flow cytometry, a machine analyses hundreds of thousands of cells at high speed, measuring the light each cell emits when it passes through a laser. The software identifies any cells that match the abnormal pattern seen in your child’s leukemia at diagnosis. For PCR-based MRD, the laboratory looks for the presence or absence of the specific genetic sequence identified at diagnosis, and if present, measures how much of it there is.

4. 4

   The result — what the numbers mean

   The result is expressed as a number: for example, “MRD 0.01%” means that 1 in every 10,000 cells analysed was a leukemia cell. “MRD undetectable” or “MRD negative” means no leukemia cells were found at the sensitivity level of the test.

   Flow cytometry results are usually ready in two to four days. PCR-based results may take one to two weeks. Your oncologist will call you as soon as the result is available to discuss what it means in the context of your child’s full treatment picture.

5. 5

   Tumor board review and next steps

   At CION, every paediatric leukemia MRD result is reviewed by the full multidisciplinary tumor board — medical oncologists, haematologists, and other relevant specialists together. This means the decision about what to do next is never one person’s judgment.

   If the MRD result is negative, the current treatment plan is likely to continue as scheduled. If MRD is positive — particularly if it is above a threshold that signals higher risk — the team will discuss whether to intensify therapy, switch to a different approach, or evaluate further options. Your oncologist will explain the recommendation at your next consultation, with time for your questions. Decisions for healing, not billing.