Flow Cytometry Test: What It Is, How It Works, and What Your Results Mean

Flow cytometry is a laboratory technique that analyzes the physical and chemical characteristics of cells or particles suspended in fluid. It is commonly performed on blood, bone marrow, or other body fluids to identify and count different cell types, such as immune cells, and to detect abnormal cells that may point to a disease or immune system problem.

Minimal Residual Disease (MRD) testing for Acute Myeloid Leukemia (AML) is an advanced laboratory test that detects extremely small numbers of leukemia cells that remain in your body after you have completed treatment such as chemotherapy or stem cell transplant. These remaining cells are too few to be seen under a regular microscope during standard testing, but they can eventually grow and cause the leukemia to return.

In flow cytometry, cells in your sample are mixed with special fluorescent dyes called markers that bind to specific proteins on or inside the cells. The sample is then passed through a laser one cell at a time. As each cell flows through, the instrument measures how light scatters and which dyes glow, allowing the laboratory to identify and count thousands of cells quickly and accurately.

Flow cytometry is a laboratory technique that analyzes individual cells as they pass through a laser beam. The test uses special antibodies tagged with fluorescent dyes that bind to specific proteins (markers) on the surface of cells. By measuring the light emitted from these dyes, the technology can identify abnormal leukemia cells based on their unique marker patterns. This allows doctors to detect one leukemia cell among 10,000 to 100,000 normal cells.

Most flow cytometry tests use a blood sample drawn from a vein in your arm with a small needle, a procedure that takes only a few minutes. In some cases, your doctor may order a bone marrow sample, which is collected with a thin needle after the area is numbed, or may use another body fluid such as cerebrospinal fluid. Once collected, your sample is labeled and sent to the laboratory for analysis.

A bone marrow sample is collected from your hip bone using a thin needle (bone marrow aspiration and biopsy). This procedure is usually done in a doctor's office or hospital. A small amount of local anesthetic is used to numb the area. The sample is then sent to a specialized laboratory where flow cytometry analysis is performed.

Your healthcare provider may order flow cytometry if you have signs or symptoms suggesting a blood cell or immune system problem, such as unexplained fatigue, frequent infections, easy bruising, swollen lymph nodes, or abnormal results on a complete blood count. The test is also used to help diagnose and classify leukemias, lymphomas, and other disorders, to monitor how well treatment is working, and to check for disease recurrence.

Your doctor may order MRD testing at several points during your AML treatment: 1) After completion of initial chemotherapy (induction therapy), to see how well the leukemia responded; 2) After additional cycles of chemotherapy (consolidation therapy); 3) Before and after stem cell transplantation; and 4) During follow-up monitoring to check for early signs of relapse.

Your results are typically reported as the percentage and number of specific cell types in your sample, often alongside reference ranges that show what is expected in healthy individuals. Abnormal findings may indicate too many or too few of certain cells, or cells carrying unusual markers that suggest a particular condition. Your doctor will interpret the results together with your symptoms, medical history, and other test findings, so be sure to discuss what your results mean for you.

Results are typically reported as a percentage or as a ratio showing how many abnormal cells were detected. A 'negative' MRD result means no detectable leukemia cells were found, which is generally a positive sign. However, 'negative' does not mean there are absolutely no leukemia cells—only that none were detected using this method. A 'positive' MRD result indicates that detectable leukemia cells remain, which may suggest a higher risk of relapse and may influence your doctor's decisions about additional treatment.