When a cancer patient reaches his or her “nadir,” it means that the patient's blood counts are the lowest they will be during treatment. Low blood counts cause a variety of symptoms including lethargy, but they also leave the patient highly susceptible to infection. For this reason, cancer treatments are carefully timed so that doctors know when to expect the nadir, and cancer patients are usually warned ahead of time about the risks of this period. After the nadir, the patient's blood count will start to rise, decreasing the risk of danger and hopefully heralding the return of good health.
In order to understand this condition, it may help to know what a “blood count” is. Blood counts are performed by taking a blood sample and using it to determine the levels of the various components of blood in the body, including white blood cells and red blood cells. Chemotherapy lowers blood counts by interfering with the production of new blood cells in the marrow of the bones, causing the blood count to decline because no more cells are being produced.
White blood cells are of special concern during chemotherapy, because they have the shortest lifespan in the blood, and they are the body's first line of defense against infection. When the blood count starts to decline, white blood cells usually lead the way, and the patient is left defenseless. As the body processes the chemotherapy, the stem cells in the bone marrow start dividing again and producing new blood cells, and the blood count will begin to rise.
Timing of chemotherapy is important. If a treatment is given when the stem cells are actively producing new white blood cells, it can result in long-term problems for the patient, including bone loss. Therefore, the blood is tested before a treatment is given to determine where the stem cells are in their production cycle, which takes around 28 days. If more than one treatment is planned in a cycle of chemotherapy, the second treatment is given before the stem cells have a chance to fully recover, ensuring that they will not be in active production.
The timing of this period varies, depending on the drug involved, but the range is usually seven to 14 days. During the nadir, patients must avoid any potential sources of infection, because even a common cold can turn very serious for a cancer patient with low blood counts. People also usually feel especially poorly during the nadir period, which is something friends and family may want to keep in mind.