What Is Nadir?
When discussing chemotherapy side effects often you will hear the word nadir, mainly
in reference to the blood counts, particularly white blood cell count and platelet
count. Nadir basically means low point, however further explanation may clarify
this term in connection with chemotherapy treatment.
Nadir Affects White and Red Blood Cell Counts as well as Platelet Count.
When chemotherapy is given it not only affects the rapidly dividing cancer cells
but it also affects some of the normal cells of the body. These effects particularly
occur on normal cells that divide rapidly such as, the hair, the lining of the mouth,
the cells lining the intestinal tract and the blood cells (white and red blood cells
as well as platelets).
In the bone marrow, the spongy inner core of the larger bones in the body is where
blood cells are made. There are very immature cells called stem cells, from
which the various types of blood cells develop. These stem cells do not reproduce
quickly and are less likely to be affected by chemotherapy. As cells are maturing
there are certain phases in which they divide faster. It is during these times
that the cells are most sensitive to chemotherapy. The more mature cells can
continue to become fully mature cells for several days after chemotherapy is given.
When these cells live out their life span, the circulating supply is depleted and
the blood counts fall to a low point, the nadir.
Emerging from the Nadir and Returning to Normal
The blood counts will return to normal within three to four weeks, after the body's
feedback system has told the stem cells in the bone marrow to increase production
and begin making new cells. If chemotherapy is given at the time that
the stem cells in the bone marrow are increasing their production this could cause
permanent bone marrow damage. The timing of chemotherapy cycles takes this
process into account. For example some chemotherapy drugs are given on day
1 and day 8 of a 28-day cycle. The second dose of chemotherapy, one week after
the first, is tolerated because the stem cells have not yet increased their production
(they are still at the nadir). They have not increased their production because
the second treatment is given before the count of the circulating blood has reached
The nadir time is usually about 10 days after treatment, although this may vary
depending on the drugs given. The concern during the nadir time is that the
body's first line of defense against infection, white blood cells (WBC) and the
platelets, which help to clot the blood, are low leaving a person more susceptible
to infection and bleeding. The next dose of chemotherapy is given only after
a person's blood counts have left the nadir and recovered to a safe level.
More Chemotherapy Information:
Protocols - How Chemotherapy Works
How Chemotherapy Is Given
How Doctors Decide Which Chemotherapy Drugs To Give
How Long Chemotherapy Is Given
How To Tell If Chemotherapy Is Working
Cancer Cells & Chemotherapy
Short & Long Term Side Effects of Chemotherapy
Cancer Clinical Trials