The number of reticulocytes present in the blood reflects bone marrow activity.
If the reticulocyte count and ratio is higher than normal, it shows increased activity of the bone marrow to replace the red blood cells in the blood. This is common after major blood loss (accident, surgery), gastrointestinal bleeding (e.g. ulcers), a disease that causes red blood cells to break down, but it can also be a side effect of medicines after the red blood cells die. However, in case of iron deficiency anaemia, the effectiveness of the treatment is indicated by the increased number and proportion of reticulocytes. Elevated reticulocyte counts can also result from smoking, pregnancy, and the body’s adaptation to higher altitudes.
If the reticulocyte count is low, it indicates a malfunction of the bone marrow. This can be caused by bone marrow disease, a lack or inadequate absorption of vitamin B12 and folic acid, or inadequate production of the hormone erythropoietin produced by the kidneys.