Low hemoglobin counts may be linked to certain diseases and conditions such as cancer, cirrhosis, hypothyroidism, iron deficiency anemia, kidney disease, leukemia and certain medications. Additional causes may include an enlarged spleen, vasculitis and blood loss resulting from a wound, bleeding in the digestive or urinary tract, nosebleeds, heavy menstrual periods and frequent blood donation.
The Mayo Clinic defines hemoglobin as the protein in an individual's red blood cells that transports oxygen. A low count is linked to a lower than normal concentration of the number of oxygen-carrying hemoglobin proteins in the blood. The same source typically defines a low hemoglobin count as under 13.5 grams of hemoglobin per deciliter, or 135 grams per liter for men, and under 120 grams per liter for women.
The Mayo Clinic also suggests that while low hemoglobin levels can be a sign of an underlying problem, they may simply be low in certain individuals, such as pregnant women. In these instances no further exam or evaluation is necessary and the low levels are not cause for concern unless the individual exhibits symptoms or signs of an underlying issue.
According to the National Heart Lung and Blood Institute, anemia can occur when the red blood cells do not have enough hemoglobin.