Mayo Clinic states that normal hemoglobin levels for adult males are between 13.5 and 17.5 grams per deciliter of blood, and normal female levels are 12.0 to 15.5 grams per deciliter of blood. Normal levels for children vary by age and gender.
Mayo Clinic notes that having low hemoglobin levels is a condition called anemia. This condition is caused by a number of factors, including kidney and liver diseases; iron, vitamin B-12 or folate deficiency; bleeding; bone marrow cancers, such as leukemia; hypothyroidism; and thalassemia. A higher than normal hemoglobin level is caused by extreme vomiting or physical exercise, dehydration, polycythemia vera (a blood disorder in which the body produces too many red blood cells), lung disease, living high above sea level, smoking and burns.