Roughly one in four people worldwide is anemic, a finding from the most recent global disease-burden analysis, which counted 1.92 billion cases in 2021. Many go undiagnosed for years, and the number that quietly catches them sits on almost every routine blood test.
That number is hemoglobin, the iron-rich protein in red blood cells that carries oxygen from the lungs to the rest of the body. The World Health Organization defines anemia as a condition in which the number of red blood cells or the hemoglobin concentration within them is lower than normal.
What counts as low depends on age, sex and pregnancy. Under the WHO 2024 hemoglobin cutoffs, anemia begins at these values.
Group Also read: Normal eGFR levels by age: what your kidney function number means for you | Anemia if hemoglobin is below |
|---|---|
Men (15 to 65 years) | 13.0 g/dL |
Non-pregnant women (15 to 65 years) Also read: 9 early warning signs of type 2 diabetes most people mistake for aging | 12.0 g/dL |
Pregnant, 1st trimester | 11.0 g/dL |
Pregnant, 2nd trimester Also read: How eating broccoli every day may affect your gut, heart and cancer risk | 10.5 g/dL |
Pregnant, 3rd trimester | 11.0 g/dL |
Children 12 to 14 years Also read: Your Long COVID may be quietly raising your heart and kidney risk | 12.0 g/dL |
Children 5 to 11 years | 11.5 g/dL |
Children 24 to 59 months Also read: 8 warning signs of low blood pressure and when it becomes dangerous | 11.0 g/dL |
Children 6 to 23 months | 10.5 g/dL |
A normal adult reading generally falls between 12.0 and 17.4 g/dL, though the exact reference range shifts with the laboratory, age, race and sex, according to the Cleveland Clinic.
Why the number runs low
The dominant cause worldwide is iron shortage. WHO figures show that globally, 40 percent of children aged 6 to 59 months, 37 percent of pregnant women and 30 percent of women aged 15 to 49 are anemic. Iron deficiency is the leading nutritional driver.
Iron-deficiency anemia is the most common type of anemia, according to the National Heart, Lung, and Blood Institute. It usually starts with blood loss such as heavy menstrual periods, gastrointestinal bleeding from ulcers or colon cancer, or surgery.
Poor absorption is the second route, common in celiac disease, Crohn's disease and ulcerative colitis. Endurance athletes and people who have had weight-loss surgery also run a higher risk.
A second common driver is vitamin B12 deficiency, which develops when the body cannot make enough healthy red cells because it lacks B12. Causes include pernicious anemia (a shortage of the stomach protein intrinsic factor), long-term use of metformin or acid-suppressing drugs, autoimmune disease and strict vegan diets.
Signs of low B12 range from fatigue and pale skin to tingling in the hands and feet, seven warning signs you can spot before a blood test.
Anemia can also stem from chronic kidney disease, in which the kidneys make less erythropoietin, the hormone that tells the bone marrow to produce red cells. Long-standing inflammation, sickle cell disease and thalassemia are other causes.
When the number runs high
High hemoglobin is less common but not harmless. Recognized causes listed by the Cleveland Clinic include dehydration, chronic lung disease such as COPD and pulmonary fibrosis, congenital heart defects, some kidney diseases and polycythemia vera, a bone-marrow disorder that produces too many red cells.
Living at altitude and smoking can also push the number up.
A single reading outside the reference range does not settle a diagnosis. A doctor will usually repeat the test and add ferritin, vitamin B12, folate and a full blood count before deciding what, if anything, needs treating.
This article is made and published by Jesper Bengtson, who may have used AI in the preparation.