Low hemoglobin means your blood isn’t carrying enough oxygen to your tissues and organs. For adult men, that threshold is below 13.0 g/dL. For non-pregnant women, it’s below 12.0 g/dL, and for pregnant women, below 11.0 g/dL. Whether this is a minor issue or something more serious depends on how low your levels are, how quickly they dropped, and what’s causing them to fall.
How Low Hemoglobin Feels
Hemoglobin is the protein inside red blood cells that picks up oxygen in your lungs and delivers it throughout your body. When there isn’t enough of it, your organs don’t get the oxygen they need to function well. Your body compensates by speeding up your heart rate and breathing, which is why fatigue, shortness of breath, and a fast or pounding heartbeat are the hallmark symptoms.
Mild drops in hemoglobin sometimes cause no symptoms at all, especially if they develop slowly and your body has time to adjust. As levels fall further, you may notice pale skin and gums, headaches, dizziness, difficulty concentrating, and a general sense of feeling wiped out even after rest. Cold hands and feet are common too, since your body prioritizes sending oxygen to vital organs over your extremities.
Severe drops can cause confusion, extreme restlessness, chest pain, and in rare cases a bluish tint to the skin. Chest pain in particular signals that your heart is struggling to keep up with the extra workload.
What Causes It
Low hemoglobin falls into three broad categories: your body isn’t making enough red blood cells, it’s destroying them too fast, or you’re losing blood somewhere.
The most common cause worldwide is iron deficiency. Your body needs iron to build hemoglobin, and when stores run low, production slows. This can happen from a diet that doesn’t provide enough iron, but it’s frequently a sign of blood loss. Heavy menstrual periods are a leading cause in premenopausal women. Slow, invisible bleeding in the digestive tract from ulcers, polyps, or hemorrhoids is another common culprit, and it’s one reason doctors take low hemoglobin seriously even when you feel fine.
Deficiencies in vitamin B12 or folate also impair red blood cell production. Chronic kidney disease reduces a hormone that signals your bone marrow to make red blood cells. Inflammatory conditions like rheumatoid arthritis and inflammatory bowel disease can suppress production as well. Less commonly, blood cancers like leukemia or lymphoma interfere with the bone marrow directly.
On the destruction side, conditions like sickle cell disease and thalassemia cause red blood cells to break down faster than they can be replaced. An enlarged spleen can also trap and destroy red blood cells prematurely.
How Doctors Figure Out the Cause
A complete blood count tells your doctor that hemoglobin is low, but it doesn’t explain why. The next step is usually checking your iron stores through a blood test called ferritin. A ferritin level below 30 ng/mL strongly suggests iron deficiency, with 92% sensitivity at that cutoff. If you also have a chronic inflammatory condition like rheumatoid arthritis or Crohn’s disease, the threshold shifts upward because inflammation artificially inflates ferritin numbers. In those cases, iron deficiency is likely when ferritin is below 50 ng/mL. Levels at or above 100 ng/mL generally rule it out.
If iron deficiency is confirmed, your doctor will want to know where the iron is going. For women with heavy periods, that may be explanation enough. For men or postmenopausal women, unexplained iron deficiency often prompts a closer look at the digestive tract to check for sources of bleeding.
When ferritin is normal but hemoglobin is still low, testing shifts toward B12 and folate levels, kidney function, thyroid hormones, and sometimes a closer examination of the blood cells themselves to look for unusual shapes or sizes that point toward specific conditions.
When It Becomes Dangerous
Chronic low hemoglobin forces your heart to pump harder to move oxygen-depleted blood faster. Over time, this extra strain can lead to an enlarged heart, irregular heart rhythms, and eventually heart failure. These risks climb the lower your hemoglobin drops and the longer it stays there.
In pregnancy, untreated anemia raises the risk of preterm delivery, low birth weight, and developmental problems for the baby. It can also affect fetal growth, particularly during the first trimester.
Hospital guidelines generally consider a blood transfusion when hemoglobin falls to 7.0 g/dL or below in stable patients. For people with heart disease or those undergoing cardiac or orthopedic surgery, that threshold is 8.0 g/dL. Active bleeding or rapid drops change the calculus regardless of the exact number.
How Low Hemoglobin Is Treated
Treatment depends entirely on the cause. For iron deficiency, oral iron supplements are the standard first step. Therapeutic doses typically range from 100 to 200 mg of elemental iron per day, split across one to three doses. The most commonly prescribed form is ferrous sulfate, where a standard 300 mg tablet contains about 60 mg of actual elemental iron. Your doctor adjusts the dose based on how low your levels are and how well you tolerate the supplements.
Iron supplements are notorious for causing stomach upset, constipation, and nausea. Taking them on an empty stomach improves absorption but makes side effects worse. If you can’t tolerate oral iron or your body isn’t absorbing it well enough, intravenous iron infusions are an alternative that bypasses the digestive system entirely.
For B12 or folate deficiency, supplementation corrects the problem relatively quickly. Chronic kidney disease may require injections of a synthetic hormone that stimulates red blood cell production. When low hemoglobin stems from an underlying condition like inflammatory bowel disease or a blood disorder, treating that condition is the priority.
Getting More Iron From Food
Iron from animal sources (called heme iron) is absorbed significantly better than iron from plant sources (non-heme iron). Red meat, poultry, and seafood are the richest sources of the easily absorbed form. Beans, lentils, spinach, and fortified cereals provide non-heme iron, which your body has a harder time using on its own.
Pairing plant-based iron sources with vitamin C dramatically improves absorption. Adding bell peppers to a bean dish, squeezing lemon over lentils, or eating strawberries alongside fortified oatmeal all make a real difference. On the other hand, calcium supplements, bran fiber, tea, and coffee contain compounds that block non-heme iron absorption. If you’re trying to rebuild iron stores, spacing these away from iron-rich meals helps.
Diet alone is usually not enough to correct established iron deficiency anemia. It takes months of supplementation to refill depleted stores. But dietary changes support the process and help prevent levels from dropping again once they’ve been restored.
What to Watch For
If a blood test shows your hemoglobin is mildly low and you feel fine, it still warrants follow-up to identify the cause. A number that looks harmless on paper could reflect slow internal bleeding or an early nutritional deficiency that will worsen without intervention.
Symptoms that call for prompt attention include a fast or irregular heartbeat, shortness of breath during activities that didn’t used to wind you, unusual paleness, and fatigue that doesn’t improve with rest. These suggest your body is running low enough on oxygen that it’s straining to compensate.