An HGB blood test measures the amount of hemoglobin in your blood. Hemoglobin is a protein inside red blood cells that picks up oxygen in your lungs and delivers it to every tissue in your body. The test result is reported in grams per deciliter (g/dL), and it’s one of the most commonly ordered lab values, usually included as part of a routine complete blood count (CBC).
What Hemoglobin Actually Does
Think of each red blood cell as a delivery vehicle. Hemoglobin sits in the driver’s seat, loading up oxygen in the lungs and dropping it off wherever your body needs it. It also carries a portion of carbon dioxide back to the lungs so you can exhale it. When hemoglobin levels are too low, your tissues don’t get enough oxygen and you feel the effects. When levels are too high, your blood thickens and flow becomes less efficient.
Normal Ranges for Adults
Healthy hemoglobin levels differ between men and women:
- Men: 13.2 to 16.6 g/dL
- Women: 11.6 to 15.0 g/dL
Your result landing within this range generally means your red blood cells are carrying oxygen effectively. A value slightly outside the range isn’t always cause for concern on its own. Labs may have slightly different cutoffs, and your doctor will interpret the number alongside your symptoms and other test results.
Normal Ranges During Pregnancy
Pregnancy naturally expands your blood volume, which dilutes hemoglobin and lowers your reading even when nothing is wrong. Because of this, the thresholds for anemia are adjusted by trimester:
- First trimester: below 11 g/dL is considered anemic
- Second trimester: below 10.5 g/dL
- Third trimester: below 11 g/dL
Routine prenatal bloodwork checks hemoglobin at least once, often more, because untreated anemia during pregnancy can affect both energy levels and fetal development.
Normal Ranges for Children
Children’s hemoglobin levels shift substantially from birth through adolescence. Newborns start high, around 16.5 g/dL on average, because they needed extra oxygen-carrying capacity in the womb. By two months that drops to roughly 11.2 g/dL as the body breaks down the extra red blood cells it no longer needs. From six months to age six, a typical level is about 12 to 12.5 g/dL. During the teen years, boys’ levels climb to an average of 14.5 g/dL while girls average around 14 g/dL, with the gap widening after puberty due to hormonal differences.
In children, anemia is defined as a hemoglobin level falling more than two standard deviations below the average for their age. Pediatricians use age-specific charts rather than a single cutoff.
What Causes Low Hemoglobin
A low hemoglobin result is the lab’s way of saying you’re anemic. How you feel depends on how low the number is and how quickly it dropped. Common symptoms include fatigue, pale skin, shortness of breath during activity, dizziness, and cold hands or feet. Several categories of causes account for most cases.
Iron Deficiency
This is the most common type of anemia worldwide. Your bone marrow needs iron as a raw material to build hemoglobin. Without enough of it, production slows. Heavy menstrual periods, poor dietary intake, and bleeding in the digestive tract (sometimes from ulcers or polyps) are frequent culprits. Treatment typically involves iron-rich foods or iron supplements, and improvement shows up on repeat labs within a few weeks.
Vitamin Deficiency
Your body also needs folate and vitamin B-12 to produce healthy red blood cells. A diet low in these nutrients, or a condition that prevents B-12 absorption in the gut (sometimes called pernicious anemia), can drive hemoglobin down. This type of anemia often produces unusually large red blood cells, which your doctor can spot on the same CBC.
Chronic Disease
Conditions like kidney disease, cancer, rheumatoid arthritis, Crohn’s disease, and diabetes can suppress red blood cell production over time. Ongoing inflammation signals the body to hold back iron from the bone marrow, even when iron stores are adequate. This form of anemia tends to be mild to moderate and often improves when the underlying condition is managed.
What Causes High Hemoglobin
A hemoglobin level above the normal range is less common than a low one, but it still signals something worth investigating. When hemoglobin is elevated, blood becomes thicker and moves through vessels less smoothly, raising the risk of clots.
Smoking is one of the most frequent causes. Carbon monoxide from cigarettes binds to hemoglobin and makes it less effective at carrying oxygen, so the body compensates by producing more red blood cells. Chronic lung conditions like emphysema or COPD trigger the same response because oxygen levels in the blood are persistently low. Severe dehydration can also push the number up temporarily by reducing the liquid portion of blood and concentrating the cells that remain.
In rarer cases, a blood cancer called polycythemia vera causes the bone marrow to overproduce red blood cells due to a genetic mutation. This condition is typically caught when routine bloodwork reveals a persistently elevated hemoglobin level along with other abnormal counts.
How Altitude Affects Your Results
If you live at elevation, expect a higher baseline hemoglobin level. A large study of young men in Switzerland found that hemoglobin concentrations increased in a stepwise pattern with every 300-meter gain in residential altitude, rising by nearly 3% between the lowest and highest elevations studied. This happens because thinner air contains less oxygen, and the body’s oxygen-sensing system responds by ramping up red blood cell production. The adjustment is precise enough to detect even modest altitude differences. If you’ve recently moved to a higher or lower elevation, your results may shift over the following weeks as your body adapts.
How the Test Works
The hemoglobin test is a standard blood draw, usually from a vein in your arm. It takes less than a minute and requires no fasting or special preparation. The sample goes to a lab where automated analyzers measure hemoglobin concentration using light-based techniques. Results are typically available within a day, often within hours.
Hemoglobin is almost always reported as part of a complete blood count, which also includes your hematocrit (the percentage of blood volume occupied by red blood cells), red blood cell count, white blood cell count, and platelet count. Hematocrit and hemoglobin tend to move in the same direction and are calculated from related measurements. If one is abnormal, the other usually is too. Together, these values give a fuller picture of your blood’s oxygen-carrying capacity and overall health.
What to Do With Your Results
If your hemoglobin comes back normal, no follow-up is needed on that front. If it’s mildly low, your provider may recheck it in a few weeks or add iron and vitamin levels to the next round of labs. A significantly low result often leads to additional testing to pinpoint the cause, such as checking stored iron levels, B-12, or markers of inflammation.
For a high result, the next step usually depends on context. If you’re a smoker or live at altitude, the elevation may be expected. If not, repeat testing and further investigation into lung function or bone marrow activity may follow. In either direction, a single hemoglobin value is a starting point. Its meaning becomes clearer when paired with your symptoms, medical history, and the rest of your CBC.