Hemoglobin
The oxygen-carrying protein in your red blood cells. It is the main number used to check for anemia.
AI-verified against cited sources. Awaiting expert reviewAlso called Hgb, Hb, HGBLOINC 718-7
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The usual range for Hemoglobin depends on sex. Choose female or male above to see where you stand.
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What it is
Hemoglobin is an iron-rich protein inside your red blood cells. It picks up oxygen in your lungs and delivers it to every part of your body. A hemoglobin test measures how much of it is in a given amount of blood. It is part of a complete blood count (CBC). It is not the same test as hemoglobin A1c, which tracks blood sugar.
Why it matters
Your cells need oxygen to make energy. When hemoglobin runs low, your blood carries less oxygen, which can bring tiredness, weakness, shortness of breath or a pale look. Very high levels can make blood thicker. Many results outside the usual range have simple, treatable causes, such as low iron, blood loss, dehydration or living at altitude. The number is most useful when read with your other red cell results and how you feel.
If it’s low
A low hemoglobin is called anemia when it falls below the usual range for your age and sex. It means your blood is carrying less oxygen than expected. It is common, and the cause can often be found with a few more tests.
Common causes
- Low iron, the most common cause worldwide, from low intake, poor absorption or ongoing blood loss
- Blood loss, including heavy periods, frequent blood donation or bleeding in the digestive tract
- Low vitamin B12 or folate
- Long-term conditions such as kidney disease or ongoing inflammation
- Pregnancy, when extra fluid in the blood dilutes the red cells
- Inherited conditions that change hemoglobin, such as thalassemia or sickle cell disease
- Less often, bone marrow conditions or the breakdown of red cells
What can help
- Ask which tests could find the cause, such as ferritin, vitamin B12, folate or a reticulocyte count
- Eat iron-rich foods such as beans, lentils, leafy greens, meat and fortified cereals, and pair them with vitamin C
- Ask your clinician before taking an iron supplement, because extra iron is not right for everyone
If it’s high
A high hemoglobin often has an everyday explanation, such as being low on fluids, smoking or living at a high altitude. It can also mean the body is making extra red blood cells, which is worth a closer look if it stays high on repeat tests. Your clinician can put it in context.
Common causes
- Dehydration, which makes the blood more concentrated
- Smoking, because carbon monoxide lowers oxygen delivery and the body responds by making more red cells
- Living or training at high altitude
- Testosterone therapy or other hormone products that stimulate red cell production
- Conditions that lower oxygen levels, such as sleep apnea or long-term lung disease
- Some medicines, including SGLT2 inhibitors used for diabetes, heart or kidney conditions
- Less often, a bone marrow condition that makes too many red cells (polycythemia vera) or a tumor that makes erythropoietin
What can help
- Tell your clinician if you smoke, snore heavily, live at altitude or use testosterone or other hormones
- Ask whether being low on fluids could explain it, and whether a repeat test makes sense
- Ask whether any other tests would help find the cause if it stays high
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex and age. Choose women or men to see the one that applies.
- Men, 16+13–17.7 g/dL
Sources: Labcorp, Mayo Clinic Laboratories, ARUP Laboratories, Te Whatu Ora Health New Zealand, Waikato
- Women, 16+11.1–15.9 g/dL
Sources: Labcorp, Mayo Clinic Laboratories, ARUP Laboratories, Te Whatu Ora Health New Zealand, Waikato
Children and teens 8 ranges
- Men, 13–1512.6–17.7 g/dL
Source: Labcorp
- Women, 13–1511.1–15.9 g/dL
Source: Labcorp
- 8–1211.7–15.7 g/dL
Source: Labcorp
- 1–710.9–14.8 g/dL
Source: Labcorp
- 0.249–010.4–14.1 g/dL
Source: Labcorp
- 0.085–-0.7518.8–14.3 g/dL
Source: Labcorp
- 0.022–-0.91510.5–18.7 g/dL
Source: Labcorp
- under 0.02210.7–20.5 g/dL
Source: Labcorp
See Hemoglobin by age and sex, with the U.S. survey numbers where they exist.
WHO 2024 anemia severity, men aged 15-65
- Severe anemiabelow 80 g/L
- Moderate anemia80 to under 110 g/L
- Mild anemia110 to under 130 g/L
- No anemia130 and above g/L
WHO 2024 anemia severity, non-pregnant women aged 15-65
- Severe anemiabelow 80 g/L
- Moderate anemia80 to under 110 g/L
- Mild anemia110 to under 120 g/L
- No anemia120 and above g/L
WHO 2024 anemia severity, pregnancy (first trimester)
- Severe anemiabelow 70 g/L
- Moderate anemia70 to under 100 g/L
- Mild anemia100 to under 110 g/L
- No anemia110 and above g/L
WHO 2024 anemia severity, pregnancy (second trimester)
- Severe anemiabelow 70 g/L
- Moderate anemia70 to under 95 g/L
- Mild anemia95 to under 105 g/L
- No anemia105 and above g/L
WHO 2024 anemia severity, pregnancy (third trimester)
- Severe anemiabelow 70 g/L
- Moderate anemia70 to under 100 g/L
- Mild anemia100 to under 110 g/L
- No anemia110 and above g/L
If this applies to you
Hemoglobin means a little more for some people. Open the one that fits you.
Had weight-loss surgery
Hemoglobin is the main number on a blood count for spotting anemia, and anemia from low iron is common after bariatric surgery. BOMSS suggests a blood count and ferritin at 3, 6 and 12 months, then at least yearly.
Celiac disease or IBD
Anemia is common in both conditions. Unexplained iron deficiency anemia is one of the reasons ACG lists for celiac testing, and in IBD, BSG notes that low iron, B12 or folate can all lie behind anemia.
Endurance athlete
Endurance training expands plasma, the watery part of blood, so hemoglobin and hematocrit can read a little lower even though the body has more red cells in total. This is sometimes called sports anemia and isn't anemia in the medical sense. Iron deficiency and under-fuelling can lower hemoglobin too.
Hemochromatosis or iron overload
Each phlebotomy removes red cells, so hemoglobin is checked at each session. ACG checks it before and during treatment to make sure it stays above 11 g/dL. EASL suggests fewer sessions when it is below 12 g/dL and a pause below 11 g/dL.
Kidney disease or at risk
Anemia becomes more common as kidney function falls. KDIGO 2024 notes that average hemoglobin is lower in people with an eGFR below 60 and keeps falling as eGFR drops, so clinicians often check hemoglobin in people with CKD.
Low iron or anemia
Hemoglobin shows whether low iron has led to anemia. BSG notes that hemoglobin usually starts to rise within 2 weeks of starting iron by mouth when low iron is the cause, so it is the main number used to follow the response.
Age 65 or older
Anemia is common in older adults. About a third of cases come from low iron, B12 or folate, about a third from inflammation or kidney disease, and about a third have no clear cause. Even a drop in hemoglobin that stays above the anemia cutoff has been linked to health problems at older ages.
Perimenopause or menopause
Heavy periods are more likely in the menopause transition than at other times of life, a review of midlife studies notes. NICE suggests a full blood count, which includes hemoglobin, for anyone with heavy periods.
Pregnant or postpartum
Hemoglobin falls in the first and second trimesters because blood volume expands, so pregnancy has its own anemia cutoffs. The USPSTF notes that ACOG, the AAFP and the CDC recommend checking for anemia at the first prenatal visit, and that ACOG recommends checking again at 24 to 28 weeks.
Vegan or vegetarian
In Western vegetarians, hemoglobin and most other iron measures are similar to those of meat-eaters, according to the Academy, because iron absorption adapts. Hemoglobin shows whether lower iron stores have gone on to cause anemia.
On gender-affirming hormones
Hemoglobin follows hematocrit. After about 6 months on full-dose therapy, it tends to settle into the range of your affirmed gender: higher on testosterone, and lower on estradiol with an androgen blocker.
Taking methotrexate
Hemoglobin is the red cell part of the blood count. The label warns that methotrexate can lower all the blood cell lines, so hemoglobin is read with white cells and platelets.
On testosterone therapy
Hemoglobin rises along with hematocrit on testosterone. The FDA label lists both among the tests to check periodically, and notes that a higher red cell mass may raise the risk of blood clots.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Hemoglobin by age and sex: every percentile as a table, with a download.
What can affect your result
- Sex: levels are higher in men than in women after puberty. Hormones and monthly blood loss both play a part
- Age: levels are high at birth, drop over the first months of life, and reach adult levels in the teen years
- Pregnancy: blood volume grows faster than red cell mass, so levels fall. WHO uses a different cutoff for each trimester
- Altitude: living higher raises hemoglobin. WHO suggests raising the anemia cutoff by about 4 g/L (0.4 g/dL) at 500-999 m and by 11 g/L (1.1 g/dL) at 1,500-1,999 m
- Smoking: raises hemoglobin by roughly 3 to 6 g/L depending on how much you smoke (WHO adjustment)
- Hydration and posture: dehydration and standing before the draw both raise the result
- Ancestry: some studies find average hemoglobin about 10 g/L lower in Black than in White individuals. WHO does not recommend separate cutoffs
- Recent blood donation, a transfusion or IV fluids
- Lab method: very high blood fats (lipemia) can falsely raise results on some analyzers
- Standing before the draw raises hemoglobin compared with sitting or lying down (about 7% higher standing than lying down in one small study).
- Dehydration or a long tourniquet time can concentrate the blood and push the result up.
- Very high blood fats (lipemia) can falsely raise hemoglobin on some analyzers.
- Recent blood donation, a transfusion or IV fluids change the result.
Any time of day. When you compare results over time, try to keep your posture and hydration similar. Red blood cells live about 120 days, so changes usually show over weeks to months. Rebuilding after a blood donation or blood loss takes several weeks.
When to talk to a clinician
If you have chest pain, trouble breathing or fainting, call 911 or your local emergency number. Call your clinician soon if a low result comes with a racing heartbeat at rest, new weakness, or black or bloody stools. Labcorp's critical limits for hemoglobin are below 6.1 g/dL (61 g/L) and above 21.4 g/dL (214 g/L), levels where labs call the ordering clinician right away. WHO classes adult hemoglobin below 8.0 g/dL (80 g/L) as severe anemia, and below 7.0 g/dL (70 g/L) in pregnancy. A result that stays outside your lab's range is worth raising at your next visit.
Questions you could ask
- How does my hemoglobin compare with my past results?
- Does my altitude, pregnancy status or smoking history change how to read this number?
- Could dehydration, smoking, altitude or any of my medicines explain this result?
- Should we repeat the test, and is anything else worth checking alongside it?
- What might be causing my hemoglobin to be low?
- Should we check iron (ferritin), vitamin B12 or folate?
Questions people ask
Why is my lab's range different from the WHO anemia cutoffs?
A lab's range is meant to cover the middle 95% of a reference group, while WHO's cutoffs are set to flag anemia: below 12.0 g/dL for non-pregnant women and below 13.0 g/dL for men aged 15 to 65. They answer different questions, so they do not have to match. Your clinician looks at both, along with your symptoms and other results.
Is hemoglobin the same as hemoglobin A1c?
No. Hemoglobin is the oxygen-carrying protein in your red blood cells. Hemoglobin A1c reflects your average blood sugar over the past few months. They often appear on the same report, so they are easy to mix up.
Do altitude and smoking change what is usual for me?
Yes. Your body makes more red cells when oxygen is harder to get. WHO's 2024 guideline suggests raising the anemia cutoff by about 4 g/L (0.4 g/dL) at 500-999 m, 8 g/L at 1,000-1,499 m and 11 g/L (1.1 g/dL) at 1,500-1,999 m, and by 3 to 6 g/L for smoking. The range printed on your report does not include these adjustments, so mention both to your clinician.
Can dehydration or the way I was sitting change my result?
A little. Being low on fluids makes blood more concentrated, so hemoglobin can read higher, and standing before a draw can raise it too. Drawing at a similar time, in the same posture and with similar hydration makes trends easier to compare.
How do I convert hemoglobin units?
To go from g/dL to g/L, multiply by 10, so 13.5 g/dL is 135 g/L. To go from g/dL to mmol/L, multiply by 0.6206, which uses the usual monomer basis for mmol/L. To go the other way, divide by the same number. If your lab's mmol/L numbers look about four times smaller, it may use a different basis, so check with the lab.
Show the science and sources
Units
- 1 g/dL = 1 g/dL
- 1 g/dL = 10 g/L
- 1 g/dL = 0.6206 mmol/L
Open the Hemoglobin unit converter
Is a change real?
Hemoglobin naturally varies about 2.71% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 8% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters (Coskun A et al., EFLM WG-BV).
For clinicians and researchers
Hemoglobin is measured photometrically after the red cells are lysed. The ICSH reference method converts hemoglobin to cyanmethemoglobin (HiCN), and many analyzers use cyanide-free reagents calibrated to it. Results are mass per volume (g/dL in the US, g/L in most other countries). Some labs report mmol/L on a monomer (Hb(Fe)) basis, where 1 g/dL = 0.6206 mmol/L; a tetramer basis gives numbers about four times smaller, so check the unit your lab used before converting. A lab reference interval describes the central ~95% of a reference group and is not an anemia cutoff. Labcorp's lower limit for women is 11.1 g/dL, while WHO (2024) defines anemia as below 120 g/L in non-pregnant women and below 130 g/L in men aged 15 to 65, with mild, moderate and severe bands and trimester-specific values in pregnancy. WHO derived the cutoffs from 5th percentiles in apparently healthy populations, recommends adjustments for altitude and smoking, found too little evidence to recommend ancestry-specific cutoffs, and does not give cutoffs for adults over 65. Lipemia can falsely raise photometric hemoglobin readings, and HiCN-based methods count carboxyhemoglobin and methemoglobin as hemoglobin. Capillary and point-of-care readings (for example HemoCue) measure the same quantity but can differ slightly from a venous draw. Monitoring thresholds for testosterone therapy are framed in hematocrit (Endocrine Society 2018), while the WHO 2016 major criterion for polycythemia vera is hemoglobin above 16.5 g/dL in men or 16.0 g/dL in women (or hematocrit above 49% or 48%), alongside other findings.
LOINC 718-7 (primary), 59260-0, 30350-3, 30352-9, 20509-6. Specimen: whole-blood.
Sources
- Critical (Panic) Values, with adult reference intervals (document DX_TL_811850, January 2024), Labcorp (2024)
- Pediatric Testing Reference Ranges (CBC With Differential/Platelet, test 005009), Labcorp (2022)
- CBC - Overview: Complete Blood Cell Count (CBC) with Differential, Blood, Mayo Clinic Laboratories
- CBC with Platelet Count and Automated Differential (test 0040003), Hotline effective March 1, 2021, ARUP Laboratories (2021)
- CBC reference intervals (procedure HEM-2597.01, effective 14 November 2024), Te Whatu Ora Health New Zealand, Waikato (2024)
- Guideline on haemoglobin cutoffs to define anaemia in individuals and populations, World Health Organization (2024)
- Normal Laboratory Values (Fact Sheet 120A), US to SI conversion factors, New Mexico AIDS InfoNet
- Hemoglobin Test, MedlinePlus (National Library of Medicine)
- Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, Journal of Clinical Endocrinology & Metabolism (2018)
- Patient posture for blood collection by venipuncture: recall for standardization after 28 years, Revista Brasileira de Hematologia e Hemoterapia (2017)
- Hemoglobin, Wikipedia
- Mechanistic investigation and data-driven correction of lipemic interference in hematological parameters on the Mindray BC-6800 hematology analyzer, Practical Laboratory Medicine (2026)
- Polycythemia vera: historical oversights, diagnostic details, and therapeutic views, Leukemia (2021)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.