Lab result explainedBlood count (CBC)Last updated November 8, 2026

RBC blood test: what a high or low red blood cell count means

Red blood cell count (RBC) · Complete blood count (CBC) · reported in million cells/µL (equivalently ×10⁶/µL or ×10¹²/L; 4.5 million/µL = 4.5 ×10¹²/L)

The red blood cell count (RBC) is the number of red cells in a given volume of blood, reported in millions of cells per microlitre (million/µL) on a complete blood count. Red cells carry hemoglobin, the protein that binds oxygen in the lungs and releases it in the tissues, so the count is one of three linked measures of your oxygen-carrying capacity, alongside hemoglobin and hematocrit. For adult men the usual range is about 4.5 to 5.9 million/µL and for adult women about 4.1 to 5.1 million/µL, with some variation between laboratories.

A low RBC is one of the definitions of anemia, and the common causes are the same as for low hemoglobin: iron deficiency, blood loss, vitamin B12 or folate deficiency, kidney disease and chronic inflammation. A high RBC (erythrocytosis) is less common and is most often a response to something that lowers oxygen delivery, such as smoking, sleep apnea, lung disease or living at altitude, or simply dehydration concentrating the blood. A small number of people with a persistently high count have polycythemia vera, a bone marrow disorder that needs specific treatment.

The RBC is rarely read alone. Dividing hematocrit by RBC gives the mean cell volume (MCV), and the relationship between the count and the size of the cells is diagnostic in itself: iron deficiency produces few small cells, thalassemia trait produces many small cells, and B12 deficiency produces few large cells. If your RBC is flagged, the hemoglobin, MCV, RDW and reticulocyte count on the same report usually explain why.

RBC at a glance

What it is: the number of red blood cells per microlitre of blood, part of the complete blood count.
Normal (adults): men about 4.5–5.9 million/µL; women about 4.1–5.1 million/µL; children about 4.0–5.5. Labs differ slightly.
Low RBC means anemia or dilution; the usual causes are iron deficiency, blood loss, B12 or folate deficiency, kidney disease, chronic inflammation and pregnancy.
High RBC usually means dehydration, smoking, low oxygen (sleep apnea, lung disease, altitude), testosterone therapy or, less often, polycythemia vera.
Read it with hemoglobin, hematocrit and MCV: a high RBC with a low MCV and normal hemoglobin is a classic pattern for thalassemia trait, not iron deficiency.
Next step: for a low count, ferritin, B12, folate, kidney function and a reticulocyte count; for a high count, repeat when well hydrated, check oxygen saturation and, if still high, erythropoietin and JAK2 testing.

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What RBC measures

Red blood cells are made in the bone marrow under the direction of erythropoietin (EPO), a hormone released by the kidneys when they sense low oxygen. Each cell lives about 120 days before it is removed by the spleen, so the marrow replaces roughly one percent of your red cells every day. The count you see is the balance between production and loss or destruction, adjusted for how much plasma (the fluid part of blood) you have at that moment.

Automated analyzers count red cells by passing a diluted blood sample through a narrow aperture or laser beam one cell at a time, measuring the electrical impedance or light scatter of each cell. The same pass yields the MCV, and the analyzer calculates hematocrit as RBC multiplied by MCV. The count is precise to within about 2 percent, so a change from 4.6 to 4.4 million/µL is within the noise, while a change from 4.6 to 3.8 is real.

The count is affected by plasma volume as much as by the cells themselves. Dehydration, diuretics and a sample drawn after prolonged standing concentrate the blood and raise the count by 5 to 10 percent; pregnancy, overhydration and lying flat dilute it. Athletes who train hard have an expanded plasma volume and often a count at or below the lower limit despite an above-average total red cell mass. Living above about 2,500 metres raises the count, as does smoking.

Normal range for RBC

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (million cells/µL (equivalently ×10⁶/µL or ×10¹²/L; 4.5 million/µL = 4.5 ×10¹²/L))	Notes
Adult men	About 4.5–5.9 million/µL	Some labs use 4.35–5.65 or 4.7–6.1. Use the reference range printed on your report.
Adult women	About 4.1–5.1 million/µL	Some labs use 3.9–5.1 or 4.2–5.4. Values are lower during menstruation-related iron loss and in pregnancy.
Children (1–12 years)	About 4.0–5.5 million/µL	Falls to a low point of around 3.0–3.5 at 2 to 3 months of age (physiological nadir) before rising.
Newborns	About 4.8–7.2 million/µL	High at birth because of the low-oxygen environment in the womb; falls over the first weeks.
Pregnancy	About 3.5–4.5 million/µL by the third trimester	Plasma volume expands by 40 to 50 percent, diluting the count even though red cell mass rises.
Mild erythrocytosis	Men above 5.9, women above 5.1 million/µL	Most often dehydration, smoking or sleep apnea. Repeat after good hydration and read with hematocrit.
Hematocrit thresholds for polycythemia work-up	Hematocrit above 49% (men) or 48% (women)	World Health Organization 2016 criteria; equivalent hemoglobin thresholds are above 16.5 g/dL (men) and 16.0 g/dL (women).
Hematocrit on testosterone therapy	Above 54%	Endocrine Society guidance to pause or reduce testosterone because of clotting risk.

High RBC (erythrocytosis)

A high red cell count means either that your plasma volume is low, so the same number of cells is more concentrated (relative or apparent erythrocytosis), or that your marrow is genuinely making more red cells (absolute erythrocytosis). Relative erythrocytosis from dehydration, diuretics, vomiting, diarrhoea or heavy sweating is by far the most common reason for a single high reading and corrects within hours of rehydration. Smoking and stress produce a persistent version, sometimes called Gaisböck syndrome, in middle-aged men with high blood pressure and a hematocrit of 50 to 55 percent.

Absolute erythrocytosis is usually secondary: the kidneys sense low oxygen and release more erythropoietin. Smoking (carbon monoxide binds hemoglobin), obstructive sleep apnea, COPD, congenital heart disease, living at altitude and hemoglobin variants that hold on to oxygen too tightly all do this. Testosterone and anabolic steroids stimulate red cell production directly and raise the count in a large minority of men on injectable testosterone. Rarely a kidney cyst, kidney cancer, liver cancer or uterine fibroid secretes erythropoietin.

Primary erythrocytosis, polycythemia vera (PV), is a bone marrow disorder in which a mutation in the JAK2 gene (found in about 98 percent of cases) lets red cell precursors multiply without erythropoietin, which is therefore suppressed to low levels. PV affects roughly 2 people per 100,000 a year, typically in their 60s, and often comes with a high white cell and platelet count, an enlarged spleen, itching after hot showers and a raised risk of blood clots. Keeping the hematocrit below 45 percent with venesection and aspirin cut cardiovascular deaths and major clots about fourfold in the CYTO-PV trial.

Common causes

Dehydration and low plasma volume
Fluid loss from vomiting, diarrhoea, sweating, diuretics or simply not drinking concentrates the blood and raises RBC, hemoglobin and hematocrit together by 5 to 10 percent. A repeat test after a day of normal fluids is the first step.
Smoking
Carbon monoxide occupies 5 to 15 percent of hemoglobin in heavy smokers, so the kidneys sense less oxygen and raise erythropoietin. Smokers' hematocrit runs 2 to 4 points higher than non-smokers' and can reach 55 to 60 percent; it falls within weeks to months of quitting.
Obstructive sleep apnea and hypoventilation
Repeated overnight oxygen dips raise erythropoietin. A mildly raised RBC in someone who snores, is overweight and is tired in the day is a reason to ask about a sleep study. Obesity hypoventilation syndrome does the same more severely.
Chronic lung disease and congenital heart disease
COPD, pulmonary fibrosis and right-to-left cardiac shunts lower arterial oxygen, and the marrow compensates. Resting oxygen saturation below about 92 percent is the usual trigger.
Living or training at altitude
Above about 2,500 metres the count rises over weeks; permanent residents of high cities commonly have hematocrits of 50 to 55 percent. The count falls back over one to two months at sea level.
Testosterone, anabolic steroids and erythropoietin
Testosterone stimulates erythropoietin and suppresses hepcidin; a rise in hematocrit is the most common laboratory side effect of therapy and is the reason it is checked at 3, 6 and 12 months. Injected EPO and androgen misuse in sport have the same effect.
Polycythemia vera
A JAK2-driven myeloproliferative neoplasm; red cell production runs independently of erythropoietin, which is low. Often accompanied by a high white cell count, high platelets, an enlarged spleen, itching and a history of clots or bleeding.
Erythropoietin-secreting tumours and kidney disease
Kidney cancer, hepatocellular carcinoma, cerebellar hemangioblastoma, large uterine fibroids and pheochromocytoma can secrete EPO. Kidney cysts, kidney artery narrowing and the first year after a kidney transplant (post-transplant erythrocytosis affects 10 to 15 percent of recipients) also raise it.
High-oxygen-affinity hemoglobin variants and congenital erythrocytosis
Inherited hemoglobin variants that release oxygen poorly, and rare mutations in the oxygen-sensing pathway (EPO receptor, VHL, PHD2, HIF2A), cause a lifelong high count that often runs in families and is picked up young.
Thalassemia trait (high count, small cells)
Beta or alpha thalassemia trait typically produces an RBC above 5.5 million/µL with an MCV below 75 fL and a normal or slightly low hemoglobin. The cells are small, so more of them are needed to carry the same hemoglobin. This is a normal variant for the carrier, not a disease needing treatment.

Symptoms that can go with it

Often none; a mildly high count is usually an incidental finding
Headache, dizziness, blurred vision or a feeling of fullness in the head from thicker blood
Red or ruddy complexion, bloodshot eyes
Itching after a warm bath or shower, a characteristic symptom of polycythemia vera
Burning pain and redness in the hands or feet (erythromelalgia)
Fatigue, night sweats and a full feeling under the left ribs from an enlarged spleen
Unexplained blood clots (deep vein thrombosis, stroke, heart attack) or nosebleeds and easy bruising
Snoring, daytime sleepiness or breathlessness, pointing to the underlying cause

Low RBC

A low red cell count is anemia unless the blood has been diluted by extra plasma, as in pregnancy, over-hydration in hospital or endurance training. The practical questions are how low it is, how quickly it fell and what size the cells are. A count that has drifted down over months with small cells (MCV below 80 fL) is iron deficiency until proved otherwise, and in adults that means finding where iron is being lost: heavy periods, the gut, or poor absorption from celiac disease or stomach surgery.

A low count with normal-sized cells points to blood loss, kidney disease (not enough erythropoietin), chronic inflammation or a marrow that is being suppressed by medication, alcohol or a chronic illness. Large cells (MCV above 100 fL) with a low count suggest vitamin B12 or folate deficiency, alcohol excess, liver disease, hypothyroidism or, in older adults, a marrow disorder such as myelodysplastic syndrome. The reticulocyte count separates a marrow that is trying and failing (high reticulocytes: bleeding or hemolysis) from one that is not producing (low reticulocytes: deficiency or marrow suppression).

Severity is judged by hemoglobin rather than the RBC itself. The World Health Organization defines anemia as hemoglobin below 13 g/dL in men, 12 g/dL in non-pregnant women and 11 g/dL in pregnancy. A hemoglobin below 7 to 8 g/dL, or any level with chest pain, breathlessness at rest or fainting, needs urgent assessment.

Common causes

Iron deficiency
The most common cause worldwide. Heavy menstrual bleeding, slow gastrointestinal bleeding (ulcers, polyps, bowel cancer, aspirin or NSAIDs), pregnancy, vegetarian diets and malabsorption (celiac disease, H. pylori, bariatric surgery) deplete iron, and the marrow makes fewer, smaller, paler cells. Ferritin is usually below 30 ng/mL.
Acute or chronic blood loss
Trauma, surgery, heavy periods, a bleeding ulcer or frequent blood donation. Immediately after a bleed the count can look normal because cells and plasma are lost together; it falls over 24 to 72 hours as plasma is replaced.
Vitamin B12 or folate deficiency
Pernicious anemia, long-term metformin or acid-suppressing drugs, vegan diets, alcohol excess and bowel disease impair DNA synthesis in red cell precursors, so the marrow releases fewer, larger cells (MCV often above 100 fL) and many die before leaving the marrow.
Chronic kidney disease
Damaged kidneys make less erythropoietin. Anemia becomes common once eGFR falls below about 45 mL/min and is nearly universal below 30; the cells are normal in size and the reticulocyte count is low.
Anemia of chronic disease (inflammation)
Rheumatoid arthritis, inflammatory bowel disease, chronic infection, cancer and heart failure raise hepcidin, which locks iron away from the marrow and shortens red cell survival. Ferritin is normal or high while iron saturation is low.
Bone marrow disorders
Myelodysplastic syndrome, aplastic anemia, leukemia, lymphoma, multiple myeloma, myelofibrosis and cancer spread to bone crowd out or disable red cell production, usually with abnormal white cell or platelet counts as well.
Hemolysis (red cell destruction)
Autoimmune hemolytic anemia, sickle cell disease, hereditary spherocytosis, G6PD deficiency, mechanical heart valves and some drugs destroy cells faster than the marrow can replace them; reticulocytes, bilirubin and LDH are high and haptoglobin is low.
Pregnancy and overhydration (dilution)
Plasma volume rises 40 to 50 percent in pregnancy, so RBC and hemoglobin fall even when red cell mass is rising. Intravenous fluids, heart failure and kidney failure dilute the blood in the same way.
Medications, alcohol and chemotherapy
Chemotherapy, azathioprine, methotrexate, zidovudine, chloramphenicol and heavy alcohol use suppress the marrow directly; long-term proton pump inhibitors and metformin lower B12 absorption.
Hypothyroidism and other endocrine causes
Low thyroid hormone, low testosterone and adrenal insufficiency each reduce erythropoietin drive modestly, producing a mild normocytic or macrocytic anemia that corrects when the hormone is replaced.

Symptoms that can go with it

Tiredness, weakness and reduced exercise tolerance
Breathlessness on climbing stairs or exertion
Pale skin, inner eyelids and nail beds
Dizziness, light-headedness on standing, or fainting
Fast or pounding heartbeat, chest discomfort in severe anemia
Headache, poor concentration, feeling cold
Brittle or spoon-shaped nails, cravings for ice (pica) and restless legs with iron deficiency
Numbness, tingling and balance problems with B12 deficiency

Read it alongside

Hemoglobin and hematocrit — the three move together; hemoglobin decides whether anemia is present and how severe it is.
MCV (mean cell volume) — small cells with a low count mean iron deficiency; small cells with a high count mean thalassemia trait; large cells point to B12, folate, alcohol or marrow disease.
RDW — high when cells vary in size, as in iron deficiency and mixed deficiencies; normal in thalassemia trait and anemia of chronic disease.
Reticulocyte count — tells you whether the marrow is responding (high in bleeding and hemolysis) or failing (low in deficiencies, kidney disease and marrow disorders).
Ferritin and iron saturation — confirm or exclude iron deficiency before anything else is considered.
Vitamin B12 and folate — ordered when the MCV is high or the picture is mixed.
White cell and platelet counts — all three lines high suggests polycythemia vera; all three low suggests a marrow problem or an enlarged spleen.
Erythropoietin level and JAK2 mutation — the two tests that separate polycythemia vera (low EPO, JAK2 positive) from secondary erythrocytosis (normal or high EPO) when a high count persists.

What usually happens next

For a low RBC, expect ferritin, iron saturation, B12, folate, a reticulocyte count and kidney function, with the MCV guiding which comes first; in men and post-menopausal women iron deficiency leads to a look at the gut (stool test for blood, endoscopy or colonoscopy) because a bleeding source must be excluded.
For a high RBC, the first step is a repeat test after normal hydration, ideally having not smoked that morning, with a resting oxygen saturation reading; if still high, erythropoietin level, JAK2 V617F testing and sometimes an abdominal ultrasound follow.
Calculate the Mentzer index if cells are small: MCV divided by RBC below 13 favours thalassemia trait and above 13 favours iron deficiency; hemoglobin electrophoresis confirms beta thalassemia trait.
If you take testosterone, ask for hematocrit to be checked at 3, 6 and 12 months and then yearly; a value above 54 percent usually means pausing or lowering the dose.
Questions worth asking: Is the count actually abnormal for me, or borderline? What is my ferritin? Could sleep apnea, smoking or a medication explain this? Do I need a specialist (hematology) referral?

Diet, lifestyle and natural levers with evidence

What can move RBC once the cause is known. Nothing here replaces finding the cause.

Iron-rich foods paired with vitamin C (for low counts from iron deficiency)

Strong evidence

Heme iron from red meat, poultry and fish is absorbed at 15 to 35 percent regardless of what else is eaten, while non-heme iron from beans, lentils, tofu, fortified cereals and leafy greens is absorbed at 2 to 20 percent and is strongly affected by the meal. Adding 50 to 100 mg of vitamin C (a glass of orange juice, half a bell pepper) to a plant-based meal raises non-heme iron absorption two- to threefold in isotope studies. Dietary change alone corrects mild deficiency over months; established iron-deficiency anemia almost always needs a supplement as well, typically raising hemoglobin by about 1 g/dL every two to three weeks.

Do not take iron supplements for a low RBC without a ferritin result: a low count with normal or high ferritin is not iron deficiency, and iron is harmful in hemochromatosis and thalassemia. Keep iron tablets away from children.

Vitamin B12 and folate (for low counts with large cells)

Strong evidence

In confirmed deficiency, replacing B12 produces a reticulocyte surge within 5 to 8 days and normalises the red cell count over 6 to 8 weeks. Oral B12 at 1,000 to 2,000 µg daily corrects blood levels as effectively as injections in randomised trials, including in pernicious anemia, because about 1 percent is absorbed by passive diffusion. Folate 400 µg to 1 mg daily corrects folate-deficiency anemia in weeks; food sources are leafy greens, legumes, citrus and fortified grains.

Taking folate without checking B12 can correct the blood count while nerve damage from B12 deficiency progresses; both should be measured first.

Stopping smoking (for high counts)

Moderate evidence

Carbon monoxide from cigarettes raises the red cell count and hematocrit by 2 to 4 percentage points on average, and heavy smokers can run hematocrits of 55 to 60 percent. Observational studies show hematocrit falls toward non-smoker values within weeks to a few months of quitting as carboxyhemoglobin clears and erythropoietin drive settles. Quitting is the single most effective step for smoking-related erythrocytosis and is checked by repeating the CBC after three months.

Hydration before the test and in daily life (for borderline high counts)

Moderate evidence

Plasma volume shifts move the RBC count by 5 to 10 percent in either direction. Studies of dehydration show hematocrit rising about 1 point for every 1 to 2 percent of body weight lost as fluid, and a sample taken after a night's fast, a morning run or hours of standing reads higher than one taken seated and hydrated. A borderline high count that normalises on a well-hydrated repeat needs no further work-up.

Treating sleep apnea and losing excess weight (for high counts)

Moderate evidence

Obstructive sleep apnea raises erythropoietin through overnight oxygen dips, and observational studies find that effective CPAP use lowers hematocrit by about 1 to 3 percentage points over 3 to 12 months in people whose counts were raised, with the largest falls in those with the most severe nocturnal hypoxaemia. Weight loss of 10 percent or more reduces apnea severity by roughly a quarter to a half and improves oxygenation.

Regular aerobic training (lowers hematocrit through plasma expansion)

Moderate evidence

Endurance training expands plasma volume by 10 to 20 percent within one to two weeks, so hematocrit and RBC fall by 2 to 4 points even though total red cell mass rises over months. This 'sports anemia' is a healthy adaptation that improves blood flow; it is also why trained athletes often have a count at the lower limit of normal. For people with mild secondary erythrocytosis it is a reasonable adjunct, not a replacement for treating the cause.

Hard exercise in someone with a very high hematocrit (above 55 percent) and no diagnosis should wait until a clinician has excluded polycythemia vera because of clot risk.

When to see a clinician promptly

A hemoglobin below 7 to 8 g/dL, or any low count with chest pain, breathlessness at rest, fainting or a racing heart: possible severe anemia needing same-day assessment and possibly transfusion.
Black, tarry stools, vomiting blood or heavy ongoing menstrual or rectal bleeding with a falling count.
A hematocrit above 54 percent, or a high count with headache, visual disturbance, confusion, chest pain or one-sided weakness: thicker blood raises the risk of clots and stroke and needs prompt evaluation.
A high RBC together with high white cells and platelets, itching after bathing, or a full feeling under the left ribs, which point to polycythemia vera.
A low RBC with easy bruising, frequent infections, bone pain, night sweats or unexplained weight loss, suggesting a marrow disorder.
Any low count in a man or a post-menopausal woman: iron deficiency in these groups needs the gut examined to exclude a bleeding source such as bowel cancer.

Frequently asked questions

What is a normal RBC count?

For adult men roughly 4.5 to 5.9 million cells per microlitre and for adult women roughly 4.1 to 5.1 million/µL, although laboratories set slightly different limits (some use 4.35–5.65 for men and 3.92–5.13 for women). Children fall around 4.0 to 5.5 and newborns are higher, at 4.8 to 7.2. Use the reference range printed next to your result.

Is an RBC of 5.8 or 6.0 high?

For a woman, 5.8 million/µL is above the usual upper limit of about 5.1 and would be flagged; for a man, 5.8 is at the top of normal and 6.0 is just above it. A single value in this zone is most often dehydration, smoking or a lab quirk, so the first step is a repeat test when well hydrated. If hematocrit is also above 48 to 49 percent on the repeat, further tests (oxygen saturation, erythropoietin, JAK2) are reasonable.

What does a low RBC count mean?

It usually means anemia: too few red cells to carry oxygen comfortably. The most common reasons are iron deficiency, blood loss, vitamin B12 or folate deficiency, kidney disease and chronic inflammation, with pregnancy and over-hydration causing a harmless dilutional fall. The MCV on the same report points toward the cause, and ferritin, B12, folate and a reticulocyte count usually confirm it.

What causes a high red blood cell count?

Dehydration is the most frequent cause of a one-off high result. Persistent causes are smoking, obstructive sleep apnea, chronic lung disease, living at altitude, testosterone or anabolic steroid use, kidney cysts or tumours that secrete erythropoietin and, less commonly, polycythemia vera, a bone marrow disorder driven by a JAK2 mutation. Thalassemia trait also gives a high count, but with small cells and normal hemoglobin.

Can dehydration raise RBC?

Yes. Losing fluid shrinks the plasma volume, so the same number of red cells is packed into less blood and the count, hemoglobin and hematocrit all rise, typically by 5 to 10 percent. Diuretics, vomiting, diarrhoea, heavy sweating and a long fast before the test have the same effect. The count returns to baseline within hours of rehydration, which is why a well-hydrated repeat is the first step for any mildly high result.

Why is my RBC high but my hemoglobin normal or low?

This pattern, many small cells carrying a normal total amount of hemoglobin, is characteristic of thalassemia trait, a common inherited variant in people of Mediterranean, Middle Eastern, South Asian, Southeast Asian and African ancestry. The MCV is usually below 75 fL and the Mentzer index (MCV divided by RBC) is below 13. It needs no treatment, but it is worth knowing about before pregnancy and so that you are not given iron unnecessarily.

How can I increase my red blood cell count?

Only by correcting the cause. If ferritin is low, iron-rich foods with vitamin C and, in most cases, an iron supplement raise hemoglobin by about 1 g/dL every two to three weeks. If B12 or folate is low, replacing them produces a response within one to two weeks. If the cause is kidney disease, inflammation, a medication or a marrow disorder, diet will not help and treatment is directed at the underlying condition. Taking iron without a confirmed deficiency can cause harm.

Is a high RBC dangerous?

A mildly high count from dehydration or altitude is not. A persistently high count with a hematocrit above about 50 to 54 percent makes blood more viscous and raises the risk of clots, stroke and heart attack, which is why polycythemia vera is treated to keep hematocrit below 45 percent and testosterone therapy is paused above 54 percent. Most secondary causes improve when the trigger (smoking, sleep apnea, a medication) is addressed.

References

Red blood cell (RBC) count. MedlinePlus, US National Library of Medicine (2023)View source
Complete blood count (CBC). Mayo Clinic (2023)View source
Polycythemia vera. Mayo Clinic (2024)
Secondary erythrocytosis. Merck Manual Professional Version (2024)
Evaluation of anemia. Merck Manual Professional Version (2024)
Arber DA, Orazi A, Hasserjian R, et al.. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood (2016)
Marchioli R, Finazzi G, Specchia G, et al.. Cardiovascular events and intensity of treatment in polycythemia vera (CYTO-PV). New England Journal of Medicine (2013)
Smith JR, Landaw SA. Smokers' polycythemia. New England Journal of Medicine (1978)
Bhasin S, Brito JP, Cunningham GR, et al.. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism (2018)
Mentzer WC. Differentiation of iron deficiency from thalassaemia trait. Lancet (1973)
Lanier JB, Park JJ, Callahan RC. Anemia in older adults. American Family Physician (2018)
Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. World Health Organization (2011)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.