Table of ContentsView AllTable of ContentsWhat Is Hemoglobin?What Is Hematocrit?How the Tests Are DoneNormal RangesWhat Low Values MeanWhat High Values Mean
Table of ContentsView All
View All
Table of Contents
What Is Hemoglobin?
What Is Hematocrit?
How the Tests Are Done
Normal Ranges
What Low Values Mean
What High Values Mean
Hematocrit(HCT) andhemoglobin(Hb) are two blood tests used to detect abnormalities in yourred blood cells (RBCs). Hematocrit is the percentage of RBCs in your blood, while hemoglobin is a protein in RBCs that carries oxygen to cells. The HCT and Hb values are reported as part of acomplete blood count (CBC).
If hematocrit and hemoglobin levels are below the normal range, a person is said to haveanemia. Causes for low hematocrit and hemoglobin include malnutrition, bleeding, chronic kidney disease, liver disease, bone marrow disorders, and blood cancers like leukemia or lymphoma.
Learn more about hematocrit and hemoglobin and what high or low values say about your health.
Oliver Cleve / Getty Images
Hemoglobin is an iron-containing protein in RBCs that carries oxygen and carbon dioxide. It also gives blood its red color.
Hemoglobin is essential for transporting oxygen from your lungs to your tissues and cells. As oxygen reacts withglucose(blood sugar) inside of cells, it produces carbon dioxide as a waste product that hemoglobin carries back to the lungs to be expelled.
Without hemoglobin to enable cellular respiration, tissues and cells of the body could not survive.
Hemoglobin is formed in thebone marrowas red blood cells are produced.Ironis needed to create hemoglobin, so low iron levels in the body can lead to low Hb counts.
How Hemoglobin (Hgb) Blood Tests Work
Hematocrit is the proportion of blood composed of RBCs, reported as a percentage (%). In addition to RBCs, blood is comprised ofplasma(the liquid part),white blood cells (WBCs), andplatelets.
While plasma accounts for around 55% of the total volume of blood, RBCs account for the largest share of blood cells.
Because the purpose of RBCs is to transfer oxygen from the lungs to tissues, the hematocrit level is essential for determining whether there are enough RBCs to meet the body’s demand for oxygen.
Understanding the Hematocrit Test
Verywell / Michela Buttignol
How Hemoglobin and Hematocrit Are Measured
Hemoglobin and hematocrit are among of battery of tests included in a complete blood count (CBC). Your healthcare provider might order a CBC if you have signs of an infection, anemia, blood loss, diseases of the immune system, or blood cancer.
The CBC requires a simple blood draw from a vein. Results can usually be delivered within a day of taking the test.
Hb Count
The Hb count is measured with a technology known asspectrophotometry. This is a highly sensitive tool that measures how much of a chemical substance—in this case, hemoglobin—is in a solution as a beam of light passes through it.
Because hemoglobin absorbs light differently than other components of blood, spectrophotometry can accurately measure the proportion of Hb in a small blood sample. The value can then be mathematically translated into grams of Hb per liter of blood (g/L).
HCT
Relationship of Hemoglobin and HematocritYour hemoglobin and hematocrit are typically both normal or increase and decrease in tandem with the other. Sometimes hemoglobin may be low due to vitamin B12 deficiency or iron deficiency before the hematocrit becomes low.
Relationship of Hemoglobin and Hematocrit
Your hemoglobin and hematocrit are typically both normal or increase and decrease in tandem with the other. Sometimes hemoglobin may be low due to vitamin B12 deficiency or iron deficiency before the hematocrit becomes low.
Normal Ranges of Hb and HCT
Low Hemoglobin and Hematocrit
Broadly speaking, there are three key reasons why your hemoglobin and hematocrit levels may be low:
Blood Loss
Blood loss from injury or illness can affect both your Hb and HCT levels. Examples include:
Bone Marrow Dysfunction
You can also have a low Hb or HCT if your bone marrow isn’t producing enough red blood cells. This can occur with:
Hemolysis
Hemolysisoccurs when red blood cells are being broken faster than they can be replaced. This can lead tohemolytic anemia.
Causes include:
High Hemoglobin and Hematocrit
There are two broad reasons why your hemoglobin and hematocrit levels may be rising, either chronically (over the long term) or acutely (over the short term):
Increased Need for Oxygen
When you are deprived of oxygen, your body will make more red blood cells to carry what oxygen it receives in the lungs to cells and tissues.
Causes of this include:
Some rare diseases and conditions cause the bone marrow to make too many RBCs, including:
Dehydration can also cause your hematocrit levels to rise, although it doesn’t actually increase the number of red blood cells. Instead, your hematocrit increases only because RBCs make up a larger proportion of the total blood volume.
High Hemoglobin Count
Summary
Hemoglobin and hematocrit are among a battery of tests included in a complete blood count (CBC). Hemoglobin is the iron-rich protein that carries oxygen to cells, while hematocrit is the percentage of red blood cells in relation to the total volume of blood.
Low hemoglobin and hematocrit may be due to bleeding, bone marrow diseases (including blood cancers), and hemolysis (the destruction of red blood cells). High hemoglobin and hematocrit levels occur with high altitude, heart or lung disease, or diseases like polycythemia vera that cause the overproduction of red blood cells.
10 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci. 2019;1450(1):126-146. doi:10.1111/nyas.14003Institute for Quality and Efficiency in Health Care.What does blood do?MedlinePlus.Hematocrit test.MedlinePlus.Complete blood count (CBC).Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci.2019 Aug;1450(1):126-146. doi: 10.1111/nyas.14003MedlinePlus.Hemoglobin.American Society of Hematology.Anemia.MedlinePlus.Hematocrit.Schop A, Stout3en K, Riedl JA, et al.A new diagnostic work-up for defining anemia etiologies: a cohort study in patients ≥ 50 years in general practices.BMC Fam Pract.2020;21:167. doi:10.1186/s12875-020-01241-7National Heart, Lung and Blood Institute.Hemolytic anemia.
10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci. 2019;1450(1):126-146. doi:10.1111/nyas.14003Institute for Quality and Efficiency in Health Care.What does blood do?MedlinePlus.Hematocrit test.MedlinePlus.Complete blood count (CBC).Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci.2019 Aug;1450(1):126-146. doi: 10.1111/nyas.14003MedlinePlus.Hemoglobin.American Society of Hematology.Anemia.MedlinePlus.Hematocrit.Schop A, Stout3en K, Riedl JA, et al.A new diagnostic work-up for defining anemia etiologies: a cohort study in patients ≥ 50 years in general practices.BMC Fam Pract.2020;21:167. doi:10.1186/s12875-020-01241-7National Heart, Lung and Blood Institute.Hemolytic anemia.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci. 2019;1450(1):126-146. doi:10.1111/nyas.14003Institute for Quality and Efficiency in Health Care.What does blood do?MedlinePlus.Hematocrit test.MedlinePlus.Complete blood count (CBC).Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci.2019 Aug;1450(1):126-146. doi: 10.1111/nyas.14003MedlinePlus.Hemoglobin.American Society of Hematology.Anemia.MedlinePlus.Hematocrit.Schop A, Stout3en K, Riedl JA, et al.A new diagnostic work-up for defining anemia etiologies: a cohort study in patients ≥ 50 years in general practices.BMC Fam Pract.2020;21:167. doi:10.1186/s12875-020-01241-7National Heart, Lung and Blood Institute.Hemolytic anemia.
Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci. 2019;1450(1):126-146. doi:10.1111/nyas.14003
Institute for Quality and Efficiency in Health Care.What does blood do?
MedlinePlus.Hematocrit test.
MedlinePlus.Complete blood count (CBC).
Karakochuk CD, Hess SY, Moorthy D, et al.Measurement and interpretation of hemoglobin concentration in clinical and field settings: a narrative review.Ann N Y Acad Sci.2019 Aug;1450(1):126-146. doi: 10.1111/nyas.14003
MedlinePlus.Hemoglobin.
American Society of Hematology.Anemia.
MedlinePlus.Hematocrit.
Schop A, Stout3en K, Riedl JA, et al.A new diagnostic work-up for defining anemia etiologies: a cohort study in patients ≥ 50 years in general practices.BMC Fam Pract.2020;21:167. doi:10.1186/s12875-020-01241-7
National Heart, Lung and Blood Institute.Hemolytic anemia.
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