Understanding your Hemoglobin Disorder Tests

Section Editor: Kamran Mirza MD PhD
May 28, 2026

Hemoglobin disorder tests are a group of blood tests used to detect inherited conditions that affect hemoglobin, the protein inside red blood cells that carries oxygen from the lungs to the rest of the body. Hemoglobin is normally made of a specific set of building blocks in carefully balanced amounts. When the genes that build hemoglobin contain inherited changes, the body may produce an unusual form of hemoglobin, or may produce too little of one of the normal forms. These conditions are called hemoglobinopathies and include sickle cell disease, the thalassemias, and several less common variants such as hemoglobin C, hemoglobin D, and hemoglobin E disease.

This article explains the main blood tests used to detect and diagnose hemoglobin disorders, what each test measures, what the results may mean, and how the tests are used together. The tests described here may have been ordered because of an abnormal newborn screening result, an unexplained anemia, a family history of a hemoglobin disorder, screening before or during pregnancy, or as part of preoperative evaluation in some clinical situations.

The reference ranges that apply to your results are those printed on your laboratory report, not the typical ranges shown here. Reference ranges and reporting formats vary between laboratories. Some hemoglobin variants are common in certain populations and rare in others, and your doctor will interpret your results in the context of your symptoms, family history, ancestry, and other tests.

Why hemoglobin matters

Hemoglobin is the protein inside red blood cells that picks up oxygen in the lungs and releases it to tissues throughout the body. Each hemoglobin molecule is built from four smaller protein chains called globin chains, joined to four iron-containing molecules called heme. The globin chains come in different types, and the combination of types determines which form of hemoglobin is produced.

In healthy adults, three forms of hemoglobin are normally present, in characteristic proportions:

Hemoglobin A (HbA) — the main adult hemoglobin, made up of two alpha and two beta globin chains. Normally about 95–98% of total hemoglobin.
Hemoglobin A2 (HbA2) — a minor adult hemoglobin, made up of two alpha and two delta globin chains. Normally about 2–3.5%.
Hemoglobin F (HbF) — the main hemoglobin of the fetus and newborn, made up of two alpha and two gamma chains. After birth, HbF gradually decreases and is normally less than 1% in adults.

Hemoglobin disorders fall into two broad categories:

Structural hemoglobin variants — caused by a change in the building blocks of one of the globin chains, producing a hemoglobin that has a different shape or behavior. The best-known example is hemoglobin S, the variant responsible for sickle cell disease. Hemoglobin C, hemoglobin D, and hemoglobin E are other examples.
Thalassemias — caused by reduced or absent production of one of the globin chains. When too little alpha-chain is produced, the condition is called alpha-thalassemia. When too little beta-chain is produced, it is called beta-thalassemia. The body responds by producing other hemoglobins in altered proportions.

Hemoglobin disorder tests are designed to identify abnormal hemoglobins, measure the proportions of normal hemoglobins, and detect patterns that indicate specific conditions.

Why are hemoglobin disorder tests done?

Hemoglobin disorder tests are ordered for many reasons, including:

Newborn screening. In many countries, every newborn is screened for hemoglobin disorders within the first few days of life as part of universal newborn screening programs. Early detection allows treatment to begin before serious complications develop.
To follow up on an abnormal newborn screen. An abnormal newborn screening result is usually confirmed with additional hemoglobin testing in the first weeks or months of life.
To investigate unexplained anemia. When a complete blood count shows small (microcytic) red blood cells but iron studies are normal, a hemoglobin disorder — particularly a thalassemia trait — is one of the most common explanations.
To screen before or during pregnancy. Couples may be tested before or early in pregnancy to determine whether their children could be at risk of inheriting a serious hemoglobin disorder. Carrier screening is most often offered when one or both partners are of ancestry where these conditions are more common, including African, Mediterranean, Middle Eastern, South Asian, and Southeast Asian backgrounds.
To investigate symptoms. Episodes of bone pain, unexplained jaundice (yellowing of the skin and eyes from breakdown of red blood cells), recurrent infections, or growth delay in children can all prompt testing for a hemoglobin disorder.
To follow up on findings on a peripheral blood smear. Some abnormal red blood cell shapes — sickle cells, target cells, teardrop cells — can suggest a specific hemoglobin disorder and prompt confirmatory testing.
Before surgery. In some clinical settings, testing for sickle cell disease or trait is performed before surgery, since low oxygen levels during anesthesia can trigger problems in people with hemoglobin S.
To monitor known diseases. Patients with diagnosed hemoglobin disorders may have testing repeated to monitor the proportions of different hemoglobins, particularly when treatments such as hydroxyurea (which raises HbF) or blood transfusions are being used.

How are the tests performed?

All the tests described in this article use a small blood sample drawn from a vein in the arm. In newborns, a heel-prick sample is used instead, and the blood is usually placed onto a special filter paper that is sent to a screening laboratory. No fasting or special preparation is needed.

In the laboratory, the tests work by separating the different forms of hemoglobin so they can be identified and measured. Different techniques separate hemoglobins using different physical properties — electrical charge, size, or binding behavior — but the goal of each is the same: to produce a report that shows which hemoglobins are present and in what proportions.

A typical report shows each hemoglobin detected, with its percentage of the total hemoglobin. Results are often available within a few days, although confirmatory and genetic testing may take longer.

The main tests for hemoglobin disorders

Hemoglobin electrophoresis

Hemoglobin electrophoresis is the classic test for hemoglobin disorders and remains widely used. A small blood sample is placed on a gel or a specialized strip, and an electric current is applied across it. Different hemoglobins carry slightly different electrical charges and travel at different speeds, so over time they separate into distinct bands. The bands are then stained and measured.

Most laboratories perform electrophoresis at two different acidity levels (alkaline and acidic), because some hemoglobin variants that look the same at one pH separate clearly at the other. Using both methods together improves accuracy.

The result is a report showing the percentages of HbA, HbA2, HbF, and any abnormal hemoglobins identified (such as HbS, HbC, or HbE). The percentages, together with the patient’s age and clinical context, are used to identify the underlying condition.

High-performance liquid chromatography (HPLC)

HPLC is a more modern technique that has become the most common method for hemoglobin testing in many laboratories. A small sample of blood is passed through a column that contains a material to which different hemoglobins bind with different strengths. As the hemoglobins are washed through the column, they emerge at different times, and the equipment measures the amount of each as it passes through.

HPLC results are reported as a chromatogram — a graph with peaks corresponding to each hemoglobin detected — and as a table of percentages. HPLC has several advantages over traditional electrophoresis: it is faster, more sensitive, can detect small amounts of abnormal hemoglobin, and can distinguish between some variants that are difficult to separate by electrophoresis. It is now the standard initial test in many newborn screening programs and clinical laboratories.

Capillary electrophoresis

Capillary electrophoresis is another modern technique that uses the same principle as traditional electrophoresis (separation by electrical charge) but performs the separation inside a very thin tube called a capillary. It is faster, more automated, and more sensitive than gel-based electrophoresis. Many laboratories now use capillary electrophoresis alongside or in place of HPLC. The results are reported in a similar way — as percentages of each hemoglobin detected.

Hemoglobin solubility test (sickle cell solubility test)

This is a quick screening test specifically for hemoglobin S, the variant that causes sickle cell disease. A small amount of blood is mixed with a chemical that causes hemoglobin S to precipitate from solution, making the mixture appear cloudy. If hemoglobin S is present, the mixture is turbid; if it is absent, the mixture remains clear.

The solubility test is fast and inexpensive but has important limitations. It only detects hemoglobin S — it cannot distinguish sickle cell trait (one abnormal gene) from sickle cell disease (two abnormal genes), nor can it detect other hemoglobin variants such as hemoglobin C or hemoglobin E. It also does not work reliably in newborns, in whom hemoglobin F still dominates. For these reasons, a positive solubility test must be confirmed by electrophoresis or HPLC; the solubility test alone is not sufficient to diagnose sickle cell disease.

Sodium metabisulfite test (sickling test)

This is an older test, now less commonly used, in which a drop of blood is mixed with a chemical (sodium metabisulfite) that reduces the oxygen available to red blood cells. In people with hemoglobin S, low oxygen levels cause red blood cells to take on the characteristic sickle shape, which can be seen under the microscope. As with the solubility test, this method identifies only hemoglobin S and cannot distinguish sickle cell trait from sickle cell disease. It has largely been replaced by HPLC and electrophoresis, but is still used in some settings.

Isoelectric focusing

Isoelectric focusing is a specialized form of electrophoresis used in some newborn screening programs. It separates hemoglobins very precisely based on the specific pH at which each one becomes electrically neutral. It is excellent for screening large numbers of newborn samples and for identifying small amounts of variant hemoglobin in samples that still contain mostly fetal hemoglobin.

DNA and genetic testing

DNA testing directly examines the genes that encode the globin chains and identifies the specific inherited changes that cause hemoglobin disorders. It is used in several situations:

To diagnose alpha-thalassemia. Unlike beta-thalassemia, alpha-thalassemia often does not produce a clearly abnormal result on electrophoresis or HPLC in carriers. DNA testing is usually required to confirm the diagnosis and identify the specific gene changes involved.
To confirm an unusual variant. When electrophoresis or HPLC suggests an uncommon hemoglobin variant, DNA testing can identify the specific change and confirm the diagnosis.
For carrier screening before or during pregnancy. When both parents may carry a hemoglobin disorder, DNA testing can determine the specific variants present and assess the risk that the child will be affected.
For prenatal diagnosis. In pregnancies at high risk for a serious hemoglobin disorder, DNA testing can be performed on a sample obtained by chorionic villus sampling or amniocentesis to determine whether the fetus is affected.

DNA testing is more sensitive and specific than protein-based tests but is also more expensive and slower. It is usually ordered when the result will meaningfully change management — for confirmation, family planning, or prenatal diagnosis.

Supporting tests

Several routine blood tests are usually performed alongside specific hemoglobin testing because they help interpret the results:

Complete blood count (CBC). Hemoglobin disorders almost always affect the red blood cells — their number, size, and appearance. The CBC measurements (hemoglobin level, MCV, RDW) are essential for interpreting the more specialized tests. See Understanding your complete blood count (CBC).
Peripheral blood smear. Specific abnormal red blood cell shapes — sickle cells, target cells, fragments, basophilic stippling — can suggest particular hemoglobin disorders. See Understanding your peripheral blood smear.
Iron studies. Microcytic anemia (small red blood cells) can be caused by either iron deficiency or a thalassemia trait, and these two conditions can look very similar on a CBC. An iron panel helps tell them apart. See Understanding your iron panel.

What the results may mean

The interpretation of hemoglobin testing depends on the specific hemoglobin patterns detected and their proportions. The sections below describe the most common patterns and what they typically indicate. Your doctor will interpret your specific result in context.

Normal adult pattern

A normal adult report shows approximately 95–98% HbA, 2–3.5% HbA2, and less than 1% HbF, with no abnormal hemoglobins detected. This is a reassuring result.

Sickle cell trait

Sickle cell trait is an inherited carrier state in which one copy of the hemoglobin gene produces normal hemoglobin, and the other produces hemoglobin S. The report typically shows about 55–60% HbA and 35–45% HbS, with a small amount of HbA2 and minimal HbF. People with sickle cell trait are usually healthy and do not have anemia, but they can pass the gene on to their children.

Sickle cell disease

In classic sickle cell disease (HbSS), both copies of the gene produce hemoglobin S, and no normal HbA is made. The report typically shows about 80–95% HbS, with elevated HbF (often 5–15%) and a small amount of HbA2. The absence of HbA is the key finding that distinguishes sickle cell disease from sickle cell trait. The blood smear typically shows sickle-shaped red blood cells, target cells, and other characteristic changes.

Other forms of sickle cell disease involve hemoglobin S combined with another abnormal hemoglobin — for example, HbS combined with HbC (called HbSC disease) or with a beta-thalassemia variant (called HbS/beta-thalassemia). Each has its own characteristic pattern on the report and its own clinical features.

Beta-thalassemia trait (beta-thalassemia minor)

People who inherit one normal beta-globin gene and one with reduced production usually have mild anemia, small (microcytic) red blood cells, and a characteristic pattern on hemoglobin testing: HbA2 is elevated, usually above 3.5%, and HbF may be mildly elevated. Iron studies are normal — an important distinction from iron deficiency anemia, which also causes microcytic red blood cells. Beta-thalassemia trait is usually a mild condition that does not require treatment, but it has important implications for family planning.

Beta-thalassemia major and intermedia

When both copies of the beta-globin gene are severely affected, very little or no HbA is made. The report shows greatly elevated HbF (often 50–95%), elevated HbA2, and little or no HbA. This is a serious condition that usually becomes apparent within the first year or two of life, with severe anemia and dependence on regular blood transfusions. Beta-thalassemia intermedia is a less severe form between trait and major.

Alpha-thalassemia

Alpha-thalassemia is more complicated to diagnose because the reduced production of alpha chains affects all of the normal hemoglobins (HbA, HbA2, and HbF), which still appear in roughly normal proportions on a standard report. A standard hemoglobin electrophoresis or HPLC in an adult with alpha-thalassemia trait is often essentially normal.

Alpha-thalassemia is therefore often diagnosed indirectly — by finding small microcytic red blood cells without iron deficiency and without an elevated HbA2 — and then confirmed by DNA testing. In more severe forms, abnormal hemoglobins specific to alpha-thalassemia may appear: hemoglobin Barts (made entirely of gamma chains) in newborns, or hemoglobin H (made entirely of beta chains) in older children and adults. The presence of these abnormal hemoglobins indicates a more severe form of alpha-thalassemia.

Other hemoglobin variants

Several other inherited hemoglobin variants may be identified on testing:

Hemoglobin C — most common in people of West African ancestry. Hemoglobin C trait (one abnormal gene) is usually harmless. Hemoglobin C disease (two abnormal genes) typically causes a mild chronic anemia.
Hemoglobin E — most common in people of Southeast Asian ancestry. Hemoglobin E trait is usually harmless. Hemoglobin E disease causes mild anemia and microcytic red blood cells. Hemoglobin E combined with beta-thalassemia can cause more significant anemia.
Hemoglobin D — a less common variant. In the trait state, it does not usually cause significant problems on its own, but combined with hemoglobin S it can produce a sickle cell-like syndrome.

Elevated hemoglobin F outside of infancy

An elevated level of HbF in an older child or adult may be seen with beta-thalassemia, certain inherited conditions called hereditary persistence of fetal hemoglobin, treatment with hydroxyurea for sickle cell disease, and some bone marrow conditions. The clinical context determines the significance.

What happens after hemoglobin disorder testing?

The next steps depend on the result. Possibilities include:

Normal result. If the report shows a normal pattern, no further investigation is usually needed. If the testing was done because of unexplained anemia, the doctor will look for other causes.
Carrier identified (trait). If a trait is identified — sickle cell trait, beta-thalassemia trait, hemoglobin C trait, hemoglobin E trait — additional steps may include testing other family members, providing information about the implications for future children, and referral for genetic counseling. People with traits are usually healthy themselves but may pass the gene to their children.
Disease identified. If a hemoglobin disorder is diagnosed, referral to a hematologist is the usual next step. Care for these conditions is highly individualized and depends on the specific diagnosis and severity. For sickle cell disease, this may include preventive care (vaccinations, antibiotic prophylaxis in young children), medications such as hydroxyurea, and management of pain crises. For thalassemia major, regular blood transfusions and iron chelation therapy may be needed. Newer treatments, including stem cell transplantation and gene therapy, are options for some patients.
Confirmatory and genetic testing. If the initial testing suggests an uncommon variant, alpha-thalassemia, or a complex pattern, DNA testing is often performed to confirm the diagnosis and identify the specific gene changes.
Family testing and genetic counseling. When a hemoglobinopathy is found, testing of partners (in adults) and family members is often recommended. A genetic counselor can explain inheritance patterns, the risks to future children, and the testing options available before or during pregnancy.
Repeat testing. In newborns, hemoglobin patterns change during the first months of life as the body switches from making fetal hemoglobin to adult hemoglobin. Repeat testing later in infancy or early childhood is sometimes needed to confirm a diagnosis.

Hemoglobin disorders are inherited conditions, and most cannot be “cured” in the conventional sense. However, modern treatment has substantially improved both quality of life and life expectancy for people with these conditions, and several promising newer therapies are further improving the outlook.

Questions to ask your doctor

Which hemoglobins were detected on my test, and in what proportions?
Does my result indicate a normal pattern, a carrier (trait) state, or a hemoglobin disease?
If I have a hemoglobin disorder, how severe is it expected to be?
Could the result be affected by recent blood transfusions, my age, or another condition?
Do I need additional confirmatory testing, including DNA or genetic testing?
Should my partner, my children, or other family members be tested?
If I am planning a pregnancy, what are the implications for my future children?
Should I be referred to a hematologist or a genetic counselor?
Are there specific symptoms I should watch for and report to my doctor?
How will my condition be monitored over time?