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Hemoglobin S (HbS)

How much of your hemoglobin is the sickle type, HbS. Most people have none. A result above zero needs the full hemoglobin report to interpret.

AI-verified against cited sources. Awaiting expert reviewAlso called HbS, Hb S, HGB SLOINC 4625-0

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What it is

Hemoglobin S (HbS) is a changed form of hemoglobin caused by a variant in the beta-globin gene. A person who inherits one copy of the variant and one normal copy has sickle cell trait, and makes about 60% normal hemoglobin (HbA) and about 40% HbS. Inheriting two copies, or one copy with another variant such as HbC or beta-thalassemia, causes sickle cell disease. Labs measure the percent of HbS with HPLC or capillary electrophoresis, and may confirm it with a solubility test.

Why it matters

Sickle cell trait usually causes no symptoms, and average life span is similar to the general population. In rare situations it has been linked to problems such as blood in the urine, kidney disease, and complications from extreme exertion, so people with trait often want to know. Sickle cell disease is a lifelong condition with pain crises and other complications. An HbS result also matters for family planning, because a child who inherits HbS from each parent can have sickle cell disease. In the United States, about 1 in 13 Black babies is born with sickle cell trait.

If it’s high

Any HbS above zero means the sickle hemoglobin variant was found. A share near 40% fits sickle cell trait, while a much higher share is more typical of sickle cell disease or a related pattern. The number alone cannot tell them apart, so your clinician reads it with your HbA, HbF, HbA2, red cell indices and symptoms.

Common causes

  • Sickle cell trait (one copy of the variant, inherited from one parent)
  • Sickle cell disease, including HbSS, HbSC and HbS with beta-thalassemia (a larger share of HbS)

What can help

  • Ask for the full hemoglobin report and a review with a clinician who knows hemoglobin conditions
  • Ask about genetic counseling, especially if you are planning a pregnancy
  • Ask whether anything about your activities, such as intense endurance exercise, high altitude or dehydration, is worth planning around

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.

For adults: up to 0 %. Source: ARUP Laboratories, Mayo Clinic Laboratories, University of Iowa Hospitals & Clinics, National Heart, Lung, and Blood Institute (NIH), NHS England (NHS Sickle Cell and Thalassaemia Screening Programme).

What can affect your result

  • Inheritance: one copy gives trait, two copies or a second variant give disease
  • Coinherited alpha-thalassemia or iron deficiency, which can lower the HbS share in trait
  • A recent blood transfusion or treatments such as hydroxyurea
  • The lab method: HPLC, capillary electrophoresis and solubility tests work differently
  • Ancestry: the variant is most common in people with roots in Africa, the Mediterranean, the Middle East and India
  • A recent blood transfusion adds donor red cells (which have normal hemoglobin) and lowers the HbS share. One hospital lab does not run the test within three months of a transfusion.
  • Treatments such as hydroxyurea change the mix of hemoglobins.
  • Iron deficiency and alpha-thalassemia can lower the HbS share in someone with sickle cell trait.
  • On some HPLC systems, HbS adducts can appear in the HbA window and be mistaken for a small amount of HbA, and HbS and HbC can run together, so labs may confirm with a second method.
  • Hemoglobin variants including HbS trait can affect the accuracy of some HbA1c methods.

HbS is an inherited pattern that stays the same for life. The share can change after a transfusion or some treatments.

When to talk to a clinician

A result above zero is not an emergency, but share the full report with your clinician. Sickle cell disease can cause sudden severe pain, chest problems, stroke and infections, so follow your care team's plan if you have the disease. For anyone with an HbS result, get prompt care for sudden severe pain, chest pain, trouble breathing, weakness on one side of the body or trouble speaking. Call 911 or your local emergency number for these signs.

Questions you could ask

  • Would genetic counseling be useful for me or my family?
  • Does my full hemoglobin report fit with sickle cell trait or with another pattern?
  • Should my partner or family members be offered testing?
  • Is my HbA1c method reliable with this hemoglobin type?

Questions people ask

Does sickle cell trait mean I have sickle cell disease?

No. Trait means you carry one copy of the variant and one normal copy. Most people with trait have no symptoms. Sickle cell disease needs two copies of the variant, or one copy plus another variant such as HbC or beta-thalassemia. Trait does matter for family planning, because two carriers can have a child with sickle cell disease.

My HbS is lower than the 40% I read about. Why?

The share varies. Many people with trait have about 30% to 40%. A lower share can happen when alpha-thalassemia or iron deficiency is also present, and different lab methods read a little differently. In one study the median was about 39.6% in trait and 34.2% when alpha-thalassemia was suspected. Your clinician reads it with your red cell size and the rest of the report.

Can sickle cell trait affect my HbA1c result?

It can, depending on the HbA1c method your lab uses. The National Glycohemoglobin Standardization Program lists which methods are affected by HbS trait. If you have an HbS result, ask your clinician whether your HbA1c method is reliable for you or whether another blood sugar test would help.

Show the science and sources

For clinicians and researchers

HbS (alpha2-beta2 6Glu>Val) is quantified by cation-exchange HPLC or capillary electrophoresis, with solubility testing, isoelectric focusing or mass spectrometry as confirmation. Healthy people have no HbS (ARUP 0.0, Mayo variant 0.0, University of Iowa 0%). NHLBI describes sickle cell trait as about 60% HbA and 40% HbS. The NHS England screening handbook treats a variant share of 30% to 40% as typical for a carrier (25% to 35% if the variant is HbE), noting that this includes possible alpha-plus thalassemia carriers; 40% to 50% should prompt a check that the HbA peak is truly HbA; 50% or more should raise the possibility of HbS with beta-plus thalassemia; and 30% or less with an MCH under 25 pg suggests a carrier with coexisting alpha-thalassemia or iron deficiency. In a 2026 capillary electrophoresis study the median HbS was 39.6% in HbAS and 34.2% when alpha-thalassemia was suspected, with HbS under 37.6% and HbA over 59% as the discriminating pattern. ARUP's HbS evaluation does not distinguish trait from homozygous disease or other combinations such as S/C, S/D, S/E or S/thalassemia, and recommends full hemoglobin evaluation for that. Some HPLC systems show HbS adducts in the HbA window, which can make sickle cell disease look like S/beta-plus thalassemia. Sickle cell trait is associated with hematuria, renal papillary necrosis, hyposthenuria, splenic infarction, exertional rhabdomyolysis, exercise-related sudden death and rare renal medullary cancer, and probably with venous thromboembolism and some pregnancy complications (Tsaras 2009). A 2025 meta-analysis found higher odds of an eGFR of 60 mL/min/1.73 m² or lower and of proteinuria in adults with trait, and its authors concluded trait raises the risk of chronic and end-stage kidney disease. Trait prevalence is about 30% to 40% in parts of sub-Saharan Africa and about 300 million people worldwide. HbS trait and variants can alter HbA1c accuracy depending on the method (NGSP). No critical value was found.

LOINC 4625-0 (primary), 44923-1, 32683-5, 4621-9. Specimen: whole-blood.

Sources

  1. Hemoglobin Evaluation by HPLC With Reflex to Electrophoresis and/or RBC Solubility (test 3017101), ARUP Laboratories
  2. Hemoglobin S Evaluation with Reflex to RBC Solubility (test 3016616), ARUP Laboratories
  3. Hemoglobin Variant, A2 and F Quantitation, Blood (test HGBCE), Mayo Clinic Laboratories
  4. Hemoglobin Evaluation, Quantitation with Interpretation (Pathology Handbook), University of Iowa Hospitals & Clinics
  5. Sickle cell and thalassaemia screening: laboratory handbook, Interpretation and reporting of antenatal screening results, NHS England (NHS Sickle Cell and Thalassaemia Screening Programme)
  6. Sickle Cell Disease: Causes and Risk Factors, National Heart, Lung, and Blood Institute (NIH) (2025)
  7. Sickle Cell Disease, National Heart, Lung, and Blood Institute (NIH) (2025)
  8. Complications associated with sickle cell trait: a brief narrative review, American Journal of Medicine (2009)
  9. Chronic kidney disease in adults with sickle cell trait: a systematic review and meta-analysis, Blood Advances (2025)
  10. A machine-learning capillary electrophoresis-based pattern to identify suspected sickle cell trait and alpha-thalassemia co-inheritance, Advances in Laboratory Medicine (2026)
  11. Factors that Interfere with HbA1c Test Results, National Glycohemoglobin Standardization Program (NGSP) (2026)
  12. Alpha- and Beta-thalassemia: Rapid Evidence Review, American Family Physician (2022)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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