A sickle cell screen test checks whether a blood sample contains hemoglobin S, the abnormal hemoglobin linked to sickle cell trait and sickle cell disease. The result is usually reported as positive or negative, but that simple wording can be misleading. A positive screen does not automatically mean a person has sickle cell disease. It means hemoglobin S was detected and more specific testing is needed to tell whether the pattern fits sickle cell trait, sickle cell anemia, hemoglobin SC disease, sickle beta-thalassemia, or another hemoglobin condition. A negative result usually means hemoglobin S was not detected in that sample, but timing matters, especially in newborns and people who recently had a blood transfusion. The most useful next test is often a hemoglobin separation test, such as electrophoresis, high-performance liquid chromatography, isoelectric focusing, or capillary electrophoresis. Genetic testing may be used when the hemoglobin pattern is unclear or family planning decisions depend on exact results.
- A positive sickle cell screen means hemoglobin S is present; it does not by itself separate trait from disease.
- A negative result usually means no hemoglobin S was detected, but recent transfusion or newborn timing can affect interpretation.
- Sickle cell trait usually means one hemoglobin S gene and one usual hemoglobin A gene; most people with trait do not have sickle cell disease symptoms.
- Sickle cell disease usually means two significant hemoglobin gene changes, such as HbSS, HbSC, or HbS beta-thalassemia.
- Confirmatory testing commonly uses hemoglobin electrophoresis, HPLC, isoelectric focusing, capillary electrophoresis, or genetic testing.
- Newborn screening results that show hemoglobin S need prompt follow-up, even when the baby looks healthy.
Table of Contents
- What the Sickle Cell Screen Test Checks
- Positive, Negative, and Indeterminate Results
- Trait, Disease, and Hemoglobin Patterns
- When the Test Is Used
- Newborn Screening and Children
- Follow-Up Tests and Related Labs
- What to Do After Results
What the Sickle Cell Screen Test Checks
A sickle cell screen test checks for hemoglobin S, often written as HbS. Hemoglobin is the oxygen-carrying protein inside red blood cells. Most adults mainly have hemoglobin A, or HbA. People with sickle cell trait or sickle cell disease make some hemoglobin S because of a change in the HBB gene, which gives instructions for part of hemoglobin.
The phrase “sickle cell screen” can mean different things depending on the lab, the setting, and the person’s age. In adults, it may refer to a sickle solubility test. This test looks for the behavior of hemoglobin S in a prepared blood sample. It is fast and inexpensive, but it is only a screening test. It can detect the presence of HbS, but it cannot reliably tell how much HbS is present or which sickle cell condition a person has.
In newborn screening, the test is usually not a simple solubility screen. Newborn programs commonly use methods that separate hemoglobin types, such as high-performance liquid chromatography, isoelectric focusing, or capillary electrophoresis. These methods can identify patterns involving fetal hemoglobin, adult hemoglobin, sickle hemoglobin, and other variants.
A sickle cell screen is different from a full hemoglobin electrophoresis test. Electrophoresis and similar hemoglobin separation methods show which hemoglobin types are present and often their relative amounts. That extra detail is what helps separate sickle cell trait from sickle cell disease.
A screen is also different from a complete blood count. A CBC test can show anemia, red blood cell size, white blood cell count, and platelet count, but it does not identify hemoglobin S by itself. Many people with sickle cell trait have a normal CBC. People with sickle cell disease often have anemia or signs of increased red blood cell turnover, but the diagnosis still depends on hemoglobin or genetic testing.
There is no “normal range” for a basic sickle cell screen. Results are usually qualitative:
| Result wording | Usual meaning | What it cannot prove alone |
|---|---|---|
| Negative | No hemoglobin S was detected in that sample | It may not fully rule out problems if the sample was affected by transfusion, timing, or technical issues |
| Positive | Hemoglobin S was detected | It cannot separate trait from disease without more specific testing |
| Abnormal hemoglobin pattern | The lab found HbS or another hemoglobin variant pattern | The exact condition may still need confirmation |
| Indeterminate or inconclusive | The result could not be interpreted confidently | It should not be treated as a final diagnosis |
The most important limitation is simple: a screening test answers whether hemoglobin S appears to be present. It does not give the full genetic or clinical picture.
Positive, Negative, and Indeterminate Results
A positive sickle cell screen means hemoglobin S was found. In many adults, this means the person has sickle cell trait or a form of sickle cell disease. It can also appear in people with compound hemoglobin conditions, such as hemoglobin SC disease or sickle beta-thalassemia.
A positive result should lead to confirmatory testing rather than assumptions. Two people can both have a positive screen but very different health meanings. One may have sickle cell trait and no anemia. Another may have sickle cell disease, chronic anemia, pain episodes, and organ-related risks. A third may have a mixed hemoglobin condition that needs specialist interpretation.
A negative result usually means hemoglobin S was not detected. For most adults who have not recently received a blood transfusion, that makes sickle cell trait and sickle cell disease unlikely. Still, the word “negative” should be interpreted with the clinical setting. A negative screen does not explain anemia, pain, jaundice, or abnormal red blood cell findings if those symptoms are present. It simply says the sample did not show HbS by that method.
False negative results are uncommon in routine adult testing, but they can happen. A recent transfusion can dilute a person’s own red blood cells with donor red blood cells. Very young infants have high fetal hemoglobin, which is one reason newborn screening relies on specialized methods rather than a basic adult-style screen. Rare technical or sample problems can also interfere.
False positive results are also possible, especially with older or less specific screening methods. Some abnormal hemoglobins or sample conditions can interfere. This is another reason a positive screen should be confirmed with a hemoglobin separation method or genetic test.
Indeterminate results are not a diagnosis. They may happen when the hemoglobin pattern is hard to classify, when there has been a recent transfusion, when the sample quality is poor, or when a person has more than one inherited hemoglobin change. In that situation, the lab may recommend repeating the test, using a different method, or ordering DNA testing.
The report should ideally answer four questions:
- Was hemoglobin S detected?
- Was hemoglobin A detected?
- Were other hemoglobin variants, such as hemoglobin C, detected?
- Do the amounts and pattern fit trait, disease, or something uncertain?
A basic screen often answers only the first question. The rest usually come from confirmatory testing.
Trait, Disease, and Hemoglobin Patterns
Sickle cell trait and sickle cell disease are related, but they are not the same condition. The difference comes from how many hemoglobin gene changes a person inherited and what kind of hemoglobin their body makes.
Sickle cell trait usually means a person inherited one usual hemoglobin A gene and one hemoglobin S gene. This pattern is often written as HbAS. Most people with HbAS do not have sickle cell disease. Their red blood cells usually contain more HbA than HbS, which helps keep the cells flexible in everyday conditions. Trait can still matter for family planning because a person with trait can pass the HbS gene to a child.
Sickle cell disease usually means a person inherited two clinically significant hemoglobin changes. The most familiar form is HbSS, often called sickle cell anemia. Other forms include HbSC and HbS beta-thalassemia. These conditions can cause chronic hemolytic anemia, pain episodes, infection risk, acute chest syndrome, stroke risk, kidney problems, eye problems, and other complications.
The table below shows common patterns in simplified terms. Exact percentages vary by age, transfusion history, hydroxyurea use, coexisting thalassemia, and lab method.
| Pattern or condition | Common hemoglobin finding | Usual meaning |
|---|---|---|
| HbAA | Mostly HbA, no HbS | Usual adult hemoglobin pattern |
| HbAS | HbA and HbS, usually with more HbA than HbS | Sickle cell trait |
| HbSS | Mostly HbS, no HbA unless recently transfused | Sickle cell anemia, a form of sickle cell disease |
| HbSC | HbS and HbC | Hemoglobin SC disease, a form of sickle cell disease |
| HbS beta-zero thalassemia | HbS with no HbA, often with increased HbA2 | A form of sickle cell disease |
| HbS beta-plus thalassemia | HbS with some HbA, often with increased HbA2 | A form of sickle cell disease that can vary in severity |
The inheritance pattern is also important. If both biological parents have sickle cell trait, each pregnancy has a 25% chance of a child with sickle cell disease, a 50% chance of a child with sickle cell trait, and a 25% chance of a child with neither HbS nor trait. These chances reset with every pregnancy.
If one parent has sickle cell trait and the other parent has a different hemoglobin trait, such as hemoglobin C trait or beta-thalassemia trait, a child may still be at risk for a sickle cell disease pattern. This is why partner testing matters. A person can have normal energy, normal hemoglobin, and no symptoms but still carry a hemoglobin gene that affects future children.
A positive screen in a person planning pregnancy should not stop at “trait present.” The more useful information is the exact hemoglobin pattern for both partners. Genetic counseling can help explain the chances, the testing options, and prenatal or preimplantation options when relevant.
When the Test Is Used
A sickle cell screen may be used when a person does not know whether they carry hemoglobin S, when a newborn screening program identifies an abnormal hemoglobin pattern, or when symptoms suggest a sickle cell condition. It may also be ordered before pregnancy, during pregnancy, before certain athletic or military activities, or before medical decisions where sickle status could affect risk planning.
Many adults first learn their status during family planning. This is useful even when they feel completely well. Sickle cell trait usually does not cause sickle cell disease symptoms, but it can be passed to children. If the other biological parent also carries HbS or another important hemoglobin variant, the child may have a form of sickle cell disease.
Testing may also be used when symptoms or lab results raise concern. Examples include unexplained anemia, yellowing of the eyes, episodes of severe pain, a history of childhood hand-foot swelling, splenic problems, blood in the urine, or a family history of sickle cell disease. In those cases, a basic screen may be too limited, and a full hemoglobin evaluation is often more appropriate.
A CBC can help show the effect of a sickle cell condition on blood counts. Low hemoglobin, a high reticulocyte count, high bilirubin, and certain smear findings can support the picture of hemolysis, which means red blood cells are breaking down faster than usual. A hemoglobin blood test result may be low in sickle cell disease, while it is often normal in sickle cell trait.
Preparation is simple. Most people do not need to fast, stop medicines, or change activity before the test. The sample is usually taken from a vein in the arm. For babies, newborn screening uses blood from a heel stick on a special card. The blood draw itself is quick, although confirmatory testing may take longer depending on the lab.
Tell the clinician or lab if the person had a red blood cell transfusion in the past several months. Transfused red cells can change the hemoglobin pattern and may make results harder to interpret. Also mention if the person is a newborn, premature infant, or taking treatment that changes hemoglobin patterns, such as hydroxyurea, because those details help the lab and clinician read the report correctly.
Sickle cell testing should not be limited only by appearance, race, or a broad assumption about ancestry. Sickle hemoglobin is more common in people with ancestry from parts of Africa, the Mediterranean, the Middle East, India, the Caribbean, and Central and South America, but it can occur in any family. Testing is most accurate when it follows the person’s medical question, family history, and reproductive needs rather than stereotypes.
Newborn Screening and Children
Newborn screening for sickle cell disease is one of the most important uses of hemoglobin testing. Babies with sickle cell disease often look healthy at birth because fetal hemoglobin is still high. Symptoms commonly develop later as fetal hemoglobin falls and hemoglobin S becomes a larger share of the baby’s hemoglobin.
A newborn screening result may show patterns such as FA, FAS, FS, FSC, or FSA. The letters are listed in order of amount, and F stands for fetal hemoglobin. A normal newborn pattern is often FA, meaning fetal hemoglobin is highest and adult hemoglobin A is present. FAS usually suggests sickle cell trait. FS, FSC, or patterns involving S with little or no A may suggest sickle cell disease or a related hemoglobin disorder.
Newborn screening is not the same as a final diagnosis. Any baby with a result suggesting sickle cell disease needs prompt confirmatory testing on a separate blood sample. Follow-up should happen quickly because early care lowers the risk of severe infection and other complications. Families may be referred to a pediatric hematologist, newborn screening follow-up team, or genetic counselor.
Early diagnosis allows care to begin before serious problems occur. Depending on the diagnosis, a baby may need penicillin or another antibiotic plan, routine immunizations on schedule, additional vaccines for infection risk, education about fever, and regular visits with a sickle cell care team. Parents and caregivers are often taught to seek urgent medical care for fever, unusual sleepiness, poor feeding, breathing trouble, severe pain, swollen hands or feet, or signs of splenic enlargement.
A newborn result showing sickle cell trait is not an emergency, but it should still be documented and explained. The child does not have sickle cell disease from trait alone, but the information matters later for sports, military service, high-altitude exposure, kidney-related symptoms, and future family planning. It also means at least one biological parent carries hemoglobin S, and testing may be useful for parents and siblings.
Prematurity, transfusion, and timing can complicate newborn results. If a baby received a transfusion before the blood spot was collected, the screening result may be inaccurate because donor red blood cells can affect what hemoglobins are detected. In that situation, the baby may need repeat testing according to the newborn screening program’s instructions.
Parents should keep a copy of the confirmed hemoglobin result. Years later, people may remember only that they “had a positive newborn screen” or “carry sickle cell,” but exact wording matters. HbAS, HbSS, HbSC, and HbS beta-thalassemia have different meanings.
Follow-Up Tests and Related Labs
The best follow-up test depends on the first result and the clinical question. If the result is a positive adult sickle screen, the usual next step is a hemoglobin separation test. This may be called hemoglobin electrophoresis, HPLC, capillary electrophoresis, isoelectric focusing, or a hemoglobinopathy evaluation. The name varies, but the purpose is the same: identify which hemoglobins are present and in what pattern.
Genetic testing may be used when the hemoglobin pattern does not clearly separate HbSS from HbS beta-zero thalassemia, when a rare hemoglobin variant is suspected, when transfusion makes protein-based testing hard to interpret, or when reproductive planning requires exact genetic information. Genetic testing looks at the DNA rather than only the hemoglobin proteins in circulating red blood cells.
A CBC often helps show whether the person has anemia or another blood count pattern. In sickle cell disease, hemoglobin may be chronically low. The hemoglobin and hematocrit results help describe the degree of anemia but do not diagnose the specific sickle cell genotype. Red blood cell size can also help. A low MCV may suggest iron deficiency, thalassemia, or both, which can complicate interpretation.
A reticulocyte count measures young red blood cells. In many people with sickle cell disease, the reticulocyte count is high because the bone marrow is trying to replace red blood cells that break down early. A reticulocyte count test can help show whether the marrow is responding appropriately to anemia.
A peripheral blood smear may show sickled cells, target cells, nucleated red blood cells, Howell-Jolly bodies, or other red blood cell changes. Smear findings can support the diagnosis and help assess complications, but they are not enough to classify the exact hemoglobin pattern. A red blood cell morphology test can be especially helpful when anemia, hemolysis, or abnormal cell shapes are part of the workup.
Other labs may include bilirubin, lactate dehydrogenase, haptoglobin, kidney tests, urine testing, ferritin, transferrin saturation, and liver tests. These do not diagnose sickle cell trait or disease, but they help assess hemolysis, iron status, organ effects, or transfusion-related issues.
Common follow-up combinations include:
| Situation | Helpful follow-up | Reason |
|---|---|---|
| Positive adult screen | Hemoglobin electrophoresis, HPLC, or capillary electrophoresis | Separates trait from disease patterns |
| Abnormal newborn screen | Repeat confirmatory hemoglobin testing on a separate sample | Confirms the newborn screening pattern before long-term diagnosis |
| Recent transfusion | Clinician-guided repeat testing or genetic testing | Donor red cells can mask the person’s own hemoglobin pattern |
| Family planning | Hemoglobin testing for both biological partners, with genetic counseling when needed | Clarifies the chance of a child with sickle cell disease |
| Unexplained anemia or hemolysis | CBC, reticulocyte count, bilirubin, LDH, haptoglobin, smear, hemoglobin analysis | Connects the hemoglobin pattern with the person’s blood count and symptoms |
One common mistake is ordering only a solubility screen when a full hemoglobin pattern is needed. Another is assuming a positive result means “sickle cell anemia.” Sickle cell anemia is usually HbSS, but a positive screen can also reflect trait or other sickle hemoglobin combinations.
What to Do After Results
After a negative result, the next step depends on why testing was ordered. If the person was tested only to check carrier status and has no recent transfusion or special concern, a negative result is usually reassuring for HbS. If symptoms, anemia, or family history remain concerning, the clinician may still order a broader hemoglobinopathy evaluation or genetic test.
After a positive result, ask for the exact hemoglobin pattern. The words “positive for sickle cell” are not specific enough. The report should ideally identify whether the pattern is consistent with HbAS, HbSS, HbSC, HbS beta-thalassemia, or another variant. If the test was only a screen, the next step is confirmatory testing.
For sickle cell trait, most people do not need sickle cell disease treatment. They should know their status, avoid severe dehydration during intense exertion, tell clinicians about the trait when relevant, and seek medical evaluation for blood in the urine or unusual symptoms. Trait status should also be shared during reproductive planning so the other biological parent can be tested.
For sickle cell disease, the result should lead to ongoing care with a clinician experienced in sickle cell management. Care may include infection prevention, vaccines, pain plans, stroke-risk screening in children, kidney and eye monitoring, discussion of disease-modifying medicines, and emergency instructions. The exact plan depends on age, genotype, symptoms, complications, and treatment history.
For an abnormal newborn screen, prompt follow-up is essential. Parents should not wait for symptoms. Babies with sickle cell disease can become seriously ill before the family realizes anything is wrong. Confirmatory testing, pediatric hematology care, infection prevention, and fever instructions are time-sensitive.
For family planning, testing both biological partners is more useful than testing only one. If both carry HbS or another significant hemoglobin variant, a genetic counselor can explain the chances for each pregnancy and discuss options. This does not force any one decision; it gives families accurate information before or during pregnancy.
Bring these questions to the next visit:
- Was hemoglobin S detected?
- Is this result a screen or a confirmatory test?
- What exact hemoglobin pattern was found?
- Could a recent transfusion, newborn timing, or treatment affect the result?
- Does my partner or family need testing?
- Do I need a hematology referral?
- What symptoms should lead to urgent care?
Seek urgent medical care right away for a person with known or suspected sickle cell disease who has fever, chest pain, trouble breathing, severe pain, one-sided weakness, confusion, severe headache, sudden vision changes, unusual sleepiness, signs of dehydration, or a rapidly enlarging painful abdomen. These symptoms can signal serious complications and should not be managed by lab interpretation alone.
References
- Sickle Cell Disease 2025 (Review)
- About Sickle Cell Disease 2025 (Official Page)
- What Is Sickle Cell Trait? 2024 (Official Page)
- Sickle Cell Disease Diagnosis 2024 (Official Page)
- S,S Disease (Sickle Cell Anemia) 2026 (Official Page)
Disclaimer
A sickle cell screen result should be interpreted with a qualified healthcare professional, especially for newborns, pregnancy planning, recent transfusion, anemia, or symptoms. This article explains common result patterns but cannot diagnose sickle cell trait, sickle cell disease, or a specific hemoglobin disorder for an individual person. Seek urgent medical care for fever, chest pain, breathing trouble, stroke-like symptoms, severe pain, or concerning symptoms in anyone with known or suspected sickle cell disease.
