A sickle cell test is a blood test that looks for haemoglobin S (HbS), the abnormal haemoglobin that causes sickle cell disease. A quick screening test only shows whether HbS is present. Confirmatory tests, such as haemoglobin electrophoresis, high-performance liquid chromatography (HPLC), or DNA testing, show how much HbS there is and which other haemoglobins are present. That tells us whether a person has sickle cell trait, sickle cell disease, or neither.
In this article I cover what each test measures, how to read the results, who should be tested, and what happens after a positive result.
What the Sickle Cell Test Detects
Sickle cell disease (SCD) comes from a single change in the HBB gene, which makes the beta-globin part of adult haemoglobin. The sickle cell mutation swaps one amino acid (valine for glutamic acid), and the result is HbS. When oxygen levels drop, HbS molecules stick together into long polymers that bend the red cell into a rigid sickle shape.
These stiff cells block small blood vessels and break down early. That causes pain crises, chronic haemolytic anaemia, and gradual organ damage. The trait is most common in people with African, Mediterranean, Middle Eastern, and Indian ancestry, which reflects its origins in regions where malaria was widespread.
Types of Sickle Cell Tests
Several different tests get called “the sickle cell test”. They do different jobs, and it helps to know which one you had.
| Test | What it does | Main use |
|---|---|---|
| Sickle solubility test | Shows whether HbS is present by making the sample turn cloudy | Rapid screening; cannot tell trait from disease |
| Haemoglobin electrophoresis | Separates haemoglobin types by electrical charge | Confirms diagnosis and identifies HbS, HbC, HbF, HbA2 |
| HPLC | Separates and measures each haemoglobin type precisely | Newborn screening and confirmation; measures percentages |
| Isoelectric focusing | High-resolution separation of haemoglobin variants | Newborn screening in many programmes |
| DNA (HBB gene) testing | Reads the gene directly | Unclear cases, prenatal diagnosis, family studies |
A positive solubility test should always be followed by electrophoresis or HPLC. On its own it cannot separate a healthy carrier from someone with disease, and it can give a false negative in young infants, whose blood is still mostly fetal haemoglobin.
Reading the Results
Confirmatory testing shows a pattern of haemoglobins. The labels below are the ones you will see on most reports.
- HbAA (normal): mostly adult haemoglobin A and no HbS.
- HbAS (sickle cell trait): both HbA and HbS, with more HbA than HbS. Carriers are usually healthy, but they can pass the gene on.
- HbSS (sickle cell anaemia): mostly HbS, no HbA, and a variable amount of fetal haemoglobin (HbF). This is the most common severe form.
- HbSC disease: HbS plus haemoglobin C. It is usually milder than HbSS, but it can still cause serious complications.
- HbS/beta-thalassaemia: HbS inherited with a beta-thalassaemia gene. Severity depends on whether any HbA is still made.
Recent blood transfusion can hide the true pattern, because the donor’s normal red cells dilute the patient’s own. Always tell the laboratory about any transfusion in the past few months.
Who Should Be Tested and When
Many countries screen every newborn using a heel-prick blood spot. Screening at birth matters because babies look well at first. Symptoms usually start from around six months of age, when protective fetal haemoglobin falls and HbS takes over. The early warning signs include painful swelling of the hands and feet, severe infections, and splenic sequestration, where blood pools suddenly in the spleen.
Testing is also recommended for:
- Adults planning a pregnancy, especially when either partner has ancestry from a region where the trait is common.
- Pregnant women, as part of antenatal screening.
- Anyone with unexplained haemolytic anaemia, jaundice, or pain episodes that suggest a haemoglobin disorder.
- Relatives of someone newly diagnosed.
When both parents carry the trait, each pregnancy has a 25% chance of a child with sickle cell disease, a 50% chance of a carrier child, and a 25% chance of a child with neither. For a couple at risk, prenatal diagnosis can be done using chorionic villus sampling or amniocentesis.
What Happens After a Positive Result
A diagnosis of sickle cell disease leads to referral to a specialist haematology team. For infants, early care includes penicillin prophylaxis, full vaccinations, and teaching parents to spot fever and an enlarging spleen. For children, regular transcranial Doppler scans help find those at higher risk of stroke.
Ongoing treatment may include pain management plans, hydroxyurea (hydroxycarbamide), which raises fetal haemoglobin and reduces sickling, and blood transfusion for specific complications. A stem cell transplant using donor bone marrow can cure the disease, but it is limited by donor availability and its risks. Gene therapies that modify the patient’s own stem cells are now approved in some countries for selected patients.
With early diagnosis and modern care, outlook has improved a great deal. You can read more in our article on the life span of sickle cell patients and in our sickle cell guide.
Key Takeaways
- The sickle cell test finds haemoglobin S. Screening shows whether it is there, and confirmatory tests show the full haemoglobin pattern.
- Electrophoresis or HPLC is needed to tell trait (HbAS) apart from disease (HbSS, HbSC, HbS/beta-thalassaemia).
- Newborn screening lets care start before symptoms appear, usually from around six months.
- Carriers are generally healthy, but two carrier parents have a 1 in 4 chance of an affected child in each pregnancy.
- A recent transfusion can hide results, so tell the laboratory about it.
Frequently Asked Questions
How is a sickle cell test done?
Adults and older children have a small sample taken from a vein in the arm. Newborns have a few drops taken from a heel prick. No fasting or special preparation is needed.
Can the test tell if I have sickle cell trait or the disease?
A confirmatory test such as haemoglobin electrophoresis or HPLC can, because it measures how much of each haemoglobin you have. A basic solubility screen only shows that HbS is present, so it cannot make this distinction.
Do I need to be tested if I was screened as a baby?
If you have a documented newborn result, you usually do not need testing again. Many adults cannot find their result, though, so testing before pregnancy is a sensible step if you are unsure.
How long do results take?
A rapid solubility screen can be ready the same day. Electrophoresis, HPLC, and newborn screening results usually come back within days to a couple of weeks, and DNA testing can take longer.
