Thalassaemia minor means you are a thalassaemia carrier: you have an inherited change in the genes that make haemoglobin; it is not a disease or cancer, and most carriers have no symptoms and need no treatment [1, 2]. On a blood test it shows as small red blood cells (low MCV and MCH) with a normal or high red cell count, and it is confirmed with an HbA2 test and sometimes a genetic test [7, 8]. The most important step is testing your partner: if you both carry beta thalassaemia, in each pregnancy there is a 1 in 4 chance that the child will have thalassaemia major [1].
Key points
- Thalassaemia minor means you are a thalassaemia “carrier”: you have an inherited change in the genes that make haemoglobin. It is not a disease or cancer, and it does not turn into thalassaemia major [1, 2].
- Most carriers have no symptoms or only mild anaemia and need no treatment [1, 19]. Their outlook is very good [1].
- On a blood test it shows as small red blood cells (low MCV and MCH) with a normal or even high red cell count [7, 8]. Beta thalassaemia trait is confirmed with an HbA2 test, while alpha thalassaemia trait often needs a genetic (DNA) test [8, 2].
- Iron tablets do not make a carrier’s small red cells normal; iron is needed only when a ferritin test also shows iron deficiency [2, 3].
- If you and your partner both carry beta thalassaemia, in each pregnancy there is a 1 in 4 chance that the child will have thalassaemia major; genetic counselling and testing the baby early in pregnancy help you make an informed decision [1, 3].
What is thalassaemia minor?
Haemoglobin is the protein in red blood cells that carries oxygen around the body, and it is built from two kinds of chains, called alpha and beta. In thalassaemia, the body makes less of one of these chains, so the red blood cells are smaller and contain less haemoglobin [1, 2].
Thalassaemia minor (also called being a “thalassaemia carrier” or having “thalassaemia trait”) means you inherited this gene change from one of your parents. Thalassaemia major, a serious disease that needs regular blood transfusions from early childhood, happens when a child inherits a changed gene from both parents [1]. So a carrier always stays a carrier and does not develop thalassaemia major.
There are two main types [1, 2]:
- Beta thalassaemia carrier (beta thalassaemia minor): one of the two beta genes is changed. On testing, a type of haemoglobin called HbA2 is slightly raised [1].
- Alpha thalassaemia carrier: everyone has four alpha genes. If one of them is not working, the blood count may be completely normal; if two are not working, the red cells become small. Alpha carriers also usually have no symptoms [2, 4].
Thalassaemia trait is common in many regions, including the Mediterranean, the Middle East, Africa and South and South-East Asia [1, 2]. In northern and southern Iran, for example, about 1 in 10 people carries beta thalassaemia, and alpha carriers are even more common [4].
Thalassaemia minor is not cancer, and the outlook for carriers is very good [1]. In a large study, carriers lived as long as other people [18].
Symptoms of thalassaemia minor
Most carriers have no symptoms and find out they are carriers only from a blood test, such as a premarital screening test or routine pregnancy tests [1, 2]. Some have mild anaemia that usually causes no problems and does not need blood transfusions [19].
If you are a carrier and have marked tiredness, shortness of breath or paleness, do not put it down to thalassaemia. These symptoms are uncommon in carriers and are more often due to another problem, such as a lack of iron, vitamin B12 or folic acid, which your doctor should find and treat [2]. Read: Iron-deficiency anaemia and Vitamin B12 deficiency.
In some studies, gallstones were slightly more common in beta thalassaemia carriers [1, 18].
Which tests? Thalassaemia trait or iron deficiency
Thalassaemia trait and iron deficiency both cause small red blood cells, and a full blood count (CBC) alone cannot tell them apart [8]. These tests help:
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Full blood count (CBC)
In carriers, the red blood cells are small (low MCV) and pale (low MCH); screening programmes, such as Iran’s premarital programme, use an MCV below 80 or an MCH below 27 as the threshold for further testing [3, 8]. In beta carriers the red cell count (RBC) is usually normal or high, and the cells are smaller than the degree of anaemia would explain [7, 9]. How to read your report: How to read a CBC.
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Genetic (DNA) test
When the red cells are small but iron and HbA2 are normal, you may carry alpha thalassaemia; alpha trait can usually be confirmed only with a DNA test [2, 8]. If your HbA2 is borderline (close to 3.5) and your partner is a carrier, your doctor may also ask for a DNA test for beta thalassaemia [10, 11].
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Sometimes both are present: iron deficiency is common in carriers, especially women [12]. In this case your doctor treats the iron deficiency and repeats the tests if needed [3, 7].
If your anaemia comes with unexplained fever, repeated infections, unexplained bruising or bleeding, or swollen lymph nodes, these are not caused by thalassaemia and you should have a blood count within 2 days [23]. Read: What does leukaemia look like on a blood test (CBC)?
For physicians
| Condition | Hb | MCV and MCH | RBC count | Ferritin | HbA2 and HbF | Confirmation |
|---|---|---|---|---|---|---|
| Beta thalassaemia trait | Normal or slightly low [1] | Low; screening thresholds in Iran MCV <80 fL or MCH <27 pg [3] | Normal to high [7] | Normal unless there is coexisting iron deficiency (20.7% of carriers in one study) [12] | HbA2 above 3.5% (mean 5.4%) [3, 12] | HPLC or capillary electrophoresis; DNA if HbA2 is borderline [8, 10] |
| α+ trait (-α/αα) | Normal [2] | Normal or slightly low (silent carrier) [2, 4] | — | Normal [2] | HbA2 normal or low [2] | DNA only (gap-PCR) [4] |
| α0 trait or two-gene deletion (--/αα or -α/-α) | Normal or slightly low [2] | Clearly low [4] | High [2] | Normal [2] | HbA2 below 3.5% and HbF below 2% [4] | DNA; Hb Bart's in the newborn [2] |
| Iron-deficiency anaemia | Low [9] | Low [9] | Lower than in beta trait [7] | 30 ng/mL or less [21] | May fall slightly [7] | Ferritin, plus TSAT in inflammation; response to iron [9, 21] |
Do not call a borderline HbA2 (about 3.1–3.9%) normal or put it down to iron deficiency; molecular testing is needed, especially when the partner is a carrier [10, 11].
National programme (Iran). Original algorithm: CBC in the man; if MCH is below 27 pg or MCV below 80 fL, the woman is tested; if both are microcytic, HbA2 is measured; HbA2 above 3.5% in both: referral for genetic counselling; microcytosis with normal HbA2: iron and repeat indices [3]. The main problem is persistent microcytosis with a normal HbA2, which is usually α+ thalassaemia but can be normal-HbA2 beta thalassaemia [3]; these people remain in the programme for molecular work-up, and there is no separate α screening [4]. Under the national instructions, couples with MCV 75–80, MCH 26–27, HbA2 below 3.5 and HbF below 3 are classed as low risk and genetic testing is not obligatory; among 5624 people in Isfahan (2012–2016) the programme’s sensitivity was 99.7% and specificity 53.12%, and 10 carriers (0.18%; 3 with combined α and β mutations and 7 with HbS) had MCV ≥80 and MCH ≥26 [6]. The programme does not detect HbS [3]. A 90.13% reduction in expected beta thalassaemia births was reported in 2015 [5].
HbA2 cut-off and borderline values. The diagnostic cut-off is not uniform: laboratories use 4.0%, 3.5% or 3.3% [10]. Of 410 partners of carriers with HbA2 3.1–3.9%, 22.9% had a molecular defect in the beta, delta or alpha genes [11]; across studies, 35.4% of 1766 people with borderline HbA2 had a molecular defect: 17% beta, 7.7% alpha, 2.7% KLF1, 2.3% beta with alpha, 2.0% beta with delta and 1.8% alpha triplication [10]. Borderline HbA2 in a microcytic person, especially when the partner is a carrier, needs molecular testing [10, 11].
Interpretation pitfalls. Coinherited α thalassaemia can normalise the red cell indices while HbA2 stays in the beta-carrier range, so HbA2 should always be measured; coinherited δ thalassaemia can normalise HbA2; silent beta mutations give normal indices with a normal or borderline HbA2 [1]. Classic teaching: coexisting iron deficiency lowers HbA2 and should be corrected before electrophoresis is interpreted [7]. However, among 752 obligate beta carriers (parents of patients with thalassaemia major), iron deficiency was present in 20.7% (33.3% of women), mean HbA2 was 5.4% in both groups, and HbA2 below 4.0% was seen in 6.4% of iron-deficient versus 2.2% of iron-replete carriers, half of these iron-deficient carriers having the silent CAP+1 allele; all 5 carriers with Hb below 80 g/L had HbA2 above 4.5% [12]. In 213 child carriers, median HbA2 was 4.1% with iron deficiency versus 4.9% without (P<0.007), but most stayed in the diagnostic range [13]. Conclusion: do not attribute a low or borderline HbA2 to iron deficiency alone; repeat after iron repletion or genotype [12, 13]. A TSAT below 20% indicates iron restriction, particularly in carriers [9].
α thalassaemia. Diagnosis is usually by exclusion: microcytosis with normal haemoglobin analysis and normal iron studies; definitive diagnosis by family studies and DNA analysis [8]. Testing starts with multiplex gap-PCR for the common deletions (-α3.7, -α4.2 and --MED), and MLPA detects unknown deletions [4]. Among 10,849 Iranian carriers, -α3.7 was the most common allele (67.1%); -α4.2 4.68%, --MED 3.6%, α5NT 6.99% and PolyA2 6.78% [4].
Discriminant indices. In a meta-analysis of 99 articles on 12 indices, none was 100% sensitive and specific; the ratio of microcytic to hypochromic red cells (M/H) performed best (DOR 100.8), followed by the RBC index (47.0), Sirdah (46.7) and Ehsani (44.7); RDW (Bessman) was the weakest (6.8), and all performed better in adults than in children; their only role is to select who needs confirmatory testing [14]. BSG: haemoglobin electrophoresis for microcytosis with normal iron studies, to avoid unnecessary GI investigation; in thalassaemia the MCV is reduced out of proportion to the anaemia [9].
Treatment: are iron tablets needed?
Thalassaemia minor needs no treatment [2, 19]. A carrier’s red cells are small because of the gene, not because of a lack of iron, so iron tablets do not make them normal [1, 3].
Take iron tablets only if a ferritin test shows iron deficiency. Taking iron for a long time without a reason can raise the body’s iron too high [2]. On the other hand, if you are short of iron, it should be treated as in anyone else; iron deficiency is not rare in carriers, especially women [2, 12]. How to take iron tablets: see Iron-deficiency anaemia.
Carriers do not need a special diet [1]. Folic acid is not routinely needed for carriers either, but all women who are planning a pregnancy or are pregnant, carriers or not, should take folic acid [2, 20].
For physicians
Management. α carriers usually need no treatment because the anaemia is very mild or offset by a high RBC count; coexisting iron, folate or B12 deficiency must be treated properly, but prophylactic iron should never be given because of the risk of iron overload [2]. The prognosis of beta carriers is excellent; the risk of gallstones is higher, especially with the Gilbert mutation [1]. In a retrospective Sicilian cohort (4943 carriers versus 21,063 controls), beta trait was associated with more hospital admissions for cirrhosis (OR 1.94), kidney disorders (OR 2.11), gallstones (OR 1.39) and mood disorders (OR 2.08), but life expectancy did not differ (HR 1.090) [18].
When is it more than trait? Beta thalassaemia intermedia: Hb 7–10 g/dL, MCV 50–80 fL and MCH 16–24 pg; beta trait with α-gene triplication can produce an intermedia phenotype [1]. HbH disease (three α genes affected; in Iran mostly -α3.7/--MED): mild to moderate haemolytic anaemia, hepatosplenomegaly, jaundice and gallstones [4], with Hb 2.6–13.3 g/dL and HbH 0.8–40% [2]. The screening programme does not detect HbS [3]. Anaemia more severe than expected for trait, splenomegaly, evidence of haemolysis or a discordant laboratory pattern calls for haematology assessment [1, 2].
Marriage: what if we are both carriers?
Many countries where thalassaemia is common offer carrier tests before marriage or pregnancy. In Iran, for example, thalassaemia testing has been part of the compulsory premarital blood tests since 1997 [3]. In that programme the man’s blood count is checked first; if his red cells are small, the woman is tested too. If both have small red cells, HbA2 is measured, and if both are beta carriers they are referred for genetic counselling [3].
If only one of you is a carrier, your children will not have thalassaemia major; they may only be carriers [1].
If you are both beta carriers, in each pregnancy [1]:
- 1 in 4 chance: the child has thalassaemia major
- 2 in 4 chance: the child is a carrier like you
- 1 in 4 chance: the child is neither a carrier nor affected
These chances start afresh with each pregnancy; having one healthy or affected child does not change the chances for the next pregnancy [1].
In alpha thalassaemia the picture is more complicated. If both partners carry the severe form of alpha trait (two genes missing on the same chromosome), in each pregnancy there is a 1 in 4 chance of a very severe condition in the unborn baby (hydrops fetalis); and if one carries the severe form and the other the mild form, there is a 1 in 4 chance of HbH disease (moderate anaemia) [2]. If one partner carries beta and the other alpha thalassaemia, the child will not have thalassaemia major; but small red cells with a normal HbA2 are sometimes due to a less common form of beta thalassaemia, and a DNA test makes this clear [1, 3, 4].
Genetic counselling explains the test results, the chances and the options, and the decision is the couple’s own; each couple has as many sessions as they need, usually two to three [1, 3]. Carrier couples who marry can have the baby tested during pregnancy [1, 3]. Iran’s programme has been successful: in 2015, births of babies with beta thalassaemia were about 9 in 10 fewer than expected [5].
Pregnancy and thalassaemia trait
If you are a carrier, your pregnancy usually goes well [15]. In some studies, anaemia in pregnancy and slower growth of the baby were more common in carrier women, so your doctor may check your haemoglobin regularly and follow the baby’s growth with ultrasound [15, 16].
Talk to your doctor about iron tablets in pregnancy: iron deficiency does occur in pregnant carriers, especially alpha carriers, and your doctor decides with a ferritin test [17]. As for all women, folic acid is best started before pregnancy [20].
If your partner is also a carrier or has not been tested, contact your doctor or a genetic counselling service as soon as you know you are pregnant. The baby can be tested by sampling the placenta (chorionic villus sampling) at about week 11 of pregnancy, or by amniocentesis (a sample of the fluid around the baby) at about weeks 15 to 18, and for this both partners’ gene changes must be known beforehand [1]; so the best time for the couple’s DNA tests is before pregnancy. If the baby is affected, the decision to continue or end the pregnancy is possible, where the law allows it, only in the early months, which is why an early visit matters [3]. Another option is IVF with genetic testing of the embryo before it is placed in the womb [1].
For physicians
Pregnancy in carriers. Among 159,195 deliveries (261 with beta thalassaemia minor), beta trait was associated with oligohydramnios (OR 2.1) and IUGR (OR 2.4), but birth weight, low Apgar scores, malformations and perinatal mortality did not differ; ultrasound surveillance of fetal weight was recommended [15]. In a retrospective diagnosis-code cohort (TriNetX; 22,770 matched pairs), thalassaemia trait was associated with anaemia in pregnancy (RR 3.00), blood transfusion (RR 1.90), pre-eclampsia (RR 1.54), caesarean delivery (RR 1.43), delivery before 37 weeks (RR 1.40), IUGR (RR 1.96), VTE (RR 1.57) and intrauterine fetal death (RR 1.37) [16]. Among 714 anaemic pregnant women, iron deficiency was found in 40.00–77.78% of silent α genotypes and 18.18–84.21% of α-thalassaemia minor genotypes but in under 10.85% of beta-minor genotypes, and beta-minor carriers had higher ferritin; iron supplementation should be monitored dynamically [17].
Counselling and prenatal diagnosis. Both partners beta carriers: in each pregnancy 25% affected, 50% carrier and 25% non-carrier; both mutations must be identified before prenatal diagnosis; CVS at about 11 weeks or amniocentesis at about 15–18 weeks; PGD for families with known mutations [1]. Both partners α0 carriers (--/αα): 25% risk of Hb Bart's hydrops fetalis, with risk to the mother; α0 with α+: 25% risk of HbH disease, and 50% if the α+ carrier is homozygous [2]. In Iran, a 1998 government decision permitted termination before 16 weeks from the LMP for an affected fetus, and a DNA laboratory network has operated since 2001 [3].
Children
If only one parent is a carrier, each child may be a carrier but will not have thalassaemia major [1]. Being a carrier usually gives a child no symptoms and needs no treatment [1, 2].
Beta trait usually does not show on a newborn’s blood test, because production of the beta chain is not yet complete at birth [8]. If a child has small red cells, the doctor checks ferritin before giving iron drops or syrup; iron deficiency also occurs in child carriers, and the two can be present together [13, 2].
When your carrier child grows up, tell them they are a carrier so that they take their future partner’s test seriously before marriage; testing the relatives of carriers is part of prevention [3].
If both parents are carriers and the baby was not tested in pregnancy, watch for signs of thalassaemia major. These usually start between 6 months and 2 years of age: increasing paleness, poor weight gain, feeding problems, irritability, repeated fevers and a swelling tummy due to an enlarged liver and spleen [1]. If you see these, take your child to a doctor soon.
When should I see a doctor urgently?
Call your local emergency number or go to an emergency department straight away if you feel very dizzy when you stand up, are breathing very fast or have a very fast heartbeat, or feel faint; these are not caused by thalassaemia trait and may be signs of severe anaemia [22, 2].
See a doctor in the next few days if:
- you are pregnant and your partner is also a carrier or has not been tested; testing the baby is only possible within a limited time [1, 3]
- both of a child’s parents are carriers and the child is becoming pale, is not gaining weight or has a swelling tummy [1]
- your anaemia comes with unexplained fever, repeated infections, unexplained bruising or bleeding, or swollen lymph nodes; you should have a blood count within 2 days [23]
- you have yellowing of the skin or eyes, or an enlarged spleen; these are not usual in thalassaemia trait, and your doctor will check for another condition such as HbH disease [2, 4]
- you have new tiredness or shortness of breath, or your haemoglobin is lower than usual; iron deficiency or another cause may have been added [2]
Frequently asked questions
Is thalassaemia minor dangerous?
Can thalassaemia minor turn into thalassaemia major?
No. Thalassaemia major happens only when a person inherits a changed gene from both parents; a carrier has one changed gene and remains a carrier for life [1].
I am a thalassaemia carrier; should I take iron tablets?
Only if a ferritin test shows iron deficiency [2, 21]. Iron tablets do not make a carrier’s small red cells normal, and taking them without a reason may raise the body’s iron too high [2, 3]. Read: Iron-deficiency anaemia: symptoms, ferritin test and treatment
My partner and I both carry beta thalassaemia; what should we do?
See a genetic counselling service. In each pregnancy there is a 1 in 4 chance of thalassaemia major [1]. It is best to have DNA tests before pregnancy so that the baby can be tested at about week 11 of pregnancy [1]. In Iran, for example, these tests are part of the national thalassaemia prevention programme [3].
My HbA2 is close to 3.5; what does it mean?
I carry alpha thalassaemia; how is it different from beta?
Related links
References
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Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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- 6Can Couples With MCV≥80, MCH<26, HbA2<3.2, HbF<3 be Classified as Low-risk β-Thalassemia Group?
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- 14Discriminant indices for distinguishing thalassemia and iron deficiency in patients with microcytic anemia: a meta-analysis
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- 22Anaemia (fact sheet)
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