Screening of antenatal patients in a multiethnic community for beta thalassaemia trait

Role of red cell distribution width in screening for Hb E trait in population screening for hemoglobin disorders

The national screening policy for hemoglobinopathies uses the cutoffs for red cell indices mean corpuscular volume >80 and mean corpuscular hemoglobin >27, a strategy known to miss some individuals with Hb E trait (EBT), the most common abnormal hemoglobin in Sri Lanka. We wanted to determine if red cell distribution width (RDW) cutoff values would help in increasing the sensitivity of screening for Hb E trait. High-performance liquid chromatography was carried out as the gold standard to detect hemoglobinopathies and red blood cell parameters with colter counter. Receiver operating characteristic curve was drawn to determine the cutoff value for EBT against β-trait (BTT) and other anemias. Of the 504 patients, 246 had BTT, 110 had EBT, and 151 had other types of anemias. Mean (SD) RDW among patients with BTT was 16 (2.8), with EBT 14.5 (2.9), and with other anemias 15.8 (4.2) (P>0.001). With 14.45 as the cutoff for RDW and considering accepted values for mean corpuscular volume >80 and mean corpuscular hemoglobin >27, it gave a predictive sensitivity of 98.2% for EBT. By using RDW cutoff at 14.45 in addition to the accepted screening indices, sensitivity of Hb E trait detection went up to 98.2% from 86.6%. This study highlights the importance of taking RDW into consideration for screening.

Problems in determining thalassemia carrier status in a program for prevention and control of severe thalassemia syndromes: a lesson from Thailand

BACKGROUND

Prevention and control of severe β thalassemia by carrier detection and identification of couples at risk in developed countries is one of the most successful stories in modern medicine. Similar programs in developing countries especially Southeast Asia, are more problematic because both α and β thalassemias are highly prevalent. In Thailand, there are limited data on whether we could determine, based on hematological phenotypes, the mutation severity and/or coinheritance of α thalassemia in β thalassemia traits.

METHODS

Comprehensive molecular, hematology and hemoglobin analyses of the α and β globin genes were performed in 141 healthy individuals identified as β thalassemia carriers.

RESULTS

Seventeen different β globin mutations were successfully identified out of all cases analyzed. Although the majority of the mutations identified were the β⁰ or severe β⁺ thalassemia alleles, a high proportion of mild mutations (25%) was observed. Of these β thalassemia traits, 22.3% were found to co-inherit the α thalassemias. Milder hematological phenotypes were noted in β⁺ compared with β⁰ thalassemia traits when the α globin genes were intact. Although co-inheritance of α⁰ thalassemia might be suspected in cases with skewed profiles, due to the overlapping values, it remains difficult to apply these parameters for reliable carrier determination.

CONCLUSIONS

A combination of hemoglobin analysis and DNA testing seems to be the best way to confirm carrier status in a region with high frequency for both α and β thalassemias. Underdiagnoses of carrier status could hamper the effectiveness of a thalassemia prevention and control program.

Carrier detection for beta-thalassemia trait in general Pakistani population: a way forward

OBJECTIVE

To determine the frequency of beta-thalassemia minor in subjects with no family history of hemoglobinopathy.

METHODS

Subjects were self-recruited on thalassemia day by advertisement through media. Those with indexed cases of beta-thalassemia major were excluded. Participants were interviewed regarding their marital status and screening of partners. Complete blood counts and peripheral smear review were performed on EDTA samples. Hemoglobin (Hb) electrophoresis was performed in cases with mean corpuscular volume (MCV) <76 fl, mean corpuscular Hb (MCH) <27 pg. HbA(2) level >3.5% was diagnostic for beta-thalassemia trait.

RESULTS

Out of 192 subjects, 11 were excluded based on family history of beta-thalassemia major and minor. Remaining 181 subjects (115 males and 66 females) were enrolled for further analysis. Median age was 27±9.7 years and included 101 married and 80 unmarried individuals. The mean Hb was 12.6 g/dl. MCV <76 fl and MCH <27 pg was seen in 29 subjects. Diagnosis of beta-thalassemia trait was made in 10 subjects (5.5%).

CONCLUSION

Though the carrier rate quoted is similar to previous studies, targeting families with indexed cases for screening might result in failure of carrier detection, since a large population would be overlooked. Implementation of national screening program is the need of the hour in Pakistan to evaluate the true burden of beta-thalassemia.

Proposed screening criteria for beta-thalassemia trait during early pregnancy in southern China

This study was carried out to evaluate whether it is effective to use mean corpuscular volume (MCV) <80 fL as a screening test in the first step of screening for beta-thalassemia (beta-thal) trait in southern China. The data of hematological testing in the first or early second trimester of gestation of 449 pregnant women who underwent prenatal diagnosis for beta-thal were retrospectively reviewed. Of these, six (1.3%) had an MCV value >80 fL, ranging from 80.3 to 83.4 fL. This meant that six at-risk pregnancies would have been missed if only an MCV cut-off value of <80 fL had been used for screening. All subjects having a normal MCV value carried the same -28 (A>G) mutation, accounting for 9.8% (6/61) of the total number of mother with this mutation. If screening had been based on the mean corpuscular hemoglobin (MCH) <27 pg, all 449 pregnant women with beta-thal trait would have been detected. We suggest that all pregnant women presenting at an antenatal clinic with an MCH of <27 pg rather than an MCV of <80 fL should be investigated further to confirm or exclude a diagnosis of beta-thal trait in our region.

Prevalence of elevated hemoglobin A2 measured by the CAPILLARYS system

Hemoglobin (Hb) A2 electrophoresis has been used for prenatal screening for the beta-thalassemia trait (betaTT). We retrospectively reviewed Hb capillary electrophoresis performed in our laboratory. We found that of the 122 cases showing elevated HbA2 levels, 79 cases were due to hemoglobinopathies, mostly HbS. Review of the RBC indices suggested that 3 of 36 cases with elevation of HbA2 in the HbAA-pregnancy group had betaTT and 29 had normal RBC indices; data were not available for 4 patients. Among 7 cases with elevation of HbA2 in the HbAA-other group, 5 had betaTT and 2 were normal. The number of patients without betaTT but with HbA2 elevation in the pregnant group was significantly higher than that in the nonpregnant group. When a higher HbA2 cutoff (3.5%) was used, only 3 pregnant patients without betaTT had HbA2 elevation, similar to the nonpregnant group. We found that a significant number of pregnant women with mild HbA2 elevation had no evidence of betaTT, compared with the nonpregnant group.

Screening for β-Thalassaemia Trait in Anaemic Pregnant Women

AIMS

To find a clinically practicable parameter for the identification of beta-thalassaemia trait (beta-TT) in anaemic pregnant women on the basis of routine use of haematological examination.

METHODS

During 1998-2002, 304 anaemic pregnant women were observed in anaemia consultation hours. A retrospective study was carried out with the aim of finding a screening method for beta-TT in anaemic pregnant women. We compared a sensitivity and a specificity of six different parameters for identification of beta-TT. On the basis of a sensitivity and a specificity for each parameter, we calculated Youden's index, the likelihood ratio and determined the receiver-operating curves. The logistic regression of the variables MCV, MCH and microcytosis was accomplished.

RESULTS

The analysis using receiver-operating curves as well as a calculation of Youden's index showed that the best parameter for screening of beta-TT in anaemic pregnant women is MCV < or = 75 fl. For differentiation between patients with iron deficiency anaemia (IDA) alone and patients with beta-TT and concomitant IDA, microcytosis > or = 15% was the most sensitive. By using MCH we identified 100% of patients in the group with beta-TT but only 67% of patients in the group with IDA.

CONCLUSION

Our results suggest identification of beta-thalassaemia on the basis of quantification of HbA2 in all patients with MCV < or = 75 fl and normal iron status.

Heterogeneity in alpha-thalassemia interactions in Malays, Chinese and Indians in Malaysia

AIM

Interactions between different determinants of alpha-thalassemia raises considerable problems, particularly during pregnancies where antenatal diagnosis is necessary. This study aims to determine the different types of deletional alpha-thalassemia and Hemoglobin Constant Spring (HbCS), and their frequency in Malays, Chinese and Indians in Malaysia.

METHODS

DNA from 650 pregnant women from the Antenatal Clinic of the University of Malaya Medical Center in Kuala Lumpur, Malaysia who showed mean cell volume < or =89 fL and/or mean cell hemoglobin < or =28 pg were analyzed for the double alpha-globin gene South-East Asian deletion (--SEA), the -alpha3.7 and -alpha4.2 single alpha-globin gene deletions and HbCS.

RESULTS

One hundred and three (15.8%) of the pregnant women were confirmed as alpha-thalassemia carriers: 25 (3.8%) were alpha-thalassemia-1 carriers with the --SEA/alphaalpha genotype, 64 (9.8%) were heterozygous for the -alpha3.7 rightward deletion (-alpha3.7/alphaalpha), four (0.6%) were heterozygous for the -alpha4.2 leftward deletion (-alpha4.2/alphaalpha), nine (1.4%) were heterozygous for HbCS (alphaCSalpha/alphaalpha) and one (0.2%) was compound heterozygous with the -alpha3.7/alphaCSalpha genotype. The double alpha-globin gene --SEA deletion was significantly higher in the Chinese (15%) compared to the Malays (2.5%) and not detected in the Indians studied. The -alpha3.7 deletion was distributed equally in the three races. HbCS and -alpha4.2 was observed only in the Malays.

CONCLUSION

The data obtained gives a better understanding of the interactions of the different alpha-thalassemia determinants in the different ethnic groups, thus enabling more rapid and specific confirmation of alpha-thalassemia in affected pregnancies where antenatal diagnosis is necessary.

Ten years' experience of antenatal mean corpuscular volume screening and prenatal diagnosis for thalassaemias in Hong Kong

OBJECTIVE

To determine the prevalence of thalassaemia carriers in Hong Kong.

SUBJECTS AND METHODS

From 1988 to 1997, 25,834 (53.7%) of 48,089 mothers were screened for thalassaemias by mean corpuscular volume (MCV) at the first antenatal visit.

RESULTS

In the screened population of 25,834, 2229 (8.6%) had MCV < or = 75 fl. Of these, 1121 (4.3%) were alpha-thal, 715 (2.8%) were beta-thal, 23 (0.1%) were alpha beta-thal, 57 (0.2%) were other haemoglobin variants, and 281 (1.1%) had either iron deficiency or uncertain causes. Out of 200 pregnancies at risk for homozygous alpha-thal-1 and 32 at risk for beta-thal major, 27 homozygous alpha-thal-1 and 7 beta-thal major were identified, compared favourably with the expected figures of 23 and 9.

CONCLUSION

Antenatal screening for thalassaemias by MCV is simple, effective and reliable. Universal screening has a different impact as bone marrow or cord blood stem cell transplant provides cure for beta-thal major. At risk couples have, as an alternative to termination of pregnancy, the option of early detection and treatment for their affected newborns or fetuses.

Screening criteria for beta thalassaemia trait in pregnant women

AIMS

To establish suitable screening criteria for beta thalassaemia trait during pregnancy using an automated blood counter incorporating light scattering technology.

METHODS

Pregnant women (n = 857) at a London antenatal clinic were investigated for beta thalassaemia trait if the Technicon H.2 full blood count showed either a mean corpuscular volume (MCV) < 85 fl or a mean corpuscular haemoglobin (MCH) < 27 pg. Results were then analysed to establish which of these variables was more suitable for screening and to determine suitable cut off points for calculating the haemoglobin A2 percentage.

RESULTS

The MCH was superior to the MCV for thalassaemia screening as it was a more stable measurement and fewer unnecessary tests were performed. A MCH less than 27 pg is a suitable cut off point for screening. This screening criterion was equally applicable to a Coulter impedance counter.

CONCLUSIONS

Pregnant women presenting at an antenatal clinic with a MCH < 27 pg should be investigated further to confirm or exclude a diagnosis of beta thalassaemia trait.

Hematological status of beta-thalassemics in Madras

Although rapid technical advances have taken place in the diagnosis of beta-thalassemia, still the hematological factors were found to be suitable screening test in areas like Indian subcontinent where a high prevalence of beta-thalassemia trait was observed. Among various thalassemias reported in Asian Indians, beta-thalassemia account for about 80% and is responsible for very high infantile mortality. Despite this, little is known about the hematological status of beta-thalassemias among this ethnic group which is associated with more than five different predominant beta-globin mutation with high frequency and variable number of rare ones. The present study is the first report of hematological status of beta-thalassemia among this ethnic group particularly from Tamil Nadu, Southern India, who are still practising high degree of consanguinity. In the present study, a total number of 364 beta-thalassemics were investigated. This includes 84 cases of homozygous beta-thalassemias and the remaining 280 were heterozygotes. The hematological factors such as red cell indices, hemoglobin F and hemoglobin A2 were assessed. The results revealed a wide spectrum of hematological variables ranging from severe form as that of Mediterranean thalassemias to very mild form of anemia as that of African Negro population.

Prediction and diagnosis of sickling disorders in neonates

A pilot scheme for the prediction and detection of sickle cell disease in neonates was set up and the results from its first three years of operation analysed. A total of 153 women booking at the antenatal clinic were found to have haemoglobin S. The protocol required that all partners of the women so identified be screened for abnormal haemoglobins and beta thalassaemia trait, and that the babies of these women should have cord blood electrophoresis performed. In fact this was only achieved in 75 partners (49%) and 91 of 145 infants (63%). Of 10 babies born with sickle cell disease during the study period, nine had mothers known to have haemoglobin S or C, but only four of these mothers' partners had been tested before delivery of the child. This pilot study highlights the problems in establishing effective antenatal screening programmes, especially in ethnic minority groups. The results show that detailed staff training, careful organisation of administrative arrangements, and education of 'at risk' groups should all be undertaken before the launching of major screening initiatives.