Screening for thalassemia trait by electronic measurement of mean corpuscular volume

The role of discriminant functions in screening beta thalassemia trait and iron deficiency anemia among laboratory samples

INTRODUCTION

Most important differential diagnosis for microcytosis and hypochromia is beta thalassemia trait (BTT) and iron deficiency anemia.

AIM

To study the utility of discriminant functions (DFs) and red cell indices in distinguishing BTT and iron deficiency anemia.

METHODS

The study is observational (cross sectional). A total of 350 patients, 43 BTT, and 307 iron-deficiency anemia reflecting actual disease prevalence were included. Their complete red blood cell parameters, hemoglobin A2, and serum ferritin level wherever required were obtained. Receiver operator characteristic curve was drawn for each DF and results compared with other studies.

RESULTS

Among the six DFs, the highest sensitivity (97.7%) and specificity (98.6%) was shown, respectively, by Shine and Lal (S and L) and England and Fraser index (E and F) in identifying cases of BTT. Youden index of the Mentzer index (MI) was the highest (69.0) and S and L, the lowest (13.2) indicating MI to be the most efficient and the S and L, the least in differentiating the two entities. Red cell distribution width index (RDWI) showed the highest accuracy (91.6%), whereas S and L showed the least accuracy (29.6%).

CONCLUSION

MI was the most efficient in discriminating BTT from iron deficiency anemia (IDA). RDWI stands to be the most accurate. S and L could at best be used as screening tool rather than DF. No study except one agreed with us because convenient sampling used in other studies generated bias in their results. Statistically, this study bears far more relevance than other studies because the sample distribution reflects the prevalence of IDA and BTT in the community.

Differential regulation of redox proteins and chaperones in HbEβ-thalassemia erythrocyte proteome

PURPOSE

In (hemoglobin, Hb) HbEβ-thalassemia, HbE (β-26 Glu→Lys) interacts with β-thalassemia to produce clinical manifestation of varying severity. This is the first proteomic effort to study changes in protein levels of erythrocytes isolated from HbEβ-thalassemic patients compared to normal.

EXPERIMENTAL DESIGN

We have used 2-DE and MALDI-MS/MS-based techniques to investigate the differential proteome profiling of membrane and Hb-depleted fraction of cytosolic proteins of erythrocytes isolated from the peripheral blood samples of HbEβ-thalassemia patients and normal volunteers.

RESULTS

Our study showed that redox regulators such as peroxiredoxin 2, Cu-Zn superoxide dismutase and thioredoxin and chaperones such as α-hemoglobin stabilizing protein and HSP-70 were upregulated in HbEβ-thalassemia. We have also observed larger amounts of membrane associated globin chains and indications of disruption of spectrin-based junctional complex in the membrane skeleton of HbEβ-thalassemic erythrocytes upon detection of low molecular weight fragments of β-spectrin and decrease in β-actin and dematin content.

CONCLUSION AND CLINICAL RELEVANCE

We have observed interesting changes in the proteomic levels of redox regulators and chaperons in the thalassemic hemolysates and have observed strong correlation or association of the extent of such proteomic changes with HbE levels. This could be important in understanding the role of HbE in disease progression and pathophysiology.

Approach to blood donors with microcytosis

The aim of this paper is to find microcytosis in donors, to establish prevalence of iron deficiency anaemia (IDA) and beta-thalassemia trait (BTT) in them and to evaluate which index is most effective in differentiating these two conditions. IDA and BTT are the most common causes of microcytic anaemia. Traditional approach is trial of iron treatment. Where thalassemias are common, this can lead to iron overload and failure to provide diagnosis/counselling in BTT. Initially 925 donor samples were evaluated on cell counter. Of these, 50 were found microcytic. These were subjected to Ferritin and HbA2 determination. Subsequently, additional 51, age- and sex-matched normocytic donor samples were selected as controls. These were subjected to the same tests. Nine indices namely RBC, RDW, Mentzer's, Shine and Lal, England and Fraser, Srivastava, Green and King, RDW index and Ricerca were used to differentiate IDA and BTT. Prevalence of microcytosis was 5.4%. Of these microcytic samples, 52% were IDA, 36% were BTT, 8% had both and 4% were undiagnosed. IDA had significantly lower Hb, mean corpuscular volume (MCV) and Ferritin levels than the control group. BTT had lower MCV, higher Ferritin and comparable Hb levels with control group. The Youden's index of Mentzer's was highest and RBC was the only index which had both sensitivity and specificity more than 80% for both IDA and BTT. It is desirable to routinely perform hemograms for all blood donors and further analyse the microcytic samples for Ferritin and HbA2 to diagnose IDA and BTT and to provide appropriate counselling/treatment.

Relevance of red cell distribution width (RDW) in the differential diagnosis of microcytic anaemias

The authors studied the red cell distribution width (RDW) index (obtained by Coulter Counter S Plus IV) in normal subjects and in patients with beta-thalassaemia trait and iron deficiency anaemia. Statistics and reference limits for the above three conditions are given. In order to make a differential diagnosis between beta-thalassaemia trait and iron deficiency anaemia, linear discriminant analysis was carried out. Global correct classification was 91.5% on our first sample of patients and 88.8% on a subsequent validation sample of microcytic patients. The percent of correct beta-thalassaemia trait diagnoses was 94.4% and 86.7% for the first and validation samples respectively. For iron deficiency anaemia correct diagnoses of 86.2% and 90.9% were achieved.

The low mean cell volume in routine haematology

This study establishes the prevalence and distribution of an MCV less than 80 fl by review of the Coulter indices of 7887 samples. Retrospectively, 146 patients are studied and the relationships between the low MCV, film microscopy, iron status, and clinical diagnosis assessed. Plasma ferritin measured radioisotopically in 100 patients is compared to serum iron and iron binding capacity values and some of the problems of assessing iron stores are discussed. The discriminant formulae devised to differentiate between the microcytosis of thalassaemia trait and that or iron deficiency are found to be of limited value when applied to the red cell indices of a hospital population.

Antioxidant defense status of red blood cells of patients with beta-thalassemia and Ebeta-thalassemia

Anemia in beta-thalassemia is caused by a combination of ineffective erythropoiesis and premature hemolysis of RBC in the peripheral circulation. Excess of the alpha-globin chain present in beta-thalassemic RBC is mainly responsible for oxidative damage of erythrocyte membrane protein. The activities of glucose-6-phosphate dehydrogenase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase, and the catalytic activity of catalase and superoxide dismutase, and the concentrations of non-enzymic antioxidants such as reduced glutathione were measured to estimate the status of the antioxidant defense system in the erythrocytes for protection against oxidative stress. The extent of lipid peroxidation was also estimated in thalassemic erythrocytes. Significantly lower activities of reduced glutathione indicate the cell to be in a pro-oxidant state and decreased activity of catalase favors hydrogen peroxide-mediated lipid peroxidation in beta-thalassemic and Ebeta-thalassemic RBC.

Comparison of red cell distribution width and a red cell discriminant function incorporating volume dispersion for distinguishing iron deficiency from beta thalassemia trait in patients with microcytosis

The red cell distribution width (RDW), and another red cell discriminant function incorporating RDW (MCV2 x RDW/Hgb x 100) were determined in a group of 30 patients with iron deficiency anemia, 30 patients with beta thalassemia trait, and 30 normal subjects. Both RDW and (MCV2 x RDW/Hgb x 100) mean values were significantly higher in iron deficiency anemia than in beta thalassemia trait (p < 0.001). Taking RDW equal or above 21.0 percent among microcytic anemia patients, we identified correctly 90.0 percent of patients with iron deficiency anemia. The sensitivity and specificity of the test were 90.0 percent (IC 95 percent: 0.75-0.98) and 77.0 percent (IC 95 percent: 0.60-0.88), respectively. RDW values below 21.0 percent identified correctly 77.0 percent of beta thalassemia trait with a sensitivity and a specificity of 77.0 percent (IC 95 percent: 0.60-0.88) and 90.0 percent (IC 95 percent: 0.75-0.96), respectively. Taking values of (MCV2 x RDW/Hgb x 100) above and below 80.0 percent as indicative of iron deficiency and beta thalassemia trait, respectively, we identified correctly 97.0 percent of those patients in each group. Both sensitivity and specificity were 97.0 percent (IC 95 percent: 0.84-0.99). These results indicated that the red cell discriminant function incorporating volume dispersion (MCV2 x RDW/Hgb x 100) is a highly sensitive and specific method in the initial screening of patients with microcytic anemia and is better than RDW in differentiating iron deficiency anemia from beta thalassemia trait.

Comparison of two screening methods, modified Hb H preparation and the osmotic fragility test, for alpha-thalassemic traits on the basis of gene mapping

We evaluated 61 patients with two screening tests for alpha-thalassemia traits on the basis of endonuclease gene mapping. Comparing these two methods--the osmotic fragility test of the red cell and modified hemoglobin H inclusion staining for the sensitivity--we found that the latter was much superior to the former with 100% sensitivity in detecting heterozygous alpha-1 thalassemia and it was also specific as a confirmatory test for thalassemia traits. Red cell indices are still the basic screening tool and can be used together with modified Hb H inclusion staining. The osmotic fragility test was not better than the red cell indices and was not confirmatory. Besides the MCV, RBC, and discrimination functions, we found that RBC distribution width-standard deviation (RDW-SD) was consistently low in heterozygous alpha-1 thalassemia but not in heterozygous alpha-2 thalassemia. None of the above tests was shown to be really helpful in screening in the latter situation. We conclude that the modified Hb H inclusion staining is superior to the osmotic fragility test in screening of alpha-1 thalassemia.

Anaemia and thalassaemia in healthy adolescents from southern Chinese families

A study was conducted on 447 healthy high school students of southern Chinese descent to determine the prevalence of anaemia and thalassaemia. Haematological data and serum ferritin levels were determined on all venous blood samples. Haemoglobin (Hb) electrophoretic study was conducted on 43 students who had anaemia (Hb less than 12 g/dL), and/or mean corpuscular volume (MCV) less than 80 fL. They were re-assessed after 1 month of oral iron therapy. Three girls had definite iron deficient anaemia (less than 1%). Thirty-nine students had either alpha, or beta-thalassaemia, only seven of whom showed anaemia. Since the overwhelming majority of both the thalassaemic students (38 of 39) and the participants (429 of 447) were of Cantonese extraction (native of Guangdong province), the overall incidence of 8.8% (alpha-thalassaemia 5.4%, beta-thalassaemia 3.4%) reflected the high frequency of the thalassaemia gene among this group of southern Chinese. MCV measurement, rather than Hb, was more useful in its detection.

Inadequate utilization of routine electronic RBC counts to identify beta thalassemia carriers

We investigated physician awareness of the diagnosis of beta thalassemia minor as suggested by RBC indices obtained from routine electronic counts; and, the knowledge of the carriers of their genetic trait. Out of 17,000 counts, 324 were compatible with the diagnosis of beta thalassemia minor, but, only 175 (54 per cent) were identified by physicians as possibly thalassemic and in 47 of these (27 per cent) was the diagnosis verified. Twenty-four of 39 interviewed patients in whom the diagnosis of beta thalassemia minor was established knew about their carrier state.

The different types of alpha-thalassemia: practical and genetic aspects

From May 1985 to October 1987, 1,564 Southeast Asians living in Hawaii were screened for hereditary anemias. Microcytosis was determined by electronic red cell indices and morphology; iron deficiency was ruled out by normal red cell distribution width and normal protoporphyrin levels; Hb E was determined by electrophoresis; beta-thalassemia (thal) heterozygotes were identified by raised Hb A2 on column chromatography. alpha-Thalassemia heterozygotes were diagnosed by exclusion. Family studies helped identify or confirm diagnoses, especially for the alpha-thal-2 heterozygotes (-alpha/alpha alpha) and homozygotes (-alpha/-alpha). Provisional diagnoses are being checked by DNA analyses. Iron deficiency prevented detection of possibly coexisting alpha-thalassemias in 97 individuals. Technical problems included the obscuring of standard criteria for recognizing the alpha-thal variants by the presence of Hb E or beta-thal. In such cases, alpha-thal could only be detected by family studies or DNA analyses. Problems with hemoglobin (Hb) electrophoresis included Hb H migrating beyond the edge of the strip if incubation was not closely monitored, and difficulty in detecting the small amounts of unstable Hb Constant Spring. DNA analyses also had limitations, since the nondeletion alpha-thalassemias would not be detected by routine Southern blotting. DNA analyses suggested that about 50% of presumed alpha-thalassemias were alpha-thal-2 (-alpha/alpha alpha) variants, and a corresponding number of alpha-thal-2 variants were among the apparent normals. Gene frequencies in the unselected Lao subjects were approximately 0.2 for Hb E, at least 0.1 for (-alpha), usually a rightward (alpha -3.7) type, 0.04 for (-), and 0.01 for a beta-thal. Multistep screening for the alpha- and beta-thalassemias was an effective and efficient strategy.

Osmotic fragility test in heterozygotes for alpha and beta thalassaemia

This study shows that the combination of heterozygous beta thalassaemia and deletion heterozygous (-alpha/alpha alpha) or homozygous (-alpha/-alpha) alpha+ thalassaemia may result in the production of erythrocytes which have normal mean volume and haemoglobinisation but decreased osmotic fragility. Based on this finding and previous studies, which have shown that beta thalassaemia screening by the osmotic fragility test may miss a significant proportion of beta thalassaemia heterozygotes, we conclude that beta thalassaemia screening in a population in which both alpha and beta thalassaemia are prevalent should combine the one tube osmotic fragility test with electronic measurement of red blood cell indices in the initial screening process.

Anemia in male adolescents in Singapore

Among 990 young male adolescents studied, only 7 were anemic. Three of the anemics had beta-thalassemia trait and 4 had probable alpha-thalassemia trait. Forty-six individuals with hemoglobinopathies were detected: 29 with probable alpha-thalassemia trait, 10 with beta-thalassemia trait and 7 with heterozygous HbE. Heterozygous alpha and beta-thalassemia occurred predominantly in Chinese while heterozygous HbE was found entirely in Malays. There were no cases of established iron deficiency anemia and only 1 had iron deficient erythropoiesis. Folate deficiency occurred only in 8 subjects with thalassemia traits, and no vitamin B12 deficiency was detected.

Community-initiated screening programme for beta-thalassaemia trait

Seven hundred and ninety-five people, (96% of whom were of Greek origin) were screened for thalassaemia trait. A prevalence rate of 7.1% for beta-thalassaemia carriers was found. The red cells of individuals with the alpha-1-thalassaemia, beta-thalassaemia, and haemoglobin Lepore traits all had a mean corpuscular volume (MCV) of less than 76 fL and a mean corpuscular haemoglobin (MCH) of less than 25 pg, thus confirming the usefulness of these indices as a preliminary thalassaemia screening test. However, in three of the six people provisionally diagnosed as having delta-beta-thalassaemia trait, an overlap of MCV and MCH values with the normal range occurred. Community attitudes to the survey and its implications are discussed.

The laboratory evaluation of microcytic red blood cells

Microcytic red blood cell states are common clinical problems in both adult and pediatric age groups. The recent widespread availability of electronic blood cell counters for performing routine blood counts has increased the detection of microcytic red blood cells. Physicians must workup both symptomatic and asymptomatic patients with microcytic red blood cells before they can initiate proper therapy and/or counseling. The purpose of this review is threefold: (1) to discuss the causes of microcytic red blood cells in terms of disorders of decreased heme production vs. disorders of decreased globin production, (2) to review the clinical laboratory tests useful in differentiating microcytic red blood cell states, and (3) to present a practical approach for the laboratory workup of microcytic red blood cells.

Effectiveness of one tube osmotic fragility screening in detecting beta-thalassaemia trait

The effectiveness of the one tube method of osmotic fragility with three buffered solutions (0.32% saline, 0.36% saline, and tyrode) as a screening test for beta-thalassaemia trait was evaluated in several groups of subjects from Greece, Yugoslavia, and Thailand. The results clearly demonstrated that 0.36% saline is the most sensitive and effective solution since it could detect 96 to 100% of heterozygotes with beta-thalassaemia, compared to about 80% with both 0.32% saline and tyrode. However, 0.36% saline gave false positive results in normal subjects and was also positive in haematological disorders which influence osmotic fragility. The screening test with 0.36% saline was applied more precisely in 1371 subjects. The test was false positive in 41 (9.1%) of 455 normal subjects while of 438 confirmed heterozygotes with beta-thalassaemia it was positive in 431 (98%) and negative in only seven (2%). The test was also found to be positive in 80% of patients with iron deficiency anaemia and alpha-thalassaemia trait, in 68% of patients with Hb E trait, in 40% of patients with Hb S trait, and in 78% of heterozygotes with rare haemoglobin variants. The increased sensitivity and effectiveness of 0.36% saline in detecting beta-thalassaemia trait and other disorders influencing osmotic fragility as compared to 0.32% saline and tyrode solutions was also confirmed in a study of 384 unselected schoolchildren.

Hematology of beta-thalassemia trait--age-related developmental aspects and intrafamilial correlations

Beta-thalassemia trait is a frequent cause of microcytic anemia in Mediterranean children. Because striking age-related changes occur in hemoglobin and mean corpuscular volume during childhood, we assessed developmental hematologic characteristics of 132 patients less than or equal to 18 years of age with beta-thalassemia trait. Thirty-nine kindred were studied to examine intrafamilial correlations of hematologic abnormalities. Patients with beta-thalassemia trait demonstrated Hgb values about 2 gm/dl below normal standards, with a progressive rise with age paralleling normal trends. Thalassemic MCV values showed a far greater deviation from normal than Hgb levels. In contrast to normal developmental trends which show a sharp increase in the first five years of life, the MCV in thalassemia trait showed no age-related increase prior to adolescence. No age-related changes in hemoglobin A2 levels were noted. Kindred studies demonstrate a correlation of the degree of anemia, microcytosis, and elevated hemoglobin A2 levels in affected family members (r = 0.318 P < 0.004, r = 0.525 P < 0.001, r = 0.416 P < 0.0015, respectively). Our findings support the use of electronically determined MCV values as an initial screening procedure for children with beta-thalassemia trait. Values of < 70 fl prior to adolescence and < 75 fl during adolescence were present in nearly all thalassemic subjects. Intrafamilial correlations of Hgb, MCV, and hemoglobin A2 levels suggest that these characteristics are genetically determined.

Thalassemia and pregnancy: results of an antenatal screening program

A thalassemia screening program was implemented at our institution using the finding of a mean corpuscular volume less than 80 fl as the index of abnormality. Further evaluation using hemoglobin (Hb) electrophoresis and serum iron studies was carried out according to the scheme detailed below. A diagnosis of thalassemia was made in 33 women (42 pregnancies). Eight patients had alpha-thalassemia trait, 23 beta-thalassemia trait, and two Hb H disease. Thalassemia trait did not have any adverse effect on pregnancy outcome. In two couples the fetuses were at risk for homozygous disease and in one couple the fetus was at risk for sickle cell beta-thalassemia. The screening program described is an effective and inexpensive means of detecting thalassemia in an antenatal population and is applicable to most every clinic or office setting.

The quantitation of haemoglobin A2 and haemoglobin F: a report of the techniques review group of the Thalassaemia Society of Victoria

A techniques review group was established in 1975 to investigate the reproducibility of tests for HbA2 and HbF for the diagnosis of beta thalassaemia. Over a 3-year period, 22 samples were distributed for analysis by up to 14 laboratories. Of 250 estimations of HbA2, 26 (10.4%) were at variance with the majority result. The largest number of variant results were obtained in samples with a HbA2 close to the upper limit of normal. Of 238 HbF determinations, 29 (12%) were equivocal or at variance with the majority result. It is concluded that the techniques of HbA2 and HbF estimation as currently practised by several laboratories are not sufficiently accurate, and that, therefore, a number of cases of beta thalassaemia are not being diagnosed. It is the opinion of those participating in the study that the survey is of value in providing a continuing review of techniques and a forum for discussion.

Beta 0 thalassemia trait in Sardinia

The red cell indices and results of globin chain synthesis in peripheral blood of obligate beta 0 thalassemia (beta 0 thal) carriers (parents of homozygous beta 0 thal children) and beta thalassemia (beta thal) carriers identified during mass screening are reported. Red cell indices were similar in obligate beta 0 carriers and in carriers diagnosed during mass screening. However there was a higher incidence of anemia in female obligate beta 0 thal carriers. In Sardinia the beta 0 thal carrier showed the usual hematological characteristics of the high Hb A2 beta thal carrier with microcytosis, hypochromia, reduced osmotic fragility; Hb F greater than 1% was found in 30% of the carriers. With MCV, MCH, osmotic fragility test (OFT) and Shine and Lal discriminant function we found 3.5%, 1.5%, 3.5% and 4.0% respectively false negatives in carrier identification. A part from one subject, all obligate carriers had elevated Hb A2 levels. The alpha/beta ratio in obligate carriers (mean +/- SD) was 1.83 +/- 0.26 (N = 30).

Methods for detection of hemoglobin variants and hemoglobinopathies in the routine clinical laboratory

Many mutant hemoglobins and hemoglobinopathies can be identified with a high degree of specificity in the routine clinical laboratory. The most frequent abnormalities--those involving Hb S or C--are usually easily detectable in small amounts of sample analyzed by two simple methods of electrophoresis: cellulose acetate at pH 8.5 and citrate agar at pH 6. Some rarer mutants, e.g., Hb O, Hope, and Camden, can also be recognized by these two methods. Presumptive identification of other relatively frequent mutants, such as Hb D Los Angeles (Punjab) and Hb G Philadelphia, can be accomplished with additional data obtained from globin electrophoresis on cellulose acetate in acidic and alkaline buffers containing urea and 2-mercaptoethanol (or dithioerythritol). Electrophoretic profiles are presented of about a dozen hemoglobins likely to be encountered in screening programs in the U.S. Methods are also presented for identifying other genetic hemoglobin abnormalities--various types of thalassemia, Hb M, unstable hemoglobins, and those of the newborn.

Comparison of haematological features of the beta0 and beta+ thalassaemia traits in Jamaican Negroes

Haematological characteristics have been compared in 29 subjects with heterozygous beta0 thalassaemia and in 33 subjects with heterozygous beta+ thalassaemia, identified by the type of sickle cell-beta thalassaemia among close relatives, in a Jamaican Negro population. Total haemoglobin, MCV and MCH were significantly lower in the beta0 type but the level of Hb A2 was not significantly different. Individual values for MCV, MCH and Hb A2 in the beta+ type occasionally overlapped those in the normal population casting doubt on the adequacy of these criteria in identifying all cases of heterozygous beta+ thalassaemia. The haematological differences are those which would be expected on theoretical grounds. The inability to confidently differentiate the two types of heterozygous beta thalassaemia has implications for genetic counselling. The inability to distinguish heterozygous beta+ thalassaemia from normals on any single haematological index suggests that surveys depending on estimations of Hb A2 or on MCV alone may have underestimated the prevalence of the beta+ thalassaemia gene.

A strategy to detect beta-thalassaemia minor

Over the past three years 25 302 adults in Kentucky have been tested for haemoglobinopathies, and of these, haemoglobin A2 was measured on 3734, 1973 with microcytosis and 1761 within the normal range. The best methods of detecting beta-thalassaemia minor using red-blood-cell indices were compared. No method detected all heterozygotes. A new method was devised consisting of three parts: (1) haemoglobin electrophoresis, (2) calculation of the product of the square of the mean corpuscular volume (M.C.V.) multiplied by the mean corpuscular haemoglobin (M.C.H.) measured in units of one hundred, (3) A2 determination on all AA samples with (M.C.V.)2 X M.C.H. less than 1530 and on those with variant genotypes consistent with thalassaemia. In this series this new method detected 137 out of 138 heterozygotes with 4-4% false-positives.

Developmental change in red blood cell volume: implication in screening infants and children for iron deficiency and thalassemia trait

The mean corpuscular volumen when determined by electronic counter is an accurate tool for identification of children with microcytosis due to either iron deficiency or thalassemia trait. The purpose of this report is to describe the normal developmental changes in MCV that occur in children afler 6 months of age. In 211 healthy infants and children screened to exclude those with borderline or overt iron deficiency, thalassemia trait, or hemoglobinopathy, we found that the lower limit of normal for MCV is 70 ft between 10 and 17 months of age and that there is a gradual increase of MCV with age; the lower limit is 74 between 1 1/2 and 4 years and 76 between 4 and 7 years. All of these values are well below the minimum adult level of 80 fl.

The diagnosis of beta-thalassemia trait: a review

Diagnostic and screening methods for beta-thalassemia trait are reviewed in the order of their development, including identification by homozygous offspring, erythrocyte morphology, osmotic fragility, hemoglobin composition, globin synthetic rates, and red blood cell indices.