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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 39  |  Issue : 3  |  Page : 91-97

Blood indices to differentiate between β-thalassemia trait and iron deficiency anemia in adult healthy Egyptian blood donors


1 Department of Internal Medicine, Clinical Hematology and Bone Marrow Transplant Unit, Faculty of Medicine, Ain Shams University, Cairo, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Ain Shams University, Cairo, Egypt

Date of Submission04-Nov-2014
Date of Acceptance02-Dec-2014
Date of Web Publication31-Dec-2014

Correspondence Address:
A Elsalakawy Walaa
Clinical Hematology and Bone Marrow Transplant Unit, Department of Internal Medicine, Faculty of Medicine, Ain Shams University, Ramses Street, Abbassia, Cairo 11566
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-1067.148223

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  Abstract 

Background β-Thalassemia trait (BTT) often shows microcytosis, a normal or an increased red blood cell (RBC) count, and an elevated level of HbA 2 , which provide the basis for laboratory screening. BTT is an important differential diagnosis of iron deficiency anemia (IDA). Donors with BTT have hemoglobin values comparable with normal; hence, they are accepted for donation and they usually escape diagnosis.
Aim The aim of this work was to differentiate BTT from IDA through blood indices performed in routine complete blood count.
Patients and methods A total of 200 samples were obtained from apparently healthy adult Egyptian blood donors randomly. Complete blood count and mean corpuscular volume (MCV) were performed to all individuals. Hemoglobin electrophoresis and/or serum ferritin was performed to samples with MCV less than 78 fl.
Results Prevalence of BTT in this study was 6%, whereas IDA represented 4.5% of total 200 samples investigated. The cutoff value of MCV 73 fl was 91.7% sensitive and 100% specific in differentiating BTT from IDA. Red blood cell distribution width at level 14.5% or below can differentiate BTT from IDA with 83.3% sensitivity and 100% specificity. RBCs count at value above 5.47 million/mm 3 can differentiate BTT from IDA with 100% sensitivity and 100% specificity.
Conclusion The cutoff values of MCV 73 fl or less, RBC count above 5 × 10 6 /mm 3 , and red blood cell distribution width 14.5% or less were suggested to be associated with a high probability of BTT.

Keywords: β-thalassemia trait, blood donors, iron deficiency anemia


How to cite this article:
Soliman A R, Kamal G, Walaa A E, Sallam Mohamed T H. Blood indices to differentiate between β-thalassemia trait and iron deficiency anemia in adult healthy Egyptian blood donors. Egypt J Haematol 2014;39:91-7

How to cite this URL:
Soliman A R, Kamal G, Walaa A E, Sallam Mohamed T H. Blood indices to differentiate between β-thalassemia trait and iron deficiency anemia in adult healthy Egyptian blood donors. Egypt J Haematol [serial online] 2014 [cited 2017 Jun 25];39:91-7. Available from: http://www.ehj.eg.net/text.asp?2014/39/3/91/148223


  Introduction Top


Thalassemias are a group of hemoglobinopathy caused by genetic mutations of the hemoglobin (Hb) genes, resulting in reduced production or total absence of one or more globin chains [1] .

β-Thalassemia major is commonly caused by homozygous deletion of the b-globin chain gene. It is clinically characterized by lifelong severe hemolytic anemia that eventually affects many organs and is associated with high morbidity and mortality [1] .

β-Thalassemia minor [or b-thalassemia trait (BTT)] is the heterozygous form. Most patients are asymptomatic, and some patients have only mild anemia [2] .

BTT often shows microcytosis, a normal or an increased red blood cell (RBC) count, and an elevated level of HbA 2 , which provide the basis for laboratory screening [2] .

HbA 2 is a normal Hb variant consisting of 2a chains and 2d chains. d and b chains have identical sequences in all but 10 of the 146 amino acids. HbA 2 has a function similar to that of HbA. The percentage of HbA 2 varies depending on the assay but generally is in the range of 1.5-3.5% [1] .

The majority of patients with BTT show elevated HbA 2 levels, and some authors have used an HbA 2 level of more than 4% to diagnose BTT [3] .

BTT is an important differential diagnosis of iron deficiency anemia (IDA). In addition, the mild anemia in BTT can be aggravated during pregnancy, and the incidence of intrauterine growth restriction and oligohydramnios has been reported to increase in patients with BTT [4] .

Although patients with BTT do not usually have increased morbidity and mortality, they have a significant risk of having a child with the devastating b-thalassemia disease. [1]

The frequency of the b-thalassemia gene is population dependent. β-Thalassemia is prevalent in a broad belt extending from the Mediterranean basin to Southeast Asia. It is estimated that 1.5% of the world's population carries b-thalassemia - that is, at least 80-90 million people with an estimated 60 000 new carriers born each year [5] . The prevalence of β-thalassemia in Egypt is not precisely defined yet.

IDA is the most common microcytic hypochromic anemia worldwide. It has been estimated that about 20% of the world population are iron deficient and have IDA [6],[7] . Iron deficiency modulates the synthesis of HbA 2 , resulting in reduced HbA 2 levels in patients with IDA [8] . Affected individuals show RBC morphological change of microcytosis, hypochromia, anisocytosis, and poikilocytosis. Carriers have less severe RBC morphological changes than the affected individuals. Percentage of hypochromic red cells may be high before the anemia develops. It is found that a reduction in Hb concentration is a late feature of iron deficiency [9] .

Our study was designed to compare the complete blood count (CBC) parameters in BTT with IDA in adult. Their demographic characteristics were also studied.


  Patients and methods Top


A total of 200 samples obtained from apparently healthy adult Egyptian blood donors volunteers presenting to National Blood Transfusion Center (either at the blood bank or at the outdoor blood donation campaigns) were included in this study. The donors were selected randomly.

Before blood donation, all 200 donors were subjected to predonation counseling. Predonation Hb measurement was performed by finger prick method. The cutoff Hb for accepting or deferring a donor was 13 g/dl for men and 12 g/dl for women.

Routinely, two postdonation samples were collected from all blood donors in vacuumized tubes after 350 ml whole blood donation:

  1. Sample in EDTA tube for blood grouping. It was used for the investigation of microcytosis for this study through CBC.
  2. One clotted sample used in measuring serum ferritin level.


CBC was obtained for all samples. Samples were run on Coulter LH750 counter (Beckman Coulter, Hialeah, Florida, USA) on the day of collection (day 0) to avoid any changes in mean corpuscular volume (MCV) that may occur on sample storage in EDTA.

We investigated for microcytosis in blood donors, and once microcytosis (defined as MCV less than 78 fl) is detected in donor's samples, the following were performed:

  1. Measuring HbA 2 level by HPLC (BioRad D10; BioRad, France). Diagnosis of BTT was made on the basis of HbA 2 levels more than 3.5%.
  2. For microcytic samples with normal Hb typing by HPLC and HbA 2 level less than 3.5%, serum ferritin level was measured.


Diagnosis of IDA was made on the basis of ferritin values lower than 15 ng/ml.


  Results Top


According to CBC/MCV performed for all 200 samples, healthy blood donors were grouped into the following:

Group I: the normal MCV group (MCV > 78 fl).

Group II: the microcytosis group (MCV < 78 fl).

According to Hb electrophoresis results and serum ferritin level, group II was subdivided into the following:

Group IIA: the IDA group.

Group IIB: the BTT group.

Age ranged from 18 to 47 years. The study included 36 female (18%) and 164 male participants (82%). There was a nonsignificant difference between all groups with respect to age or sex ([Table 1] and [Table 2]).
Table 1 Comparison between groups I, IIA, and IIB regarding age shows nonsignifi cant differences between all groups

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Table 2 Comparison between groups I, IIA, and IIB regarding sex shows nonsignifi cant differences between all groups

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In this study, BTT represents 6% (n = 12) from total number of donors, whereas IDA represents 4.5% (n = 9) ([Table 2]).

With respect to RBCs count, a highly significant difference was detected between group I (5.056 ± 0.475 × 10 6 /mm 3 ) and group IIB (5.856 ± 0.178 × 10 6 /mm 3 ). In addition, a highly significant difference was noticed between group IIA (5.098 ± 0.273 × 10 6 /mm 3 ) and group IIB (5.856 ± 0.178 × 10 6 /mm 3 ). No significant difference was detected between groups I and IIA ([Table 3]).
Table 3 Comparison between groups I, IIA, and IIB regarding RBCs count shows highly signifi cant differences between the three groups and between group IIB and the other two groups

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With respect to Hb level, statistically highly significant difference was detected between group I (14.316 ± 1.337 g/dl) and group IIA (12.467 ± 0.897 g/dl). No significant difference was found between either groups I and IIB or groups IIA and IIB ([Table 4]).
Table 4 Comparison between groups I, IIA, and IIB regarding Hb concentration shows highly signifi cant differences between the three groups and between group I and group IIA

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With respect to hematocrit value (HCT), a highly significant difference was detected between groups I (43.199 ± 3.144%) and IIA (37.844 ± 2.873%). In addition, a highly significant difference between groups IIA and IIB was detected (37.844 ± 2.873 and 42.775 ± 2.545%, respectively). No significant difference was detected between groups I and IIB ([Table 5]).
Table 5 Comparison between groups I, IIA, and IIB regarding HCT value shows highly signifi cant differences between the three groups and between group IIA in comparison with the two others

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Red blood cell distribution width (RDW) was the highest in group IIA followed by group IIB and then group I (15.3 ± 0.4, 14.3 ± 0.6, 12.7 ± 0.37%, respectively). It showed highly significant differences between the three groups ([Table 6]).
Table 6 Comparison between groups I, IIA, and IIB regarding RDW shows highly signifi cant differences between the three groups and between each group in comparison with the two others

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The least MCV values were seen in group IIB compared with the other groups. A highly significant difference was seen between groups IIA and IIB regarding MCV (75.122 ± 1.266 and 70.742 ± 2.212 fl, respectively) ([Table 7]).
Table 7 Comparison between groups IIA and IIB regarding MCV showing a highly signifi cant difference between both groups with a lower mean MCV in group IIB (70.7 fl )

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On performing receiver operator characteristic curve, MCV at level 73 fl or less can differentiate BTT from IDA with 91.7% sensitivity and 100% specificity ([Figure 1]).
Figure 1 ROC curve between groups IIA and IIB regarding MCV. MCV at level 73 fl can differentiate BTT from IDA with 91.7% sensitivity and 100% specifi city of the test. BTT, β-thalassemia trait; IDA, iron deficiency anemia; MCV, mean corpuscular volume; ROC, receiver operating characteristic.

Click here to view


In parallel, RBCs count at value above 5.47 million/mm 3 can differentiate BTT from IDA with 100% sensitivity and 100% specificity ([Figure 2]).
Figure 2 ROC curve between groups IIA and IIB regarding RBCs count. RBCs count at value more than 5.47 can differentiate BTT from IDA with 100 % sensitivity and 100% specifi city. BTT, β-thalassemia trait; IDA, iron deficiency anemia; RBC, red blood cell; ROC, receiver operating characteristic.

Click here to view


In addition, RDW at level 14.5% or less can differentiate BTT from IDA with 83.3% sensitivity and 100% specificity of the test ([Figure 3]).
Figure 3 ROC curve between group IIA and IIB regarding RDW. RDW at level 14.5% can differentiate BTT from IDA with 83.3% sensitivity and 100% specificity of the test. BTT, β-thalassemia trait; IDA, iron deficiency anemia; RBC, red blood cell; RDW, red blood cell distribution width; ROC, receiver operating characteristic.

Click here to view



  Discussion Top


IDA and b-thalassemia minor are recognized as the most important causes of hypochromia and microcytosis [10],[11] . To avoid much more expensive, time-consuming, and complicated procedures for discrimination between these disorders, researchers attempt to use either RBC indices such as MCV, MCH, and RDW, or formulas derived from these indices. This process helps to select appropriate individuals for more detailed examination.

Of the 200 samples investigated in our study, microcytic samples were 21 samples representing 10.5% in healthy Egyptian adult blood donors. The reported prevalence of microcytosis in similar studies ranged from 5.4 to 45% according to the ethnic background of the study population.

In our study, BTT was found in 12 samples representing 6% of all 200 tested samples and 57.1% of all 21 microcytic samples.

Comparable results with differences related to ethnic backgrounds of the studied groups were reported. In the Yemeni study by Al-Nood [12] , BTT was detected in 31 patients representing 4.43% of all tested samples and 30% of microcytic samples. In an Indian study, Tiwari et al. [13] studied the prevalence of BTT in microcytic blood donor samples and it was 36% of all microcytic donor samples (18 from 50 microcytic samples). However, the study by Tiwari et al. [13] involved both deferred and actual blood donors on different ethnic group at Blood Bank of Uttarakhand, Dehradun, Uttarakhand, India. In the study by Ali et al. [14] , of the 181 patients studied, diagnosis of BTT was made in 10 patients (5.5%). This study was conducted in general Pakistani population.

In the study by Rahim et al. [15] , totally 323 individuals (173 children and 150 adults) with microcytosis were investigated at Research Center of Thalassemia & Hemoglobinopathies, Ahwaz, Iran. Of the 323 patients, 153 (59 children and 94 adults) were diagnosed to have BTT representing 47.36% of microcytic samples, which was comparable with our results.

Comparing another study in India by Parthasarathy [16] who searched for BTT in 200 adult samples with microcytosis but not in healthy blood donors, BTT was found in 39 samples representing 19.5% of the total 200 microcytic samples. Parthasarathy used 80 fl as a cutoff for microcytosis in their study, which is higher than what we used and could have attributed to their lower results.

Much lower prevalence of b-thalassemia minor was detected in other previous reports. Bolaman et al. [17] screened a total of 14 200 couples before their marriage for BTT in Denzili, Turkey and found that carriers for b-thalassemia represent 2.2%. This was less than that found in our study, may be due to involvement of much more larger scale of population of different ethnic origin.

In our study, nine of the 200 samples had IDA representing 4.5% of all tested samples and 42.9% of the 21 microcytic samples.

Similar results were detected by Tiwari et al. [13] who found IDA in 26 donors representing 2.81% of all tested samples and 52% of 50 microcytic samples.

In the study by Al-Nood [12] , iron deficiency accounted for only a small proportion (12/699 patients) representing 1.72% of all tested samples and 11.65% of microcytic samples, but he investigated samples in outpatient clinic not in blood donors.

Higher prevalence rate of IDA was detected by Al-Dabbagh et al. [18] who found that 16% of the studied Emirati healthy women had IDA (33/204) and 65.0% had ferritin values of less than 30.0 μg/l (133/204). Similarly, Parthasarathy [16] found IDA in 120 samples representing 60% of their study population.

IDA is well known to be the most common cause of microcytic anemia especially in underdeveloped countries. In our study, the prevalence of IDA was lower than that of BTT among our study population (4.5 and 6.0%, respectively). We can only explain these findings by that the majority of our studied population was donation campaign derived, and the possible geographical distribution of the campaigns in middle and high socioeconomic and education standards could be one reason.

In addition, our IDA group showed a highly significant reduction in their mean Hb levels (P = 0.000) when compared with the normocytic group, whereas the mean Hb of the BTT group showed no significant difference compared with the normocytic group. This indicates that the BTT group had higher Hb concentration and less degree of anemia than the IDA group. It therefore needs to be emphasized that, unless the hemograms are performed routinely for all donors and the microcytic samples further analyzed, donors with BTT are more likely to be accepted for blood donation and escape diagnosis than those with IDA. These findings are in agreement with those of both Tiwari et al. [13] and Parthasarathy [16] .

In our study, a lower mean value of MCV for the BTT group than the IDA group was detected with highly significant statistical difference. In addition, we found that MCV less than 73 fl was able to differentiate between the two groups with 91.7% sensitivity and 100% specificity.

RBCs count showed a highly significant elevation in BTT than in IDA (P = 0.000) and also showed a highly significant elevation than in the normal group (P = 0.000). RBCs count was the only parameter that had both sensitivity and specificity of 100% for differentiating both IDA and BTT. Tiwari et al. [13] also found that RBC count is the only parameter that had both sensitivity and specificity more than 80%. This difference may be due to involvement of deferred anemic donors in their study.

In addition, RDW showed a highly significant difference between BTT and IDA (P = 0.000). The highest RDW was found in IDA followed by the BTT with cutoff value between two groups of 14.5% reflecting more anisocytosis in IDA than BTT. Both Rahim et al. [15] and Parthasarathy [16] also found that RDW was higher in IDA than in BTT patients.

In our study, the cutoff values of MCV 73 fl or less, RBC count above 5.47 × 10 6 /mm 3 , and RDW 14.5% or less were suggested to be associated with a high probability of BTT.

Controversy continues regarding the ideal red cell indices and their cutoff values for differentiating BTT and IDA. Kotwal et al. [19] conducted a study with 640 adult patients with microcytosis (MCV<80 fl), plotting receiver operator characteristic curves and recalculating the cutoff values for the Indian setting. The cutoff values of MCV less than 76 fl, RBC count at least 4.9 × 10 12 /l, and RDW 18% or less were suggested to be associated with a high probability of BTT.

However, Parthasarathy [16] in India concluded that cutoff values of MCV below 76 fl, RBC count at least 4.9 × 10 6 /mm 3 , and RDW 18% or less were suggested to be associated with a high probability of BTT. Another Indian study [20] had cutoff values of MCV 78.0 fl or less, MCH 28 pg or less, and HbA 2 more than 3.8% for BTT diagnosis.

In the present study, the RBC count and MCV have greater sensitivity than RDW. Shalev et al. [21] reported that the combination of a high RBC count and low MCV is characteristic of BTT. It has been suggested that the RBC count is the most efficient single test for differentiating BTT and IDA [19],[21],[22] . Other studies showed superiority of RDW, followed by the RBC count and MCV in differentiating IDA and BTT [23] . Therefore, we think a combination of MCV, RDW, and the RBC count is more effective for identifying BTT and differentiating it from other nonthalassemic microcytosis; however, it should be noted that patients with BTT and concomitant iron, vitamin B 12 , or folic acid deficiency, and double heterozygous dβ-thalassemics can have an elevated RDW [5],[24],[25] . Concomitant nutritional deficiency can also alter HbA 2 levels in BTT. Microcytosis accompanied by a high RBC count and normal RDW is suggestive of BTT.

These automated red cell parameters are routinely examined and offer a rapid and reliable method for BTT screening. Adequate utilization of these parameters can facilitate identification of the majority of BTT cases at no additional cost to the healthcare system. Identifying carriers and counseling them about the genetic implications of marrying another carrier is the most effective method for preventing β-thalassemia major.


  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.

 
  References Top

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Ali N, Moiz B, Bin Azhar W, Zaidi N, Memon R. Carrier detection for beta-thalassemia trait in general Pakistani population: a way forward. Hematology 2012l; 17 :237-240.  Back to cited text no. 14
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
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