one of the globin chains syntheses may be defective either due to mutation or deletion resulting in excess production of the other chain which damages the red cell membrane . on the basis of the affected globin chain , the thalassemias are classified into  or  types . the  thalassemia is prevalent throughout the world while  is found more in the mediterranean region , middle east,[24 ] south asia and south east asia.[79 ] the hematological parameters in the thalassemic patients vary with the type and severity of anemia . however , varying degrees of microcytosis is invariably a common feature of almost all types of thalassemias . the final diagnosis of the type of thalassemia is made after a battery of laboratory tests like complete blood count , peripheral smear study , hemoglobin electrophoresis , high performance liquid chromatography ( hplc ) , isoelectric focusing and dna techniques like pcr , restriction fragment length polymorphism ( rflp ) . however , the facilities for dna study are not available at each and every hospital . the blood picture and the study of hematological parameters are the key to decide further course of investigation . many discriminatory indices are available to differentiate  thalassemia trait from iron deficiency anemia ( ida)[1012 ] but no index is described to differentiate clearly between different types of thalassemias itself on the basis of hematological findings . the studies carried out to discriminate between various types of thalassemias on the basis of hematological findings and especially on red cell indices are very limited . the present study is a comparative study of hematological parameters of  and  thalassemias . the study was designed to lay keen emphasis on the differences in the red cell indices of two types of thalassemias . several studies have been carried out in the past and at different places on thalassemias and their blood picture,[48 ] but specific comparative studies of hematological parameters done on saudi thalassemic patients are rare . in saudi arabia where some of the regions have a high prevalence of thalassemias the present study was carried out in the hematology department of riyadh medical college of health , saudi arabia and its associated hospitals from november 2008 to january 2011 . the study sample consisted of 991 cases divided into two groups : adults and children . the blood samples of patients were collected in edta vacutainers and run on coulter stks hematology analyzer . complete blood counts including hemoglobin ( hb ) and red cell indices ; mean cell volume ( mcv ) , mean cell hemoglobin ( mch ) and mean cell hemoglobin concentration ( mchc ) were estimated . the patients suffering concomitantly with iron deficiency anemia were first treated and then considered for hemoglobin electrophoresis . for gene deletion studies in cases of  thalassemia , rflp technique using the restriction endonucleases bam hi was applied . statistical analysis was carried out by statistical package for social sciences , ( spss inc . the average age of the patients in the adult and children groups was 35.6  15.9 and 6.8  3.7 years respectively . the cellulose acetate hemoglobin electrophoresis and gene studies revealed that there were 406 ( 40.96% ) and 59 ( 5.95% ) cases of  thalassemia trait and  thalassemia major respectively including adults and children . the breakup of different gene deletion types of  thalassemias is given in table 1 . number of cases of  and  thalassemias in two age groups the level of hemoglobin was lowest ( 6.69  0.64 ) in cases of  thalassemia major . hetrozygous -thalassemia trait ( -/ ) showed almost normal levels of hemoglobin and the patients were asymptomatic . other thalassemia traits like  and homozygous -thalassemia ( --/ ) and ( -/- ) had mild degree of anemia . there was no significant difference in the hemoglobin levels of adults and children in each type of disorder ( p < 0.05 ) [ table 2 ] . red cell indices in  and  thalassemias in two age groups moderate degree of microcytosis ( mcv =  78fl ) and hypochromia ( mch =  27pg ) was a feature of  thalassemia trait and homozygous -thalassemias . however , microcytosis was more marked in  thalassemia trait compared to heterozygous -thalassemias . it was observed that there was statistically no significant difference between the red cell indices of  thalassemia trait and homozygous -thalassemias ( --/ , -/- ) . ( p < 0.01 ) [ tables 24 ] , rbc count was lowest in cases of  thalassemia major and highest in  thalassemia minor . comparative scatter gram of mcv in thalassemias comparative scatter gram of mch in thalassemias  thalassemia major was characteristic of mild degree of microcytosis and hypochromia . compared to children , the microcytosis was more frequently seen among adults ( p < 0.023 ) [ table 2 ] . hetrozygous -thalassemia trait ( -/ ) was the only disorder in which all the hematological parameters were normal . here also , there was no significant difference in the findings of adults and children [ table 2 ] . comparative scattergram of values of mcv and mch in different thalassemias is given in tables 3 and 4 . -thalassemia are the most common single - gene hemoglobin disorders in the world . it is more prevalent in areas endemic for malaria . south east asia,[79 ] india , mediterranean region[24 ] and middle east including saudi arabia[21417 ] are the regions from where large number of cases are reported . the change in hematological parameters depends on the type of thalassemia . unlike  -thalassemia trait and iron deficiency the key to successful detection and characterization of the hemoglobinopathies , particularly the thalassemias , is the initial hematological data . the clue for thalassemia is low mean corpuscular volume ( mcv ) < 78 fl or low mean corpuscular hemoglobin ( mch ) < 27 pg . although iron deficiency is the most common cause of a low mcv or a low mch , it is likely that this finding will point to thalassemia in regions of countries with thalassemia - prone ethnic populations.there are several causes of the anemia produced by different abnormal hemoglobins . microcytic hypochromic anemia is a common hematological abnormality in clinical practice and usually is caused by iron deficiency and thalassemia trait . red cell indices are taken to be the differentiating factor in anemias due to thalassemias and those from iron deficiency and are very necessary as both occur in the same areas . the degree of microcytosis and type of mutation in thalassemias have shown wide variations in ranges of mcv . there is limited data reported in the literature for prevalence of -gene deletion in patients with microcytosis.[2022 ] carriers of -gene deletion have mild microcytosis with or without anemia . although anemia is absent or unremarkable , it is important to diagnose  -thalassemia to ascertain the cause of microcytosis and to avoid repeated expensive analysis and/or prolonged iron therapy . so far , no biochemical diagnostic test is available for detection of -thalassemia carriers and globin chain synthesis studies are time consuming.molecular methods like southern blot hybridization and sequencing are conventionally used for diagnosis of -thalassemia . however , molecular diagnosis by pcr has proven to be less time - consuming and less expensive , with a more definite outcome in the clinical setup . the most widely used method in detection of  -thalassemiamutation is the amplification refractory mutation system ( arms ) . unlike the  -thalassemias , hematological parameters in patients with  -thalassemia were compared with those in patients with  -thalassemia . individuals with the single - gene deletion had lower levels of hemoglobin , mcv and mch as compared to normal controls . the carriers of  -thalassemia have a mild microcytic hypochromic anemia as observed by other authors . however , their mcv and mch were better than those of patients with iron deficiency anemia . mch is a better discriminator than other red cell indices in the diagnosis of -thalassemia . since there is no definitive hematological marker that can give the diagnosis of  -thalassemia , molecular analysis remains the only diagnostic approach in microcytic hypochromic anemia patients . our findings are in accordance with previous reports , where microcytosis was explained on the basis of number of -gene deletions . the identification of  and  -thalassemia carrier status is important before going for expensive investigations to define the etiology of anemia , as well as to prevent unnecessary prolonged iron supplementation . thus screening for thalassemia should be considered during genetic counseling of couples at high risk of thalassemia , for prenatal and premarital diagnosis.identification of rare thalassemia gene mutations in our population was necessary because of consanguineous marriages in saudi arabia . the use of more comprehensive diagnostic tools is more useful in the diagnosis of unresolved cases . however , hematological parameters remain the earliest and most cost effective method in differentiating  thalassemia from iron deficiency anemia and many discriminating indices are also available to differentiate between the two , but none to differentiate between various types of thalassemias . we observed that hematological parameters are helpful in differentiating  thalassemia major from  thalassemias minor but not of much help in differentiating  thalassemias from . varying degree of microcytosis is a common feature in both types of thalassemias . there is a dire need to develop a discrimination index to differentiate  thalassemia from  thalassemias on the pattern of indices available for discriminating  thalassemia trait from iron deficiency anemia . if such an index is developed , it would help physicians to adapt the right protocol to investigate the patients of thalassemias and would reduce the time and cost of reaching the final diagnosis .
background and aims : saudi arabia falls in the high prevalent zone of  and  thalassemias . 
 early screening for the type of thalassemia is essential for further investigations and management . 
 the study was carried out to differentiate the type of thalassemia based on red cell indices and other hematological parameters.materials and methods : the study was carried out on 991 clinically suspected cases of thalassemias in riyadh , saudi arabia . 
 the hematological parameters were studied on coulter stks . 
 cellulose acetate hemoglobin electrophoresis and high - performance liquid chromatography ( hplc ) were performed on all the blood samples . 
 gene deletion studies were carried out by restriction fragment length polymorphism ( rflp ) technique using the restriction endonucleases bam hi.statistical analysis : statistical analysis was performed on spss 11.5 version.results:the hemoglobin electrophoresis and gene studies revealed that there were 406 ( 40.96% ) and 59 ( 5.95 % ) cases of  thalassemia trait and  thalassemia major respectively including adults and children . 
 426 cases of various deletion forms of  thalassemias were seen . 
 microcytosis was a common feature in  thalassemias trait and ( -/- ) and ( --/ ) types of  thalassemias . 
 mch was a more significant distinguishing feature among thalassemias . 
 thalassemia major and  thalassemia ( -/ ) had almost normal hematological parameters.conclusion:mcv and rbc counts are not statistically significant features for discriminating between  and  thalassemias . 
 there is need for development of a discrimination index to differentiate between  and  thalassemias traits on the lines of discriminatory indices available for distinguishing  thalassemias trait from iron deficiency anemia .