International Journal of Laboratory Hematology The Official journal of the International Society for Laboratory Hematology
ORIGINAL ARTICLE
INTERNAT IONAL JOURNAL OF LABORATO RY HEMATO LOGY
Differential diagnosis of microcytic anemia: the role of microcytic and hypochromic erythrocytes E. URRECHAGA*, J. J. M. L. HOFFMANN † , S. IZQUIERDO ‡ , J. F. ESCANERO §
*Hematology Laboratory, Hospital Galdakao – Usansolo, Galdakao, Spain † Medical and Scientific Affairs, Abbott Diagnostics, WiesbadenDelkenheim, Germany ‡ Department of Genetics, Biochemical Chemistry Service, University Hospital Miguel Servet, Zaragoza, Spain § Department of Pharmacology and Physiology, Faculty of Medicine, University of Zaragoza, Zaragoza, Spain Correspondence: Dr Eloısa Urrechaga, Hematology Laboratory, Hospital Galdakao-Usansolo, 48960 Galdakao, Vizcaya, Spain. Tel.: +34 94 400 7000; Fax: +34 94 400 7102; E-mail: eloisa.urrechagaigartua @osakidetza.net doi:10.1111/ijlh.12290
Received 29 May 2014; accepted for publication 24 July 2014
S U M M A RY Introduction: Various indices derived from red blood cell (RBC) parameters have been described for distinguishing thalassemia and iron deficiency. We studied the microcytic to hypochromic RBC ratio as a discriminant index in microcytic anemia and compared it to traditional indices in a learning set and confirmed our findings in a validation set. Methods: The learning set comprised samples from 371 patients with microcytic anemia mean cell volume (MCV < 80 fL), which were measured on a CELL-DYN Sapphire analyzer and various discriminant functions calculated. Optimal cutoff values were established using ROC analysis. These values were used in the validation set of 338 patients. Results: In the learning set, a microcytic to hypochromic RBC ratio >6.4 was strongly indicative of thalassemia (area under the curve 0.948). Green-King and England-Fraser indices showed comparable area under the ROC curve. However, the microcytic to hypochromic ratio had the highest sensitivity (0.964). In the validation set, 91.1% of microcytic patients were correctly classified using the M/ H ratio. Conclusions: Overall, the microcytic to hypochromic ratio as measured in CELL-DYN Sapphire performed equally well as the Green-King index in identifying thalassemia carriers, but with higher sensitivity, making it a quick and inexpensive screening tool.
Keywords Anemia, erythrocytes, hypochromic, iron deficiency, microcytic, thalassemia
INTRODUCTION The most common causes of microcytic anemia are iron deficiency and thalassemia trait. Distinguishing these two conditions is important in order to provide © 2014 John Wiley & Sons Ltd, Int. Jnl. Lab. Hem.
genetic counseling and avoid unnecessary, potentially harmful iron therapy in thalassemia carriers. The differential diagnosis normally requires additional laboratory investigations such as serum ferritin concentration, hemoglobin-A2 assay, and molecular analysis. 1
2
E. URRECHAGA ET AL. | M/H RATIO IN MICROCYTIC ANEMIA
Many discriminant formulas have been published that are based on red cell parameters only and that can provide a reasonable or good indication whether thalassemia is a likely cause of microcytosis [1–5]. In that way, additional tests may be selected for the most efficient diagnostic strategy. Some of these discriminant functions are very simple, whereas others are more complicated and require some mathematics to be performed [1]. One of the simplest and yet most powerful discriminant functions is the ratio of microcytic to hypochromic red blood cells (RBC), the M/H ratio [3, 6]. This index is based on the observation that RBC are generally more hypochromic in iron deficiency anemia than in thalassemia trait [7, 8]. Measurement of microcytic and hypochromic RBC was first offered in Technicon hematology analyzers (now Adviaâ, by Siemens Medical), using multidimensional light scatter by sphered RBC, following Mie theory principles [9–11]. Diagnostic application of this new technology in microcytic anemia followed soon [7, 12–14]. Later, other manufacturers developed RBC parameters, which, although essentially different from the original Technicon parameters, had more or less similar clinical utility [15–17]. In this respect, it is of note to realize that hypochromic RBC are not uniformly defined: Advia 2120 uses cellular Hb concentration (
ORIGINAL ARTICLE
INTERNAT IONAL JOURNAL OF LABORATO RY HEMATO LOGY
Differential diagnosis of microcytic anemia: the role of microcytic and hypochromic erythrocytes E. URRECHAGA*, J. J. M. L. HOFFMANN † , S. IZQUIERDO ‡ , J. F. ESCANERO §
*Hematology Laboratory, Hospital Galdakao – Usansolo, Galdakao, Spain † Medical and Scientific Affairs, Abbott Diagnostics, WiesbadenDelkenheim, Germany ‡ Department of Genetics, Biochemical Chemistry Service, University Hospital Miguel Servet, Zaragoza, Spain § Department of Pharmacology and Physiology, Faculty of Medicine, University of Zaragoza, Zaragoza, Spain Correspondence: Dr Eloısa Urrechaga, Hematology Laboratory, Hospital Galdakao-Usansolo, 48960 Galdakao, Vizcaya, Spain. Tel.: +34 94 400 7000; Fax: +34 94 400 7102; E-mail: eloisa.urrechagaigartua @osakidetza.net doi:10.1111/ijlh.12290
Received 29 May 2014; accepted for publication 24 July 2014
S U M M A RY Introduction: Various indices derived from red blood cell (RBC) parameters have been described for distinguishing thalassemia and iron deficiency. We studied the microcytic to hypochromic RBC ratio as a discriminant index in microcytic anemia and compared it to traditional indices in a learning set and confirmed our findings in a validation set. Methods: The learning set comprised samples from 371 patients with microcytic anemia mean cell volume (MCV < 80 fL), which were measured on a CELL-DYN Sapphire analyzer and various discriminant functions calculated. Optimal cutoff values were established using ROC analysis. These values were used in the validation set of 338 patients. Results: In the learning set, a microcytic to hypochromic RBC ratio >6.4 was strongly indicative of thalassemia (area under the curve 0.948). Green-King and England-Fraser indices showed comparable area under the ROC curve. However, the microcytic to hypochromic ratio had the highest sensitivity (0.964). In the validation set, 91.1% of microcytic patients were correctly classified using the M/ H ratio. Conclusions: Overall, the microcytic to hypochromic ratio as measured in CELL-DYN Sapphire performed equally well as the Green-King index in identifying thalassemia carriers, but with higher sensitivity, making it a quick and inexpensive screening tool.
Keywords Anemia, erythrocytes, hypochromic, iron deficiency, microcytic, thalassemia
INTRODUCTION The most common causes of microcytic anemia are iron deficiency and thalassemia trait. Distinguishing these two conditions is important in order to provide © 2014 John Wiley & Sons Ltd, Int. Jnl. Lab. Hem.
genetic counseling and avoid unnecessary, potentially harmful iron therapy in thalassemia carriers. The differential diagnosis normally requires additional laboratory investigations such as serum ferritin concentration, hemoglobin-A2 assay, and molecular analysis. 1
2
E. URRECHAGA ET AL. | M/H RATIO IN MICROCYTIC ANEMIA
Many discriminant formulas have been published that are based on red cell parameters only and that can provide a reasonable or good indication whether thalassemia is a likely cause of microcytosis [1–5]. In that way, additional tests may be selected for the most efficient diagnostic strategy. Some of these discriminant functions are very simple, whereas others are more complicated and require some mathematics to be performed [1]. One of the simplest and yet most powerful discriminant functions is the ratio of microcytic to hypochromic red blood cells (RBC), the M/H ratio [3, 6]. This index is based on the observation that RBC are generally more hypochromic in iron deficiency anemia than in thalassemia trait [7, 8]. Measurement of microcytic and hypochromic RBC was first offered in Technicon hematology analyzers (now Adviaâ, by Siemens Medical), using multidimensional light scatter by sphered RBC, following Mie theory principles [9–11]. Diagnostic application of this new technology in microcytic anemia followed soon [7, 12–14]. Later, other manufacturers developed RBC parameters, which, although essentially different from the original Technicon parameters, had more or less similar clinical utility [15–17]. In this respect, it is of note to realize that hypochromic RBC are not uniformly defined: Advia 2120 uses cellular Hb concentration (
