Combined use of zinc protoporphyrin (ZPP), mean corpuscular volume and haemoglobin measurements for classifying microcytic RBC disorders in children and young adults

The diagnostic potential of the combined use of zinc-protoporphyrin (ZPP), mean corpuscular volume (MCV) and haemoglobin measurements for discriminating between iron deficiency anaemia, beta-thalassaemia minor and lead poisoning has been studied. Lead poisoning could be identified by ZPP greater than 50 micrograms/dl in the presence of normal MCV or ZPP greater than 150 micrograms/dl in the presence of microcytosis (MCV less than 80 fl) with a sensitivity of 97% and specificity 94%. Beta-thalassaemia minor was identified by the coexistence of microcytosis and ZPP less than 50 micrograms/dl with a sensitivity of 91% and specificity 79%. Iron deficiency anaemia defined by the combination of microcytosis and ZPP ranging from 50 to 150 micrograms/dl was identified with a sensitivity of 95%, but the specificity was only 51%, with many of the patients overlapping with thalassaemia minor. This problem did not exist in iron-deficiency anaemia with haemoglobin less than 10 g/dl as at that range no patients with uncomplicated thalassaemia minor have been encountered. A great advantage of the combined use of ZPP, MCV and haemoglobin for the initial screening of microcytic anaemia is its ease of performance and low cost. However, this information should only be regarded as presumptive evidence of disease, requiring subsequent confirmation by appropriate direct measurements such as transferrin saturation, serum ferritin, haemoglobin electrophoresis, or blood lead determinations.     

Quantitative anisocytosis as a discriminant between iron deficiency and thalassemia minor

The coefficient of variation (CV) of red cell size, as measured by electronic red cell sizing (erythrography), was less than 14.0% in 20 normal subjects. In 22 of 25 patients with beta-thalassemia minor and microcytosis (mean corpuscular volume [MCV] less than 70 fl), CV was less than 14.0%; in the other 3, CV was 14.0%--14.9%. In 53 patients with iron deficiency anemia and MCV less than 70 fl, CV always was greater than 14.0%. In 7 patients with alpha-thalassemia minor and MCV less than 70 fl, CV was less than 14.0% in all 7. Among patients with microcytosis, erythrography appears to be an excellent technique for rapidly distinguishing between iron deficiency and alpha or beta thalassemia minor.     

Evaluation of microcytosis using serum ferritin and red blood cell distribution width

Out of 104 patients with microcytosis (MCV less than 80 fl), 69% had an iron deficiency, 21% a chronic disease and 10% hemoglobinopathy or thalassemia trait. The absence of bone marrow iron stores or the response to iron supplementation were used to establish the diagnosis iron deficiency. On the basis of sensitivity (90%) and specificity (100%), the serum ferritin concentration is more suitable for assessment of iron deficiency than the serum iron concentration, the total iron-binding capacity or the percentual saturation of transferrin. The red cell distribution width (RDW) is the parameter with the highest sensitivity for iron deficiency (94%). An RDW value within the reference interval can be used to exclude iron deficiency in those cases in which the serum ferritin concentration does not accurately reflect the iron stores owing to severe tissue damage, as in inflammation or malignancy.     

The measurement of erythrocyte zinc protoporphyrin/heme ratio in various anemias in childhood]

The measurement of erythrocyte zinc protoporphyrin (ZPP) with a hematofluorometer is known to be a simple and cost-effective method to screen iron deficiency and lead poisoning. We measured ZPP on blood samples from 201 children suffering from various diseases, which revealed that ZPP has better sensitivity and specificity for identifying iron deficiency than serum ferritin and percent transferrin saturation. ZPP levels in various anemias were also measured. ZPP rose markedly (> 200 mumol/mol heme) in untreated iron deficiency anemia and returned to normal in 3-4 months since the initiation of iron therapy. Moderate elevation of ZPP was observed in acute leukemia (at onset and during induction therapy), MDS, aplastic anemia and some other anemic conditions. These findings suggest that erythrocyte ferrochelatase may be unexpectedly affected in anemias even except lead poisoning.     

The diagnosis of iron deficiency anemia in sickle cell disease

We determined the prevalence and optimal methods for laboratory diagnosis of iron deficiency anemia in patients with sickle cell disease. Laboratory investigations of 38 nontransfused and 32 transfused patients included transferrin saturation, serum ferritin, mean corpuscular volume (MCV), and free erythrocyte protoporphyrin (FEP). Response to iron supplementation confirmed the diagnosis of iron deficiency anemia in 16% of the nontransfused patients. None of the transfused patients were iron deficient. All iron-deficient patients (mean age 2.4 yr) had a low MCV, serum ferritin less than 25 ng/ml, transferrin saturation less than 15%, and FEP less than 90 micrograms/dl RBC. Following therapy, all parameters improved and the hemoglobin concentration increased greater than 2 g/dl. A serum ferritin below 25 ng/ml was the most reliable screening test for iron deficiency. There were 13% false positive results with transferrin saturation, 3% with MCV, and 62% with FEP. FEP values correlated strongly with reticulocyte counts. The high FEP was in part due to protoporphyrin IX and not completely due to zinc protoporphyrin, which is elevated in iron deficiency. We conclude that iron deficiency anemia is a potential problem in young nontransfused sickle cell patients. Serum ferritin below 25 ng/ml and low MCV are the most useful screening tests.     

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.     

The influence of iron deficiency on erythrocyte deformability.

The influence of iron deficiency on erythrocyte deformability is controversial. The present study was designed to analyse cell deformability in 14 patients with iron deficiency and controls in a comprehensive way by three different methods, namely erythrocyte filtration, erythrocyte elongation, and measurement of membrane elasticity. Suspensions of washed erythrocytes (haematocrit 0.10) free of leucocytes were used. Erythrocyte deformability measured by filtration was increased by iron deficiency: The relative filtration resistance of a cell in a 3 microns pore was 26.5 +/- 6.9 and 75.8 +/- 23.8 in iron deficiency and controls, respectively (P less than 0.0001). In 5 microns pores the values were 2.80 +/- 1.23 and 3.46 +/- 0.51 (not significant); when the red cell number/volume was adjusted to that in control samples, the value for iron deficiency became significantly lower than in controls (2.32 +/- 0.60, P less than 0.0001). Erythrocyte elongation by centrifugation was unaffected (ratio length/width 1.66 +/- 0.11 and 1.60 +/- 0.10 in iron deficiency and controls, respectively). Membrane elasticity, as assessed by a filter aspiration technique, was also unchanged (membrane elastic modulus 3.94 +/- 0.31 and 3.94 +/- 0.37 x 10(-3) dyn/cm, respectively). It is concluded that iron deficiency does not affect erythrocyte membrane elasticity and that the deformability of whole cells is not impaired, but improved under certain conditions such as the passage of 3 microns pores because of microcytosis with preserved surface/volume ratio. These results are in contrast to earlier studies and they have pathophysiological and clinical implications.     

Microcytic anaemia in juvenile chronic arthritis

The degrees of anaemia and microcytosis in 100 patients with juvenile chronic arthritis (JCA) were analysed according to the pattern of disease and its activity. Microcytosis was common (40% of patients had a mean corpuscular volume (MCV) of less than 75 fl), sometimes severe (MCV less than 65 fl in 14 patients), and closely correlated with the severity of the anaemia. The degrees of microcytosis and anaemia were both directly related to disease activity as measured by the ESR, and were most severe in cases with the systemic form of JCA. In 50 patients iron status was assessed. The serum iron concentration was directly related to the MCV, whereas the serum ferritin was inversely related to MCV and haemoglobin concentration and directly related to the ESR. Bone marrow iron stores were normal or increased in 6 patients with severe microcytic anaemia. These data suggest that the anaemia of JCA is typically microcytic, and that this microcytosis is associated with the disturbance of iron metabolism seen in the 'anaemia of chronic disorders' rather than overall depletion of body iron.     

Investigation of microcytosis: a comprehensive approach

Abstract: Microcytosis is a highly prevalent finding during blood examination. This study investigates the causes of microcytosis (defined as mean corpuscular volume (MCV)<82 fl) in 466 patients referred to our laboratory for suspected hemoglobinopathy. The following data were obtained: Hb, MCV, serum iron, transferrin, ferritin, HbA2, HbF, isoelectric focusing of the Hb, gene mapping of chromosome 16 with Xba I and Bgl II and hybridization with an α- and a ζ-probe, inflammatory status. Results show that iron deficiency remains the first cause of microcytosis (35.2% of our patients), even in a selected population such as ours. Deletional α-thalassemia, probably the most frequent hemoglobinopathy throughout the world, represents the second most frequent cause of microcytosis (31.1%), followed by β-thalassemia heterozygous state (18.9%). Of our patients, 1.3% had microcytosis due to the presence of an abnormal hemoglobin (HbC, Hb S/C, HbE). Three cases (0.6%) had other possible causes of microcytosis. Of the remaining 60 cases, 28 had an inflammatory state. Finally, 32 cases (6.9%) remain unexplained; taking into consideration the origin of these cases, their hematological parameters and their family history, we postulate that these cases are at high risk for non-deletional α-thalassemia.     

Iron deficiency anaemia in hospitalised patients: value of various laboratory parameters. Differentiation between IDA and ACD.

BACKGROUND: for the diagnostic evaluation of microcytic or normocytic anaemia in a heterogeneous group of patients, the value of newer parameters, such as zinc protoporphyrin (ZPP), plasma transferrin receptor (PtrfR) and PtrfR/ferritin ratio is not clear. We have performed a prospective study to determine the predictive value of these parameters and ferritin, for diagnosing iron deficiency anaemia (IDA). METHODS: sixty-two patients with Hb<8.2 (men) or <7.0 (women) and mean cell volume (MCV)<96 fl were included. Exclusion criteria were: known haematological disease, pregnancy, bone marrow suppression or iron therapy within the previous 7 days. Bone marrow examination was used as a golden standard to discriminate between IDA and non-IDA. RESULTS: twenty-four patients had depleted iron stores. We found that the reticulocyte response on iron supplementation correlated well with the iron-status of the bone marrow. Univariate analysis showed that ferritin, PtrfR/ferritin ratio, ZPP and PtrfR have significant predictive values for differentiating IDA from non-IDA. Interestingly, multivariate analysis revealed that ferritin was the only significant, independent predictor of IDA, with a cut-off point of 32 microg/l (sensitivity 79.2%, specificity 96.9%). CONCLUSIONS: the low sensitivity and specificity of ZPP, PtrfR and PtrfR/ferritin ratio render them insufficient to be used as a single 'best' test for the identification IDA in a non-selected group of anaemic patients and do not even add to the prediction if the value of ferritin is known.     

Erythrocyte ferritin in thalassemia syndromes

Basic ferritin (liver-type) was measured in erythrocytes of subjects with alpha- and beta-thalassemia trait, thalassemia intermedia and Cooley's disease, and compared with normals and patients with abnormal iron metabolism without erythrocyte metabolic defect (iron deficiency anemia and idiopathic hemochromatosis). In all the thalassemic syndromes considered, erythrocyte ferritin was significantly higher than in normals (p less than 0.001) and increased progressively with the increasing 'severity' of the thalassemic disorder. In both thalassemic and non-thalassemic subjects, erythrocyte ferritin levels were related to body iron status, but in the thalassemic group, the increased erythrocyte ferritin values seemed also to be closely related to the intracellular metabolic abnormality. The severity of the defect in globin chain synthesis seemed to play an important role in determining ferritin accumulation in red cells of thalassemic subjects.     

Soluble transferrin receptor and zinc protoporphyrin – competitors or efficient partners?

OBJECTIVES: Soluble transferrin receptor (sTfR) and zinc protoporphyrin (ZPP) are both parameters of iron deficient erythropoiesis (IDE), the sTfR measurement is commonly regarded to be the more sensitive test. sTfR also reflects erythropoietic activity, it is increased in enhanced erythropoiesis. METHODS: We investigated the diagnostic accuracy of sTfR in assessment of iron deficiency (ID) and compared it with ZPP. The study was performed on 174 subjects, in which ID has been precisely staged. RESULTS: Individuals without ID and patients with storage iron depletion only, had normal sTfR values. Patients classified as IDE and patients with iron deficiency anemia had significantly increased sTfR. There was a good correlation between sTfR and hemoglobin (r = -0.86; P < 0.0001) and between sTfR and ZPP (r = 0.86; P < 0.0001). When diagnosing ID, ZPP was the more sensitive test. In mildly developed IDE associated with ZPP-ratios between 40 and 70 micromol/mol heme, the sTfR concentration was elevated in only 25% of the cases. Reliably elevated sTfR values were observed only in more advanced IDE, associated with ZPP > 70 mumol/mol heme. CONCLUSIONS: ZPP is not inferior to sTfR when diagnosing IDE. Given the good correlation between sTfR and ZPP and because ZPP is uninfluenced by the erythropoietic activity, sTfR and ZPP are not competitors, rather efficient partners in diagnosing anemias. By measuring ZPP and sTfR simultaneously, the diagnostic uncertainty inherent in each of them individually can be eliminated. In particular, the simultaneous determination of ZPP and sTfR enhances the diagnostic power of sTfR in assessment of the erythropoietic activity.     

Clinical utility of the reticulocyte hemoglobin content in the diagnosis of iron deficiency

Determination of the reticulocyte hemoglobin content (CHr) provides an early measure of functional iron deficiency because reticulocytes are the earliest erythrocytes released into blood and circulate for only 1 to 2 days. The CHr in 78 patients undergoing bone marrow examination was measured to assess its clinical utility for the diagnosis of iron deficiency. Twenty-eight patients were iron deficient, based on the lack of stainable iron in the aspirate. The diagnostic power of CHr is limited in patients with high mean cellular volume (MCV) or red cell disorders such as thalassemia. However, when patients with MCV more than 100 fL are excluded, receiver operator curve analysis of CHr, ferritin, transferrin saturation, and MCV demonstrates that CHr has the highest overall sensitivity and specificity of these peripheral blood tests for predicting the absence of bone marrow iron stores.     

Serum transferrin receptor: a quantitative measure of tissue iron deficiency

This study was undertaken to evaluate the role of serum transferrin receptor measurements in the assessment of iron status. Repeated phlebotomies were performed in 14 normal volunteer subjects to obtain varying degrees of iron deficiency. Serial measurements of serum iron, total iron-binding capacity, mean cell volume (MCV), free erythrocyte protoporphyrin (FEP), red cell mean index, serum ferritin, and serum transferrin receptor were performed throughout the phlebotomy program. There was no change in receptor levels during the phase of storage iron depletion. When the serum ferritin level reached subnormal values there was an increase in serum receptor levels, which continued throughout the phlebotomy program. Functional iron deficiency was defined as a reduction in body iron beyond the point of depleted iron stores. The serum receptor level was a more sensitive and reliable guide to the degree of functional iron deficiency than either the FEP or MCV. Our studies indicate that the serum receptor measurement is of particular value in identifying mild iron deficiency of recent onset. The iron status of a population can be fully assessed by using serum ferritin as a measure of iron stores, serum receptor as a measure of mild tissue iron deficiency, and hemoglobin concentration as a measure of advanced iron deficiency.     

Diagnostic utility of zinc protoporphyrin to detect iron deficiency in Kenyan preschool children: a community-based survey

Background

Zinc protoporphyrin (ZPP) has been used to screen and manage iron deficiency in individual children, but it has also been recommended to assess population iron status. The diagnostic utility of ZPP used in combination with haemoglobin concentration has not been evaluated in pre-school children. We aimed to a) identify factors associated with ZPP in children aged 12–36 months; b) assess the diagnostic performance and utility of ZPP, either alone or in combination with haemoglobin, to detect iron deficiency.

Methods

We used baseline data from 338 Kenyan children enrolled in a community-based randomised trial. To identify factors related to ZZP measured in whole blood or erythrocytes, we used bivariate and multiple linear regression analysis. To assess diagnostic performance, we excluded children with elevated plasma concentrations of C-reactive protein or α ₁-acid glycoprotein, and with Plasmodium infection, and we analysed receiver operating characteristics (ROC) curves, with iron deficiency defined as plasma ferritin concentration < 12 μg/L. We also developed models to assess the diagnostic utility of ZPP and haemoglobin concentration when used to screen for iron deficiency.

Results

Whole blood ZPP and erythrocyte ZPP were independently associated with haemoglobin concentration, Plasmodium infection and plasma concentrations of soluble transferrin receptor, ferritin, and C-reactive protein. In children without inflammation or Plasmodium infection, the prevalence of true iron deficiency was 32.1%, compared to prevalence of 97.5% and 95.1% when assessed by whole blood ZPP and erythrocyte ZPP with conventional cut-off points (70 μmol/mol and 40 μmol/mol haem, respectively). Addition of whole blood ZPP or erythrocyte ZPP to haemoglobin concentration increased the area-under-the-ROC-curve (84.0%, p = 0.003, and 84.2%, p = 0.001, respectively, versus 62.7%). A diagnostic rule (0.038689 [haemoglobin concentration, g/L] + 0.00694 [whole blood ZPP, μmol/mol haem] >5.93120) correctly ruled out iron deficiency in 37.4%–53.7% of children screened, depending on the true prevalence, with both specificity and negative predictive value ≥90%.

Conclusions

In young children, whole blood ZPP and erythrocyte ZPP have added diagnostic value in detecting iron deficiency compared to haemoglobin concentration alone. A single diagnostic score based on haemoglobin concentration and whole blood ZPP can rule out iron deficiency in a substantial proportion of children screened.

Trial registration

ClinicalTrials.gov NCT02073149 (25 February 2014).

     

Prevalence of hypochromia (without microcytosis) vs microcytosis (without hypochromia) in iron deficiency

The usefulness of hypochromia (MCH or = 80 (fl) vs. counterparts with MCV < 80 fl (in the presence of MCH > or = 26 pg). Fifteen per cent of the 201 iron deficient subjects were also shown to have coexisting vitamin B12 deficiency. There was a comparable (16%) prevalence of this haematinic deficiency in the subgroup of 31 iron deficient patients with MCH < 26 pg in the presence of MCH > or = 80 fl.     

The Natural History of Iron Deficiency Induced by Phlebotomy

1. The sequence of characteristic changes of progressive iron deficiency wasdemonstrated by serial bleeding of normal volunteers and polycythemic patients.

2. After bloodletting, changes occurred in peripheral blood in the followingorder: a) fall in hemoglobin concentration; b) decreased plasma iron; c)reticulocytosis, increased MCV and MCH; d) diminution of MCV and MCH,increased total iron-binding protein; and e) decreased MCHC.

3. Characteristic changes of iron deficiency returned to prephlebotomylevels in the following sequence: a) hemoglobin concentration; b) cellularindices; c) serum iron; d) serum iron binding protein; and e) bone marrowhemosiderin, and finally the increased gastrointestinal absorption of ironreverted to normal.

4. Accelerated production of red cells continued in polycythemic patientsdespite the induction of moderate iron deficiency. Quality was sacrificed forquantity, and thereby a more profound microcytosis occurred than in normalsubjects with a similar degree of iron deficiency.

Submitted on February 16, 1962 Accepted on April 11, 1962     

Simultaneous measurement of reticulocyte and red blood cell indices in healthy subjects and patients with microcytic and macrocytic anemia

Using the new Bayer H*3 hematology analyzer (Leverkusen, Germany), we have determined red blood cell and reticulocyte indices in 64 healthy subjects, in patients with microcytosis due to iron deficiency (58 patients) and heterozygous beta-thalassemia (40 patients), and in patients with macrocytosis (28 patients). We found in all cases that reticulocytes were larger than mature red cells by 24% to 35%, with a hemoglobin concentration 16% to 25% lower and a similar hemoglobin content. The correlation between red cell and reticulocyte indices was strikingly tight (r = .928 for volume, r = .929 for hemoglobin concentration, r = .972 for hemoglobin content) in all four groups, regardless of red blood cell size. The ratio of reticulocyte to red blood cell mean corpuscolar volume (MCV ratio) was constantly above 1. Inversion of the MCV ratio was observed only in four patients. It was always abrupt and transitory and was associated with erythropoietic changes leading to the production of red blood cells of a different volume (treatment of megaloblastic anemia, functional iron deficiency, bone marrow transplantation). In two cases of marrow transplantation, reticulocyte volume fell during the aplastic phase after conditioning chemotherapy and then rapidly increased up to values higher than before; this production of macroreticulocytes was the earliest sign of engraftment.     

Microcytic and hypochromic anemias

In the majority of cases, microcytosis is the result of impaired hemoglobin synthesis. Disorders of iron metabolism and protoporphyrin and heme synthesis, as well as impaired globin synthesis, lead to defective hemoglobin production and to the generation of microcytosis and microcytic anemia. Iron deficiency anemie, anemia of chronic diseases, thalassemias, congenital sideroblastic anemias and homozygous HbE disease are the main representatives of microcytosis and microcytic anemias. Serum iron, total iron binding capacity, transferrin saturation, serum ferritin, serum transferrin receptor, transferrin receptor-ferritin index, and zinc-protoporhyrin concentration in erythrocytes are tests used for assessment of iron deficiency. The convention laboratory test for diagnosing iron deficiency is the measurement of serum ferritin. The most precise method for evaluating body iron stores is the examination for iron on aspirated bone marrow or marrow biopsy. Increased content of Hb A2 over 3.5% is diagnostic for beta-thalassemia. Presence of ringed sideroblasts is characteristic of sideroblastic anemias. Hemoglobin electrophoresis is required for the diagnosis of hemoglobinopathy E. The optimal therapeutic regimen in iron deficiency anemia used in this country is to administer 100 mg of elemental iron twice daily separately from meals. Ferrous sulphate (Ferronat Retard tbl. or Sorbifer Dulures tbl.) which are slow-releasing iron formulations are preferred because of their low cost, high bioavailability and low side-effects. Parenteral iron therapy is justified only in patients who cannot absorb iron, who have blood losses that exceed the maximal absorptive capacity of their intestinal tract or who are totally intolerant of oral iron. However, parenteral iron therapy may be associated with serious and even fatal side-effects.     

Serum transferrin receptor levels in patients undergoing evaluation of iron stores: correlation with other parameters and observed versus predicted results

Serum transferrin receptor (sTfR) concentrations were measured in specimens from 77 patients undergoing serum ferritin determination, and the results correlated with serum ferritin, serum iron, serum total iron-binding capacity (TIBC) saturation, erythrocyte mean corpuscular volume (MCV), and mean corpuscular haemoglobin (MCH). All parameters exhibited the expected inverse correlation with sTfR; this correlation was statistically significant for all parameters except serum iron concentration. The frequency with which iron deficiency (defined as absence of stainable marrow iron) is observed in patients with particular ferritin values in this centre was determined and used to estimate the expected number of iron deficient patients in the present study. In no setting were significantly fewer sTfR levels > 3.05 μg/ml observed than expected. However, significantly greater than expected numbers of elevated sTfR values were observed in patients with serum ferritin > 220 μg/l (P = 0.002). The results suggest that the sTfR level is probably not useful as a single test for identification of iron deficiency in unselected patients.