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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 24  |  Issue : 4  |  Page : 195-200

Relationship between foetal haemoglobin and haematological indices in children with sickle cell anaemia from South Western Nigeria


1 Department of Paediatrics, Obafemi Awolowo University Teaching Hospital, Ile-Ife, Nigeria
2 Department of Paediatrics and Child Health, Obafemi Awolowo University, Ile-Ife, Nigeria

Date of Web Publication18-Jan-2018

Correspondence Address:
Dr. Morenike Agnes Akinlosotu
Department of Paediatrics, Obafemi Awolowo University Teaching Hospital, Ile-Ife
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/npmj.npmj_107_17

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  Abstract 

Background: Foetal haemoglobin (HbF, α2γ2) retards polymerisation of haemoglobin (Hb) in sickle cell anaemia (SCA). In Nigeria, studies on the levels of HbF and its relationship with haematological indices are scanty. This study evaluated HbF concentrations of children with SCA from Southwestern Nigeria and correlated the levels with various haematological indices. Materials and Methods: HbF levels were quantified by high-performance liquid chromatography and haematological parameters determined with automated haemoanalyser. The relationship between steady-state HbF levels and blood parameters were assessed by statistical analyses. Results: The mean HbF of the 91 children with SCA (9.6% ± 5.9%) was significantly higher than 0.5 ± 0.7% for the 91 age- and sex-matched controls, P < 0.001. About two-third of children with SCA, sixty (65.9%) had low HbF levels (HbF of < 10%) whereas about one-third, 31 (34.1%) had high HbF level (HbF of ≥ 10%). The mean Hb concentration, haematocrit (Hct) and total red blood cell count were significantly lower amongst children with SCA, whereas the total white blood cell (WBC) counts, neutrophils, monocyte and lymphocyte percent, platelet counts, mean corpuscular Hb (MCH) and MCH concentration were significantly higher. HbF had a positive but weak correlation with Hct (r = 0.24, P = 0.014), Hb concentration (r = 0.21, P = 0.047) and red cell distribution width (r = 0.25, P = 0.015) and an inverse correlation with WBC count (r = -0.23, P = 0.038). Conclusion: Children with SCA had higher levels of HbF than matched controls. HbF had an inverse correlation with the WBC count and direct relationship with Hct and Hb concentration. It is recommended that routine determination of HbF and its induction are essential to maintain optimal haematological state of patients with SCD.

Keywords: Children, foetal haemoglobin, haematological indices, sickle cell disease


How to cite this article:
Akinlosotu MA, Adegoke SA, Oseni SB, Adeodu OO. Relationship between foetal haemoglobin and haematological indices in children with sickle cell anaemia from South Western Nigeria. Niger Postgrad Med J 2017;24:195-200

How to cite this URL:
Akinlosotu MA, Adegoke SA, Oseni SB, Adeodu OO. Relationship between foetal haemoglobin and haematological indices in children with sickle cell anaemia from South Western Nigeria. Niger Postgrad Med J [serial online] 2017 [cited 2018 Jul 21];24:195-200. Available from: http://www.npmj.org/text.asp?2017/24/4/195/223456


  Introduction Top


Sickle cell disease (SCD), a primary disorder of red blood cell (RBC), is inherited in an autosomal recessive fashion. About 5%–7% of the world population carry an abnormal haemoglobin (Hb) gene, with sickle cell anaemia (SCA) being the most common form of haemoglobinopathy globally.[1] It affects an estimated 4 million Nigerians and accounts for 5%–16% of under-five mortality in the West African subregion.[2]

Foetal Hb (HbF, α2γ2) inhibits polymerisation of sickle Hb (HbS, α2βs2), the major underlying pathophysiologic process in SCD crisis.[3],[4] HbF levels steadily decline from about 85% at birth by 3%–5% per week, such that it is <2% at 6 months and <1% at age 1 year.[4] Changes in the levels of HbF are associated with some peculiarities in individuals with SCA. First, the switch from HbF to HbS is usually delayed such that most adults with SCA have increased levels of HbF when compared with matched HbAA counterparts. Second, the level of HbF continues to drop and stabilises at age 5–10 years.[3],[4]

For over 30 years in many high-income countries, individuals with SCD are now being treated with hydroxyurea. The drug increases the production of HbF, improves Hb levels and erythrocyte rheological characteristics and reduces total white blood cell (WBC) count, absolute neutrophil and platelet counts.[5],[6] High levels of HbF improve the lifespan of the RBCs in addition to reducing rates and severity of vaso-occlusion and haemolysis.[7] Regular evaluation of the levels of HbF and its relationship with other haematological parameters in patients with SCD is essential due to the importance of HbF in this biochemical process. Amongst Nigerian children with the disease, potential effect of HbF on these haematological indices is largely understudied. The current study was designed to evaluate the HbF concentrations of children with homozygous SCD from Southwestern Nigeria and correlate the levels with the Hb concentrations, haematocrit, leucocyte and platelet counts, mean corpuscular volume, mean corpuscular Hb and mean corpuscular Hb concentration.


  Materials and Methods Top


The protocol for this study (protocol number ERC/2013/11/12) was approved by the Ethics and Research Committee of Obafemi Awolowo University Teaching Hospitals Complex, Ile-Ife in November 2013. Subsequently, this cross-sectional comparative study was done between March 2014 and April 2015 in the Paediatric SCD clinic of the hospital. Written informed consent was obtained from parents/caregivers of all cases and controls. In addition, assent was obtained from older children (7 years and above) before the commencement of the study. The minimum number of participants needed for the study to provide adequate power for the statistics was determined using the formula for comparing two independent means in a quantitative case–control study i.e., ([r + 1]/r [Zα+ Zβ]2 σ2)/d 2; where r = ratio of case to control, chosen as 1 in this study, d = difference in the means of outcome variable in cases and control, Zα= desired level of statistical significance, this is 1.96 for 95% confidence interval, Zβ= desired power of a study, this is 1.28 if the power is set at 90% and σ = standard deviation (SD) of the outcome variable. From a recent study on HbF in children with SCA and healthy controls in Sokoto, Nigeria, d = 2.99%–0.73% =2.26%; SD of the outcome variable = 4.46. Substituting these values, the minimum number (n) per group = 82 children. With an additional 10% of 'n' for attrition, sample size per group was 91. Hence, a total of 182 children comprising 91 children with SCA and 91 apparently healthy Hb AA children matched for age, sex and socioeconomic status were recruited and studied. The included children were aged 1 to 15 years. The included children were aged 1 to 15 years.

The children with SCA were in steady state at the time of recruitment i.e. there was no crisis, infection or fever for at least 4 weeks and no blood transfusion in the preceding 3 months.[8] Children with other haematological disorders such as glucose-6-phosphate dehydrogenase deficiency and those with chronic liver, kidney and heart diseases were excluded from the study. Furthermore those on hydroxyurea and children without parental consent/assent were not included in the study. The Hb genotype of controls was determined using cellulose acetate paper electrophoresis at pH 8.6. A data pro forma was used to obtain the sociodemographic characteristics such as age, sex and socioeconomic class of participants as described by Oyedeji based on the rank assessment of parental occupation and the level of education.[9]

Haematological data

Venous blood sample was obtained and analysed for the complete blood count using ABX Micros ES 60® automated haemoanalyser and HbF levels using BIO-RAD ® D10 high-performance liquid chromatography (HPLC) at the Haematology Laboratory of the National Sickle cell Foundation Lagos, Nigeria. The HPLC machine was preferred because of it is reproducible, faster and easier compared to the alkali denaturation technique.[10] Using earlier classification by Fatunde and Scott-Emuakpor,[11] HbF levels were classified as high (HbF ≥10%) or low (HbF <10%).

Statistical analysis

Data were analysed using the statistical package for the social sciences software for windows version 17.0 (IBM SPSS Inc. Chicago, IL). Means ± SD, median, proportions and percentages were determined as applicable. Categorical variables such as high or low HbF levels of participants and controls were compared with Chi-squared or Fisher's exact tests, whereas continuous data such as means/medians of haematological indices were compared with independent sample t-test, Mann–Whitney U-test or analysis of variance as indicated. The degree of correlation of continuous data was determined by Pearson's correlation analysis. Statistical significance was established when 'P' < 0.05.


  Results Top


A total of 182 children (91 with SCA and 91 matched HbAA controls) were recruited for this study. One hundred and one (55.5%) of them were males comprising 53 (58.2%) with SCA and 48 (52.7%) with HbAA. There was no statistical difference in the gender distribution between children with SCA and the controls (χ2 = 0.556, P = 0.456). Furthermore, the mean ages of the two groups were statistically similar; SCA was 7.6 ± 3.5 years whereas controls were 7.3 ± 3.3 years, t = 0.59, P = 0.553. Sixty-eight (37.4%) of the population were from the lower social class (Classes IV and V), whereas the middle and upper classes constituted 33.5% and 29.1%, respectively. Participants and controls had similar pattern of socioeconomic class distribution as shown in [Table 1].
Table 1: Sociodemographic characteristics of cases and controls

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Foetal haemoglobin levels in the participants and controls

The HbF levels of children with SCA ranged from 0.8% to 27.6%. Their mean HbF was significantly higher (9.6% ± 5.9%) than that of the controls (0.5% ± 0.7%), t = 14.624, P < 0.001. About half, 46 (50.5%) of the controls had HbF value of 0%. The remaining 45 (49.5%) of the controls had HbF values ≤2.8%. Although none of the children with SCA had HbF values of 0%, majority of them 60 (65.9%) had low HbF levels, i.e. HbF of <10%. Thirty-one (34.1) had high HbF level (HbF of ≥10%).

Haematological profile of the cases and controls

The Hb concentration of the participants ranged from 4.9 to 10.7 g/dl, with a mean of 7.6 ± 1.1 g/dl. Total leucocyte counts ranged from 4600 to 26,800/mm 3 whereas the mean platelet counts were 401,600 ± 161,500/mm 3 with a range from 80,000 to 834,000/mm 3. The Hb concentration of the controls ranged from 8.2 to 13.2 g/dl, with a mean of 10.9 ± 1.3 g/dl. Total leucocytes counts ranged from 3,600 to 10,300/mm 3, whereas the mean platelet count was 300,400 ± 86,210/mm 3 with a range from 126,000 to 542,000/mm 3.

[Table 2] shows that the mean values of all the assessed haematological parameters were significantly different between participants and controls except the Mean cell volume (MCV) and Mean platelet volume (MPV). While the mean RBC count, Hb concentration and haematocrit concentration were significantly lower, the total WBC counts, neutrophils percent, monocyte percent, lymphocyte percent, mean corpuscular Hb (MCH), MCH concentration and platelet counts were significantly higher amongst participants than controls.
Table 2: Comparison of the mean values of haematological profile of subjects and controls

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[Table 3] summarizes a breakdown of the important haematological indices of the participants, traditionally of particular relevance for use regarding clinic follow-up management and prognostication of children with SCA. One (1.1%) participant had Hb concentration >10 g/dl amongst children with SCA compared to 68 (74.7%) of the controls (P< 0.001). A similar trend was also observed for the haematocrit concentration. While 66 (72.5%) of the participants had leucocytosis, all the controls had normal WBC count (P< 0.001). Thirty-one (34.1%) of the participants compared to four (4.4%) of the controls had thrombocytosis (P< 0.001). [Table 4] summarises the relationship between HbF levels and various haematological indices.
Table 3: Comparison of the degree of anaemia, leucocytosis, thrombocytosis, hypochromia and microcytosis between subjects and controls

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Table 4: Correlation between haematological indices and foetal haemoglobin levels of children with SCA

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Correlation between haemoglobin F and haematological profile amongst the 91 participants

Haematocrit levels, Hb concentration, WBC count and red cell distribution width (RDW) of the subjects had a significant correlation with the HbF levels (P< 0.05) using Pearson's correlation analysis. While HbF had a positive correlation with haematocrit (r = 0.24, P = 0.014), Hb concentration (r = 0.21, P = 0.047) and RDW (r = 0.25, P = 0.015); an inverse correlation existed between HbF levels and WBC count (r = -0.23, P = 0.038). There was no significant correlation between HbF levels and other haematological parameters. [Figure 1]a and [Figure 1]b shows the correlation between HbF and haematocrit and WBC count using scatter plots.
Figure 1: (a) Scatter plot showing correlation between foetal haemoglobin level and haematocrit of children with sickle cell anaemia. (b) Scatter plot showing correlation between foetal haemoglobin level and total white blood cell count in children with sickle cell anaemia

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  Discussion Top


This study examined the modifying role of HbF on haematological indices of children with SCA from South Western Nigeria. The participants had significantly higher HbF levels compared to controls. This may be due to the adaptive genetic modulators present in SCA children that induce higher HbF production in them compared to HbAA individuals.[12] Furthermore, in SCA, there is a delay in the genetically controlled postnatal switch of HbF to HbA which consequently leads to a surge in the levels of HbF in them. Although the exact mechanism for this delayed switch is unknown, it might be related to accelerated expansion of early erythroid progenitors which still possess the ability to express γ-globin. The increased expansion of progenitor cells is linked directly to increased haemolysis and associated increased erythropoiesis that occurs in SCD.[13] This finding of higher levels of HbF in SCA than HbAA control is similar to reports of some authors in developing nations.[14],[15],[16],[17] On the other hand, about two-third of the children with SCA (65.9%) were found to have low HbF levels. This possibly is the subgroup predisposed to more severe disease and complications. This is consistent with findings by Mpalampa et al.[17] amongst children with SCA in Uganda where 63% were reported to have HbF level <10%.

The mean HbF level of the children with SCA in this study is higher than what have been reported previously in most previous studies.[18],[19],[20] Isah in Sokoto found mean HbF levels of 2.99% ± 5.16% as against 9.6% ± 5.9% in the present study.[18] Furthermore, the mean HbF level in this study is higher than 7.2% ± 5.0% reported by Tshilolo in Congo.[16] This may be due to the difference in the methods used for HbF estimation. The Betke method of alkali denaturation was used by Isah whereas HPLC which is a more sensitive method was used in the present study.[10] In addition, age difference might also account for the differences in the Hb F level obtained in the studies of adult sickle cell patients by Omoti in Benin (2.17% ± 1.81%), Durosinmi in Ife (4.26% ± 4.33%) and Olaniyi in Ibadan (5.16% ± 4.04%).[14],[15],[21]

This study has shown that the mean haematocrit and Hb concentrations of the children with SCA were significantly lower than the controls. Similar finding has been reported in Nigerian studies by Akinbami et al. in Lagos and Omoti in Benin.[22],[23] This is probably due to the reduced lifespan of RBCs in these children coupled with both ongoing and chronic haemolysis.[24] Consequently, this leads to a shift to the right of the Hb dissociation curve which enables them to adapt to this low Hb concentration without features of heart failure.[25]

It was also found that the total white cell count, platelet count, absolute neutrophils, lymphocyte and monocyte counts, mean corpuscular Hb and mean corpuscular Hb concentrations were significantly higher in children with SCA compared to their HbAA controls. This is similar to finding from Lagos by Akinbami et al.[22] and other studies.[15],[23] The reason for this finding is not clearly understood. However, it may be due to increased bone marrow activities in this group of children compared to the HbAA controls. Leucocytosis may also be due to the stress of recurrent pain, anxiety, nausea and vomiting which often occur in these patients. Stress can cause demargination of the marginated pool of WBC leading to the increase in blood samples taken.[26] Furthermore, autosplenectomy or functional asplenia may also be responsible for the higher values of white blood cells seen in them.[27] Some other studies have demonstrated that leucocytosis is associated with increased episodes of vaso-occlusive crisis, acute chest syndrome, priapism and stroke because of increase viscosity, activation of adhesive molecules, vascular endothelium and coagulation pathways.[28] High platelet count may be due to the negative feedback effect of erythropoietin production. Erythropoietin is homologous in structure to thrombopoietin which may invariably stimulate thrombopoiesis in these patients, consequently resulting into thrombocytosis. Furthermore, reduced or absent splenic sequestration of platelets due to hyposplenism may contribute to thrombocytosis seen in these children.[29]

HbF was found to have a positive though weak correlation with haematocrit and Hb concentration whereas white blood count had significant inverse relationship (also weak) with HbF levels. Understandably, administration of hydroxyurea which has been used in myeloproliferative disorders to reduce neutrophils count has also been found useful in reducing white blood cells in children with SCA, thereby reducing risk of developing severe complications such as stroke and acute chest syndrome in these children.


  Conclusion Top


That children with SCA had a higher mean HbF levels than matched controls although about two-third of these patients had levels <10%. It is also shown that HbF had an inverse correlation with the WBC count and a direct relationship with haematocrit and Hb concentration. Basic complete blood count is, therefore, an absolute necessity for the periodic management of children with SCA. HbF levels may need to be assayed in those with persistent abnormalities.

Acknowledgement

Authors hereby acknowledge all children and caregivers who participated in the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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