Clinical, Laboratory and Demographic characteristics of study participants
Children (n = 217, aged 1-192 months) presenting with acute febrile conditions (temperature > 37.5oC) were recruited in the study. Out of these, 100 were females while 117 were males (See Additional File I). A total of 148 (66 females and 82 males) had HbAA genotype, 45 (22 males and 23 females) had HbAS and 24 (13 females and 11 males) had HbSS genotype. The proportions of sex with regard to malaria infection between the clinical groups in each genotype stratum were comparable (P = 0.964, P = 0.921 and P = 0.167) for genotypes HbAA, HbAS and HbSS, respectively. Across group comparison on sex distribution demonstrated that this was also comparable across the genotypes (P = 0.880). Malaria of any parasite density, (asexual form of P. falciparum trophozoite or schizont) was microscopically confirmed in 58 HbAA, 14 HbAS and 13 HbSS with genotype-specific prevalence of 39.2% (58/148), 31.1% (14/45) and 54.2% (13/24), respectively. The remaining children (90 HbAA, 31 HbAS and 11 HbSS) were P. falciparum negative. In the HbAA group, children with P. falciparum infection group [median (IQR); 36 (63.3)] were older compared to those in non-infected group [median (IQR); 29.5 (37), P = 0.022]. Otherwise age did not differ between infected and non-infected groups both in HbAS [median (IQR); 36.3 (32.3)] and [median (IQR); 36 (50), P = 0.731] and HbSS [median (IQR); 31 (76)] and [median (IQR); 16 (27), P = 0.569], respectively. Haematological parameters were compared in the infected and non-infected children (controls) of the equal genotype (within the group) and in the infected children of different genotypes (across the group) i.e. HbAS versus HbSS. As shown in Table 1, haemoglobin (P = 0.001), haematocrit (P = 0.001) and RBC (P = 0.004) count were relatively lower in the infected group compared to non-infected group within each genotype. The RDW (P = 0.007) was moderately higher in the infected group compared to non-infected group in each stratum. Haemoglobin, haematocrit, RBC count and RDW were the most significantly different red cell parameter across the genotypes (P = 0.001, P = 0.001, P = 0.004 and P = 0.007, respectively). Furthermore, MCV (P = 0.332), MCH (P = 0.784) and MCHC (P = 0.179) were higher in the non-infected group relative to infected group in each genotype.
Table 1
Demographic and Laboratory characteristics of all the study participants
Characteristics | HbAA (n = 148 ) | HbAS (n = 45 ) | HbSS (n = 24 ) | P value+ |
Malaria positive (n = 58) | Malaria Negative (n = 90 ) | P value | Malaria Positive (n = 14 ) | Malaria Negative (n = 31 ) | P value | Malaria Positive (n = 13 ) | Malaria Negative (n = 11 ) | P value |
Sex, n (%) Male | 32 (55.2%) | 50 (55.6%) | 0.964a | 7 (50%) | 15 (48.4%) | 0.921a | 5 (38.5%) | 8 (72.7%) | 0.167a | 0.880a |
Female | 26 (44.8%) | 40 (44.4%) | 7 (50%) | 16 (51.6%) | 8 (62.5%) | 3 (27.3%) | |
Age, (Months) | 36 (63.3) | 29.5 (37) | 0.022b | 36 (32.3) | 36 (50) | 0.731b | 31 (76) | 16 (27) | 0.569b | 0.507c |
Red cell parameters and its indices | |
Haemoglobin, gdL− 1 | 10.2 (2.2) | 10.5 (2.2) | 0.190b | 10.4 (1.6) | 10.8 (2.3) | 0.659b | 7.3 (1.3) | 9.2 (2.8) | 0.018b | 0.001c |
Haematocrit, % | 34.6 (8.3) | 35.1 (5.7) | 0.356b | 32.9 (6.0) | 36.8 (9.7) | 0.185b | 26.4 (4.4) | 33.7 (6.8) | 0.002b | 0.001c |
RBC, (× 1012µL− 1) | 4.6 (1.0) | 4.8 (0.7) | 0.302b | 4.8 (1.5) | 5.0 (1.3) | 0.532b | 3.2 (1.7) | 4.7 (1.2) | 0.167b | 0.004c |
RDW, % | 11.4 (2.2) | 11.2 (2.2) | 0.817b | 11.5 (2.6) | 11.7 (3.6) | 0.589b | 14.9 (3.3) | 12.1 (10.3) | 0.910b | 0.007c |
MCV, fL | 75.1 (10.5) | 75.7 (11.2) | 0.327b | 74.1 (11.8) | 76.3 (17.3) | 0.540b | 79.5 (15.9) | 76.8 (7.3) | 1.000b | 0.332c |
MCH, fL/cell | 22.15 (3.7) | 22.9 (3.5) | 0.277b | 31.0 (1.7) | 28.6 (3.2) | 0.440b | 23.1 (3.5) | 22.5 (3.7) | 0.569b | 0.784c |
MCHC, gdL− 1 | 29.7 (2.2) | 29.9 (4.1) | 0.574b | 31.0 (1.7) | 28.6 (3.2) | 0.008b | 27.7 (4.1) | 28.2 (2.4) | 1.00b | 0.179c |
Leucocyte parameters | |
WBC(× 103µL− 1) | 7.8 (4.8) | 8.46 (5.5) | 0.817b | 9.58 (5.2) | 8.3 (5) | 0.433b | 12.68 (4.6) | 12.2 (7.0) | 0.569b | 0.004c |
Lymphocytes, % | 36.6 (27.2) | 45.1 (24.3) | 0.050b | 37 (36.2) | 43.6 (34.2) | 0.844b | 50.9 (29.1) | 39.6 (17.8) | 0.733b | 0.873c |
Monocytes, % | 11.2 (7.4) | 9.7 (4.6) | 0.300b | 12 (7.8) | 8.4 (4.8) | 0.140b | 8.1 (6.1) | 9.3 (3.5) | 0.865b | 0.866c |
Granulocytes, % | 51.5 (27.2) | 45.6 (26.4) | 0.186b | 48.9 (27.5) | 46.1 (28.1) | 0.844b | 39.3 (28.2) | 51.1 (16.4) | 0.649b | 0.833c |
Platelet parameter and its indices | |
Platelet, (× 103µL− 1) | 220 (127) | 271 (116) | 0.001b | 232 (129) | 288 (102) | 0.061b | 236 (140) | 265 (187) | 0.955b | 0.001c |
MPV, fL | 5.4 (0.6) | 5.5 (0.5) | 0.321b | 5.3 (0.9) | 5.5 (0.7) | 0.258b | 5.2 (0.8) | 5.5 (0.6) | 0.733b | 0.710c |
PDW, % | 9.6 (1.4) | 9.35 (1.5) | 0.632b | 9.5 (1.9) | 9.5 (1.5) | 0.556b | 9.5 (0.4) | 9 (1.5) | 0.277b | 0.611c |
PCT, % | 0.13 (0.1) | 0.15 (0.1) | 0.003b | 0.1 (0.1) | 0.2 (0.1) | 0.102b | 0.1 (0.1) | 0.15 (0.1) | 0.649b | 0.260c |
Data are presented as the median (interquartile range; IQR) values unless stated otherwise. Study participants were stratified into sickle cell genotype (HbAA, HbAS and HbSS). Each stratum was further categorised into infected and non-infected groups. a Statistical significance was determined by the Chi-square (χ2) analysis. b Statistical significance was determined using Mann Whitney test. c Statistical significance was determined using Kruskal Wallis test. P values in bold are statistically significant. Abbreviations: MCV; Mean corpuscular volume; MCH; mean corpuscular haemoglobin: MCHC; mean corpuscular haemoglobin WBC concentration; RBC-Red blood cells, RDW; Red cell distribution width; WBC; White blood cells, MPV; mean platelet volume; PDW; platelet distribution width and PCT. plateletcrit |
Even though the WBC count were numerically lower in the infected group relative to non-infected group in HbAA genotype (P = 0.817) but higher in the infected group within both HbAS (P = 0.433) and HbSS (P = 0.569) genotypes, these differences were not statistically significant. However, the WBC count was statistically significant across the genotypes (P = 0.004). Lymphocyte was lower in the infected group relative to non-infected group within the HbAA genotype [median (IQR); 36.6 (27.2), and [median (IQR); 45 (224.3), P = 0.05], respectively. Both monocytes (P = 0.866) and granulocytes (P = 0.833) were comparable within the genotypes.
Among the platelet parameters and its indices, platelet count was more exceptional in its comparability within the HbAA genotype. Infected group had lower platelet count relative to non-infected group [median (IQR); 220 (127), and [median (IQR); 271 (116), P = 0.001], respectively. This significance was equally simulated in the comparison across the three genotypes (P = 0.001). The MPV (P = 0.710) and PDW (P = 0.611) were comparable across the genotypes. The PCT was only statistically significant within HbAA genotype with [median (IQR); 0.13 (0.1), and [median (IQR); 0.15 (0.1), P = 0.003] for infected and non-infected groups, respectively. All the determined demographic and laboratory characteristics are summarized in Table 1.
Association between haematological parameters and sickle cell genotypes in P. falciparum infected children
Considering the distribution of haematological parameters in the three stratified study groups, their association with sickle cell genotypes in P. falciparum infected children were modelled using logistic regression model while controlling for the infection status. Infection status was controlled for since sickle gene has an influence of the haematological parameters regardless of infection, however, malaria infection can further worsen the levels of these parameters. Using the homozygous wild-type genotypes (HbAA) as the reference group, results revealed no association between HbAS and haemoglobin [OR = 1.098, 95% CI = 0.555–2.171, P = 0.789], haematocrit [OR = 1.140, 95% CI = 0.568–2.287, P = 0.713], RBC count [OR = 0.706, 95% CI = 0.235–2.123, P = 0.100] and RDW [OR = 0.093, 95% CI = 0.514–2.323, P = 0.818]. However, there was a significant association between HbSS and haemoglobin [OR = 0.310, 95% CI = 0.101–0.956, P = 0.041], haematocrit [OR = 0.318, 95% CI = 0.128–0.793, P = 0.014], RBC count [OR = 0.124, 95% CI = 0.045–0.337, P = 0.001] and RDW [OR = 2.993, 95% CI = 0.952–9.409, P = 0.061] (See Table 2). Reduced MCV (microcytosis) was neither associated with HbAS [OR = 1.193, 95% CI = 0.609–2.334, P = 0.606] nor HbSS [OR = 2.094, 95% CI = 0.854–5.137, P = 0.106]. Furthermore, increased MCV (macrocytosis) [OR = 1.058, 95% CI = 0.107–10.452, P = 0.962] was not associated with HbAS, however, association between HbSS and increased MCV did not run in the regression model. Additional analyses revealed that reduced MCH did not show any association with HbAS [OR = 0.763, 95% CI = 0.263–2.219, P = 0.620]. Moreover, reduced MCH did not show any association with HbSS [OR = 0.507, 95% CI = 0.110–2.340, P = 0.383] while reduced MCHC did not reveal association with HbAS [OR = 0.819, 95% CI = 0.373–1.798, P = 0.619]. However, reduced MCHC showed association HbSS [OR = 0.325, 95% CI = 0.118–0.892, P = 0.029].
Table 2
Association between haematological parameters and sickle cell genotypes
Parameter | Dichotomised haematological outcome | Sickle cell genotype | OR | 95%CI | P value |
Haemoglobin | Anaemia (Haemoglobin < 10 gdL− 1) | HbAS | 1.098 | 0.555–2.171 | 0.789 |
HbSS | 0.310 | 0.101–0.956 | 0.041 |
Haematocrit | (Haematocrit < 33%) | HbAS | 1.140 | 0.568–2.287 | 0.713 |
HbSS | 0.318 | 0.128–0.793 | 0.014 |
RBC count | Erythrocytopaenia (RBC count < 3.8 × 1012µL− 1) | HbAS | 0.706 | 0.235–2.123 | 0.100 |
HbSS | 0.124 | 0.045–0.337 | 0.001 |
RDW | (< 12%) | HbAS | 0.093 | 0.514–2.323 | 0.818 |
HbSS | 2.993 | 0.952–9.409 | 0.061 |
MCV | Microcytosis (MCV < 76 fL) | HbAS | 1.193 | 0.609–2.334 | 0.606 |
HbSS | 2.094 | 0.854–5.137 | 0.106 |
Macrocytosis (MCV > 96 fL) | HbAS | 1.058 | 0.107–10.452 | 0.962 |
HbSS | XXX | XXX | XXX |
MCH | (< 25 Pg) | HbAS | 0.763 | 0.263–2.219 | 0.620 |
HbSS | 0.507 | 0.110–2.340 | 0.384 |
MCHC | (< 28 gdL− 1) | HbAS | 0.819 | 0.373–1.798 | 0.619 |
HbSS | 0.325 | 0.118–0.892 | 0.029 |
WBC | Leucocytopaenia (WBC < 4 × 103µL− 1) | HbAS | 0.131 | 0.011–1.528 | 0.105 |
HbSS | XXX | XXX | XXX |
Leucocytosis (WBC > 10 × 103µL− 1) | HbAS | 1.485 | 0.692–3.185 | 0.310 |
HbSS | 9.283 | 3.167–27.210 | 0.001 |
Lymphocytes | Lymphoctopenia (Lymphocytes < 20%) | HbAS | 0.625 | 0.265–1.473 | 0.283 |
HbSS | 3.014 | 0.646–14.069 | 0.160 |
Lymphocytosis (Lymphocytes > 40%) | HbAS | 0.607 | 0.180–2.052 | 0.422 |
HbSS | 0.636 | 0.101–4.018 | 0.630 |
Monocytes | Monocytosis (Monocytes, > 10%) | HbAS | 0.800 | 0.406–1.574 | 0.518 |
HbSS | 0.319 | 0.123–0.830 | 0.019 |
Granulocytes | Granulocytopaenia (Granulocytes, < 30%) | HbAS | 0.446 | 0.182–1.089 | 0.760 |
HbSS | 2.201 | 0.459–10.547 | 0.324 |
Granulocytosis (Granulocytes, > 70%) | HbAS | 0.941 | 0.354–2.503 | 0.903 |
HbSS | 0.538 | 0.117–2.473 | 0.426 |
Platelets | Thrombocytopaenia (Platelet count <150 × 103µL− 1) | HbAS | 1.746 | 0.330–9.243 | 0.512 |
HbSS | XXX | XXX | XXX |
Thrombocytosis (Platelet count >300 × 103µL− 1) | HbAS | 0.984 | 0.463–2.095 | 0.968 |
HbSS | XXX | XXX | XXX |
MPV | Micro platelets (Platelets < 6 fL) Megathrombocytes (platelets > 12.3 fL) | HbAS | 3.269 | 1.291–8.276 | 0.012 |
HbSS | 4.781 | 0.355–6.470 | 0.238 |
NA | NA | NA | NA |
PDW | (PDW, < 6%) | HbAS | 0.932 | 0.286–3.035 | 0.907 |
HbSS | XXX | XXX | XXX |
PCT | (PCT, < 0.22%) | HbAS | 1.017 | 0.304–3.405 | 0.978 |
HbSS | 0.552 | 0.220–13.900 | 0.718 |
Children (n = 217) with acute febrile condition were categorized on the basis of sickle cell genotype (HbAA and HbSS). Odds ratios (OR) and 95% confidence intervals (CI) were determined using multivariate logistic regression analysis controlling for infection status. P-values in bold were statistically significant at P ≤ 0.05. XXX; did to run in the regression model. NA; not applicable. The reference groups in the logistic regression analysis were the homozygous wild-type genotypes (HbAA). |
Total reduction in white blood cell count (leucocytopaenia) was not associated with HbAS [OR = 0.131, 95% CI = 0.011–1.528, P = 0.105]. However, leucocytosis showed increased association with HbSS [OR = 9.283, 95% CI = 3.167–27.210, P = 0.001]. Both elevated and reduced lymphocyte and granulocyte counts did not reveal association with either HbAS or HbSS in P. falciparum infected children. However, increased monocyte count (monocytosis) revealed association with HbSS [OR = 0.319, 95% CI = 0.123–0.830, P = 0.019].
With regard to platelet parameters and its indices, reduced platelet count (thrombocytopenia) did not show association with HbAS [OR = 1.746, 95% CI = 0.330–9.243, P = 0.512]. Furthermore, increased thrombocyte count (thrombocytosis) equally showed no association with HbAS [OR = 0.984, 95% CI = 0.463–2.095, P = 0.968]. Unfortunately, the model could not determine association of either thrombocytopenia or thrombocytosis with HbSS genotype in children infected with malaria. Micro-platelet was defined as a platelet with reduced mean platelet volume (MPV) to below 6 fL (37). Micro-platelet was associated with HbAS [OR = 3.269, 95% CI = 1.291–8.276, P = 0.012] but was no associated with HbSS [OR = 4.781, 95% CI = 0.355–6.470, P = 0.238]. Furthermore, PDW did not show any association with HbAS [OR = 0.932, 95% CI = 0.286–3.035, P = 0.907], however, its association with HbSS was undetermined. Finally, PCT did not show any association with HbAS [OR = 1.017, 95% CI = 0.304–3.405, P = 0.978] and with HbSS [OR = 0.552, 95% CI = 0.220–13.900, P = 0.718] (See Table 2).
Association between Sickle cell genotype and Plasmodium falciparum infection
With HbAA as the reference group, bivariate logistic regression analysis was modelled to determine association between sickle cell genotypes and P. falciparum infection. Results revealed that both HbAS [OR = 0.701, 95% CI = 0.344–1.429, P = 0.328] and HbSS [OR = 1.834, 95% CI = 0.774–4.369, P = 0.171], was not associated with P. falciparum infection (See Table 3).
Table 3
Association between Sickle cell genotype and P. falciparum infection
Sickle cell genotypes | P. falciparum infection |
OR | 95% CI | P-value |
HbAA, (n = 148) | Ref | - | - |
HbAS, (n = 45) | 0.701 | 0.344–1.429 | 0.328 |
HbSS, (n = 24) | 0.1834 | 0.774–4.369 | 0.171 |
Children with acute febrile condition (n = 217) were grouped based on the haemoglobin genotype. Odds ratios (OR) and 95% confidence intervals (CI) were determined across genotypes using bivariate logistic regression model controlling for age, sex.. P-values in bold was statistically significant at P ≤ 0.05. The reference groups in the regression analysis were the homozygous wild-type genotypes (HbAA). |