The Data collected was analyzed using the SPSS software (version 16). Descriptive statistics were summarized using means and standard deviation for continuous data and percentages for categorical data. Continuous variables were analyzed using the student’s t-test. Odds ratios and 95% confidence interval was reported. P values less than or equal to 0.05 was considered significant. Correlation studies were used to evaluate the relationship between two variables within the same group.
45
CHAPTER FOUR RESULTS 4.1 Socio-demographic distribution of the individuals
One hundred and twenty sickle cell anaemia individuals in steady-state were studied.
Majority of the participants were females 91 (76%) with males accounting for only 29 (24%) with M: F ratio of 1: 3.1. The mean age was 22.6 ± 4.9 years with a range between 18 and 43years. Females were younger (22.1 ± 4.72 years) than males (24.4 ± 5.2 years); p = 0.028.
Table: 4.1 shows the age and sex distribution of the individuals with SCA.
4.2 Steady state haematologic and haemolytic parameters of SCA individuals
Table 4.2 shows the steady state haematologic parameters of the 120 sickle cell aindviduals with sickle cell anaemia. The mean haemoglobin concentration was 7.7 ± 3.1 g/dl;
haematocrit was 23.3 ± 4.5 %; MCV 87.5 ± 8.7 fl; MCH 31.1 ± 3.5 pg; MCHC 35.5 ± 1.3 g/dl; RDW 23.9 ± 3.4; WBC 12.1 ± 3.6 x 109/l; Plt 366.1 ± 131.2 x 109/l; and HbF 7.5 ± 4.3
%. Table 4.3 shows the steady state haemolytic markers of individuals with SCA. The mean LDH was 617.8 ± 279.0 U/l; Total bilirubin 24.9 ± 20.3 µmol/l; Direct bilirubin 10.5 ± 11.9
µmol/l; Indirect bilirubin 14.4 ± 12.6 µmol/l; AST 45.9 ± 19.7U/l; and Retics 5.2 ± 3.2%. The mean ISC was 6.1 ± 3.1 % among 97 subjects.
4.3 Pattern of clinical presentation
Table 4.4 shows the distribution of clinical features of individuals with SCA in the different quartiles. The commonest presentations reported were painful crisis 112 (93.3%), osteonecrosis/hip replacement 17 (14.2%), CLU 16 (13.3%), stroke 13 (10.8%), priapism 7 (5.8%), ACS 6 (5%), renal impairment 6 (5%). Sixty six out of the 120 patients with SCA presented with at least one complication of SCA during the steady state. Only stroke showed a statistically significant difference between the three quartile groups (lower, middle and upper) with p = 0.032 while the rest showed no difference (painful crisis = 0.546,
46
osteonecrosis/ hip replacement = 0.362, CLU = 0.448, priapism = 0.131, ACS = 0.544 and renal impairment = 0.426). Further analysis showed that individuals with stroke are more likely to be in the upper quartile than the lower quartile (O.R 5.8, 95% CI 1.4 – 24.3, p = 0.017). Table 4.5 shows that the mean LDH of individuals with stroke was significantly higher than that of those without stroke (p = 0.008), while the mean LDH was not significantly different between those that had other complications and those without them.
Figure 4.2 shows the mean LDH levels in relation to the number of painful crisis experienced in a year. Of the 112 patients with painful crisis 39.2% experience at least one episode of painful crisis in a year. Fourteen individuals (12.5%) had between 3 – 4 episodes of painful crisis in a year and five (4.5%) presented with 4 or more episodes in a year. However the mean LDH values of the groups have no relationship with the number of painful crisis experienced in a year (p = 0.842).
4.4 Evaluation of the relationship between steady state haemolytic markers and clinical presentations.
Figure 4.3 shows the degrees of disease severity compared to steady state mean LDH levels of individuals with SCA. The majority of the individuals had moderate disease 65 (52%), 49 (40.8%) mild disease and 6 (5%) had severe disease. The mean LDH of the groups increases with disease severity even though the relationship was not statistically significant (p = 0.191).
Table 4.6 shows the mean haematologic and haemolytic markers of the individuals in the upper quartile and other LDH quartile groups. Individuals in the lower quartile group have higher haematocrit 23.6 ± 4.5%, haemoglobin concentration 7.8 ± 4.4 g/dl and HbF 8.1 ± 5.6% with lower markers of haemolysis. The middle quartile was associated with both high haematocrit and haemolysis while those in the upper quartile have higher levels of AST 53.2
± 20.1U/l, total bilirubin 23.0 ± 14.1µmol/l, direct bilirubin 11.3 ± 12.4µmol/, indirect bilirubin 11.7 ± 4.4µmol/l, reticulocyte count 6.2 ± 3.3% and ISC 6.5 ± 2.9% with lower
47
mean haematocrit of 21.6 ± 4.1%. However, there was no statistical difference between the three groups in haematological parameters (p > 0.05), even though trends were observed in platelet count, HbF, ISC, indirect bilirubin, and AST. Significant difference was observed in the level of haemolysis between the groups (total bilirubin p=0.004, direct bilirubin p=0.046, indirect bilirubin p = 0.006). Table 4.7 shows the pattern of blood transfusion of individuals in the different LDH quartile groups. Seventy five individuals have never received blood transfusion in the past, 38 received between 1 and 9 units while only seven have received 10 units and above. Subjects in the upper quartile received 43.2% of the total blood transfusions in the study while those in the lower quartile received only 13.2%. However, there was no statistically significant difference in the number of units transfused between the LDH quartile groups (p = 0.068). Table 4.8 shows the mean severity score of the 120 individuals with SCA. The mean severity score of all the patients was 2.9 ± 1.3, while the mean severity scores for the lower, middle and upper quartiles were 2.6 ± 1.2, 2.9 ± 1.4, 3.1 ± 1.4 respectively (p = 0.421). Table 4.9 shows the correlation of severity score with steady state haemolytic makers of SCA individuals. Severity score showed significant positive correlation with LDH (r = 0.196, p = 0.032) and other markers of haemolysis (total bilirubin r = 0.229, p
= 0.012; direct bilirubin r = 0.259, p = 0.004; and AST r = 0.215, p = 0.019).
48
Table 4.1: Age and Sex distribution of the individuals with SCA
Sex
male (n= 29) female (n= 91) total: 120 Mean age (SD) 24.4 ± 5.2 22.1 ± 4.7 22.64 ± 4.9
Age range 18 – 34 18 - 43 18 - 43
(P =0.028)
49
Table: 4.2 Steady state haematologic parameters of the 120 individuals with sickle cell anaemia
Parameter Mean(±SD)
Normal reference
range Minimum Maximum
Hb (g/dl) 7.7 (3.1) 11.5-17.5 5.3 12.0
Hct (%) 23.2 (4.5) 40-54 16.2 36
MCV (fl) 87.5 (8.7) 80-95 63.1 102.2
MCH (pg) 31.1 (3.5) 27-34 21.7 37.7
MCHC (g/dl) 35.5 (1.3) 20-35 31.6 39.3
RDW (%) 23.9 (3.4) 11.6-14 16.5 35.1
WBC (×109/l) 12.1 (3.6) 2.6-10.2 4.3 21.1
Platelet count (×109/l) 366.1 (131.2) 100-300 108 735
HbF (%) 7.5 (4.3) <1 0.4 19.5
Hct= Haematocrit, MCV= Mean cell volume, MCH= Mean cell haemoglobin, MCHC=Mean cell haemoglobin concentration, RDW= Red cell distribution width, WBC= White blood cell count, HbF=Foetal haemoglobin, Hb=haemoglobin concentration.
50
Table: 4.3 Steady state haemolytic markers of the 120 individuals with sickle cell anaemia
Marker Mean (±SD)
Normal
reference range Minimum Maximum
LDH (U/l) 617.8 (279.0) 125 - 220 202 1376
Total Bil (µmol/l) 24.9 (20.3) 2 - 12 8 104
Direct Bil (µmol/l) 10.5 (11.9) <7 3 68
Indirect Bil (µmol/l) 14.4 (12.6) <12 5 80
AST (U/l) 45.9 (19.7) <12 11 129
Retics (%) 5.2 (3.2) 0.5 – 2.5 0.6 16.6
+ISC (%) 6.1 (3.1) 1.3 19.0
LDH= Lactate dehydrogenase, Total Bil= Total bilirubin, Indirect Bil= Indirect bilirubin, AST= Aspartate aminotransferase, Retics= Reticulocyte count, ISC= irreversibly sickled cell count. + Among 97 individuals.
51
Table 4.4: Distribution of clinical features of individuals with SCA within the lower, middle and upper quartiles
Clinical feature LDH QUARTILES
Prevalence Fisher's p-value
Lower Middle Upper
Painful crisis present 33 48 31
112
(93.3%) 0.546
absent 5 5 2
Osteonecrosis/hip replacement
present 2 11 4 17 (14.2%)
0.362
absent 28 49 26
Chronic leg ulcer present 2 10 4 16 (13.3%)
0.448
absent 50 28 26
Stroke present 3 3 7 13 (10.8%)
0.032*
absent 44 40 23
Priapism present 2 4 1 7 (5.8%)
0.131
absent 28 50 29
Renal impairment
present 0 4 2 6(5%)
0.426
absent 30 56 28
ACS present 3 2 1 6 (5%)
0.544
absent 27 58 29
Further analysis showed that participants with stroke are more likely to be in upper quartile compared to middle quartile (O.R 5.8, 95% CI 1.4 - 24.3), p = 0.017).
KEY: Lower quartile= LDH ≤398.75 U/l Middle quartile= LDH 398.75-772.50 U/l Upper quartile= LDH ≥772.50 U/l
52
Table 4.5: Mean LDH values of individuals with SCA with and without the different clinical features
Clinical features Mean N Std. Deviation p-value Painful crisis present 607.3 112 269.3 0.532
absent 610.9 8 270.8
Osteonecrosis/hip
replacement present 653.2 17 191.6 0.574
absent 611.9 103 291.2
Chronic leg ulcer present 705 16 305.5 0.18 absent 604.4 104 273.8
Stroke present 810.9 13 399.7 0.008*
absent 594.3 107 253.3
Priapism present 544.1 7 112.8 0.474
absent 622.4 113 285.7
ACS present 547.5 6 233.8 0.529
absent 621.5 114 281.5
Renal impairment present 687.2 6 177.7 0.534
absent 614.2 114 283.4
*Statistically significant ACS= Acute chest syndrome
53
Table 4.6: Categorization of steady state mean haematological and haemolytic parameters of individuals with SCA in LDH quartiles.
Parameters
Lower quartile (LDH≤398.75 U/l)
Middle quartile (LDH>398.75<772.50)
Upper quartile (LDH≥772.50 U/l)
p-value Mean ± SD
(n=30)
Mean ± SD (n=58)
Mean ± SD (n=32)
Hct (%) 23.6 ± 4.5 23.8 ± 4.5 21.6 ± 4.1 0.067 Hb (g/dl) 7.8 ± 4.4 7.9 ± 4.1 7.2 ± 4.6 0.081 MCV (fl) 87.0 ± 8.2 87.5 ± 8.1 87.2 ± 8.1 0.55
MCH 30.7 ± 3.4 32.0 ± 3.1 31.2 ± 3.9 0.221
MCHC (g/dl) 35.0 ± 1.6 34.7 ± 1.3 35.4 ± 1.1 0.079 RDW (%) 22.9 ± 3.0 23.6 ± 3.3 23.9 ± 3.6 0.134 WBC (X109/L) 11.6 ± 4.4 12.4 ± 3.6 12.0 ± 2.7 0.57 Plt (X109/L) 359.6 ± 144.1 366.8 ± 124.0 371.3 ± 136.4 0.941 HbF (%) 8.1 ± 5.6 7.1 ± 3.8 6.6 ± 3.6 0.392 Retics (%) 5.2 ± 3.4 4.6 ± 2.9 6.2 ± 3.3 0.098 ISC (%) 4.7 ± 2.0 5.9 ± 3.1 6.5 ± 2.9 0.24 Total bilirubin
(µmol/L) 15.8 ± 5.2 30.4 ± 25.4 23.0 ± 14.1 0.004*
Direct bilirubin
(µmol/L) 5.9 ± 3.3 12.4 ± 13.9 11.3 ± 12.4 0.046*
Indirect bilirubin
(µmol/L) 9.9 ± 2.6 17.9 ± 16.8 11.7 ± 4.4 0.006*
AST (U/l) 42.0 ± 20.8 44.2 ± 18.2 53.2 ± 20.1 0.054
*statistically significant
One hundred and nineteen (119) individuals have LDH value above the normal reference range of 125-220 U/l.
54
Table 4.7: Pattern of blood transfusion among individuals in the different LDH quartile groups
Number of Transfusions
LDH QUARTILE
Total Lower
Quartile (n=30)
Middle Quartile
(n=58)
Upper Quartile
(n=32)
0 18 41 16 75
1 < 10 12 16 10 38
≥ 10 0 3 4 7
p= 0.068 (Fisher’s test)
55
Table 4.8: Disease Severity Score of the 120 individuals with SCA
Quartile Mean SD p-value
Lower 2.6 1.2 0.421
Middle 2.9 1.4
Upper 3.1 1.4
Total 2.9 1.3
56
Table 4.9: Correlation of severity score with steady state haemolytic markers of 120 individuals with SCA
Parameter Pearson Correlation p-value
Severity score vs LDH 0.196 0.032*
Severity score vs total bilirubin 0.229 0.012*
Severity score vs direct bilirubin 0.259 0.004*
Severity score vs indirect bilirubin 0.122 0.183
Severity score vs AST 0.215 0.019*
*statistically significant
57
Figure 4.2: Mean LDH levels in relation to number of painful crisis requiring hospital visitation/year among 112 individuals with SCA.
48
44 14 5
0 100 200 300 400 500 600 700
0 1 to 2 3 to 4 >4
Mean LDH levels
Number of painful crisis requiring hospital visitation per year
p-value=0.842
58
Figure 4.3: Degrees of disease severity compared to steady state mean LDH levels among individuals with SCA
n=49
n=65
n=6
0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0
mild moderate severe
Mean LDH level
Disease severity
p-value=0.191
59 DISCUSSION
A total of 120 steady state sickle cell anaemia individuals were recruited for the study to determine the prevalence of clinical phenotypes of patients with SCA in Kano using markers of haemolysis. In this study majority of the subjects were females with a mean age of 22.6 years that was significantly lower than in males (24.4 years). This suggests that females are more regular to follow-up than males probably due to the higher health seeking behavior in females compared to males as was previously documented.98 It could also mean that there may be more surviving female individuals with SCA than males as was reported from the southern part of the country.98,99 Nonetheless, this must be interpreted with caution because males may be more preoccupied by responsibilities in a typical Hausa-Fulani setting.
Therefore, male patients may likely present to the hospital only when they are in crisis.
Majority (52%) of individuals in the study had moderate disease severity, while 40.8% had mild disease and 5% severe disease. Disease severity was assessed using a scoring system recently used by Okocha et al, 2016.100 Similar studies in the country have reported higher frequency of severe disease in the past.100,101 The low disease severity observed in this study may be attributed in part to the fact that those on hydroxyurea were excluded from the study since they were more likely to have severe disease. Patients on top-up or exchange transfusion programs due to sickle cell complications such as stroke and recurrent abortion were excluded, constituting another group with severe disease.
The commonest clinical presentation among the participants was painful crisis. Similar pattern was reported from other parts of Nigeria102 and also from Saudi Arabia103 66.3% and 98% respectively. Although the prevalence of painful crisis is believed to reduce with age,104 this study suggests that it remains the most common presentation even in adulthood. Some of the factors that may have contributed to the high prevalence in this study may be attributed to the weather in Kano which is characterized by cold and dusty harmattan season and hot
non-60
harmattan season that promotes skin cooling and dehydration.105 Other factors that may have contributed to the high prevalence include the predominance of the severe Benin haplotype in Nigeria,106 and also the low HbF levels found compared to higher values reported from parts of Saudi Arabia where the prevalence of painful crisis is low.58 Osteonecrosis/ hip replacement is the second most common presentation among the studied population. The prevalence obtained is similar to what was documented (13.1%) in a previous 5 year retrospective study of patients with SCA aged 6–49 years at the University of Nigeria Teaching Hospital Enugu .107 Moreover, regional variability may also be contributory just as a study from USA with 2,590 patients aged 5 years and above had a lower prevalence of osteonecrosis while other studies from the UK and Kuwait in the Middle-East had higher prevalence of 27% and 41% respectively.71–73 The higher prevalence rates reported by the UK and Kuwait studies may be attributed to the use of Magnetic Resonance Imaging (MRI) which is a more sensitive diagnostic tool than the plain X-ray, therefore those with early disease might have been missed by plain X-ray used in this study. Chronic leg ulcer contributed significantly to the clinical presentation of the participants with SCA in the steady state. The prevalence reported in this research (13.3%; Table 4.4) is close to that reported by Bazuaye et al (2010; 9.6%) but higher than that presented by Hassan et al (2012, 3.1%).59,108 The high prevalence recorded may be attributed to the difference in the study population, which consisted of SCD patients59 and SCA in this present research. The type of haemoglobin variant (HbSS or HbSC) have been shown to influence the development of CLU as reported earlier in a study among 630 patients with SCD in Ibadan by Durosinmi et al (1991)109 who reported a CLU prevalence of 1.7% for HbSC and 7.5% for HbSS.The type of haemoglobin variant may not explain the entire difference because a previous study from South America on a similar population of 183 patients with SCA from Jamaica reported a very high prevalence of 43%,110 suggesting possible environmental and genetic differences
61
between the regions. The prevalence of stroke obtained is similar to that reported by Lagunju et al (2012; 8.4%), in a study conducted at the University College Hospital Ibadan among 214 SCA children,111 which is in contrast to a multicenter study of stroke involving 11 tertiary institutions in Nigeria including AKTH, that reported a national prevalence of 1.24%.112 The multicenter study of Jude et al (2014)112 observed that the majority of the patients with stroke are from the northern part of the country. The prevalence of priapism among the males in this study was 31.8%. This is similar to the 35% documented by a multicentre study involving some African countries including Nigeria,56 but lower than the 50% reported in a study of priapism in SCA patients from Jamaica.55 Nonetheless, studies from southwestern Saudi Arabia reported a lower prevalence of 2.6%.58 This may suggest lower prevalence of priapism in patients with the Arab-Indian haplotype which is dominant in Saudi Arabia. The prevalence of ACS reported is similar to an earlier report by Fawibe et al (2008)69 but contrary to the 22% and 47% reported by a multicentre study in patients from Saudi Arabia, recruited from the Southeastern and Southwestern provinces.103 The frequency of ACS obtained in this study may be underreported due to under diagnosis especially in the absence of cough and in the background of painful crisis which may make localization of pain to the chest difficult, and therefore many cases that resolve early and go undetected. The prevalence of renal impairment obtained is similar to that reported by Bolarinwa et al (2012)24 from two centers in Southwestern Nigeria ( 5.7%). A similar prevalence of 4.2%
was also reported outside the continent by Powars et al (1991)113 among 725 patients with SCA in the USA. However, a across-sectional study in a neighboring country, Ghana, at Tema General Hospital obtained a much higher prevalence of 40.8% among 194 patients,114 while a multicenter study in USA reported by Platt et al (1994)70 involving 23 centers with 3,764 patients aged from birth to 66 years also showed a high prevalence of 24%. These differences in the prevalence of renal impairment in patients with SCA may be due to
62
differences in age of study population and diagnostic tools used for screening. Some of the patients in the USA study were more than 60 years old and therefore have higher risk of renal impairment and other sickle cell related complications than the population in this study that was less than 46 years old. It is noteworthy to know that the Ghana study used microalbuminuria to screen their patients which is a sensitive screening tool that is not routinely used in our center.
The haematological parameters of individuals in steady state showed moderate anaemia with elevated total WBC, platelet count and percentage of HbF. A similar pattern was reported in Kano by Sagir et al (2010).115 The low mean haematocrit obtained in this study was similar to other reports in the country.83,99 The low haematocrit level is consistent with findings by Akinola et al (1992)82 that SCA is associated with some red cell sickling and haemolysis commensurate with crisis even in the steady state. The reason for the low haematocrit in SCA may be due to blunted response to erythropoietin secretion, resulting in haemoglobin rise that is not proportional to the degree of anaemia.116 Red cell distribution width (RDW) is an electronically determined index of anisocytosis.117 Elevated RDW provides a clue for heterogenous nature of the red cell size or the presence of two red cell populations. Such dimorphic RBC populations are seen in sideroblastic anaemia or combined iron deficiency anaemia and megaloblastic anaemia.118 Studies have shown that RDW in SCA individuals is higher than that of normal (HbAA) individuals and is not different related to crisis or steady state.119 Elevated RDW obtained in this study is similar to that reported by other studies.99,117 The elevated RDW found is due to the presence of erythrocytes with different sizes at different stages of maturation due to increased erythropoiesis.99 The results of this study demonstrate an elevated level of mean WBC that is consistent with earlier studies among patients with SCA in steady state.99,115 This is largely due to the redistribution of white blood cells from the marginated to the circulating pool and to some extent due to accelerated release
63
from the bone marrow due to raised cytokine levels.120,121 This study also reported elevated platelet count similar to reports from previous studies in Kano and Benin City, Nigeria.99,115 An elevated platelet count in SCA may be attributed to the loss of the splenic platelet pool as a consequence of autosplenectomy and erythropoietin derived as a result of anaemia from chronic haemolysis.122 This study reported 7.5 ± 4.3 % (Table 4.2) as the mean HbF level of the individuals with SCA in the steady state. An earlier report by Kotila et al (2000)123 and Lena et al (2012)124 showed similar levels of 7.9% in Nigeria and Uganda respectivel, while some authors reported values much lower than this, that is, 2.17% and 3.60%
respectively.99,125 However, this difference may not be attributed to genetic differences between individuals and tribes since some of the studies were conducted in the same region of the country. Patients with SCA who have increased levels of HbF tend to have a relatively mild clinical disease because HbF does not participate in the sickling process and delays HbS polymerization.3,13 The level at which HbF prevents vaso-occlusive crisis and other complications is still debatable.126 However, studies have shown that any increase in HbF level in an individual with SCA is beneficial as seen with hydroxicabamide treatment.127 In the present study, increased levels of haemolytic markers were observed in the steady state of SCA. The elevated mean LDH of 617.8 U/l reported in this research corroborate values (610.6 U/l and 680.8 U/L) that were reported by the National Institute of Health study (2007) and Cooperative Study of Sickle Cell Disease in USA (1988) respectively.17 Akinola et al (1992)82 reported a slightly higher mean LDH value of 875 U/l in patients in the steady state of SCA. On the other hand, Nduka et al (1995)128 in a study from Eastern Saudi Arabia reported a lower level of 356U/l. The low LDH reported from the Saudi is consistent with low haemolysis associated with the Arab-Indian haplotype due to high levels of HbF.25 The high LDH in SCA is attributed to red cell lysis mainly, thus widely accepted as a surrogate marker of haemolysis in SCD.29,30 Elevated mean AST of 45.9IU/l observed in this study was
64
in line with the 39.63IU/l and 48.5IU/l reported previously in other parts of the country from Zaria and Ibadan respectively.129,130 A recent study of 57 individual with SCD in the steady state from North India also reported an elevated AST of 51.20U/l.131 The elevated AST in this study may be attributed to red cell lysis only since confounding from liver damage has been ruled out by excluding subjects with high ALT levels ≥ 80IU/l. Increased mean total bilirubin, direct bilirubin and indirect bilirubin also found in this present study (24.9µmol/L, 10.5µmol/L, 14.4 µmol/L) were consistent with that reported in the literature.37,41 A similar pattern of raised total bilirubin of 46.6µmol/L , direct bilirubin of 15.6µmol/L and indirect bilirubin of 31.0µmol/L was reported by Shehu et al (2014).132 The elevated bilirubin levels may be attributed to red cell breakdown and microinfarcts in the liver.133 This study is not the first to report reticulocytosis in this group of patients in Kano. A previous study in Kano by Sagir et al (2010)115 also reported elevated levels of both reticulocytes and ISCs similar to that obtained in this study. The findings of reticulocytosis and increased ISCs in the presence of low mean haematocrit and elevated mean serum levels of LDH, AST and bilirubin, suggest an ongoing steady state haemolysis in the study population.
The results of this study showed that the clinical features of individuals with SCA could not be categorized into either of the haemolysis-associated and vaso-occlusion phenotypes using LDH because the clinical presentations of these patients were associated with variable levels of LDH which made it difficult to categorize the patients. Only stroke could be categorized into the haemolysis associated phenotype (p = 0.032) while painful crisis, osteonecrosis, priapism, acute chest syndrome and renal impairment could not be categorized into any particular phenotype (Table 4.4; p = 0.546; 0.362; 0.131; 0.544; and 0.426 respectively) having overlapping LDH values. Attempt to categorize the subjects into three using the LDH quartile levels (lower; the middle quartile- LDH >398.75<772.50 U/l; and upper) could not separate the clinical features. The use of haematological parameters measured could not
65
distinguish between the LDH categories (Table 4.6; p > 0.05). The only biochemical parameters that were able to significantly separate the difference groups was serum bilirubin (total bilirubin, direct bilirubin and indirect bilirubin; p = 0.004; 0.046; and 0.006 respectively). To the best of our knowledge this is the first study in our locality that has tried to classify SCA patients into the different clinical phenotypes using markers of haemolysis so there is paucity of local data to compare with locally. However, a similar study in Jamaica by Alexander et al (2004)18 was able to classify 78% of patients with SCA using the two phenotype model proposed by Ballas et al (1991)20 that believes that environmental and genetic factors are likely to contribute to most manifestations of SCD. The finding of this study showed that the majority (52%) of patients in Kano were in the middle quartile (mixed phenotype) and therefore it may be difficult to categorize them into different clinical phenotypes. The pathological basis of these clinical phenotypes is not fully understood.16,18 However studies suggest the role of NO bioavailability in the propensity to develop the haemolysis-associated phenotype.16,45 Genetic and environmental factors have also been suggested to influence the development of the clinical phenotypes.126 Trauma preceding CLU, air pollution predisposing to acute chest syndrome and parvovirus B19 infection in aplastic crisis are examples of environmental factors that may influence the development of a particular clinical phenotype.126 Genetic abnormalities such as glucose-6-phosphate dehydrogenase deficiency, thalassemias and β-globin haplotype may also alter the clinical presentation of the disease and therefore the clustering into clinical phenotypes.50,126
The finding of higher rate of blood transfusion among the individuals in the upper quartile confirms the presence of more haemolysis in the group, and also support the trend observed in the three quartiles (increasing platelet count and ISC count from lower to upper quartile and decreasing HbF). The increasing platelet count is expected because of the effect of chronic anaemia on thrombopoiesis.122 While the ISC count correlates with haemolysis, HbF
66
reduces haemolysis because of anti-sickling effect.32,125 Therefore the trends observed were in line with what is known in the literature. However, this is not the only study that has reported variability of SCA in Africa. A recent multicentre study of hyperhaemolysis and vascular complications in SCD sub-Saharan African patients found osteonecrosis to be associated with haemolysis-associated phenotype.134 These findings suggest variability of SCA clinical phenotypes in Kano and sub-Saharan Africa in general. Furthermore, the small size of the different clinical features may have affected the clustering of features into the distinct clinical phenotypes.
Interestingly, this study found statistically significant positive correlation between LDH, total bilirubin, direct bilirubin and AST and severity score (Table 4.8; p = 0.032; 0.012; 0.004; and 0.019 respectively). However the mean LDH levels of disease severity groups (mild, moderate and severe) showed no significant difference. This may be due to the significant overlap between disease severity groups. Some studies in Nigeria and beyond have also reported significant relationship between some markers of haemolysis (bilirubin, AST and LDH) and disease severity.49,101 This finding is encouraging because serum bilirubin and AST measurements are readily available and affordable in most State Government owned General Hospitals (secondary health care facilities) where the majority of individuals with SCA are managed in Nigeria. However, the relationship does not merit a surrogate status in this study.
67
CONCLUSION
In conclusion, the clinical phenotype of individuals with SCA in the steady state was mixed, being a combination of both vaso-occlusive and haemolytic phenotypes. Therefore it may be difficult to categorize them into different clinical phenotypes.
Majority of individuals in the study had moderate disease severity with painful crisis, osteonecrosis/hip replacement, CLU, stroke, priapism, ACS and renal impairment as the common clinical presentations.
Stroke was the only clinical presentation that could be categorized with the use of LDH levels, into haemolysis-associated phenotype.
In addition, baseline steady state parameters showed moderate anaemia with elevated red cell distribution width (RDW), white blood cell count, platelet count and elevation of all the markers of haemolysis measured.
Markers of haemolysis (LDH, AST and serum bilirubin) were found to correlate significantly with SCA disease severity score, but not strongly enough to be useful in predicting disease severity.
The data obtained may contribute to existing knowledge in diagnosis, clinical profiling and
management of patients with SCA in Africa.
68
LIMITATIONS OF THE STUDY
1. Cell-free haemoglobin, haptoglobin and other markers of haemolysis such as arginase were not measured because of technical and financial constraints.
2. Patients were not screened for pulmonary hypertension and this may have under estimated the true prevalence in Kano.
3. Disease modifiers of sickle cell anaemia such as α-thalassaemia and other genetic associations could not be included because of financial limitations and logistic problems.
4. Relatively small frequency of the various clinical features may have affected the clustering and evaluation of the clinical phenotypes.
69
RECOMMENDATION
1. Lactate dehydrogenase levels may be useful in monitoring children who are at risk of developing stroke so that preventive measures can be instituted.
2. There is need for more studies with larger sample size to determine the role of haemolytic markers in predicting disease severity among patients with sickle cell anaemia.
3. More studies are needed to evaluate the role of genetic and environmental factors in determining the clinical phenotypes of sickle cell anaemia.
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