CONCLUSION
BIBLIOGRAPHY
Figures 2, 3, 4 and 5 show the relationship between USACR and plasma urea and creatinine, ACR and SSA in SCA patients. There was a positive correlation between USACR and plasma urea ( r= 0.27, p=0.03, Fig 2) and creatinine (r=
0.13, p=0.31; Fig 3) as well as ACR (r= 0.43, p< 0.001; Fig 4) and SSA (r= 0.37, p< 0.001; Fig 5).
49
TABLE 1: Age, WHR and Blood pressure measurements in controls (non sickle cell anaemia patients) and sickle cell anaemia patients.
SCA patients (n=68) Mean (S.D)
Control (non SCA)
(n=30)
Mean (S.D) P-value Sex
Male
Female 26
42 15
15
Age (years) 28.35 (3.46) 33.12 (6.24) 0.04 BMI (kg/m2) 20.85 (3.13) 24.63 (3.73) <0.001
WHR 0.89 (0.08) 0.86 (0.05) 0.04
dBP (mmHg) 72.35 (0.08) 75.00 (4.98) 0.19 sBP (mmHg) 111.62 (8.25) 116.00 (8.54) 0.04
Key:
BMI – Body Mass Index WHR – Waist Hip Ratio
sBP – Systolic Blood Pressure dBP - Diastolic Blood Pressure BMI and systolic blood pressure were found to be significantly (p<0.05) lower in control subjects than in SCA patients while WHR was significantly(p<0.05) higher in the SCA patients than in control subjects.
50
TABLE 2: Clinical characteristics in Control and SCA patients in steady state Control (non SCA
patients) (n = 30)
SCA patients steady state
(n = 34) p-value
Sex M/F 15/15 12/22
Age (Years) 33.12 (6.24) 27.04 (4.78) <0.001 BMI (kg/m2) 24.63 (3.73) 20.35 (2.45) <0.001 sBP (mmHg) 116.00 (8.54) 120.35 (10.85) 0.08
dBP (mmHg) 75.00 (8.98) 81.47 (10.50) 0.01 PCV (%) 40.65 (3.40) 24.71 (4.67) <0.001
WHR 0.86 (0.05) 0.89 (0.06) 0.04
Key:
BMI – Body Mass Index WHR – Waist Hip Ratio
sBP – Systolic Blood Pressure dBP - Diastolic Blood Pressure PCV – Packed Cell Volume
The body mass index, and packed cell volume were significantly (p<0.05) lower in SCA patients in steady state while the diastolic blood pressure, and waist hip ratio was significantly higher in SCA patients in steady state
compared to controls.
51
TABLE 3: Clinical characteristics of SCA patients with and without micro- albuminuria
SCA patients with microalbuminuria
(n = 47)
SCA patients without microalbuminuria
(n = 21) p-value
Sex M/F 18/29 8/13
Age (years) 28.77 (9.46) 27.74 (8.71) 0.67
BMI (kg/m2) 20.76 (3.31) 21.04 (2.67) 0.71
sBP (mmHg) 120.64 (13.44) 110.81 (21.55) 0.04
dBP (mmHg) 82.34 (8.43) 73.38 (12.20) 0.04
PCV (%) 20.17 (4.27) 23.48 (4.32) 0.01
WHR 0.89 (0.09) 0.90 (0.06) 0.48
Key:
BMI – Body Mass Index WHR – Waist Hip Ratio
sBP – Systolic Blood Pressure dBP - Diastolic Blood Pressure PCV – Packed Cell Volume
Systolic and diastolic blood pressure were significantly (p<0.05) lower while packed cell volume was significantly (p<0.05) lower in SCA patients with microalbuminuria than in those without microalbuminuria.
52
TABLE 4: Biochemical characteristics in control (non SCA patients) and SCA patients in steady state.
control
(non SCA patients) n = 30
SCA patients steady state
n = 34
p-value Plasma urea
(mmol/L) 3.33 (0.88) 4.84 (2.62) 0.004
Plasma creatinine (µmol/L)
73.98 (16.16) 70.61 (31.49) 0.60
Urinary albumin
(mg/dl) 254.48 (72.14) 307.07 (59.07) 0.002 ACR (mg/mmol) 2.19 (0.55) 4.29 (1.81) <0.001
SSA (mmol/L) 1.93 (3.67) 1.55 (0.17) 0.04
USA (mmol/L) 0.78 (0.22) 0.98 (0.35) 0.01
USACR
(mmol/mol) 60.52 (18.57) 111.47 (31.11) <0.001 Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid
USA - Urinary Sialic Acid
USACR – Urinary Sialic Acid Creatinine Ratio
Plasma urea, ACR, and USACR were significantly higher (p<0.05) while SSA is significantly lower (p>0.05) in SCA patients in steady state than in the control.
However, no significant (p>0.05) change occurred with plasma creatinine.
53
TABLE5: Biochemical parameters of SCA patients in Steady State with microalbuminuria (n=21) and SCA patients in steady state without microalbuminuria (n=13)
Steady State SCA Patients With
microalbuminuria Mean (SD)
n=21
Without microalbuminuria
Mean (SD) n=13
p-value
Plasma Urea
(mmol/L) 8.59 (5.47) 5.29 (3.20) 0.03
Plasma Creatinine
(µmol/L 131.94 (45.00) 74.42 (38.85) 0.02
ACR (mg/mmol) 5.35 (1.49) 2.71 (0.43) <0.001
SSA (mmol/L) 2.31 (0.36) 1.54 (0.20) <0.001
USA (mmol/L) 1.41 (0.42) 0.91 (0.37) 0.001
Urinary Albumin
(mg/dl) 313.58 (57.27) 296.55 (62.78) 0.42
USACR (mmol/mol) 130.45 (29.81) 121.41 (42.72) 0.51 Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid USACR – Urine Sialic Acid Creatinine Ratio USA- Urinary Sialic Acid The mean plasma urea and creatinine, ACR and SSA were significantly (p<0.05) higher in SCA patients in steady state with microalbuminuria than in those without microalbuminuria.
54
TABLE 6: Plasma urea and creatinine, ACR, SSA and USACR in control (non SCA) and SCA patients
Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid USACR – Urine Sialic Acid Creatinine Ratio USA- Urinary Sialic Acid The mean serum sialic acid was significantly (p<0.05) lower while albumin creatinine ratio, plasma urea and urine sialic acid creatinine ratio were significantly (p<0.05) higher in the SCA patients than in the control group.
Control (non-SCA anaemiapatients)
(n=30)
SCA patients
(n=68) p-value
Plasma Urea
(mmol/L) 3.33 (0.88) 6.43 (4.45) <0.001
Plasma creatinine
(µmol/L 73.98 (16.16) 86.70 (49.73) 0.06
SSA (mmol/L) 1.93 (3.67) 1.88 (7.92) 0.82
Urinary Albumin
(mg/dl) 254.48 (72.14) 249.89 (70.67) 0.01
ACR (mg/mmol) 2.19 (0.55) 4.50 (1.98) <0.001
USA (mmol/L) 0.78 (0.22) 1.13 (0.41) <0.001
USACR (mmol/mol) 60.52 (18.57) 169.39 (42.07) <0.001
55
TABLE 7: Biochemical characteristics of SCA patients with and without microalbuminuria
SCA patients with microalbuminuria (ACR≥3.5 mg/mmol,
n = 47)
SCA patients without microalbuminuria
(ACR < 3.5
mg/mmol, n = 21) p-value Plasma Urea
(mmol/L) 6.70 (4.73) 5.82 (3.16) 0.43
Plasma creatinine (µmol/L)
85.15 (22.21) 90.16 (28.11) 0.75
SSA (mmol/L) 1.89 (0.48) 1.86 (0.46) 0.81
USA (mmol/L) 1.09 (0.41) 1.21 (0.41) 0.04
USACR
(mmol/mol) 197.06 (54.02) 108.77 (36.11) <0.001 Key:
SSA - Serum Sialic Acid USA - Urinary Sialic Acid
USACR – Urine Sialic Acid Creatinine Ratio
Urine sialic acid creatinine ratio is significantly (p<0.05) higher in SCA patients with microalbuminuria than in those without microalbuminuria.
56
Figure 1: Serum sialic acid concentration in Sickle cell anaemia patients and controls
KEY
A – Control (n=30) B – SCA patients (n=68)
C – SCA patients with renal insufficiency (n=47) D – SCA patients without renal insufficiency (n=21)
The SCA patients with and without renal insufficiency had lower levels of serum sialic acid than in the controls.
1.93
1.88 1.89
1.86
1.78 1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94 1.96
A B C D
MEAN SERUM SIALIC ACID LEVEL (mmol/L)
GROUP
57
TABLE 8: Correlation between USACR and some biochemical parameters in SCA patients in steady state (n=34)
Biochemical Parameters r - value p- value
Plasma urea (mmol/L) 0.28 0.11
Plasma creatinine
(µmol/L) 0.22 0.22
ACR (mg/mmol) 0.62 <0.001
SSA (mmol/L) 0.01 0.97
PCV (%) -0.45 0.01
Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid
PCV – Packed Cell Volume
USACR – Urine Sialic Acid Creatinine Ratio
There was a positive significant (p<0.05) correlation between urinary sialic acid creatinine ratio and ACR of SCA patients in steady state
58
TABLE 9: Correlation between USACR and some biochemical parameters in SCA patients in steady state with microalbuminuria (n=21)
Biochemical Parameters r - value p- value
Plasma urea (mmol/L) 0.247 0.28
Plasma creatinine
(µmol/L) 0.163 0.48
ACR (mg/mmol) 0.665 0.001
SSA (mmol/L) 0.281 0.22
PCV (%) -0.561 0.01
Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid
PCV – Packed Cell Volume
USACR – Urinary Sialic Acid Creatinine Ratio
There was a positive significant correlation between USACR and ACR (p<0.05) while a negative significant correlation existed between USACR and PCV of SCA patients in steady state with microalbuminuria.
59
TABLE 10 : Correlation between USACR and some biochemical parameters in SCA patients in steady state without microalbuminuria (n=13)
Biochemical Parameters r - value p- value
Plasma urea (mmol/L) 0.193 0.53
Plasma creatinine
(µmol/L) 0.361 0.23
ACR (mg/mmol) 0.530 0.06
SSA (mmol/L) -0.487 0.09
PCV (%) -0.552 0.05
Key:
ACR - Albumin Creatinine Ratio SSA - Serum Sialic Acid
PCV – Packed Cell Volume
USACR – Urinary Sialic Acid Creatinine Ratio
There was a positive non-significant correlation (p>0.05) between USACR and ACR of patients in steady state without microalbuminuria.
60
TABLE 11: Mean fractional excretion of sialic acid in SCA patients and controls
Mean fractional excretion of sialic acid in the
various study groups (%) P – value
Study ( n = 68)
0.783 ± 0.635 Subjects (n =30)
0.289 ± 0.208 < 0.001
ACR ≥ 3.5 ( n= 47)
0.670 ± 0.501 ACR < 3.5 (n= 21)
1.037 ± 0.825 0.07
61
Figure 2: Relationship between urinary sialic acid creatinine ratio and plasma urea in sickle cell anaemia patients (n=68)
A positive correlation existed between urinary sialic acid creatinine ratio and plasma urea in SCA patients
y = 0.011x + 4.595 R² = 0.073
r = 0.27
0 5 10 15 20 25
0 100 200 300 400 500 600 700
PLASMA UREA (mmol/L)
URINARY SIALIC ACID CREATININE RATIO (mmol/mol)
62
Figure 3: Relationship between urinary sialic acid creatinine ratio and plasma creatinine in sickle cell anaemia patients (n=68)
A positive correlation existed between urinary sialic acid creatinine ratio and plasma creatinine in SCA patients.
y = 0.057x + 77.23 R² = 0.016
r = 0.13
0 50 100 150 200 250 300 350
0 100 200 300 400 500 600 700
PLASMA CREATININE (μmol/L)
URINARY SIALIC ACID CREATININE RATIO (mmol/mol)
63
Figure 4: Relationship between urinary sialic acid creatinine ratio and albumin creatinine ratio in sickle cell anaemia patients (n=68)
There was a positive correlation between urinary sialic acid creatinine ratio and ACR in SCA patients.
y = 0.007x + 3.204 R² = 0.187
r = 0.43
0 2 4 6 8 10 12
0 100 200 300 400 500 600 700
ALBUMIN CREATININE RATIO (mg/mmol)
URINARY SIALIC ACID AND CREATININE RATIO (mmol/mol)
64
Figure 5: Relationship between urinary sialic acid creatinine ratio and sialic acid in sickle cell anaemia patients (n=68)
There was a positive correlation between urinary sialic acid creatinine ratio and serum sialic acid in SCA patients.
y = 0.001x + 1.632 R² = 0.138
r = 0.37
0 0.5 1 1.5 2 2.5 3 3.5
0 100 200 300 400 500 600 700
SERUM SIALIC ACID (mmol/L)
URINARY SIALIC ACID CREATININE RATIO (mmol/mol)
65
CHAPTER SIX
6.1 DISCUSSION
This study showed serum sialic acid in the SCA patients to be lower than the controls. This is supported by Ekeke and Ibeh who studied sialic acid in sickle cell disease in Portharcourt, Nigeria and concluded that the loss of sialic acid in erythrocyte membrane is reflected in a removal of sialic acid from the circulation.79
This study also showed a non significant increase in serum sialic acid in patients with micro albuminuria than in those without microalbuminuria.
According to Yokoyama et. al., raised serum sialic acid concentration preceeds onset of microalbuminuria, therefore sialic acid a marker of acute phase response may be an early signal of increased risk of vasculopathy.81
The normal plasma urea and creatinine in the SCA patients as also observed in previous studies implies that using plasma urea and creatinine as a marker of renal impairment is unreliable in SCA patients.106, 107.
The significantly higher plasma urea and creatinine, SSA and urinary sialic acid excretion in crisis than in steady state could be due to the presence of ongoing inflammation, haemolysis and acute phase response resulting in a decreased glomerular filtration rate during crisis.
66
The finding of a significantly higher mean serum sialic acid in female than male SCA patients also agrees with previous findings of Crook et. al., in London, Uk who studied sialic acid and diabetic nephropathy in type I DM. The reason for this sex difference is not clear.26
This study shows an increase in SSA with age in SCA patients. This agrees with earlier reports of Ekeke and Ibeh in Portharcout, Nigeria. who found progressive increase in serum sialic acid with age leveling out from age 15years, though their study group was in the age range of 2 – 28 years.79
The finding that urinary sialic acid excretion was higher in SCA patients than in the controls reflects the removal of sialic acid from the circulation. However there was no significant sex variation in both the controls and sickle cell anaemia patients.
The meansystolic and diastolic blood pressure in albuminuric SCA patients is significantly higher than in the non-albuminuric patients which is consistent with increased cardiovascular risk of proteinuria. This agrees with the report by Bolarinwa et al who studied renal disease in adult Nigerians with sickle cell anaemia.106
In steady state, SSA correlated negatively with plasma creatinine, and microalbuminuria indicating that the lower the SSA level, the higher the
67
plasma creatinine, and ACR in SCA patients. It was also observed that there was a negative correlation between SSA and plasma urea in the steady state.
This could be due to the presence of ongoinginflammation, haemolysis and a reduced glomerular filtration.
The association between urinary sialic acid excretion and microalbuminuria in steady states indicates that urinary sialic acid excretion increases with microalbuminuria in SCA patients. This implies that assessment of urinary sialic acid excretion can also be used as an adjuvant test of renal insufficiency in SCA patients.Also, the finding of a higher urinary sialic acid excretion in SCA patients with microalbuminuria than in those with normoalbuminuria could be due to the fact that sialic acid is filtered by renal glomeruli but not absorbed by human kidney epithelial cells as reported by previous studies.108 The finding that high plasma urea and creatinine levels were associated with increased urinary sialic acid excretion show that the presence of increased urinary sialic acid excretion is associated with progression of renal dysfunction in SCA patients. This also suggests that increased urinary sialic acid excretion can be used to assess the degree of glomerular damage and can be used as a diagnostic tool.
68
Urinary creatinine is widely used to relate urine constituents to the glomerular filtrate especially in spot urine due to the increase in creatinine excretion during life. Previous study show that free sialic acid clearance varies directly with creatinine clearance.106
Fractional excretion of sodium (FeNa) is a well known urinary index used for assessment of acute kidney injury(AKI) in distinguishing functional (prerenal) and structural AKI.109 The physiological rationale for this was that low FeNa (Classically <1%) indicates preserved tubular function.110Recent study also shows that increase in the fractional excretion of potassium may (FeK) may be a sign of a decrease in glomerular filteration rate even before a rise in serum creatinine.110
This study shows an increase in mean fractional excretion of sialic acid in SCA patients. This may also be a sign of a decrease in glomerular filtration rate and a progressive loss of tubular function.
This study found that urinary sialic acid excretion is increased with age in SCA patients. However previous studies have indicated a decrease in urinary sialic acid excretion with increasing age in spot urine as well as 24hour urine in healthy children and adults.111 This increase in urinary sialic acid with age may be associated with age related nephropathy present in patients with SCA.