STUDY OF HEMOGLOBIN AND CALCIUM PHOSPHORUS PRODUCT IN PATIENTS WITH CHRONIC KIDNEY DISEASE

Introduction: Kidneys play a vital role in the metabolism of minerals such as calcium and phosphorous. Moreover, kidney is involved in the production of erythropoietin hormone. The bone marrow suppression may occur in Chronic Kidney Disease (CKD) patients. Reduced hemoglobin and increased calcium phosphorous product concentration is also common in CKD patients.The current study is aimed to find out the impact of CKD in calcium phosphorous product and hemoglobin level in Nepalese population. Methods: One hundred consecutive diagnosed cases of CKDpatients were enrolled retrospectively for the study. Calcium, phosphorous, urea, creatinine and other biochemical parameters were measured in fully automated biochemistry analyzer and hemoglobin was measured using hematology analyzer (Beckman Coulter DxH500 Automated Hematology analyzer). Results: The current study revealed the hemoglobin and calcium phosphorous product in CKD patients.The Calcium Phosphorous Product (CaP) of 69 subjects were having less than <40mg2/dL2 and remaining 31 were having ≥ 40mg2/dL2. The negative correlation of calcium phosphorous product was seen with calcium (r= -0.478, p-value = 0.000) and sodium (r=-0.309, p-value=0.002) whereas positive correlation of calcium phosphorous product was seen with urea (r= 0.559, p-value=0.000) andCreatinine (r=0.353, p-value = 0.000). The creatinine was negatively correlated with the hemoglobin concentration (r= -0.320, p-value = 0.001). Conclusions: Calcium phosphate product can be fluctuated in chronic kidney disease patients along with the decrement of hemoglobin concentration. The serum calcium phosphorous product measurement can assist to rule out the severity of chronic kidney disease.


INTRODUCTION
Calcium and phosphorous are two essential minerals involved in various biochemical processes in human body. Calcium plays role in muscle contraction, blood coagulation pathway, role as a second messenger for hormonal action etc. 1,2 Secondly, phosphorous also plays vital role in plethora of cellular processes such as growth and maintenance, repair of tissues and formation of different phosphorylated intermediates like 2,3 bisphosphoglycerate. 3 The morbidity and mortality of the Chronic Kidney Disease (CKD) patients is high when the serum level of calcium phosphorous product is elevated. It may occur via several mechanisms including hypercalcemia related kidney injury andacute phosphate nephropathy. 4 Reduction of hemoglobin is common in CKD patients and sometimes it can be correlated to their cardiovascular outcomes. Anemia in CKD may be worsened due to various etiologies including the kidney dysfunction 5 , impaired erythropoietin production or resistance, bone marrow suppression from increased levels of proinflammatory cytokines and vitamin deficiencies. 6,7 CKD is one of the major public health problems and is rising day by day. It is also associated with the cardiovascular diseases. 8 Mineral metabolism is one of the important predictors of morbidity and mortality in CKD patients. The calcium and phosphorous metabolism is positively associated with worse outcome, not only in CKD patients but also in End Stage Renal Disease (ESRD) patients.Calcium phosphorous product derangement can be considered as the marker of renal osteodystrophy. 9 The aim of this study was to find out the impact of calcium phosphorous product and hemoglobin levels in chronic kidney disease patients.Furthermore, the correlations of hemoglobin and calcium phosphorous product with other renal function test parameters were also found out.

Date of Submission
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MATERIALS AND METHODS
This study wasa retrospective study from the data retrieved from the laboratory software at National Medical College and Teaching Hospital (NMCTH), Birgunj, Madhesh Pradesh of Nepal. Study duration wassix months (June2021 to November2021).Ethical clearance was obtained from the Institutional Review Committee (IRC) before starting the research (Ref.F-NMC/533/077-078).
Non probability convenient sampling technique was used to enroll the data of CKD patients. Hundred consecutive CKD patients were enrolled for the study. The parameters urea, creatinine, phosphorous and calcium were measured using fully automated biochemistry analyzer (Beckmann Coulter Inc. AU480, California). Sodium and potassium were measured using electrolyte analyzer. The hemoglobin was measured in the five-part differential analyzer (Beckman Coulter DxH500 Automated Hematology analyzer, California).

Statistical Analyses
All the data were entered in the Microsoft Excel 2010, converted to SPSS version 22 accordingly. Frequency and percentage were calculated for descriptive statistics. Chi square test were applied to compare the categorical variables. Student's t test was used to compare mean between two groups. Continuous data were expressed in the meanSD. Pearson correlation was applied for parametric data and Spearman's correlation was applied for non-parametric data. P value <0.05 was considered as statistically significant.RESULTS Our study investigated hemoglobin and calcium phosphorous product concentrations in one hundred consecutive CKD patients, out of which59 were male and 41 were female. The variables were expressed as mean and standard deviation as depicted in Table 1.There was significant difference of mean and standard deviation of uric acid between male and female. The patients were then categorized on the basis of calcium phosphorous product (CaP). The CaP level is categorized into two groups, <40mg 2 /dL 2 and ≥ 40mg 2 / dL 2 . Out of hundred study subjects, 69 were having less than <40mg 2 /dL 2 and remaining 31 were having ≥ 40mg 2 / dL 2 . There was statistically significant difference in mean and standard deviation of calcium (P value: 0.01) and potassium(P value: 0.009)with gender as depicted in Table 2. The hemoglobin level of the patients was then categorized into two groups, <10 g/dL and ≥10 g/dL. There was no any statistically significant difference of variables with the hemoglobin concentration. The mean and standard deviation between two categories of hemoglobin is illustrated in Table 3.  Table 4 depicts the association between the calcium phosphorous products with the hemoglobin concentration. No any statistical significant association was observed between the CaP level and the hemoglobin level.  Table 5 depicts the correlation of the study variables with the hemoglobin and the CaP levels. The negative correlation of hemoglobin was seen with age, urea and creatinine whereas positive correlation of hemoglobin was seen with sodium. The negative correlation of calcium phosphorous product was seen with calcium and sodium whereas positive correlation of calcium phosphorous product was seen with urea, creatinine, potassium and phosphorous.

DISCUSSION
The current study investigated the hemoglobin and calcium phosphate products in the chronic kidney disease patients. Our study revealed the reduced hemoglobin concentrations, mean hemoglobin concentration (male, 9.23 g/dL & in female, 9.48g/dL) in CKD populations.Androne AS et al., reported reduced hemoglobin and chronic kidney disease are common related factors. Anemia in chronic kidney disease caused by cardiovascular disease can be pseudoanemia due to hemodilution. 11 Anemia can be worsened by the kidney dysfunction 12 , impaired erythropoietin production or resistance, cytokine induced bone marrow suppression, due to increased levels of proinflammatory cytokines, 6,7 iron or vitamin deficiencies, 13 reduced levels of hemoglobin regardless of etiology is associated with the lower exercise tolerance. 14 In the present study, there is no significant association between hemoglobin and calcium phosphate product (mg 2 /dL 2 ) in CKD patients.In a study by Thongprayoon C et al., in Mississippi, United States of America, revealed that elevated Ca×P levels are independently associated with an increased risk for hospital mortality. Admission Ca×P ≥ 45mg2/dL2 is associated with the highest risk in the both CKD and non-CKD patients.They also revealed that the elevated CaP levels (≥ 45mg 2 /dL 2 ) are also associated with higher in hospital mortality in both CKD as well as non CKD patients. 15 Singh S et al.,reported CaP product less than 55 mg 2 /dL 2 in 76 patients out of 101 dialysis patients from their retrospective study at Kathmandu Nepal. 18 However, we revealed 31 patients were having more than 40mg 2 /dL 2 and 69 patients were having less than 40 mg 2 /dL 2 , when CaP was compared.
In our study significant correlation of urea, creatinine, sodium and potassium was found with the calcium phosphorous product. Serum urea and creatinine levels are raised in kidney diseases along with increment of serum phosphorous levels. Some studies reported a consequence of diminished phosphate filtration and excretion with the progression of CKD. Excess parathormone is released to excrete the phosphate during initial stages of CKD. 16 Among kidney transplant recipients the elevated CaP levels are associated with an increase in the allograft loss. 17 The limitation of our study was small sample size, no follow up of the patients and the drug history of the patients were not studied. Our study didn't measure the serum level of parathyroid hormone and staging of the chronic kidney disease patients.

CONCLUSION
We can conclude that calcium phosphate product can be fluctuated inchronic kidney disease patients along with the decrement of hemoglobin concentration. Our study recommends estimatingserum calcium phosphorous product and hemoglobin measurement in chronic kidney disease patients. The serum calcium phosphorous product measurement can assist to rule out the severity of chronic kidney disease.