Value of Calcium and Phosphorous in chronic kidney disease patients under hemodialysis: A retrospective study

Correspondence: Mr. Samir Singh, Lecturer Department of Biochemistry, KIST Medical College, Lalitpur, Nepal E-mail: samirbiochem_13@yahoo.co.in Background: Derangements of mineral metabolism occur during early stages of chronic kidney disease (CKD). Mineral metabolism has emerged as important predictors of morbidity and mortality in dialysis patients. This study aims to evaluate the values of calcium and phosphorous in reference to practice guidelines issued by National Kidney Foundation Dialysis Outcomes Quality Initiative (K/DOQI) in patients undergoing hemodialysis in KIST Medical College Teaching Hospital.

combined with hypocalcaemia, both of which are due to decreased excretion of phosphate by the damaged kidney.Healthy kidneys convert inactive vitamin D to its active metabolite, 1,25 dihydroxycholecalciferol.If renal functioning is affected, the production of 1,25 dihydroxycholecalciferol reduces that leads to hypocalcaemia because less calcium is absorbed from the intestine.In addition, the renal clearance of phosphorus decreases with a deteriorating kidney function and phosphorus concentrations increase.Hypocalcaemia in its turn leads to an increased production of parathyroid hormone (PTH) by the parathyroid glands, which is called secondary hyperparathyroidism. 4 There is no documented data related to mineral metabolism outcomes in Hemodialysis (HD) patients in Nepal.Several expert panels have issued management guidelines for the management of altered mineral metabolism in dialysis patients.Among them, the guidelines published in 2003 by K/DOQI, recommended the serum levels of phosphorus between 3.5-5.5 mg/dl; serum calcium 8.4-9.5 mg/dl and calcium-phosphorus product, < 55 mg 2 /dl 2 , and serum PTH, between 150-300pg/ml. 5This study aims to evaluate the values of calcium and phosphorous in reference to practice guidelines recommended by K/DOQI in patients undergoing HD in KIST Medical College Teaching Hospital (KISTMCTH), Nepal.

MATERIALS AND METHODS
We retrospectively evaluated the laboratory parameters of serum calcium, and phosphorus from 101 (62 male and 39 female) patients who underwent HD at KISTMCTH over three months period from October 2010 to December 2010.The calcium and phosphorous evaluation was done by using Biochemical semi-analyzer (STATFAX 3000).The values of serum calcium, phosphorus and calcium-phosphorus product were compared with K/DOQI guidelines. 5

RESULTS
Out of 101 patients, 62 were male and 39 were female.Age ranged from 20 to 80 years.Average age of the study population was 48.36±17.94years.Seventy two percent of the patients were between the ages of 20-60 years.The mean duration of HD session was 3.95 ± 0.42 hours.The mean number of HD session per week was 2.08 ± 0.46 days.Patients were given phosphate binders (calcium carbonate and/or calcium acetate and/or lanthanum carbonate) depending upon their status of serum calcium level, phosphorous level and clinical condition.
Serum value of calcium and phosphorus is presented in Table 1.Table 2 depicts the comparison of laboratory tests results in patients on HD with K/DOQI target ranges for mineral metabolism.Twenty one percent of the patients met the three considered guidelines successfully and 14 % did not meet any of the recommended guidelines as shown in Table 3.

DISCUSSION
Abnormal mineral metabolism start early in course of CKD and ESRD, and is usually accompanied by profound changes in mineral metabolism that leads to clinical problems such as bone diseases, musculoskeletal symptoms and growth retardation.Recent study has found a strong association between mortality and abnormal mineral metabolism; presumably mediated by vascular calcification. 6The disturbances include calcium, phosphate, vitamin D, and PTH homeostasis.So, mineral metabolism outcomes are gaining importance in HD treatment.Hyperphosphatemia is one of the major factors responsible for alterations in mineral and bone metabolism in dialysis patients. 7In our study, the control of serum phosphorus values was adequate in 53% of patients undergoing HD, while 42% of the patients presented with hyperphosphatemia.These findings are   9 The consequences of hyperphosphatemia include the development and progression of secondary hyperparathyroidism and a predisposition to metastatic calcification when the product of serum calcium and phosphorus is elevated.Both of these conditions may contribute to the substantial morbidity and mortality seen in patients with ESRD. 6In our study, 29% were hypocalcemic (< 8.4) and the K/DOQI guidelines for calcium was achieved in 40 % of the patients.However 32% patients had their calcium level above K/DOQI guidelines.
Similarly the product of serum calcium and phosphorus was elevated in 24 %.
A study by Schwartz et al showed an association between higher levels of serum phosphorus and calcium-phosphorus product with an unfavorable renal outcome. 10In their study higher serum phosphorus was associated with significantly higher risk for progression of CKD, even after adjustment for multiple potential confounders.The association of higher serum phosphorus with progressive CKD was more accentuated in patients with higher serum calcium levels also supports the hypothesis that tissue calcification may be the reason behind the observed associations.2][13] Reynolds et al showed that higher ambient serum calcium level led to more significant phosphorus-driven calcification of vascular smooth muscle in vitro. 14 this study, most of patients were in age group between 20-60 years of age.In developed world, mean age of CKD-5 leading to ESRD is between 60-63 years.In our study, average age of presentation was around 48 years which is similar to median age of 43 years in India. 15 this study, only 21 % of the patients met the three considered guidelines of mineral metabolism outcomes after dialysis successfully and 14 % did not meet any of the recommended guidelines.This is similar to other studies. 9,16gular dialysis treatment is unble to remove all the phosphorous ingested with a diet containing sufficient amount of protein to avoid malnutrition.In this regards, our patients were taking phosphate binders such as calcium carbonate, calcium acetate and lanthanum carbonate to decrease dietary phosphorous depending upon their serum calcium and phosphorus levels.The treatment with these calcium-based phosphate binders is not free from complications such as hypercalcaemia.The noncalcium phosphate binder such as lanthanum carbonate is an effective and well tolerated agent for the treatment of hyperphosphatemia in patients with ESRD.[19][20] Craver et al argue and emphasize on the fact that data from CKD patients from one population may not apply to other population due to differences in social, ethnic and health system characteristics as well as nutritional habits. 21

CONCLUSION
To achieve all the K/DOQI guidelines, multi-disciplinary team approach is crucial.We emphasize on the need of large scale multi-centre study of mineral metabolism of CKD patients in Nepal.This will be helpful in establishing our own local guidelines in future.