Patterns and prevalence of hyperpara thyroidism and mineral bone disease in patients with chronic kidney disease at the Kenyatta National Hospital

Abstract

Background Disorders of mineral metabolism, secondary hyperparathyroidism (SHPT), hyperphosphatemia, hypercalcemia, and deficiencies of vitamin D are common complications of chronic kidney disease (CKD). While their contributions to the development of renal osteodystrophy are well known, recent evidence has linked these factors to cardiovascular disease, including non-atherosclerotic vascular calcification, excessive activation of the renin-angiotensin system, hypertension, left ventricular hypertrophy, and death. The obvious task ahead for health authorities in the developing world is to identify patients at risk and evaluate for SHPT because early intervention may slower arrest the progression of both bone and cardiovascular disease. Objective of the study To determine and describe the patterns, prevalence of hyperparathyroidism and biochemical evidence of mineral bone disease in pre-dialysis patients with chronic kidney disease at the Kenyatta National Hospital. Methodology A cross-sectional survey was carried out in 214 patients with chronic kidney disease (CKD) consecutively recruited from the renal (nephrology) clinic, at the Kenyatta National Hospital, over a period of 3 months. Patients with CKD had their demographics, socio-economic and clinical history documented using an administered-interviewer questionnaire. Patients had their glomerular filtration rate (eGFR) estimated using Cockroft and Gault equation and staged as per the kidney disease outcome quality initiative (KJDOQI) criteria. CKD patients in stages 1 to 5, upon recruitment, had a study questionnaire administered to determine the possible aetiology of kidney disease, presence or absence of diabetesmellitus (DM), method of management of chronic kidney disease and any clinical characteristics of bone disease. A structured physical examination was then carried out. Atenrollment 6ml of blood was drawn and the measurements of serum, blood nitrogen urea, creatinine, albumin, calcium, potassium, phosphorus, alkaline phosphatase, levels were determined using automated clinical chemistry analyzer. Serum intact parathyroid hormone (iPTH) assays were performed using electro-chemiluminescence Immunoassay (ECLIA) on the fully automated immunoanalyzer Cobas Integra 400 Plus(Roche )Elecys. Outcome Measures Outcome measures were serum intact PTH levels, the KDOQI stages of CKD andbiochemical features of bone turn-over. Data management and Analysis. All data was collected on a study proforma, and was entered into a computer data base using Microsoft Access computer software and statistical analysis was done using statistical package for social scientists (SPSS) version 15 after cleaning and verification. Values were expressed as means, medians and standard deviations (SD). Point prevalence of hyperparathyroidism was determined as a percentage of the number of patients with serum iPTH above the upper limit of normal, attending the renal clinic in CKD stages 1 and 5, to the total study population. Associations between the patients' socio-demographic data, presence of Diabetes Mellitus(DM), stage of chronic kidney disease and serum iPTH level were examined using chi-square test. Differences in mean values in patients with or without DM were analyzed by Student's t-test, if normally distributed, or Mann -Whitney U test for skewed data, to determine statistical significance. Associations were considered significant only when p value was equal or less than 0.05. Analysed data was presented in the form of tables, pie-charts and graphs Results A total of 214 patients with chronic kidney disease, who were not yet on dialysis, attending the renal clinic at the Kenyatta National Hospital over a period of 3 months were studied. The study population was categorized into 5 groups as per KlDOQI staging of chronic kidney disease. CKD stage 1 had 7 participants, stages 2, 3,4 and 5 had 21, 70,42 and 74 participants respectively. The mean eGFR was 3l.342 ±24.66 ml/min/l.73m2. This prevalence, of hyperparathyroidism, was seen to increase as renal function, eGFR, declined. The mean PTH level was 52.02 ±99.02 pgl ml. There was significantly more low turn-over mineral bone disease observed in 78.4% (n= 109 out of 139) compared to high turn-over mineral bone disease observed in only 2l.6%(n=30 out of 139) patients. Women were observed to have higher iPTH levels and more high turn-over bone disease was observed. This study, did not observe a significant correlation between the presence of, diabetes mellitus, frequency of complaints of bone pain, or muscle weakness with hyperparathyroidism. There was a significant positive association between phosphorus and higher levelsof serum iPTH but no significant association was found between calcium andalkaline phosphotase. Conclusion This study demonstrated that hyperparathyroidism develops and progressively worsens as glomerular function declines. However, the overall prevalence of hyperparathyroidism in CKD patients attending renal clinic at the Kenyatta National hospital was observed to be lower than it is worldwide. This study showed a trend towards more women registering higher iPTH levels than the males. Biochemical high turn-over mineral bone disease was observed more in women, with CKD, than the men. In comparison to statistics from western countries, there seems to be more biochemical low turn-over mineral bone disease in our patients as opposed to more high turn-over mineral bone disease in the western populations.