Elevated bone aluminum and suppressed parathyroid hormone levels in hypercalcemic dialysis patients

Chronic Kidney Disease in Cats and the Risk of Total Hypercalcemia

Background

Chronic kidney disease (CKD) is a common comorbidity in cats with hypercalcemia, but whether CKD is a risk factor for hypercalcemia is unclear. Hypercalcemia often is diagnosed based on total calcium concentration (tCa), which tends to underestimate the ionized calcium concentration (iCa) in cats.

Objectives

Assessment of the performance of tCa for the diagnosis of ionized hypercalcemia, and exploration of factors influencing the relationship between iCa and tCa. Determination of risk factors for incident total hypercalcemia (ie, the development of hypercalcemia based on tCa during follow‐up).

Animals

Records of a cross‐section (n = 477) and observational cohort (n = 367) of client‐owned cats with and without azotemic CKD from first opinion practice.

Methods

Retrospective cross‐sectional and retrospective cohort study. The diagnostic accuracy of tCa as an index test for ionized hypercalcemia was evaluated, and risk factors for underestimation were explored by binary logistic and linear regression in a cross‐section of cats with and without azotemic CKD. Chronic kidney disease and clinicopathological variables were assessed as predictors of incident total hypercalcemia by both time‐invariant and time‐dependent Cox regression in a cohort of cats.

Results

Specificity of tCa for identification of ionized hypercalcemia was high (100%), but sensitivity was low. Underestimation was associated with lower venous bicarbonate concentrations. Cats with CKD had increased risk for incident total hypercalcemia (hazard ratio, 4.29; 95% confidence interval, 1.96–9.37; P < .001). Higher tCa predicted incident total hypercalcemia in both azotemic and nonazotemic cats (P < .001).

Conclusions and Clinical Importance

Chronic kidney disease is a risk factor for incident total hypercalcemia, and most cats with increased tCa had concurrent ionized hypercalcemia. Higher baseline tCa predicts incident total hypercalcemia. Prospective studies assessing changes in iCa are warranted.

Acute severe hypercalcemia after traumatic fractures and immobilization in hypophosphatasia complicated by chronic renal failure

CONTEXT

Hypophosphatasia (HPP) features deficient activity of the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP) due to loss-of-function mutation(s) within the TNSALP gene. Consequently, inorganic pyrophosphate, a TNSALP substrate and inhibitor of mineralization, accumulates extracellularly. This can cause rickets or osteomalacia.

OBJECTIVE

We report a 55-year-old man with HPP and chronic renal failure (CRF) requiring hemodialysis who developed severe hypercalcemia acutely after traumatic fractures and immobilization. He manifested HPP in childhood and in middle age received hemodialysis for CRF attributed to hypertension and anti-inflammatory medication. He took 2 g of calcium carbonate orally each day to bind dietary phosphorus, but never aluminum hydroxide or any form of vitamin D. Pretrauma serum levels of calcium spanned 8.4-10.7 mg/dL (normal [Nl], 8.6-10.3), inorganic phosphate 5.8-6.4 mg/dL (Nl, 2.5-4.5), and PTH 63-75 pg/mL (Nl, 10-55).

RESULTS

Rapid succession falls fractured multiple major bones. Six hours later, he became confused. Serum calcium was 14.9 mg/dL, ionized calcium was 7.4 mg/dL (Nl, 4.5-5.1), and PTH was 16 pg/mL. Hemodialysis quickly corrected his hypercalcemia and confusion. Low serum alkaline phosphatase persisted, and follow-up skeletal histopathology showed that his osteomalacia was severe.

CONCLUSION

Hemodialysis does not heal the skeletal disease of HPP. During sudden fracture immobilization in HPP, sufficient calcium can emerge from bone, perhaps from a rapidly exchangeable calcium pool, to cause acute severe hypercalcemia if the kidneys cannot compensate for the mineral efflux. Hence, we worry that acute hypercalcemia might accompany sudden immobilization in CRF patients without HPP if they have adynamic bone disease.

Association of bone activity, calcium load, aortic stiffness, and calcifications in ESRD

An inverse relationship between arterial calcifications and bone activity has been documented in patients with ESRD. Calcium overload is associated with arterial calcification, which is associated with arterial stiffening. Whether bone activity interacts with calcium load, aortic stiffness, or arterial calcification is unknown. This study assessed the impact of bone activity on the relationships between the dosage of calcium-containing phosphate binders and aortic stiffness (measured by pulse wave velocity) or abdominal aorta calcification score. Aortic stiffness and calcification were both positively associated with calcium load and negatively associated with bone activity. A significant interaction was found between dosage of calcium-containing phosphate binders and bone activity such that calcium load had a significantly greater influence on aortic calcifications and stiffening in the presence of adynamic bone disease. Independent of any other factor, including dosage of calcium-containing phosphate binders, adynamic bone was associated with greater aortic stiffening, suggesting cross-talk between the bone and arterial walls.

Risk factors for decreased total body and regional bone mineral density in hemodialysis patients with severe secondary hyperparathyroidism

Hyperparathyroidism contributes significantly to decreased bone mineral density (BMD) in end-stage renal disease patients, but this negative influence is not homogeneous throughout the skeleton. We studied the BMD by dual-energy X-ray absorptiometry on total body and on different regions of the skeleton in 42 patients with severe hyperparathyroidism on hemodialysis. We also evaluated the relationship between different risk factors and BMD found on the regions examined in these patients. The legs and other sites where cortical bone predominate were mostly affected, whereas trabecular bone was relatively preserved. This is probably the result of the different effects of hyperparathyroidism on cortical and trabecular bone, but we cannot rule out the interference of ectopic calcifications and sclerotic lesions of vertebral end-plates falsely increasing lumbar spine BMD. The main determinants of low total-body BMD were, in order of importance, immobility, high intact parathyroid hormone levels, low body mass index, and low albumin. Eleven patients presented with pathologic fractures, mainly in the legs, and BMD was lower in this group than in patients without fractures. In conclusion, our study makes clear that hyperparathyroidism is a great threat to bone density in hemodialysis patients, mainly in the legs, the site mostly affected by fragility fractures in our patients. Physicians must worry not only with high parathyroid hormone levels, but also with the nutritional state of these patients.

Indicações de paratireoidectomia no hiperparatireoidismo secundário à insuficiência renal crônica

O hiperparatireoidismo é uma manifestação comum na insuficiência renal crônica (IRC), com alta morbi-mortalidade e difícil manejo clínico. As indicações clássicas da paratireoidectomia são: hipercalcemia persistente, principalmente após transplante renal, prurido intratável, fraturas patológicas, dor óssea refratária ao tratamento medicamentoso e calcificação metastática. Infelizmente, esta última não responde à paratireoidectomia e a calcificação dos vasos está relacionada ao aumento da mortalidade. Assim, novos critérios para indicação mais precoce de paratireoidectomia são necessários. Níveis séricos de PTH maiores que 10 vezes o limite da normalidade, apesar da adequada reposição de cálcio e calcitriol, produto cálcio x fósforo maior que 70(mg/dl)2, tumor marrom quando é urgente a regressão da massa, artrite e/ou periartrite incapacitantes e ruptura de tendões estão entre outras indicações a serem consideradas. Alguns cuidados são necessários para excluir doenças ósseas concomitantes, como amiloidose e intoxicação por alumínio. Esta revisão visa a orientar os endocrinologistas sobre as indicações e melhor momento de realizar paratireoidectomia no hiperparatireoidismo da IRC.

Etiology of hypercalcemia in hemodialysis patients on calcium carbonate therapy

Fourteen of 39 dialysis patients (36%) became hypercalcemic after switching to calcium carbonate as their principal phosphate binder. In order to identify risk factors associated with the development of hypercalcemia, indirect parameters of intestinal calcium reabsorption and bone turnover rate in these 14 patients were compared with results in 14 eucalcemic patients matched for age, sex, length of time on dialysis, and etiology of renal disease. In addition to experiencing hypercalcemic episodes with peak calcium values of 2.7 to 3.8 mmol/L (10.7 to 15.0 mg/dL), patients in the hypercalcemic group exhibited a significant increase in the mean calcium concentration obtained during 6 months before the switch, compared with the mean value obtained during the 7 months of observation after the switch (2.4 +/- 0.03 to 2.5 +/- 0.03 mmol/L [9.7 +/- 0.2 to 10.2 +/- 0.1 mg/dL], P = 0.006). In contrast, eucalcemic patients exhibited no change in mean calcium values over the same time period (2.3 +/- 0.05 to 2.3 +/- 0.05 mmol/L [9.2 +/- 0.2 to 9.2 +/- 0.2 mg/dL]). CaCO3 dosage, calculated dietary calcium intake, and circulating levels of vitamin D metabolites were similar in both groups. Physical activity index and predialysis serum bicarbonate levels also were similar in both groups. However, there was a significant difference in parameters reflecting bone turnover rates between groups.(ABSTRACT TRUNCATED AT 250 WORDS)