Resumo Pacientes em hemodiálise são expostos ao cálcio, por meio do dialisato, pelo menos três vezes por semana. As alterações no cálcio sérico variam de acordo com a transferência de massa de cálcio durante a diálise, que é dependente do gradiente entre a concentração de cálcio no plasma e no dialisato (d [Ca]) e o estado de renovação do esqueleto que altera a capacidade do osso de incorporar cálcio. Embora subestimado, o d [Ca] pode potencialmente causar balanço positivo de cálcio que leva a danos em órgãos sistêmicos, incluindo associações com mortalidade, disfunção miocárdica, tolerabilidade hemodinâmica, calcificação vascular e arritmias. A fisiopatologia desses efeitos adversos inclui alterações do cálcio sérico, supressão do hormônio da paratireóide e calcificação vascular por meio de efeitos diretos e indiretos. Alguns órgãos são mais suscetíveis a alterações na homeostase do cálcio. Nesta revisão, discutimos os dados existentes e os mecanismos potenciais que ligam o d [Ca] ao equilíbrio do cálcio com a consequente disfunção no esqueleto, miocárdio e artérias.

Abstract Patients on hemodialysis are exposed to calcium via the dialysate at least three times a week. Changes in serum calcium vary according to calcium mass transfer during dialysis, which is dependent on the gradient between serum and dialysate calcium concentration (d[Ca]) and the skeleton turnover status that alters the ability of bone to incorporate calcium. Although underappreciated, the d[Ca] can potentially cause positive calcium balance that leads to systemic organ damage, including associations with mortality, myocardial dysfunction, hemodynamic tolerability, vascular calcification, and arrhythmias. The pathophysiology of these adverse effects includes serum calcium changes, parathyroid hormone suppression, and vascular calcification through indirect and direct effects. Some organs are more susceptible to alterations in calcium homeostasis. In this review, we discuss the existing data and potential mechanisms linking the d[Ca] to calcium balance with consequent dysfunction of the skeleton, myocardium, and arteries.

Resumo Introdução: A composição corporal é fundamental para a avaliação de pacientes com Doença Renal Crônica (DRC), e pode ser obtida por análise de impedância bioelétrica por multifrequência (BIA) ou absorciometria de dupla energia (DXA). Embora a discrepância entre os resultados obtidos pelos dois métodos já tenha sido descrita, os motivos são desconhecidos e podem estar relacionados ao hiperparatireoidismo secundário, devido à perda óssea. Métodos: Avaliamos 49 pacientes (25 homens e 24 mulheres): 20 com DRC não em diálise e 29 em hemodiálise de manutenção [18 com hiperparatireoidismo grave (HD-SHPT) e 11 submetidos à paratireoidectomia (HD-PTX)]. Todos os pacientes foram submetidos à DXA e BIA. Resultados: A mediana da idade e do índice de massa corporal (IMC) foram de 49 anos e 25,6 kg/m2, respectivamente. Os pacientes exibiram baixo conteúdo mineral ósseo (CMO) medido pelo DXA, particularmente aqueles do grupo HD-SHPT. A maior discordância da medida do CMO entre DXA e BIA foi encontrada no grupo HD-SHPT (p = 0,004). Os fatores independentemente associados a essa discrepância na medida do CMO foram fosfato sérico (p = 0,003) e grupo de pacientes (p = 0,027), mesmo após ajustes para idade, IMC e sexo (r2 ajustado = 0,186). PTX atenuou essa diferença. Discussão: A BIA deve ser interpretada com cautela em pacientes com HPTS devido a uma perda de precisão, o que pode comprometer a interpretação da composição corporal.

Abstract Introduction: Body composition is critical for the evaluation of patients with Chronic Kidney Disease (CKD) and can be obtained from either multifrequency bioelectrical impedance analysis (BIA) or dual-energy absorptiometry (DXA). Although the discrepancy between the results obtained from both methods has already been described, reasons are unknown, and might be related to secondary hyperparathyroidism, which is associated with bone loss. Methods: We have evaluated 49 patients (25 males and 24 females): 20 with CKD not on dialysis and 29 on maintenance hemodialysis [18 with severe hyperparathyroidism (HD-SHPT) and 11 submitted to parathyroidectomy (HD-PTX)]. All patients underwent DXA and BIA. Results: The median age and body mass index (BMI) were 49 years and 25.6 kg/m2, respectively. Patients exhibited low bone mineral content (BMC) measured by DXA, particularly those from the HD-SHPT group. The largest BMC measurement disagreement between DXA and BIA was found in the HD-SHPT group (p=0.004). Factors independently associated with this discrepancy in BMC measurement were serum phosphate (p=0.003) and patient group (p=0.027), even after adjustments for age, BMI, and gender (adjusted r2=0.186). PTX attenuated this difference. Discussion: BIA should be interpreted with caution in patients with SHPT due to a loss of accuracy, which can compromise the interpretation of body composition.

OBJECTIVES: Recent studies have shown a high prevalence of hypovitaminosis D, defined as a serum 25-hydroxyvitamin D level less than 30 ng/ml, in both healthy populations and patients with chronic kidney disease. Patients undergoing kidney transplant are at an increased risk of skin cancer and are advised to avoid sunlight exposure. Therefore, these patients might share two major risk factors for hypovitaminosis D: chronic kidney disease and low sunlight exposure. This paper describes the prevalence and clinical characteristics of hypovitaminosis D among patients undergoing kidney transplant. METHODS: We evaluated 25-hydroxyvitamin D serum levels in a representative sample of patients undergoing kidney transplant. We sought to determine the prevalence of hypovitaminosis D, compare these patients with a control group, and identify factors associated with hypovitaminosis D (e.g., sunlight exposure and dietary habits). RESULTS: Hypovitaminosis D was found in 79% of patients undergoing kidney transplant, and the major associated factor was low sunlight exposure. These patients had higher creatinine and intact parathyroid hormone serum levels, with 25-hydroxyvitamin D being inversely correlated with intact parathyroid hormone serum levels. Compared with the control group, patients undergoing kidney transplant presented a higher prevalence of 25-hydroxyvitamin D deficiency and lower serum calcium, phosphate and albumin but higher creatinine and intact parathyroid hormone levels. CONCLUSIONS: Our results confirmed the high prevalence of hypovitaminosis D in patients undergoing kidney transplant. Therapeutic strategies such as moderate sunlight exposure and vitamin D supplementation should be seriously considered for this population.