Peritoneal Protein and Albumin Excretion as Markers of Cardiovascular Risk and Systemic Endothelial Dysfunction

Cheuk-Chun Szeto, Kai-Ming Chow, Kwok-Yi Chung, Bonnie Ching-Har Kwan, Philip Kam-Tao Li

Background: Microalbuminuria is a marker of systemic endothelial dysfunction. We studied the relationship between peritoneal protein loss in peritoneal dialysis (PD) patients, which is conceptually analogous to microalbuminuria in non-uremic patients, and pre-existing vascular disease in new PD patients.
Methods: Peritoneal total protein and albumin loss were quantified within 2 months of initiation of dialysis in 44 consecutive new PD patients, together with a standard peritoneal equilibration test. The results were compared according to the presence of cardiovascular disease (CVD) prior to initiation of dialysis, lean body mass, and serum albumin and C-reactive protein (CRP) concentrations.
Results: The dialysate albumin concentration was closely correlated with the creatinine dialysate-to-plasma ratio at 4 hours (r = 0.601, p < 0.001). It was higher in patients with pre-existing CVD than in those without, when patients were analyzed according to diabetic status (one-way ANOVA, p = 0.004). In diabetic patients, the dialysate albumin concentration was significantly higher in patients with pre-existing CVD than in those without (0.754±0.273 vs 1.088 ± 0.280 mg/mmol creatinine, p = 0.04). Multivariate analysis showed that only diabetic status and dialysate albumin concentration, but not peritoneal transport status or serum CRP, were independent predictors of pre-existing CVD. Although dialysate protein loss accounted for only 10.5±4.4% of total protein catabolism, the dialysate protein level was significantly correlated with serum albumin concentration (r = -0.457, p = 0.002), percentage of lean body mass (r = -0.558, p < 0.001), and serum CRP concentration (r = 0.434, p = 0.003).
Conclusions: Patients with CVD prior to initiation of dialysis have higher levels of dialysate albumin and total protein excretion, indicating that dialysate protein loss is a marker of underlying CVD. Dialysate protein and albumin excretion may provide a simple and convenient measure of vascular disease and endothelial dysfunction in PD patients.

Key words: atherosclerosis, inflammation, peritoneal dialysis

背景: 微白蛋白尿症是系統性內皮功能障礙的指標。腹膜透析（PD）接受者之蛋白流失，在概念上與非尿毒症患者之微白蛋白尿症類似。本研究調查了在剛開始 PD 的病人中，腹膜性蛋白流失與既有血管性疾病的關係。
方法: 研究人員以 44 位剛開始接受 PD（2 個月內）的病人為對象，測量腹膜性總蛋白及白蛋白之流失，同時進行標準之腹膜平衡試驗；再將有關數據按病人之各項特徵作出比較，包括心血管疾病（CVD）於 PD 開始前的存在與否、身體瘦肉質量、及白蛋白與 CRP（C-reactive protein）血清濃度。
結果: 透析液之白蛋白濃度、與 4 小時之透析液/血漿肌酸酐比例呈正相關性（r = 0.601, p < 0.001）。根據糖尿病狀態作分析，可見腹膜性蛋白流失與既有血管性疾病有關（one-way ANOVA, p = 0.004）；在患有糖尿病的病人間，與非 CVD 患者相比，CVD 患者的透析液白蛋白濃度出現顯著增加（0.754 ± 0.273 vs 1.088 ± 0.280 mg/mmol 肌酸酐, p = 0.04）。多變項分析顯示，糖尿病狀態及透析液白蛋白濃度，而非腹膜運輸狀態或血清 CRP，可作為既有 CVD 的獨立預測因子。雖然自透析液的流失僅佔蛋白質分解代謝總量之 10.5 ± 4.4%，透析液之蛋白濃度仍與血清白蛋白濃度（r = -0.457, p = 0.002）、身體瘦肉質量百分比（r = -0.558, p < 0.001）、及血清 CRP 濃度（r = 0.434, p = 0.003）呈顯著相關性。
結論: 對於在開始接受透析治療前已出現 CVD 的病人，腹膜性總蛋白及白蛋白的流失高於非患者，顯示腹膜性蛋白流失可作為既有 CVD 的指標。因此，腹膜性蛋白流失的測量，可望為 PD 接受者的血管性疾病及內皮功能障礙，提供一個簡便的評估方法。

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