尿液中三聚氰胺濃度與成人尿路結石之相關性研究

Association between urinary melamine level and adult urolithiasis

吳佳芳(Chia-Fang Wu)

指導教授 ： 吳明蒼

共同指導教授 ： 吳焜裕(Kuen-Yuh Wu)

高雄醫學大學/健康科學院/職業安全衛生研究所/博士(2010年)

摘要

背景與目的：三聚氰胺毒奶粉事件導致嬰幼兒腎結石及嚴重的腎臟問題己經在中國、香港以及台灣地區陸續被報導，並引起國際上的重視，然而，目前這些報導皆著重在以奶粉為主食的嬰幼兒，尚無成人相關的研究資料。台灣地區成人尿路結石的盛行率約為9.6%，由於尿路結石疾病具有高發生率與高復發率的特性，對於醫療與經濟層面的影響非常深遠。因此，本研究目的在探討國人關於尿路結石生成與尿液中三聚氰胺濃度的相關性。

材料與方法：本研究設計採用醫院為主的病例對照研究法，從民國92年至96年，自高雄醫學大學附設中和紀念醫院和高雄市立小港醫院收集上尿路結石的個案，經過傅立葉紅外線圖譜來分析結石成份，分別診斷為尿酸上尿路結石的病人和含鈣上尿路結石的病患為病例組；對照組則是收集同時期保健科住院健檢經過超音波及X光證實沒有尿路結石同時以問卷調查亦無尿路結石疾病史，並作性別及年齡配對 (±2歲)。研究個案均接受問卷訪視；抽取周邊血液及收集清晨第一泡中段尿液檢測相關臨床指標，包括鈣、磷以及肌酸肝濃度；此外，尿液樣本使用液相層析串連式質譜儀分析三聚氰胺的濃度。

結果：
(1) 結果顯示11位尿酸上尿路結石病患 (中位數: 0.50 vs 0.06 μg/mmol creatinine, Wilcoxon test: FDR_p = 0.024) 及22位含鈣上尿路結石病患 (中位數: 0.14 vs 0.06, FDR_p = 0.024) 尿液中三聚氰胺濃度均顯著高於22位對照個案。

(2.1) 由於大部分的尿路結石都屬含鈣性結石 (89.4%)，因此本研究進一步再增加含鈣上尿路結石個案數、收集與分析臨床含鈣尿路結石的檢體，結果顯示211位含鈣上尿路結石病患 (中位數: 0.21 vs 0.02, p < 0.0001) 尿液中三聚氰胺濃度仍顯著高於211位對照個案。

(2.2) 進一步以多變項迴歸分析，發現尿液中三聚氰胺濃度每增加一單位 (2.718 μg/mmol) 即會增加1.84倍的風險 (95%CI: 1.48-2.29) 罹患含鈣上尿路結石 (Hosmer-Lemeshow goodness-of-fit test, p = 0.928)；另外將尿液中三聚氰胺濃度分成1)小於方法偵測極限者，大於方法偵測極限者再以中位數分成2) <0.47 μg/mmol creatinine及3) ≧0.47 μg/mmol creatinine，發現罹患含鈣上尿路結石的危險性隨著尿液中三聚氰胺濃度越高呈現劑量效應 [AOR = 2.91 (95%CI: 1.33-6.38); 10.00 (3.90-25.68)] (Hosmer-Lemeshow goodness-of-fit test, p = 0.590)。

(2.3) 在建立尿液中三聚氰胺濃度對含鈣上尿路結石的ROC曲線方面，顯示ROC曲線下的面積為0.84 (95%CI: 0.80-0.88, p < 0.0001)，而最佳診斷點為當尿液中三聚氰胺濃度為0.024 μg/mmol creatinine可得敏感度91.0%、特異度65.4%、陽性預測率72.5%、陰性預測率87.9%，且與本研究(1)所得的ROC曲線並無差異(p = 0.130)。

(2.4) 在計算族群可歸因風險方面，本研究考慮了尿路結石已知最重要的危險因子，包括尿液中尿酸濃度與飲水量的多寡再加上尿液中三聚氰胺濃度三個因子。單獨只考慮一個因子時，有36.6% - 68.4%可歸因於尿液中三聚氰胺濃度；有51.0% - 55.4%可歸因於飲水量的多寡；有77.4% - 80.3%可歸因於尿液中尿酸濃度，為最重要的因子。當此三個因子同時考慮時，可解釋93.9% - 95.7%的含鈣上尿路結石。

結論：本研究為第一篇報導低濃度三聚氰胺暴露對成人尿路結石的健康危害。含鈣尿路石的成因複雜，有些原因仍未知，而三聚氰胺暴露與成人尿路結石形成之機轉尚未清楚。未來的研究目標在更了解含鈣尿路結石的成因與機轉，以做為未來篩檢、預防及治療上的依據。

關鍵字

尿酸 ； 鈣 ； 上尿路結石 ； 尿液 ； 結石 ； 三聚氰胺 ； ROC曲線 ； 液相層析串連式質譜儀

並列摘要

Background and objective: The outbreak of melamine-tainted infant formula has raised concerns about causing kidney stones and adverse renal outcomes in young children worldwide, particularly in China, Hong Kong, and Taiwan. However, it is not known whether exposure to melamine might also cause urolithiasis in adults. In Taiwan, the prevalence rate of adult urolithiasis is relatively high (~9.6%), due to its high occurrence and recurrence rate of urolithiasis, burden of medical expenditure is expected to be large. This study aims to investigate the association between urinary melamine concentration and the risk of urolithiasis in adults in Taiwan.

Materials and methods: This study was designed as a hospital-based case-control study. Between 2003-2007, patients with urolithiasis were enrolled from Kaohsiung Medical University Hospital (KMUH) and Kaohsiung Municipal Hsiao-Kang Hospital. Their stone specimens were confirmed to have uric acid and calcium stones components by infrared spectroscopy analysis (FTIR). For comparison, sex- and age- matched subjects were randomly selected from people receiving general health examinations at KMUH during the same period. The controls reported no past history of stone disease or clinical findings of stones, which was confirmed by plain abdominal X-ray and abdominal ultrasound in their health examinations. A blood sample and first spot urine were obtained after getting up for biochemical analysis, including calcium, phosphate, uric acid and creatinine levels. In addition, urinary melamine concentration was measured by the method of triple-quadrupole liquid chromatography tandem mass spectrometry (LC-MS/MS).

Results:
(1) 11 uric acid urolithiasis (median: 0.50 vs 0.06 μg/mmol creatinine, Wilcoxon test: FDR_p = 0.024) and 22 calcium urolithiasis (median: 0.14 vs 0.06, FDR_p = 0.024) had significantly higher urinary melamine concentration than 22 controls.

(2.1) The majority of urolithiasis are calcium urolithiasis (89.4%), therefore, we increase the sample size to examine the relationship of melamine exposure by measuring melamine levels in urine with the risk of calcium urolithiasis. 211 calcium urolithiasis still had significantly higher urinary excretions of melamine than 211 controls (median = 0.21 vs. 0.02 μg/mmol creatinine, p < 0.0001).

(2.2) After adjusting for estimated glomerular filtration rate and other covariates, each one unit (2.718 ?慊/mmol Cr) increase in urinary melamine excretion was associated with a significant 1.84-fold risk (95% CI = 1.48-2.29) of developing calcium urolithiasis (Hosmer-Lemeshow goodness-of-fit test, p = 0.928). Further, then categorized by MDL, > MDL-0.46, and ?d0.47 ?慊/mmole creatinine, a significant trend of increasing calcium urolithiasis risk was also noted [AOR = 2.91 (95%CI: 1.33-6.38); 10.00 (3.90-25.68)] (Hosmer-Lemeshow goodness-of-fit test, p = 0.590).

(2.3) A receiver operating characteristic curve (ROC curve) examining the ability of melamine concentration to discriminate between case patients and controls showed an area under the curve of 0.84 (95%CI = 0.80 to 0.88, p < 0.0001). The optimal cut-off value for urinary melamine excretion was set at 0.024 μg/mmol creatinine with 91.0% sensitivity, 65.4% specificity, 72.5% positive predictive rate and 87.9% negative predictive rate for identifying calcium urolithiasis. When compared with the area under the ROC curve in result (1), the results were not significantly different (p = 0.130).

(2.4) The population attributable risk (PAR%) for calcium urolithiasis ranged 36.6%-68.4% in urinary melamine, after considering urinary uric acid (77.4%-80.3%), fluid intake (51.0%-55.4%), and other covariates. When all 3 factors combined together, to 93.9%-95.7%.

Conclusion: To our knowledge, this is the first one to report the positive association between melamine exposure and the risk of urolithiasis. The etiology of calcium urolithiasis is multifactorial, and some of them are not well-known. Meanwhile, the detailed mechanism about why melamine exposure causes renal stone formation is still unclear. We will focus on more understand the risk and mechanism of formation of renal calcium urolithiasis to benefit how to screen, prevent and treat those urolithiasis patients.

並列關鍵字

uric acid ； calcium ； urolithiasis ； urine ； stone ； melamine ； ROC curves ； LC-MS/MS

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