Kwuio 2010-3-26 13:56
胃繞道病患比較可能發生腎結石
作者：Nancy Fowler Larson
出處：WebMD醫學新聞
March 12, 2010 — 根據一項發表於3月號泌尿醫學期刊的研究結果，接受Roux-en-Y胃繞道（RYGB）手術的患者，因為尿液組成改變，發生腎結石的風險較高。
達拉斯德州大學西南醫學中心內科助理教授Naim Maalouf醫師與其同事們寫到，肥胖與RYGB手術分別與腎結石風險增加有關。我們比較RYGB術後病患與肥胖控制組的泌尿道結石風險，並評估RYGB提高腎結石風險的機轉。
研究者們評估38位病患，其中一半病患在過去1.8~3.5年之間接受RYGB，一種常見的減重手術，牽涉到釘或是胃隔間。研究者將這些病患的身體質量指數和年齡（手術組平均年齡49±11歲，控制組為47±10歲 [P=0.58]）與肥胖個體控制組做比較。這兩組的3位男性與16位女性都沒有腎結石病史。
這項斷面研究中，受試者食用常規飲食，完成24小時的尿液收集。藉由這些樣本，研究者測量草酸鹽、檸檬酸鹽與鈣的濃度，他們也收集病患的空腹血液樣本。
【胃繞道病患在2個區域風險較高】
結果顯示，接受RYGB手術病患的尿液有比較高濃度的草酸，這是一種在大部分腎結石裡面發現的酸（每天45±21 mg相較於30±11 mg；P=0.01）。接受RYGB手術病患的檸檬酸濃度也較低（每天358±357 mg相較於767±307 mg；P<0.01），這抑制了腎結石形成。RYGB手術患者比較容易發生尿液中草酸過高（尿液排除過多草酸）（47%相較於10.5%；P=0.02），且尿液檸檬酸鹽過低（檸檬酸鹽排除的盛行率也比較高（63%相較於5%；P<0.01）。
另一個潛在抵銷因子是胃繞道手術病患尿液鈣含量較低（每天115±93 mg相較於196±123 mg；P≦0.03），這個狀況可能抵銷了腎結石風險。除此之外，該族群腎結石形成整體風險因子是顯著的，且隨著時間增加。
Maalouf醫師在新聞稿中表示，近一半接受胃繞道手術且無腎結石病史病患的尿液草酸鹽過高、檸檬鹽濃度過低，這些因子會致使腎結石形成。由於這通常發生在胃繞道手術數月、甚至數年後，因此這個併發症部分可能不是那麼廣為人知。
研究者指出其研究有以下限制：
* 未確認造成尿液檸檬酸鹽濃度過低的原因，因為尿液收集程序使得研究者無法測量整體酸濃度。
* 這些研究結果是根據每位受試者單一24小時尿液樣本而得的；在過去的一項研究中，每位受試者收集了2次樣本，研究者表示接受RYGB手術病患的尿液，每個樣本在草酸鹽濃度方面有顯著差異。
* 這項研究是斷面性設計，無法發掘接受RYGB手術患者尿液樣本隨著時間變化的更多資訊。
有關於隨時間變化的想法，可以在針對胃繞道手術患者之危險因子的前瞻性後續追蹤研究中確認，同時也需要更多研究來評量腎結石發生的風險。
研究作者們寫到，腎結石的實際發生率，以及該族群結石形成危險因子之最佳治療仍需要進一步確立。
國家衛生研究院贊助這項研究。研究作者們表示已無相關資金上的往來。
Gastric Bypass Patients More Likely to Develop Kidney Stones
By Nancy Fowler Larson
Medscape Medical News
March 12, 2010 — Patients who have Roux-en-Y gastric bypass (RYGB) surgery develop a greater risk for kidney stones as a result of altered urine composition, according to a study published in the March issue of the Journal of Urology.
"Obesity and RYGB surgery are separately associated with an increased risk of kidney stones," write Naim Maalouf, MD, assistant professor of internal medicine, University of Texas Southwestern Medical Center, Dallas, and colleagues. "We compared urinary tract stone risk profiles in patients after RYGB and obese controls to assess the mechanism(s) by which RYGB heightens the nephrolithiasis risk."
Researchers evaluated 38 patients. Half had undergone RYGB, a common weight-loss surgery involving stapling or banding the stomach, in the previous 1.8 to 3.5 years. These patients were compared with a control group of obese individuals, matched according to body mass index and age (mean age, 49 ± 11 years for the surgery group vs 47 ± 10 years for the control group [p = 0.58]). None of the 3 men and 16 women in each group had a history of nephrolithiasis.
In this cross-sectional study, participants completed a 24-hour urine collection while on their regular diet. Using these samples, the study authors measured levels of oxalate, citrate, and calcium. Researchers also collected fasting blood samples.
Gastric Bypass Patients Have Higher Risk in 2 Areas
The results showed that the urine of patients who had RYGB surgery contained higher levels of oxalate, an acid found in most kidney stones (45 ± 21 vs 30 ± 11 mg daily; P = .01). The urine of patients who had RYGB surgery also revealed lower levels of citrate (358 ± 357 vs 767 ± 307 mg daily; P < .01), which inhibits the formation of stones. Hyperoxaluria (excessive urine oxalate) was more prevalent in patients who had RYGB surgery (47% vs 10.5%; P = .02), as was the prevalence of hypocitraturia (low urine citrates) (63% vs 5%; P < .01).
One potentially mitigating factor was the lower level of calcium in the urine of gastric bypass patients (115 ± 93 vs 196 ± 123 mg daily; P ? .03), a condition that can offset the risk for nephrolithiasis. Still, the overall risk factors for kidney stone formation in this population were significant and may increase over time.
"Almost half of the patients who had undergone gastric bypass and did not have a history of kidney stones showed high urine oxalate and low urine citrate — factors that lead to kidney-stone formation," Dr. Maalouf said in a press release. "This complication may not be well-recognized in part because it tends to occur months to years after the bypass surgery."
The investigators stated the following limitations to their study:
No cause for hypocitraturia could be determined because the urine collection process prohibited the researchers from measuring net acid.
The results are based on a single 24-hour urine sample per subject; in a previous study, in which 2 samples were collected, researchers noted marked differences in each sample regarding the amount of oxalate in the urine of patients who had RYGB surgery.
The cross-sectional design of the study prevented the discovery of extensive information about the time course of changes in urine factors in patients who had RYGB surgery.
Insight into time course changes could be determined in a prospective follow-up study of risk factors in gastric bypass patients. More research is also needed to measure the actual occurrence of kidney stones and to manage the risk.
"The true incidence of nephrolithiasis and optimal treatment for lithogenic risk factors in this population remain to be established," the study authors write.
The National Institutes of Health supported the study. The study authors have disclosed no relevant financial relationships.
J Urol. 2010;183:1026-1030.