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作者：Laurie Barclay, MD  
出處：WebMD醫學新聞

　　March 1, 2010 — 根據發表於3月美國腎臟學會臨床期刊(Clinical Journal of the American Society of Nephrology)的研究結果，在冬天開始長期透析之血中白蛋白值低的腎臟病患，幾乎都會發生維他命D缺乏。
　　
　　第一作者、波士頓麻州綜合醫院的Ishir Bhan醫師在新聞稿中表示，本篇研究確認了透析患者維他命D缺乏的風險因素，或許可以提供關於這些患者的生物學線索。
　　
　　本研究的目標在檢視例行性的檢測臨床因素和人口統計學因素是否可以確認哪些開始透析的病患會維他命D缺乏，研究世代被分成訓練組(60%)以及證實組(40%)，包括了納入「Accelerated Mortality on Renal Replacement (ArMORR)」研究世代中、偶然開始透析的908名美國病患的25-hydroxyvitamin D資料。
　　
　　研究者使用邏輯回歸模式、神經網絡、以維他命D缺乏作為依賴變項的決策樹，從訓練組例行性確認臨床與人口統計學資料中產生預測模式，為了確認有預測力的最簡單模式，研究者漸進式的減少變項。
　　
　　維他命D缺乏的定義為25-hydroxyvitamin D值低於30 ng/mL，佔研究對象的79%，維他命D缺乏的最強預測因子包括黑人、女性、冬季、低白蛋白血症(血清白蛋白值≦3.1 g/dL)。在證實組中，低白蛋白血症的因素以及冬天時開始透析，會增加缺乏維他命D的可能性，黑人婦女從90%增加到100%、黑人男性從85%增加到100%、白人婦女從82%增加到94%、白人男性從66%增加到92%。
　　
　　研究作者們寫道，在冬天開始長期血液透析的低白蛋白血症病患，幾乎都會發生25-hydroxyvitamin D缺乏。
　　
　　研究限制包括，無法一般化美國人以外的人口，無法確定因果關聯，可能有其他干擾因素，此外，需要後續研究確認充足的25-hydroxyvitamin D值是否會影響末期腎臟病(end-stage renal disease，ESRD)之高血糖、血壓、感染率、死亡率。
　　
　　研究作者們結論表示，雖然此研究確認了預測低25-hydroxyvitamin D值的臨床因素，還未證實調整這些數值是否有臨床助益，在ESRD的前瞻研究中，其中有些已經在進行了，必須確認在功能範圍內的最佳25-hydroxyvitamin D值，後續則可以說明其生物學影響，在缺乏臨床試驗下，醫師們必須獨立確認這些發現是否會影響經驗性療法或者只是促成後續研究。
　　
　　其中有些研究作者宣告與國家腎臟基金會、國家健康研究中心和/或Abbott Laboratories之各種財務關係。


Vitamin D Deficiency Likely Among Many Patients Starting Dialysis

By Laurie Barclay, MD
Medscape Medical News

March 1, 2010 — Vitamin D deficiency is almost universal in patients with kidney disease with low blood albumin levels who begin long-term dialysis during the winter, according to the results of a study reported in the March issue of the Clinical Journal of the American Society of Nephrology.

"This research identifies risk factors for nutritional vitamin D deficiency in the dialysis population and may provide clues to its biology in this population," lead author Ishir Bhan, MD, MPH, from Massachusetts General Hospital in Boston, said in a news release.

The goal of this study was to examine whether routinely measured clinical and demographic factors could identify patients starting dialysis who are deficient in vitamin D. The study cohort, which was divided into training (60%) and validation (40%) sets, consisted of 908 patients with 25-hydroxyvitamin D levels who were enrolled in the Accelerated Mortality on Renal Replacement (ArMORR) cohort of incident US patients initiating dialysis.

Using logistic regression modeling, neural networks, and decision trees with vitamin D deficiency as the dependent variable, the investigators generated predictive models from routinely determined clinical and demographic data in the training set. To identify the simplest model that remained predictive, the investigators subjected the models to progressive variable reduction.

Vitamin D deficiency, defined as 25-hydroxyvitamin D levels of less than 30?ng/mL, was present in 79% of the study population. The strongest predictors of vitamin D deficiency were black race, female sex, winter season, and hypoalbuminemia (serum albumin levels ? 3.1 g/dL). In the validation set, factors of hypoalbuminemia and dialysis started during the winter season increased the likelihood of vitamin D deficiency from 90% to 100% in black women, from 85% to 100% in black men, from 82% to 94% in white women, and from 66% to 92% in white men.

"Deficiency of 25-hydroxyvitamin D is nearly universal among patients with hypoalbuminemia initiating chronic hemodialysis in winter," the study authors write.

Limitations of this study include lack of generalizability to non-US populations, uncertain direction of causality, and possible residual confounding. In addition, further studies are needed to determine if repleting 25-hydroxyvitamin D levels affect hyperglycemia, blood pressure, infection rates, or mortality rates in end-stage renal disease (ESRD).

"Although this study identified clinical factors that predicted low 25-hydroxyvitamin D levels, it is not yet proven that correcting these levels is clinically beneficial," the study authors conclude. "Prospective studies in ESRD, some of which are now underway, are needed to identify optimal levels of 25-hydroxyvitamin D for a range of functions and to further elucidate its biology. In the absence of clinical trials, clinicians must independently determine if these findings should guide empiric therapy or simply inform future studies."

Some of the study authors have disclosed various financial relationships with the National Kidney Foundation, the National Institutes of Health, and/or Abbott Laboratories.

Clin J Am Soc Nephrol. 2010;5:460-467.