JCEM：CKD患者补充维生素D的阈值是20ng/ml

在慢性肾脏疾病（CKD）患者中维生素D缺乏非常常见。目前指南推荐的治疗策略在这类患者中与普通人群相似，然而，在CKD患者，维生素D充足的营养状态是否能预防PTH水平的增加仍不清楚。为了研究循环PTH与25（OH）D水平的关系，寻找PTH显著增加相关的25（OH）D阈值，来自法国巴黎第十一大学的Marie Metzger教授及其团队进行了一项研究，该研究发现在CKD患者，25（OH）D水平高于20ng/ml似乎足够抑制血清PTH，这个研究结果强调只要低于30ng/ml，就应补充维生素D的指导方针。该研究结果在线发表在2013年4月30日的美国《临床内分泌代谢杂志》（The Journal of clinical endocrinology & metabolism）上。
该研究在929例没有经过透析、CKD分期1至5期、且没有补充维生素D的成年患者中，测量25（OH）D、PTH，以及通过51Cr-EDTA肾脏清除率测量肾小球滤过率（mGFR）。患者的平均年龄为60.1±14.7岁，71%为男性，且9%为黑人。他们的平均mGFR为37.8ml/min/1.73m2。
该研究结果表明，在校正mGFR、年龄、种族和离子钙水平后，通过log-PTH与25(OH)D的分段线性回归模型发现25（OH）D阈值在8ng/ml,上限为20ng/ml。这个平滑曲线确认当循环25（OH）D水平降至低于20ng/ml时，PTH浓度急剧上升。
该研究发现，在CKD患者，25（OH）D水平高于20ng/ml似乎足够抑制血清PTH。这个研究结果强化只要低于30ng/ml，就应补充维生素D的指导方针。    
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• Kidney Int：3或4期CKD患者使用碳酸钙有质疑
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Relation Between Circulating Levels of 25(OH) Vitamin D and Parathyroid Hormone in Chronic Kidney Disease: Quest for a Threshold.
Abstract
Context:Vitamin D deficiency is common in patients with chronic kidney disease (CKD). Current guidelines recommend treatment strategies in these patients similar to those for the general population, but the vitamin D nutritional status sufficient to prevent PTH levels from increasing in CKD is unknown.Objective, Main Outcome Measure:To study the relation between circulating PTH and 25(OH)D levels and to search for a 25(OH)D threshold associated with a significant PTH increase.Design, Setting, and Patients:In the hospital-referred NephroTest cohort study, we measured 25(OH)D, PTH, and glomerular filtration rate (mGFR) by 51Cr-EDTA renal clearance in 929 adult patients with nondialysis CKD stages 1 to 5 and no vitamin D supplementation. Patients' mean age was 60.1 ± 14.7 years; 71% were men, and 9% were black. Their mean mGFR was 37.8 mL/min/1.73 m2.Results:We found a 25(OH)D threshold of 8 ng/mL with an upper limit of 20 ng/mL (95% confidence interval) by linear piecewise regression modeling of log-PTH for 25(OH)D adjusted for mGFR, age, race, and ionized calcium level. The smoothed curve confirmed that PTH concentration rose steeply when circulating 25(OH)D levels fell to less than 20 ng/mL.Conclusions:Spontaneous 25(OH)D levels greater than 20 ng/mL seem sufficient to control serum PTH in CKD patients. This result reinforces guidelines to supplement vitamin D only if less than 30 ng/mL.