當患者的腎臟功能逐漸衰退,體內荷爾蒙的平衡(詳情請看:維他命D在體內的旅程與敵人,副甲狀腺是裡頭的黑道)、以及鈣與磷的平衡都受到嚴重影響,會導致副甲狀腺像脫韁野馬一樣,不可避免地受到刺激,而分泌的比健康人更旺盛,這種情況,就稱為副甲狀腺機能亢進。
經常會有人問,什麼是副甲狀腺?是台語俗稱的大脖子嗎?
不是啦!大脖子病,是甲狀腺機能亢進,而腎臟病患者是容易副甲狀腺機能亢進,來看圖說明。
橘黃色的那一片,是甲狀腺,也就是大脖子病的問題處;而躲在那一片後面的四個綠色的點,才是副甲狀腺,就算副甲狀腺機能亢進,脖子也很少摸到腫塊,也不會大脖子,它們躲在後面很難摸到的。
看圖就知道,副甲狀腺一般有四個,不過,超過4顆的情況並不少見,這就是為什麼在開刀之前,需要做一些確認檢查,看到底有沒有漏網之魚。
一般人的副甲狀腺素正常值,是12-72 pg/ml,而腎臟病患的副甲狀腺值,隨著腎臟功能衰退,會逐步上升,KDIGO治療指引告訴我們,常規洗腎的患者,副甲狀腺素建議的範圍值,是實驗室正常值上限的2倍到9倍,用剛剛那個數值範圍來看,上限是72,換算2倍到9倍,就是144-648 pg/ml。
為什麼會這樣定呢?這是因為檢驗副甲狀腺素的方法非常多種,在2006年之前,測量副甲狀腺素的方法是”Nichols Allegro Intact PTH assay”,雖然這已經是第二代的測量方式,但是研究發現,即使是同一個病人,檢驗結果的差異實在很大,可能在這邊測出來結果是300,在另一個地方測出來是600。為了解決這個問題,又發明很多種新的測量方法,世界衛生組織(The World health organization,WHO)把這些林林總總的測量方式,做了統整以及校正,而且明訂所有實驗室應該註明自己是使用哪一種測量法,並且使用下圖中所列的“校正因子”來做校正。
表格來源:National Kidney fundation,Parathyroid Hormone and Secondary Hyperparathyroidism in Chronic Kidney Disease stage 5D
從上表看就可以看到有12種的檢驗方法,右側欄位分別是他們的校正因子,因此,檢驗室給的數據會有兩個,一個是機器直接測得的數據,一個則是使用校正因子來校正之後的數據。
不管如何,目前治療指引中所建議的副甲狀腺素控制範圍,是用標準值上限的兩倍至九倍,因此,不管是用直接測得的數據,或者校正後的數據,都使用數據後頭所列出來的標準值來計算,如此一來,腎友應該將副甲狀腺素控制在多少以內,要先看您所用的標準值上限是多少,再乘以9才知道囉。另外,副甲狀腺值不能低於多少?用標準值上限乘以2,就是答案。
下一篇,副甲狀腺功能亢進,該怎麼治療?
參考文獻:
KDIGO Clinical Practice Guideline for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD)
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