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檢驗項目：Beta 2-Microglobulin
(β2-Microglobulin) β2-M 分子量很低，容易被腎絲球所過濾，其中 99.8% 以上在近端小管被重吸收及分解代謝，僅一小部份的 β2-M 被排到尿中。血清中 β2-M 的濃度取決於下列二因素：1. 淋巴生成系統合成 β2-M 的速率。 2. 腎絲球過濾 β2-M 的速率。一旦腎絲球過濾率降低 (例如血液透析、腎臟移植等)，會導致血清 β2-M 因無法排除而升高。而腎絲球近端小管的病變 (例如重金屬中毒、Aminoglycosides 抗生素作用等) 會導致 β2-M 無法再吸收或分解而大量排至尿中。一般而言，血清 β2-M 濃度達到 5000 µg/L 時，近端小管便停止再吸收的功能。正常情況下它在人體的生理半衰期約 40 分鐘。 目前 β2-M 廣泛應用於腎臟病、癌症、Non-Hodgkin's 淋巴瘤、骨髓瘤及 AIDS 的診斷和追蹤。 臨床意義： β2-Microglobulin是淋巴球上的小蛋白質，當淋巴球壽命變短，例如淋巴球性白血病、HIV的攻擊，就大量釋出到血液中。β2-Microglobulin由腎臟代謝，99%由腎小管回收，所以腎絲球過濾障礙時，血中濃度上升，腎小管吸收障礙時，血中濃度下降，尿液濃度上升。 血清β2-Microglobulin上升於20-60%大腸癌、胰臟癌、乳癌、Lymphoma、Non-Hodgkins、Myeloma、ALL、CLL、CML，但也上升於良性的腸炎、胰臟炎、肝膽、血液疾病，通常良性疾病上升的幅度比較少，陽性率也比較低。 尿液β2-Microglobulin上升於睪丸癌，部份的腎臟病變、腎小管再吸收障礙。 在下列狀況下，血液及體液中 β2-M 的濃度會升高，包括腎臟病 (洗腎患者)、各種發炎狀態、自體免疫的疾病、淋巴癌、濾過性病毒感染 (AIDS、CMV 等)。 洗腎患者由於血液中 β2-M 長期處於高濃度狀態，β2-M 會和血清中許多種蛋白質及酵素發生「澱粉酵素化反應」(glycation) 而形成 β2-M 類澱粉樣沉澱物，這些沉澱物會堆積在關節的部位，破壞關節附近的骨骼及軟骨組織，形成關節疼痛、破壞性關節病變。洗腎患者常在洗腎 8 年後發生此類澱粉樣沉著症 (Amyloidosis)，最常見的是侵犯腕骨關節，即所謂的「腕道症」，造成手麻、疼痛、手腕無力、手部肌肉萎縮等。事實上洗腎並不可能使 β2-M 恢復正常，因此僅能以手術治療改善之，腎臟移植是解決此問題最佳辦法。 在癌症方面，下列和淋巴增殖相關的癌症會令血清 β2-M 上升，包括多發性骨髓瘤、Hodgkin's 及 Non-Hodgkin's 淋巴癌、慢性淋巴球白血病等。研究顯示，β2-M 也適合用來評估 CML (慢性骨髓性白血病) 治療後的預後。通常 CML 治療後其 β2-M 依然大於 29000 µg/L 時，代表治療效果不佳，5 年存活率僅 48%；反觀 β2-M 較低的族群其 5 年存活率可達 75%。 對於感染 HIV 的愛滋病患，血清 β2-M 是非常重要的指標。它可用來評估疾病的進展及治療控制的成效。通常血清 β2-M 逐漸升高代表死亡機率也逐漸增加。 各種自體免疫疾病，如 SLE、硬皮病、類風濕等，會使血清 β2-M 上升。 Notice: 服用 cisplatin、getamycin、nifedipine、tobramycin 等會使尿液 β2-M 測定值增高。 Reference Value： 正常人血清 β2-M 濃度介於 800 ~ 2400 µg/L，平均 1600 µg/L，此數值會隨著性別、體重而有些許差異。並隨著年齡的增長，數值也會稍高。 尿液檢體大都介於 20 ~ 300 µg/L，平均約 80 µg/L。 CSF：800 ~ 1800 µg/L；也有書籍認為是 1500 ± 200 µg/L。 |
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Clinical Significance
In patients on long-term hemodialysis, it can aggregate into amyloid fibers that deposit in joint spaces, a disease known as dialysis-related amyloidosis. Mice models deficient for the β2 microglobulin gene have been engineered. These mice demonstrate that β2 microglobulin is necessary for cell surface expression of MHC class I and stability of the peptide binding groove. In fact, in the absence of β2 microglobulin, very limited amounts of MHC class I (classical and non-classical) molecules can be detected on the surface. In the absence of MHC class I, CD8 T cells cannot develop. (CD8 T cells are a subset of T cells involved in the development of acquired immunity.) Low levels of β2 microglobulin can indicate non-progression of HIV. Levels of beta-2 microglobulin can be elevated in multiple myeloma and lymphoma, though in these cases primary amyloidosis (amyloid light chain) and secondary amyloidosis (amyloid associated protein) are more common. The normal value of beta-2 microglobulin is <0.2 mg/dL. However, with respect to multiple myeloma, the levels of beta2-microglobulin may also be at the other end of the spectrum. Diagnostic testing for multiple myeloma includes obtaining the beta2-microglobulin level, for this level is an important prognostic indicator. A patient with a level <0.004 g/L is expected to have a median survival of 43 months, while one with a level >0.004 g/L has a median survival of only 12 months. |
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Plasma and urinary levels of beta2 microglobulin in rheumatoid arthritis.
Ann Rheum Dis. 1978 August D Manicourt, H Brauman, and S Orloff Abstract Plasma and urinary levels of beta2 microglobulin have been investigated in 21 patients suffering from rheumatoid arthritis (RA). Despite a normal renal glomerular function in all patients 50% of them had supranormal plasma beta2 microglobulin levels and 30% had a higher than normal urinary output of beta2 microglobulin generally related to the high plasma level. Plasma beta2 microglobulin levels paralleled closely the lymphocytosis and the 'joint count' both indexes of the severity of the disease. beta2 Microglobulin was normally secreted by the lymphoid tissue and it is suggested that it reflects the increase of the total mass and/or membrane turnover of the lymphoid tissue in RA. beta2 Microglobulin may be considered as a good parameter of the degree of severity of the joint and extra-articular involvement as well as a useful tool for the evaluation of drug efficacy in rheumatoid arthritis. |
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Plasma levels of beta 2-microglobulin in rheumatoid arthritis.
K G Sjöblom, T Saxne, F A Wollheim Annals of the Rheumatic Diseases (Impact Factor: 9.11). 09/1980; ABSTRACT -- A simple and inexpensive method is described for the determination of beta 2-microglobulin (beta 2-MG) by enzyme-amplified single radial immunodiffusion. The values obtained with this method correlate well with those determined by means of a commerical RIA kit. Using the immunodiffusion method we have measured the plasma levels of beta 2-MG in 135 patients with rheumatoid arthritis (RA) and normal serum creatinine levels. 33% of the patients had increased concentrations of beta 2 MG, but the levels were found to correlate poorly with the values of several variables generally used as indices of the degree inflammatory activity in RA. Furthermore, in contrast to earlier claims to the contrary, beta 2-MG correlated positively with age. The value of beta 2-MG in plasma as an index of inflammatory activity in RA is questioned. |
