Frystyk J, Ivarsen P, Støving R K, Dall R, Bek T, Hagen C, Ørskov H
Institute of Experimental Clinical Research and Medical Department M, Aarhus University Hospital, Denmark.
Growth Horm IGF Res. 2001 Apr;11(2):117-27. doi: 10.1054/ghir.2001.0197.
Two fundamentally different methods are currently used for the determination of free insulin-like growth factor-I (IGF-I): ultrafiltration by centrifugation (UF) and direct immunoradiometric assay (IRMA). The aim was to evaluate a commercial IRMA (DSL, Webster, TX, USA) and to compare it with UF. In the IRMA it is recommended that samples be incubated for 2 h at 5;C. When comparing samples (n = 8) incubated for 1 and 2 h, levels increased by 27 +/- 5% (P< 0.0001). When incubating samples at 22;C instead of 5;C, levels increased by 192 +/- 32% (P< 0.0001). Addition of IGF-binding protein-1 (IGFBP-1) to normal sera (n = 6) dose-dependently decreased ultrafiltered free IGF-I only (P< 0.0007). Similarly, UF was more sensitive than IRMA to addition of IGFBP-2 (P< 0.05). In healthy subjects (n = 35) IRMA yielded 20% higher levels than UF (1.09 +/- 0.09 vs 0.91 +/- 0.12 microg/L; P< 0.0001). IRMA and UF yielded similar results in healthy subjects treated with IGF-I (n = 5) or growth hormone (n = 7) and in acromegalic patients (n = 6) before and after somatostatin analogue treatment. However, marked differences were observed in conditions with elevated IGFBP-1 and -2. In type-1 diabetics (n = 23) ultrafiltered free IGF-I was more reduced than IRMA free IGF-I (38 +/- 9 vs 76 +/- 7% of matched controls (n = 13); P< 0.0001). In patients with chronic renal failure (n = 25), IRMA free IGF-I was identical to control levels (n = 13), whereas ultrafiltered free IGF-I was decreased by 51 +/- 7% (P< 0.0001). Similarly, women with anorexia nervosa (n = 9) studied before and after weight gain showed significant changes in ultrafiltered free IGF-I only (P< 0.03). In conclusion, IRMA was not very robust with respect to variations in sample incubation and this may bias results. IRMA generally yielded higher levels than UF, in accordance with the knowledge that IRMA measures free plus readily dissociable IGF-I. IRMA was less affected than UF by added IGFBP-1 and -2, and reductions in free IGF-I were better revealed by UF than IRMA.
目前有两种根本不同的方法用于测定游离胰岛素样生长因子-I（IGF-I）：离心超滤法（UF）和直接免疫放射分析法（IRMA）。目的是评估一种商用IRMA（DSL，美国得克萨斯州韦伯斯特）并将其与UF进行比较。在IRMA中，建议样品在5℃下孵育2小时。比较孵育1小时和2小时的样品（n = 8）时，水平升高了27±5%（P < 0.0001）。当样品在22℃而不是5℃下孵育时，水平升高了192±32%（P < 0.0001）。向正常血清（n = 6）中添加胰岛素样生长因子结合蛋白-1（IGFBP-1）仅剂量依赖性地降低超滤游离IGF-I（P < 0.0007）。同样，UF对添加IGFBP-2比IRMA更敏感（P < 0.05）。在健康受试者（n = 35）中，IRMA产生的水平比UF高20%（1.09±0.09对0.91±0.12μg/L；P < 0.0001）。在接受IGF-I治疗（n = 5）或生长激素治疗（n = 7）的健康受试者以及肢端肥大症患者（n = 6）接受生长抑素类似物治疗前后，IRMA和UF产生的结果相似。然而，在IGFBP-1和-2升高的情况下观察到明显差异。在1型糖尿病患者（n = 23）中，超滤游离IGF-I比IRMA游离IGF-I降低得更多（与匹配对照（n = 13）相比为38±9对76±7%；P < 0.0001）。在慢性肾功能衰竭患者（n = 25）中，IRMA游离IGF-I与对照水平相同（n = 13），而超滤游离IGF-I降低了51±7%（P < 0.0001）。同样，神经性厌食症女性（n = 9）在体重增加前后进行研究，仅超滤游离IGF-I有显著变化（P < 0.03）。总之，IRMA在样品孵育变化方面不太稳定，这可能会使结果产生偏差。IRMA通常产生的水平比UF高，这与IRMA测量游离加易解离的IGF-I的认识一致。IRMA比UF受添加的IGFBP-1和-2的影响小，并且UF比IRMA能更好地显示游离IGF-I的降低。
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