中文摘要：

目的：建立基于ALU序列的实时荧光定量PCR（ALU-qPCR）检测游离DNA浓度的方法，并探讨结直肠癌患者血清游离DNA定量检测的临床意义。方法：随机采集结直肠癌104例、结直肠息肉63例和正常人110例血清标本，采用ALU-qPCR方法定量检测血清ALU115表达水平；用化学发光方法检测肿瘤标志物CEA的水平。结果：（1）结直肠癌患者血清ALU115浓度中位数为1046.0 ng/mL，显著高于结直肠息肉组423.3 ng/mL和对照组385.4 ng/mL，差异有统计学意义（P均＜0.001），结直肠息肉组和对照组比较差异无统计学意义（P＞0.05）。（2）结直肠癌血清ALU115和CEA联合检测灵敏度、特异性、准确度、阳性预测值和阴性预测值分别是82.69%、99.09%、91.12%、98.85%和85.82%，两者联合检测提高结直肠癌诊断率。结论：基于ALU序列的实时荧光定量PCR是一种快速简便、灵敏度高及特异性好的检测方法。血清cf-DNA浓度对结直肠癌辅助诊断有一定的价值。

英文摘要：

Objective：To establish a method that quantitative real-time PCR by amplifying the ALU repeats （ALU-qPCR） for detecting concentrations of circulating cell-free DNA （cf-DNA） and investigate the expression of circulating cell-free DNA concentrations in serum of colorectal cancer patients （CRC） and its clinical significance. Methods：Serum samples were collected at random from 104 with primary CRC, 85 with operated CRC, 63 patients with intestinal polyps who were from the Affiliated Hospital of Nantong University and 110 normal controls were collected during the same period from the Physical Examination Center of the same hospital. ALU115 in serum were determined by ALU-qPCR. Correlative serum carcinoembryonic antigen （CEA） level was detected by ARCHITECT assay. Results：The method of ALU-qPCR was established successfully. The median absolute serum ALU115 （1046.0 ng/mL） in primary CRC was significantly higher than in intestinal polyps （423.3 ng/mL） and normal controls （385.4 ng/mL） （P〈0.001）. The ALU115 of serum DNA in intestinal polyps was of no statistical differences compared with normal controls （P〉0.05）.Conclusion：The method of ALU-qPCR can detect cf-DNA rapidly, sensitively and specifically. Serum DNA concentrations may be valuable in complementary diagno-sis of CRC.