Arcangeli C G, Smith D S, Ratliff T L, Catalona W J
Department of Surgery, Washington University School of Medicine, St. Louis, Missouri, USA.
J Urol. 1997 Dec;158(6):2182-7. doi: 10.1016/s0022-5347(01)68191-6.
Measurement of total serum prostate specific antigen (PSA) is widely used as an aid to early detection of prostate cancer. Measurement of the ratio of free-to-total PSA (percentage of free PSA) may help increase specificity of PSA testing. We prospectively studied the effects of varying the storage temperature and interval on total and free PSA levels.
We measured the baseline total and free serum PSA levels in 36 volunteers (mean age 66 years) and then retested aliquots of these serum samples after varying storage intervals (24 hours, 2 weeks and 9 months) at 3 different temperatures (4C, -20C and -70C). Volunteers represented a spectrum of prostatic conditions (PSA levels 2.0 to 4.0 ng./ml., PSA levels greater than 4.0 ng./ml. without cancer and PSA levels greater than 2.0 ng./ml. with prostate cancer). We used repeated measures analysis of variance to test for changes in total and free PSA levels as a function of time and temperature. We also evaluated the impact of storage at different temperatures and times on the percentage of free PSA.
Across groups total and free serum PSA decreased from the baseline level differentially as a function of longer storage interval and higher temperature (p <0.05). No significant difference was found for change in total PSA at 24 hours, 2 weeks or 9 months for storage temperatures of -20C compared with -70C. A significant change from baseline level was found for free PSA when stored in -20C compared with -70C for 2 weeks but the magnitude of the change was modest.
For storage intervals up to 9 months total PSA is more stable than free PSA under temperature conditions ranging from 4C to -70C. This differential stability has important implications for the clinical evaluation of percentage of free PSA to distinguish between benign and malignant diseases of the prostate.
血清总前列腺特异性抗原（PSA）检测被广泛用于辅助前列腺癌的早期诊断。检测游离PSA与总PSA的比值（游离PSA百分比）可能有助于提高PSA检测的特异性。我们前瞻性地研究了不同储存温度和时间间隔对总PSA和游离PSA水平的影响。
我们测量了36名志愿者（平均年龄66岁）的基线血清总PSA和游离PSA水平，然后在3种不同温度（4℃、-20℃和-70℃）下，对这些血清样本的等分试样在不同储存时间间隔（24小时、2周和9个月）后进行重新检测。志愿者代表了一系列前列腺状况（PSA水平为2.0至4.0 ng/ml、PSA水平大于4.0 ng/ml且无癌症以及PSA水平大于2.0 ng/ml且患有前列腺癌）。我们使用重复测量方差分析来检验总PSA和游离PSA水平随时间和温度的变化。我们还评估了不同温度和时间储存对游离PSA百分比的影响。
在所有组中，血清总PSA和游离PSA随储存时间延长和温度升高而与基线水平有差异地下降（p<0.05）。与-70℃相比，-20℃储存温度下24小时、2周或9个月时总PSA的变化无显著差异。与-70℃相比，-20℃储存2周时游离PSA与基线水平有显著变化，但变化幅度较小。
在4℃至-70℃的温度条件下，储存时间长达9个月时，总PSA比游离PSA更稳定。这种差异稳定性对通过游离PSA百分比进行临床评估以区分前列腺良性和恶性疾病具有重要意义。
