尿清蛋白检测性能评价及尿清蛋白/肌酐比值联合内生肌酐清除率对2型糖尿病患者肾损伤的检测意义

目的探讨尿清蛋白（Alb）检测性能评价及尿清蛋白/肌酐比值（ACR）联合内生肌酐清除率（Ccr）对2型糖尿病患者肾损伤的检测意义。方法收集2012年6月至2015年3月珠海市斗门区侨立中医院收治的110例2型糖尿病患者作为实验组。根据其检测结果将患者分为正常Alb尿组（≤30 mg/24 h尿）,微量Alb尿组（30~300 mg/24 h尿）,大量Alb尿组（≥300 mg/24 h尿）。选取同时期来我院进行体检的健康志愿者67例为对照组。收集所有研究对象24 h全部尿液、空腹静脉血4 ml,分离血清。-20℃保存,7 d内完成检测。测定标本中尿Alb、尿Cr、血Cr。根据慢性肾脏流行病学协作组发布的Ccr计算公式,对Ccr进行计算。结果患者T2DM的ACR为10.97 mg/24 h尿,Ccr为（75.36±8.47）ml/（min·1.73 m2）。联合检测ACR与Ccr水平,随着ACR含量的增高,Ccr水平下降明显。结论尿清蛋白/肌酐比值联合内生肌酐清除率可用于2型糖尿病患者肾损伤的早期诊断,辅助临床治疗。     

上海一社区人群尿白蛋白/肌酐比值及估算肾小球滤过率异常率流行病学调查

目的分析尿白蛋白(Alb)及估算肾小球滤过率(e GFR)在上海一社区老年人群中的分布情况,分析其相关危险因子,为肾脏疾病的诊疗提供流行病学数据。方法随机选取上海市宝山区友谊社区60岁以上居民1 154名,收集受访者空腹静脉血和晨尿,计算尿Alb/肌酐(Cr)比值(ACR),并用慢性肾病流行病学协作组(CKD-EPI)方程计算e GFR。以ACR≥30 mg/mg Cr、e GFR≤60 m L/(min·1.73 m2)为切点判断Alb尿及肾小球滤过率(GFR)受损,计算人群患病率并分析不同危险因素与疾病的关系。使用肾脏疾病膳食改良(MDRD)方程计算e GFR,比较其与CKD-EPI方程计算结果间的差异。结果 1 154名60岁以上人群中有13.43%的个体出现Alb尿,29.98%存在GFR受损。随着年龄的上升,ACR和e GFRCKD-EPI的异常率明显上升。Alb尿组性别构成、年龄、糖尿病患病率和高血压患病率与正常组比较,差异均有统计学意义(其中性别构成P0.05,其余项目P均0.001);GFR受损组除年龄和高血压患病率与GFR正常组比较差异有统计学意义(P0.001、P=0.006)外,其他因素差异均无统计学意义(P0.05)。使用MDRD公式计算e GFR会较使用CKD-EPI公式得到更高的e GFR异常率,在高年龄组和ACR正常组内尤为明显。MDRD方程可能高估了e GFR的异常率,低估了健康人群的e GFR水平,CKD-EPI公式相对更为准确。结论 ACR升高及e GFR异常在老年群体中有着较高的发生率,这一群体需要增加对肾脏疾病及糖尿病和高血压等危险因素的关注。使用公式估算e GFR时需要注意不同公式在不同群体间的差异。     

胱抑素C联合尿ACR检测对糖尿病患者早期肾损伤的诊断价值

目的探讨胱抑素C(Cys-C)联合尿微量白蛋白(m ALB)/肌酐(Cr)(ACR)检测对糖尿病患者早期肾损伤的诊断价值。方法选择2011年8月至2016年8月尿蛋白试验呈弱阳性或者阴性的58例DM早期肾损伤患者作为研究组,另选取同期于医院参加体检的健康者50例作为对照组。对照组与研究组血清中的Cys-C水平均采用免疫透射比浊法进行测定,m ALB采用免疫散射比浊法进行检测分析,Cr采用酶法进行检测分析,对检测所得到的结果进行分析。结果 (1)研究组患者血清Cys-C及ACR值分别为(1.49±0.35)mg/L与(110.10±11.38)μg/mg,均分别高于对照组[(0.85±0.17)mg/L,(17.78±2.23)μg/mg],P0.05或P0.01;(2)研究组60例患者中,Cys-C阳性检测率为65.52%(38/58),ACR阳性检测率为70.69%(41/58),Cys-C及ACR均阳性检测率为86.21%(50/58),两者阳性检测率最高。结论血清Cys-C联合ACR检测,对DM患者早期肾损伤具有较高的临床诊断价值,应在临床上进行广泛应用,从而为制定临床治疗计划提供切实可行的依据。     

尿清蛋白/肌酐比值评估冠心病患者伴甲状腺功能紊乱的价值

目的探讨尿清蛋白(Alb)/肌酐(Cr)比值(ACR)在冠心病患者伴甲状腺功能紊乱诊断中的价值及与甲状腺功能各检测指标的相关性。方法收集2015年11月至2016年8月在该院确诊的863例冠心病患者尿ACR及甲状腺功能检测结果。依据美国美国肾脏病基金会和食品和药物管理局诊断标准将863例冠心病患者分为A组(ACR≤10.0mg/g·Cr)、B组(10.0mg/g·CrACR≤30.0mg/g·Cr)、C组(30.0mg/g·CrACR≤300mg/g·Cr)、D组(ACR300mg/g·Cr);另根据甲状腺功能指标参考值将患者分为甲状腺功能结果正常组和异常组。结果 863例冠心病患者ACR与游离三碘甲状腺原氨酸(FT3)呈负相关(r=-0.297,P0.05),与游离甲状腺素(FT4)呈正相关(r=0.172,P0.05);各组间甲状腺功能异常率比较差异有统计学意义(χ2=33.533,P0.05);ACR10.0mg/g·Cr与ACR≤10.0mg/g·Cr患者甲状腺功能异常率比较差异有统计学意义(P0.05),其危险度为2.083。结论 ACR可能是冠心病患者伴甲状腺功能紊乱的一个危险因素,当ACR10.0mg/g·Cr时对冠心病患者监测甲状腺功能是必要的。     

血清Cys C、尿NAG/Cr、尿mAlb/Cr在2型糖尿病早期肾功能损害诊断中的临床价值

目的探讨血清半胱氨酸蛋白酶抑制剂C(Cys C)、尿N-乙酰-β-D氨基葡萄糖苷酶/肌肝比值(尿NAG/Cr)、尿微量白蛋白/肌肝比值(尿m Alb/Cr)在2型糖尿病(T2DM)早期肾功能损害诊断中临床价值。方法对54例T2DM早期肾功能损害患者(A组)、46例T2DM无肾功能损害患者(B组)、100例健康体检者(C组)的血清Cys C、尿NAG/Cr、尿m Alb/Cr的测定结果进行比较。结果 3组研究对象血清Cys C、尿NAG/Cr、尿m Alb/Cr不全相等(P<0.05),A组血清Cys C、尿NAG/Cr、尿m Alb/Cr显著高于B组与C组(P<0.05),B组与C组血清Cys C、尿NAG/Cr、尿m Alb/Cr相比差异无统计学意义(P>0.05)。3组研究对象尿Cr相比差异无统计学意义(P>0.05)。结论血清Cys C、尿NAG/Cr、尿m Alb/Cr是T2DM患者早期肾损害的敏感指标,有利于早期发现肾脏损害,对糖尿病肾病(DN)的防治具有重要的临床意义。     

床旁检验半定量尿液清蛋白 ／ 肌酐比值在糖尿病肾病 早期筛查中的临床价值评价

目的 评价床旁检验(POCT)半定量尿液清蛋白/肌酐比值(ACR)的准确性，探讨POCT半定量ACR在糖尿病肾病(DKD)早期筛查中的临床价值。方法 选取2018年1月至6月天津市第三中心医院分院门诊及住院2型糖尿病(T2DM)患者281例。分别采用POCT尿检仪(半定量方法)和生化分析仪(定量方法)检测尿液清蛋白(Alb)及肌酐(Cr)。采用Kappa检验比较半定量和定量结果一致性。以定量ACR检测为金标准，计算半定量ACR检测微量清蛋白尿(MAU)的敏感性、特异性、阳性预测值(PPV)、阴性预测值(NPV)、拟然比等参数。另选取19 543例T2DM患者，基于半定量ACR对DKD进行早期筛查。结果 半定量Alb(Kappa系数为0.789)及Cr(Kappa系数为0.727)与定量结果均具有较好的一致性。半定量ACR检测MAU的敏感性为85.3%,特异性为81.6%,PPV为79.7%,NPV为86.7%,阳性拟然比为4.63,阴性拟然比为0.18。在T2DM患者中，87.2%(17 047例)患者未发现肾脏损伤，12.8%(2 496例)患者可能存在肾脏损伤。结论 POCT半定量...     

尿干化学分析法、散射比浊法、酶法检测尿清蛋白与尿肌酐及比值结果的一致性分析

目的 评价使用尿干化学法和散射比浊法检测尿清蛋白(Alb)、使用尿干化学法和酶法检测尿肌酐(Cr)及尿清蛋白肌酐比(ACR)的结果一致性分析。方法 收集157例清晨第一次尿液样本,尿清蛋白使用尿干化学法和散射比浊法、尿肌酐使用尿干化学法和酶法分别进行测定。采用kappa检验评价结果的一致性。结果 尿清蛋白kappa值为0.837 9(95%可信区间:0.718 1～0.957 7); 尿肌酐kappa值为0.769 7(95%可信区间:0.665 2～0.874 2); 尿清蛋白肌酐比kappa值为0.756 6(95%可信区间:0.628 6～0.884 6)。结论 尿干化学法检测尿清蛋白,尿肌酐及ACR的结果和散射比浊法检测尿Alb,酶法检测尿Cr及ACR结果具有较高的一致性。可以用于早期肾脏疾病的筛查以及CKD的分级中,初筛患者或长期病情维持过程中复查的监控手段。     

尿α_1酸性糖蛋白在2型糖尿病患者肾脏损伤监测中的价值

目的探讨尿α1酸性糖蛋白(ORM)在2型糖尿病(T2DM)患者肾脏损伤监测中的应用价值。方法选取2型糖尿病患者211例,以骨科患者60例作为应激对照组,以体检健康者68名作为正常对照组。检测所有对象尿ORM、肌酐(Cr)、白蛋白(Alb),计算尿α1酸性糖蛋白/肌酐比值(OCR)和尿白蛋白/肌酐比值(ACR),根据ACR水平,将T2DM患者分为正常尿ACR(NACR)组(117例)、低ACR(LACR)组(62例)和高尿ACR(HACR)组(32例)。采用Pearson相关分析评价尿OCR与尿ACR的相关性。采用Logistic回归分析评价尿OCR与肾脏损伤的关系。结果 T2DM组尿OCR明显高于应激对照组和正常对照组(P0.05)。NACR组、LACR组和HACR组尿OCR依次增高,各组间差异有统计学意义(P0.05)。尿OCR与尿ACR呈正相关(r=0.894,P0.01)。Logistic回归分析显示,在T2DM组中,尿OCR是LACR患者和HACR患者肾损伤的独立危险因素[以NACR组为参照,LACR组:比值比(OR)=1.140,95%可信区间(CI) 1.061～3.347;HACR组:OR=0.869,95%CI 1.123～7.333]。结论尿ORM在T2DM早期肾脏损伤监测方面有一定的辅助作用。     

4种估算肾小球滤过率公式在体检人群中的应用评价

目的评价4种基于血清肌酐(Cr)或基于血清半胱氨酸蛋白酶抑制剂C(Cys C)的估算肾小球滤过率公式在体检人群中的适用性。方法随机取出2 032例体检健康者,分别检测血清Cr、Cys C、尿清蛋白和肌酐比值(ACR),通过4种公式,即同位素稀释质谱法-肾脏病膳食改善公式(IDMS-MDRD)、慢性肾脏病流行病合作组(CKD-EPI)公式(EPI-Cr、EPI-Cys C和EPI-CrCys C),分别计算其估算的肾小球滤过率(e GFR)并进行比较。结果 2 032例体检健康者血清Cr为(65.4±14.3)μmol/L,血清Cys C为(0.77±0.19)mg/L,ACR中位数为3.1 mg/g。将4种公式计算的e GFR值按照60 m L/min/1.73 m~2、60~89m L/min/1.73 m~2、≥90 m L/min/1.73 m~2分为3组,3组分布差异均有统计学意义(P0.05)。联合4种公式计算的e GFR和ACR对CKD预后分为低危、中危、高危和极高危4期,各期分布差异无统计学意义(P均0.05)。在2 032例健康人群中,以EPI-Cr公式计算的e GFR值在45~60 m L/min/1.73 m~2之间的例数为44例(2.2%),以IDMS-MDRD公式计算的e GFR值在45~60 m L/min/1.73 m~2之间的例数为58例(2.9%),该58例人群的ACR结果有45例30 mg/g,以EPI-Cr-Cys公式计算该45例人群的e GFR值,有40例60 m L/min/1.73 m~2。结论联合e GFR和ACR对CKD预后进行分期,4种公式的一致性高。对于选用基于血清Cr的IDMS-MDRD公式计算的e GFR值,如果在45~60 m L/min/1.73 m~2之间,建议检测Cys C,并且采用血清Cr和Cys C联合公式计算e GFR,以减少对患者GFR的误判。     

糖尿病肾病患者全血白细胞与尿清蛋白/尿肌酐比相关性分析

目的分析2型糖尿病患者全血白细胞总数和分类计数与尿清蛋白/尿肌酐比(ACR)的相关性。探讨白细胞在糖尿病肾病(DN)发生中的作用。方法将137例T2DM患者根据ACR进行分组。对各组的年龄、病程、血压、血糖、血脂、吸烟等因素进行分析,评价白细胞计数与ACR的相关性。结果随着ACR的增加,白细胞总数和中性粒细胞数、单核细胞数升高,而淋巴细胞数下降。结论在T2DM患者中,处于正常范围的白细胞总数和分类计数与ACR相关。     

Radioimmunoassay for urinary albumin.

We describe a rapid, sensitive, and precise radioimmunoassay for urinary albumin (Ualb). Aliquots of diluted urine were incubated at room temperature for 1 h with 125I-labeled albumin and a rabbit antiserum monospecific for human albumin. Phase separation was effected by the double-antibody technique. The dose-response curve as linear in the range of 15.6-10000 ng, equivalent to 4 to 3000 mg/liter of urine. The limit of sensitivity was 16 ng of albumin. The coefficient of assay variation was 4.8%, both at 44 mg/liter and at 1304 mg/liter. A displacement curve obtained with a serially diluted urine sample of high albumin concentration was completely superimposable with the curve for which human albumin was used as a standard. In 26 normal individuals the range for Ualb was 2.2--12.6 mg/24h, and for albumin clearance (Calb, 1.8 x 10(-5)-19.6 x 10(-5) ml/min. After renal homografts in 25 patients, Ualb ranged from 16.9 to 9928 mg/24 h, and Calb from 2.7 x 10(-4) to 1.7 x 10(-1) ml/min. Both increased Ualb and Calb correlated well with the severity of renal homograft rejection.     

Immunoturbidimetry of urinary albumin: prevention of adsorption of albumin; influence of other urinary constituents

I describe a simple, rapid immunoturbidimetric assay for low concentrations of albumin in urine (2 to 260 mg/L). However, in this assay, the human serum albumin (HSA) in the standards binds nonspecifically to the polystyrene or glass tubes. This nonspecific binding cannot be prevented by adding bovine serum albumin (BSA) to standards, because the anti-HSA antibody cross reacts with BSA. Adding Triton X-100 (1 mL/L) to standards effectively prevents this nonspecific binding of HSA from standards to both polystyrene and glass tubes. High concentrations of compounds found in urine from normal and diabetic subjects do not interfere with this assay if pH extremes can be avoided. The between-day CV is 4.8% at means = 18.8 mg/L and 2.0% at means = 183.1 mg/L. Measurements by this immunoturbidimetric method (y) correlate well with those obtained by a radioimmunoassay (x): y = 1.078x - 0.141 mg/L (n = 98; r = 0.984) and with those obtained by a radial immunodiffusion method (x'): y = 1.026x' - 0.117 mg/L (n = 98; r = 0.983). Urinary excretion of albumin by 25 healthy, nondiabetic subjects was less than 8 micrograms/min.     

Enzyme immunoassay for urinary albumin

We describe an enzyme-linked immunosorbent assay for urinary albumin, performed on microtiter plates with use of commercially available antisera and peroxidase conjugate. The assay range is 3-1000 micrograms/L, the sensitivity 625 pg. The method is suitable for measurement of albumin excretion in either normal or pathological urine. For 20 normal children, the range of urinary albumin excretion was 1.7-22.9 mg/24 h.     

Characterization of immunochemically nonreactive urinary albumin

BACKGROUND: Conventional immunoassays underestimate the urinary albumin concentration because intact albumin in urine exists in two forms, immunoreactive and immunochemically nonreactive. METHODS: Urinary albumin concentration measured by HPLC (which measures total albumin, i.e., the sum of immunoreactive albumin + immunochemically nonreactive albumin) or RIA was compared with densitometric analysis of albumin bands in diabetic urine samples separated by either native polyacrylamide gel electrophoresis (PAGE) or reducing sodium dodecyl sulfate (SDS)-PAGE. Immunochemically nonreactive albumin was also isolated from diabetic urine (relative amount detected, 70-80% of the expected) and was tested for contamination by common urinary proteins by native PAGE, ELISA, and capillary electrophoresis. RESULTS: Urinary albumin concentrations measured by native PAGE and HPLC were better correlated (r(2) = 0.83) than concentrations measured by native PAGE and RIA (r(2) = 0.62) because under native conditions both native PAGE and HPLC detect total albumin and not only the immunoreactive albumin alone that is measured by RIA. Urinary albumin concentrations measured by reducing SDS-PAGE and RIA were better correlated (r(2) = 0.84) than concentrations measured by reducing SDS-PAGE and HPLC (r(2) = 0.65) because under reducing conditions immunochemically nonreactive albumin is unstable and fragments into many smaller peptides. The partially purified preparation was found to contain <1% contamination by common urinary proteins and is stable to freezing and frequent freeze/thaw cycles. CONCLUSIONS: The results are consistent with the interpretation that immunochemically nonreactive albumin has a limited number of polypeptide chain scissions and is held together by noncovalent intrachain bonding and disulfide bonds. Detection of this molecule is likely to be of clinical importance in diagnosing kidney disease as well as cardiovascular disease.     

尿微量白蛋白的测定及其临床意义

目的使用Beckman ICS—Ⅱ免疫分析仪测定尿微量白蛋白，对该测定方法及临床应用进行评价。方法运用手动速率散射比浊法测出抗原和抗体结合的速率峰值，其高低与抗原的含量成正相关。结果通过对糖尿病、高血压、动脉硬化、健康人群检测尿微量白蛋白，证明该法具有准确，快速，经济，操作简单，效果满意，其相关系数在0．97以上。结论Bekman ICS—Ⅱ免疫分析仪测定尿微量白蛋白，结果可靠，可用于对糖尿病、高血压等相关疾病的病情监测，评估，疗效观察等。     

Heterogeneity of urinary albumin from diabetic patients

A fundamental cause of diabetic microalbuminuria, heterogeneity of normal and diabetic urinary albumin was shown by affinity chromatography on Cibacron Blue F3GA. By changing the properties of interaction with the matrix, the protein was separated into six fractions. Samples of urinary albumin from proteinuria patients showed the same elution profiles as those of serum albumin, whereas those from controls or normoalbuminuria diabetic patients exhibited different elution patterns. The relative percentage of the resin unbound fraction of urinary albumin was ten or more times higher than that of serum albumin, and the ratio decreased with increasing albumin excretion into urine. More than 6 mol fatty acid/mol albumin combined with the unbound fraction. It is suggested that microalbumin excretion into urine is the result of excessive unesterified fatty acid binding to the protein.     

Microplate measurement of urinary albumin and creatinine

We describe microplate methods for measurement of human urinary albumin (HUA) by competitive enzyme-linked immunosorbant assay (ELISA) and creatinine with a modified commercial enzymatic kit. Incorporation of substrate mixing into the competitive ELISA changes the dynamic absorbance-concentration response, greatly simplifying calculations and improving sensitivity and accuracy. Measurement of creatinine in urine and plasma samples with a commercially available enzymatic kit modified for analysis by use of an inexpensive microplate reader produced values comparable in precision and accuracy to those obtained by an automated kinetic Jaffé method.     

尿视黄醇结合蛋白的检测及临床应用

对１０５例病人进行酶免法测定尿视黄醇结合蛋白（ＲＢＰ），糖尿病组２５例ＲＢＰ排泄增高，阳性率为４３％，其中１１例伴尿Ａｌｂ同时增高占１９％，另１４例尿Ａｌｂ正常，ＲＢＰ排泄阳性率为２９％；高血压病组７例，ＲＢＰ与Ａｌｂ同时增高，阳性率２１％；肾小球肾炎组３例ＲＢＰ与Ａｌｂ同时增高，阳性率２１％；糖尿病与高血压及肾小球肾炎对比有显著差别（Ｐ〈０．０５），表明尿ＲＢＰ测定是肾小球损害的一项敏感指标。     

人群调查中尿白蛋白检测方法的探讨

目的 探讨人群调查中尿白蛋白标本留取及检测方法.方法 选取659名北京市居民,收集其24 h尿测定UAER;并留取次日随机尿和晨尿,分别采用尿ACR及半定量尿白蛋白试纸法测定尿白蛋白.以24 h UAER作为标准,建立应用两种方法检测晨尿和随机尿白蛋白的ROC曲线,比较敏感度、特异度及ROC曲线下面积.结果 晨尿和随机尿ACR分别为9.36(5.12～33.29)mg/g及11.29(6.34～41.29)mg/g,组间比较差异无统计学意义(t=-1.382,P＞0.05),相关分析显示两者高度相关(r=0.932,P＜0.01).晨尿和随机尿ACR与24 h UAER具有高度相关性,相关系数分别为0.853及0.874,P均＜0.01.随机尿ACR诊断白蛋白尿的敏感度为77.9%,特异度为91.0%,晨尿ACR诊断白蛋白尿的敏感度为78.4%,特异度为95.7%.随机尿白蛋白试纸法诊断白蛋白尿的敏感度为90.3%,特异度为41.1%,特异度明显低于ACR法.随机尿与晨尿ACR的ROC曲线下面积分别为0.918±0.012及0.929±0.015,组间比较差异无统计学意义(χ2=2.13,P＞0.05).随机尿白蛋白试纸法ROC曲线下面积0.661±0.021,低于随机尿ACR(χ2=248.41,P＜0.01).结论 随机尿的ACR兼具简便及准确的特点,是人群调查中诊断白蛋白尿的良好指标.

Abstract：

Objective To evaluate the spot urine sample collection method and value of urinary albumin measurement in population survey. Methods Six hundred and fifty-nine Beijing residents were requested to collect 24 h urine for detection of UAER, as well as random spot urine samples and morning urine samples in the next day. Rapid semi-quantitative urinary albumin-specific dipstick and ACR were measured in each spot urine specimen. The 24 h UAER was measured as golden standard to generate ROC curves and evaluate the sensitivity, specificity and AUC of each method. Results The value of ACR in the morning spot urine samples and random spot urine samples were 9. 36(5. 12-33.29) mg/g and 11.29(6. 34-41.29) mg/g respectively and there was no significant difference between these two groups (t = - 1. 382,P＞0.05). The correlation was significant in the two groups (r = 0.932, P ＜ 0.01). The correlation coefficient between ACR in the morning spot urine samples and UAER was 0. 853 (P ＜ 0. 01). The correlation coefficient between ACR in the random spot urine samples and UAER was 0. 874 (P ＜0. 01).The sensitivity and specificity of ACR for diagnosis of albuminuria in the random urine samples were 77. 9% and 91.0%. The sensitivity and specificity of ACR for diagnosis of albuminuria in the morning urine samples were 78. 4% and 95.7%. Concerning the semi-quantitative urinary albumin-specific dipstick, sensitivity and specificity were 90. 3% and 41.1% , respectively. The specificity was much lower than that of ACR. The area under the ROC curves of ACR in the random urine specimens and the morning urine specimens was 0. 918 ±0. 012, 0. 929 ± 0. 015, respectively. There was no statistical difference between these two groups (χ2 =2. 13, P＞0. 05). The area under the ROC curves of semi-quantitative urinary albumin-specific dipstick in the random urine specimens was 0.661 ±0.021, lower than that of ACR (χ2 = 248.41, P＜0.01).Conclusion Measurement of ACR in random urine samples is a reasonable method with simplicity and accuracy for the detection of albuminuria in general population screening program.     

Reactivity of urinary albumin (microalbumin) assays with fragmented or modified albumin

BACKGROUND: Controversy exists regarding occurrence and measurement of structural variants of albumin in urine. In this study, we examined cross-reactivity of in vitro modified albumins in assays for urine albumin (microalbumin). METHODS: We analyzed albumin modified by reagents, trypsin, or physical treatments or differing in primary sequence (animal albumins) with an immunoturbidimetric assay (Beckman LX20) using goat antiserum and a competitive immunoassay (Siemens Immulite) using a monoclonal antibody. We assessed occurrence of albumin fragments in urine by use of Western blotting of 24 specimens. RESULTS: Chemical modification, modest sequence substitution (gorilla albumin), or cleavage of albumin by cyanogen bromide (CNBr) had little effect on reactivity in the LX20 assay. Albumin extensively cleaved with trypsin retained partial reactivity. The Immulite assay generally was affected more severely by albumin modifications and sequence changes. Western blots of fresh urine specimens or specimens stored at -80 degrees C showed little albumin fragmentation, but some specimens stored for 3 years at -20 degrees C had extensively fragmented albumin that was detected by the LX20 but not the Immulite assay. CONCLUSIONS: Nearly equivalent reactivity of intact albumin and CNBr fragments in the immunoturbidimetric assay indicates reactivity of antibodies with multiple epitopes throughout albumin. Therefore, it is difficult to abolish reactivity of albumin in this type of urine albumin assay. Differential sensitivity of 2 assays to albumin modification identifies a potential source of assay nonequivalence in measuring urinary albumin, particularly for specimens stored at -20 degrees C.