| Microalbuminuria is recognized as an early diagnostic marker of kidney damage caused by diabetes, hypertension or cardiovascular disease. It is very valuable for early diagnosis and treatment evaluation of kidney damage. At present, most guidelines recommend urinary albumin/creatinine ratio (ACR) as detection method of urinary albumin excretion rate (UAER). Now test of creatinine has reference method, reference materials and recommended conventional method, but urinary albumin measurement has no reference method or reference materials. There are so many different systems at domestic and abroad, lack of quality control material, and variety factors can affect test results of albumin, so standardization of urinary albumin measurement is a serious problem.Research purposeInvestigate current situation of urinary albumin measurement in clinical laboratories, analyze performance of conventional methods and differences between these methods, and detect influence of some interference factors in urine. Then recommend 1-2 methods to meet clinical needs.Research contents and methodsFour parts of this study was completed by:1. Through questionnaires and telephone counseling, investigated current situation of urinary albumin measurement in clinical laboratories of 50 hospitals in Tianjin.2. Selected conventional methods:immuno-nephelometry, immuno-turbidimetry, immuno-colloidal gold method, radioimmunoassay (RIA) and chemiluminescence immunoassay (CLIA), to perform methodological evaluation, including imprecision test, recovery rate, linearity, and verified reference interval. While compared detection results between 5 methods.3. Chosen common interfering substance in urine:bilirubin and haemoglobin to perform interference test on 5 methods of urinary albumin.4. Prepared urinary albumin quality control materials, evaluated these materials and used them into internal quality control. Meanwhile, we carried out external quality assessment among clinical laboratories of hospitals in Tianjin.Results1. Application of ACR is not common in Tianjin, there are only 4 hospitals. Detection of creatinine major used 2 methods, picric acid (32%) and liquid enzymatic method (68%). While assay systems of urinary albumin were complex:6 nephelometry systems,6 turbidimetry systems,2 colloidal gold systems. And using of sample, results reporting and biological reference interval of UAER were non-uniform.2. In test of nephelometric, turbidimetric, gold standard method, RIA and CLIA, results of average CV, recovery, linearity (r) and verify reference intervals were:①1.9%,99.6%,1和100%;②4.5%,97.8%,0.95和90%:③2.4%,96.3%,0.99和100%;④6.5%,99.8%,0.99和95%;⑤4.4%,101.6%,0.98和80%。The correlation between assays was 0.701,0.886,0.982 and 0.931, the Bland-Altman plots indicated each assay provided significantly different results from each other.3. Bilirubin and hemoglobin in urine with different concentrations could affect results of urinary albumin assay on all the 5 methods, and interference ratio increased with concentration of disruptor increased., Interference ratio (absolute value) of hemoglobin was greater than 6.72-17.43% when urine occult blood was "+"; and interference ratio was 7.89%-22.94% when urine bilirubin was "+".4. The urinary albumin quality control material has good stability:CV of 7 months was less than 10% when stored at-20℃. Difference between bottles (CV) was small, CV was only 0.64%(4℃) and 0.81%(-20℃) of high-value quality control material. In external quality assessment of Tianjin, CV of low-value quality control material was 63.3%(29.1%-70.3%) and CV of high-value was 20.5%(5.9%-22.3%).Conclusion1. ACR is not widely applied in Tianjin, it need promotion in urgent. Standardization issues of UAER measurement must be addressed.2. There is significantly difference between different methods of UAER. Base on the results of methodological evaluation, nephelometry superior to the other 4 methods.3. Bilirubin and hemoglobin in urine could affect results of urinary albumin assay. Doctors and technicians should be fully taken into account the existence of bilirubin or hemoglobin in urine can impact results of urinary albumin test.4. Urinary albumin quality control materials has good stability and easy to prepare. It can be used in internal quality control and external quality assessment of clinical laboratories. |
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