Abstract: Objective To evaluate the laboratory-made reference materials for detection of erythrocyte sedimentation rate （ESR） in internal quality control （IQC）. Methods Red blood cells separated from fresh animal blood were washed and fixed. Six batches of the reference materials with different ESR values （Lot：ESR01-ESR06） were prepared by mixing with laboratory-made simulated plasma. The homogeneity and stability of the reference materials and the commercial reference materials （Lot：QC01-QC02） were compared following ISO Guide 35 and CNAS-GL03. And three levels of the reference materials with similar ESR value of commercial reference materials were selected for internal quality control in different measuring systems. Results Homogeneity evaluation showed that both reference materials were homogeneous and no difference among bottles was noted （P>0.05）. The bottle-to-bottle homogeneity uncertainty of laboratory-made and commercial reference materials，which were of similar ESR values （e.g. ESR01 Vs QC01，ESR04 Vs QC02），was 0.2 mm/h-1.0 mm/h and 0.8 mm/h-1.5 mm/h，respectively. The results of short-term stability showed no trend change after repeated testing within 4 weeks （P> 0.05） when stored at room temperature or refrigerated condition. However，when stored at refrigerator，the reference reagents （ESR02，ESR03，ESR04 and QC02） gave rise to the fluctuation beyond the evaluation criteria. No trend change （P>0.05） of stability after long-term （25 weeks） storage at refrigerated condition was noted for laboratory-made reference materials. The long-term stability uncertainty of laboratory-made and commercial reference materials （e.g. ESR01 Vs QC01，ESR04 Vs QC02），which were of similar ESR value，was 0.1 mm/h-3.0 mm/h and 1.0 mm/h-2.9 mm/h，respectively. The difference of the ESR value over time was in the range of evaluation criteria. Additionally，the CV of laboratory-made reference materials was found to be close to that of the commercial reference with the similar ESR value in internal quality control. Conclusion The laboratory-made reference materials are of high homogeneity and stability and can be used in internal quality control of clinical laboratory diagnosis.

Key words: Erythrocyte sedimentation rate, Reference reagents, Internal quality control