Objective: To investigate the correlation of fibrinogen level and absorbance change in both PT and APTT clotting curves on BCSXP Analyzer. Methods:A serial of standard fibrinogen and 250 patient plasma samples with different qualities(normal, hemolysis, icterus, and lipemia) were run on BCSXP for assays PT, APTT and Fibrinogen. The absorbance change(DeltaA) from baseline to plateau in clotting curve was retrieved and analyzed on its correlation with the Fibrinogen result. Influence of plasma quality and PT/APTT result on this correlation was also studied respectively. Results:Both PT-DeltaA and APTT-DeltaA showed good linear regres-sion with fibrinogen level in the sample, with R2 close to 0.90 in both standard and patient samples. Hemolysis(H), itcterus(I) and lipemia(L) of the sample with valid clotting curves were found to have no significant difference in this correlation from normal(N) sample(R2: 0.83H, 0.92I, 0.81L and 0.79N in PT; 0.89H, 0.95I, 0.91L and 0.89N in APTT) in either PT or APTT curve. PT or APTT result also has little impact on this correlation(0.71 in range 7 ~ 10 sec, 0.56 in10 ~ 20 sec, and 0.70 in 20 sec~; R2 in APTT: 0.88 in 20~30 sec, 0.92 in 30~40 sec, and 0.95 in 40 sec~). Conclusion:The absorbance change in either PT or APTT clotting curve correlates well with the fibrinogen level in plasma, which is independent of plasma quality PT or APTT results. The absorbance change can be used as an alternative way to roughly estimate fibrinogen level in either PT or APTT clotting curve when the result of clauss-based fibrinogen measurement is not available.