TNFSF13B and systemic lupus erythematosus: The failure to demonstrate a meaningful association between changes in SLEDAI score and changes in plasma BLyS protein levels cannot be attributed to a skewing of the results by the patients in whom plasma BLyS levels were below the limit of detection, because the absence of association between the two persisted among the 27 SLE patients in whom plasma BLyS levels were in the detectable range in both samples (r = -0.069, P = 0.727 for plasma BLyS versus unmodified SLEDAI; r = -0.020, P = 0.919 for plasma BLyS versus modified SLEDAI).