PF4 and systemic lupus erythematosus: Interestingly, the urine levels of the biomarker proteins correlated with the serum levels of the same proteins, particularly in active LN patients, weakly (ALCAM), modestly (Hemopexin, PF-4, TFPI, VCAM-1) or strongly (properdin), as plotted in Figure 2, even though the serum levels could not distinguish active LN from other SLE patients, with most of the biomarkers.