Several prospective clinical studies on SLE have indicated that the urine concentration of PF4 is considerably higher in patients with active LN than in those with active non-renal SLE, non-active SLE, or healthy controls, indicating that PF4 is a potential non-invasive biomarker for predicting kidney disease activity in SLE [189,190,191]. This evidence concerns the gene PF4 and systemic lupus erythematosus.