It is unclear why serum PlGF did not reflect RA activity, but this finding may be associated with the very low level of PlGF in RA sera in contrast to that in RA SF; indeed, serum PlGF was detectable (above 10 pg/ml) in only 18 (11.5%) out of 157 RA patients tested, whereas serum VEGF was measurable in the majority of the RA patients (100 patients, 63.7%). This evidence concerns the gene PGF and rheumatoid arthritis.