Follistatin is a single-chain glycosylated protein that inhibits follicle stimulating hormone (FSH) release. Alternative splicing of Follistatin mRNA yields two isoforms, FS315 and FS288. FS288 is the main cell-surface form and binds to surface heparin sulphate proteoglycans. FST/4282 recognizes recombinant human Follistatin 288, allowing for detection of FSH levels using various analysis methods. This antibody also works in a two site ELISA with FST/4281.