FST and Impaired glucose tolerance: Results. Serum levels of activin A (93.3 ± 27.0 pg/mL, mean ± SD), B (81.8 ± 30.8 pg/mL), or follistatin (6.52 ± 3.15 ng/mL) were not different (P > 0.05) between subjects with normal OGTT (n = 39), impaired glucose tolerance and/or fasting glucose (n = 17), or T2D (n = 36).