Abnormal circulating protein concentration Reduced insulin-like factor 3 level 2017-05-27T11:44:58Z Reduced plasma INSL3 level Blood concentration of insulin-like factor 3 (ILF3) is below normal limits. Insulin-like factor 3 (INSL3) is a peptide hormone produced in leydig cells of the testes. Its role in the adult male is unknown but INSL3 and its receptor RXFP2 have been linked to bone cell differentiation. It is speculated that low levels of INSL3 could be responsible for low bone mineral density in patients with primary osteoporosis and Klinefelter Syndrome.