We read with interest and appreciate the letter of Wallace and colleagues on inhibin A and B measurement in umbilical cord blood. They failed to detect inhibin A in any samples from male and female babies1, and inhibin B was detected only in serum from male infants1. On the basis of their results, they were surprised by our data on inhibin A and inhibin B measurable in umbilical cord serum2.
This apparent discrepancy seems to be limited to the cord blood compartment. In fact, both in maternal serum and amniotic fluid we found low inhibin B levels in early gestation3,4 confirming previous observations of other groups1,5,6.
Probably, to explain the discrepant observations in cord blood, the contribution of free inhibin β subunits in the cross-reactivity in the assay of inhibin B and A may be hypothesised. However, we and other groups are all using the Serotec kits which show a 10% cross-reactivity of inhibin A in the assay of inhibin B, but this cross-reactivity does not explain the evidence of higher inhibin B levels in presence of low inhibin A concentrations2.
Distinguishing the relative contribution of intrauterine tissues in inhibin A and inhibin B might help in understanding their possible psychological and clinical implications.