A rise in the biologically active LH: immunologically active LH (B/I) ratio during the normal luteal phase

Biologically active (bio) LH concentrations and immunologically active (immuno) LH concentrations were measured in integrated hourly blood samples collected over 24 h study periods (n = 27) and in 5 min blood samples collected over 2 h study periods (n = 21) during different stages of the menstrual cycle in a group of regularly cyclic women. Episodic fluctuations were seen in both the bio LH and immuno LH concentrations in hourly as well as in 5 min data series. However, there was no consistent correlation between episodes of bio LH and immuno LH. Mean B/I ratio over the 24 h study periods as well as over the 2 h study periods were significantly higher during the luteal phase than during either the follicular phase (p less than 0.002) or the mid cycle (p less than 0.02).