Detecting pre-ovulatory luteinizing hormone surges in urine

The study objectives were to determine (i) if pre-ovulatory luteinizinghormone (LH) surges, undetected in urine by two immunoradiometric assays(IRMA), were detectable by an ultrasensitive immunofluorometric assay(IFMA) and (ii) the influence of creatinine adjustment on the detection andtiming of the urinary LH surges. Daily urine specimens were contributed byhealthy 25-36 year old volunteers during 14 ovulatory menstrual cycles foran epidemiological study conducted in 1983-1985. Specimens were selected ashaving been previously assayed by two IRMA without consistently detectingLH surges. These urine specimens were remeasured using an IFMA and adjustedfor creatinine concentration. IFMA measurements revealed unambiguous LHsurges in all cycles. Adjusting IRMA urinary LH values for creatinineconcentrations revealed previously undetected LH surges in four of eightcycles. Creatinine adjustment also altered the timing of IRMA and IFMA LHsurges by 1-5 days. These results demonstrate an IFMA that detects pre-ovulatory LH surges in unpreserved, frozen urine from cycles where suchsurges were previously undetectable. Further, creatinine adjustment canmarkedly affect detection and timing of the onset and peak of the urinaryLH surge. While our analysis suggests that this adjustment improves thevalidity of the LH measure, this requires further investigation.