Luteinizing hormone determinations obtained with either a monoclonal and a polyclonal antibody radioimmunoassay and their correlations with clinical findings

Non-competitive immunoassay for luteinizing hormone in human serum using capillary electrophoresis with chemiluminescence detection

A non-competitive immunoassay based on capillary electrophoresis (CE) with chemiluminescence (CL) detection has been developed for the determination of luteinizing hormone (LH) in human serum. The work involved the development of separation and CL conditions, allowing for routine analysis of serum samples. In this study, horseradish peroxidase (HRP)-labelled monoclonal anti-LH can catalyse the luminol-hydrogen peroxide reaction. The determined LH can react with excessive amount of HRP-labelled anti-LH. Within 14 min, free enzyme conjugate and immune complex could be separated in alkaline borate buffer by means of a high voltage (15 kV). To improve sensitivity, a series of measures were adopted, including the choice of para-iodophenol as a CL enhancer, unique design in detect window. Under the optimal conditions, the calibration curve for LH was established in the concentration range 1-200 mIU/mL and the detection limit was 0.08 mIU/mL. Compared with ELISA, this method decreased the detection limit by about 12 times, and it has been successfully employed in the determination of LH in human serum.

An electrochemical enzyme immunoassay for chicken luteinizing hormone: extension of the detection limit by adequate control of the nonspecific adsorption

A noncompetitive heterogeneous enzyme immunoassay for the determination of chicken luteinizing hormone (LH) was equipped with an electrochemical endpoint in order to further enhance its sensitivity. The immunological principle of the original ELISA remained essentially unchanged, except for the fact that the peroxidase label was replaced by alkaline phosphatase, since in the upgraded version of the assay, p-aminophenyl phosphate was to be used as the substrate of alkaline phosphatase. Enzyme-generated p-aminophenol was injected into a flow-injection system and detected amperometrically in a thin-layer flow cell with a glassy carbon electrode at 0.325 V vs Ag/AgCl. A classical problem associated with this type of solid-phase immunoassay is the adsorption of proteins other than the capture antibody to the solid phase. The detection sensitivity is therefore often limited by a large background signal observed in the absence of antigen. In the present study, an experiment was designed to examine in each step of the assay the contribution of each of the potential sources of background current. It was shown that the major contribution to the background current was caused by the nonspecific adsorption of biotinylated secondary antibody. Adsorption of the secondary antibody (biotinylated goat anti-rabbit IgG) to the capture antibody (mouse anti-chicken LHbeta) was clearly a case of specific aspecificity, whereas adsorption to the solid phase itself had to be treated as a nonspecific aspecificity. Addition of 0.25% mouse serum to the secondary antibody as a source of mouse immunoglobulin could overcome the cross-reaction and markedly reduced adsorption to capture antibody. The second part of nonspecific adsorption was eliminated by using combinations of Tween 20 and bovine serum albumin as blocking agents. Controlling the adsorption of the biotinylated secondary antibody in this way decreased the detection limit from 39 pg/ml in the original assay to 2.5 pg/ml in the electrochemical version. This way, the plasma volume of samples containing on the order of 1 ng/ml LH was reduced to less than 10 microl. The linear range was 2.5-625 pg/ml. The method allowed us to measure LH in buffer and in adult and juvenile chicken plasma.

Undetectable luteinizing hormone levels using a monoclonal immunometric assay

Previous studies have shown wide discrepancies among the results obtained with different immunometric assays. We present five cases (out of 4000 women) whose plasma luteinizing hormone was not detected using a LH immunometric assay (LH Stratus Baxter) but was recognized by other kits. These cases concerned one 28-year-old woman presenting with infertility and four postmenopausal women. The LH Amerlite kit gave detectable but low results. The results obtained with the other kits were > 7 IU/l. FSH levels were > 7 IU/l. In one case, sera were taken before and after the menopause; differences between the LH results increased. Discrepancies among LH assay kits have been attributed to variation both in standard curve calibration and in epitope specificity of the kit monoclonal antibodies. The Baxter kit might misrecognize some isoforms present in postmenopausal women. The present data illustrate the potential false results with such immunoassays in routine clinical laboratory testing. When undetectable LH results are not clinically explained or when disparities between LH and FSH are observed, we suggest using a second methodology or a bioassay if necessary. Improvement in LH assays and standardization might resolve the problem of discrepancies between the LH results.

Gonadotropin evaluation in the diagnosis of polycystic ovary syndrome using either a monoclonal or a polyclonal antibody radioimmunoassay

The LH/FSH ratio values between gonadotropins dosed with a monoclonal antibody assay (IRMA) in the micropolycystic ovary syndrome (PCOS), are discussed and compared to those obtained with the classic assays using polyclonal antibodies. Because of the higher selectivity of this IRMA assay it is noteworthy that the cut-off value between normal and PCOS patients is now equal to or above one. The evaluation of the LH/FSH ratio between the peak values of the two gonadotropins after a GnRH 100 micrograms iv bolus, may be useful in the diagnosis of PCOS in those patients who present an LH/FSH less than 1 in basal conditions even in the presence of clinical and ecographic aspects of PCOS.

Use of combined exogenous gonadotropins and pulsatile gonadotropin-releasing hormone in patients with polycystic ovarian disease

We previously tested a combined regimen based on the administration of gonadotropin in the early follicular phase followed by pulsatile gonadotropin-releasing hormone (GnRH) until complete follicular maturation in patients suffering from polycystic ovarian disease. Despite good clinical results, a high rate of premature luteinization was observed with this approach. We therefore evaluated in this study whether starting pulsatile GnRH therapy before gonadotropin administration might reduce premature luteinization. Eight women underwent induction of ovulation with both combined therapy and pure exogenous follicle-stimulating hormone alone using a crossover scheme. No premature luteinization and a single follicular growth were recorded with the modified combined regimen. Clinical results (8/8 versus 3/7 ovulatory cycles; 3/8 versus 1/7 pregnancies) favor the combined approach over gonadotropin alone.