CLINICAL-SIGNIFICANCE OF INVISIBLE OR PARTIALLY VISIBLE LUTEINIZING-HORMONE

It is well known that luteinizing hormone (LH), like many other glycop roteins, is heterogeneous and presents several circulating isoforms. R ecently, new sensitive immunometric assays measuring intact LH were de veloped. These assays have been found to underestimate or to be incapa ble of recognizing LH in some patients. This study was undertaken to d etermine the prevalence of such cases and to define their clinical cha racteristics. We compared three LH assays using as capture antibodies either a monoclonal antibody that reacts exclusively with intact LH (E S 600 Boehringer, Stratus Baxter) or a monoclonal antibody against the beta subunit of LH (IMX Abbott). In 17% of 90 patients tested, ES 600 measured >50% lower LH concentrations when compared with the IMX. Mor eover, in two cases LH was not detectable by ES 600 or Stratus, wherea s it was normal with the IMX. We found another five such cases and dis cuss here the clinical data and results of different hormone measureme nts in these seven cases of 'invisible LH'. Although bioactive LH (mou se Leydig cell assay) was normal, the existence of low or even undetec table LH was clinically confusing and led to expensive complementary i nvestigations such as gonadotrophin-releasing hormone analogue tests a nd magnetic resonance imaging. The uses and limitations of these assay s are illustrated by different clinical situations in which the result s of the different assays have been misleading.