<prompt> 16years old girl presents with rapid onset of hirsutism and amenorrhea . Best investigation is ___Testosterone estimationDihydroepiandrosteroneAdrenocoicoidsLH and FSH estimation  <response>: Testosterone estimation: Assays of testosterone are impoant in the diagnosis and management of a number of clinical conditions in females including precocious pubey, androgen-secreting tumors, and polycystic ovary syndrome PCOS . There are several limitations to their use, and there is currently no standardized assay in the United States. Moreover, most testosterone assays have poor sensitivity and accuracy in the female ranges normal range, 20-60 ngdl, which, even when elevated in conditions such as PCOS, tend to be well below normal male ranges 300-1000 ngdl Circulating levels in females vary according to reproductive maturity, phase of the menstrual cycle, time of day, and also feeding . There are no age and gender normal ranges, and in fact there is no testosterone standard on which to base an assay . Other steroids with similar configuration may cross-react with the antibody used in immunoassay. Measurement of total testosterone by mass spectrometry MS has been recommended as a possible solution to these problems. This is usually performed after extraction and purification by chromatography and is thought to be highly accurate, although gas chromatography GC which is more difficult and costly appears to be more precise than liquid chromatography LC Ref Dutta 4e p 524 ; speroff 7e p 502- 511 