RADIoimmunoassay(CT)forthequantitativedeterminationofFreeTestosterone(FT)inhumanserum.

Freetestosteronediffusesthroughcellmembranesandbindstospecificreceptorproteins(androgenreceptors);theTestosterone-receptorcomplexesactastranscriptionalmodulatorsoncis-regulatoryregionsofmanygenes.
ExcessofAndrogensinwomencauseshirsutismandsignsofvirilization;Testosteronelevelinserumhastobedeterminedbeforeandafterovarianandadrenalstimulationandsupressiontoidentifythesourceofexcessivehormoneproduction.
Primaryandsecondaryhypogonadisminmenresultinclinicalhypoandrogenization,correlatedwiththedegreeofgonadalfailureinTestosteroneproduction.ThedeterminationofserumTestosteronetogetherwiththatofLHallowsthecorrectassessementofthoseconditions.
Thediagnosisoftrueanorchiaalsorequirestodiscriminatethisconditionfromcryptorchidism.UnderprolongedhCGstimulation,Testosteronelevelsremainverylowintrueanorchiawhilecryptorchidtestescanrespondtostimulation.
Androgenresistancesyndromes,duetoXlinkedandrogenreceptorgenedeficiencies,aremadeofvariousdegreesofsexualambiguity.Whatevertheseverityofthephenotypicalabnormalities,serumTestosteroneissystematicallyhighinregardstoelevatedLHserumlevelsintheseconditions.
Testosteroneassaysincludetotaltestosterone(direct,extraction,coatedtubes)andfreetestosteronedeterminations.
TotalTestosteroneinplasmaincludesfreeTestosteroneandTestosteroneboundtoSHBG,albumin,CBG.Themeanpercentageofeachinnormalmenis2.7,32,65and<0.1 respectively.
SolventsbreaktheproteinbindinginextractionassayswhereasblockingagentsreleaseTestosteronefromproteinsindirectassays.Theadvantageofafreetestosteroneassayisthatfreetestosteroneconcentrationsareinequilibriumwithtestosteroneboundtoreceptorsintheorgans.