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Thread: meaning of serum and free testosterone levels?

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    Default meaning of serum and free testosterone levels?

    Just looking through an article, what does serum total and free testosterone levels mean? does it refer to testosterone as a whole, I cant find anything online to give me the answer, and I dont want to get confused thanks

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    Atlas Tatyana's Avatar
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    Free testosterone is a calculation in the majority of labs these days.

    It isn't measured anymore as it is too expensive and too time consuming.

    Really, in the clinical assessment of testosterone, you either have a high testosterone or a low testosterone, the free testosterone is really a bit outdated.

    Testosterone and SHBG are not the most accurate of assays, so two somewhat correct results give you a somewhat correct free testosterone.

    A calculator:
    http://www.issam.ch/freetesto.htm


    A comparison of five different methods of calculating free test:

    http://www.clinchem.org/cgi/content/full/52/9/1777


    And an abstract about calculating free testosterone.

    Endocrine Abstracts (2002) 4 P87
    CONCORDANCE OF RESULTS FOR TWO METHODS OF CALCULATING FREE TESTOSTERONE CONCENTRATION. ARE THE RESULTS VALID?
    FM Ivison, AC Robinson & MJ Diver
    Clinical Chemistry, Royal Liverpool University Hospital, Liverpool, UK.
    Many laboratories offer a simple ratio of total testosterone (T):SHBG as an index (FAI) of free androgens.

    Methods for measuring free T (fT) are time consuming (equilibrium dialysis, ED) or reveal concentrations at odds with accepted values (RIA).

    The validity of FAI has been questioned and an alternative assessment by computation of fT recommended (1). We use a simpler calculation (2) producing results comparable to established literature.

    We have compared results obtained by these two calculations in a series of 128 healthy men and in an unselected series of both male (191) and female (646) patients. Both methods of calculation involve measuring T & SHBG. Samples were taken with Ethical approval and informed consent. The 2 formulae are previously published (1,2).

    Calculated fT showed a strong correlation between the two formulae for patients and controls (r = 0.995, men, r = 0.996, women, r = 0.995, controls). Linear regression analysis revealed the intercepts and slopes for men, women and controls were significantly different from each other (formula 1 = 0.997xformula 2 - 35.6, formula 1 = 0.87xformula 2 - 4.0, formula 1 = 1.06xformula 2 - 66.0, respectively).

    The mean difference between calculated fT by formula 1 & 2 was comparable for the men and controls (36, 95%CI 33.7-8.3pmol per litre, and 39, 95%CI 36.3-42.1 pmol per litre, respectively) and much lower for the women (9, 95%CI 8.6-9.4 pmol per litre). If fT < 200pmol per litre is taken as the lower reference limit, 2 men with normal T had fT less than this cut-off using either formula. A further 25 men had low T & fT by either formula. An additional 9 cases had low fT calculated by formula 2 but not formula 1 and of these 4 had normal T.

    Calculation of fT offers a quick and simple alternative to ED or RIA.


    1.Vermeulen A, Verdonck L, Kaufman JM. J Clin Endocrinol Metab 1999;84:3666-72.

    2.Nanjee MN, Wheeler MJ. Ann Clin Biochem 1985;22:387-90.


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    thanks for the reply tatyana, youre a star


    http://ajpendo.physiology.org/cgi/co...281/6/E1172/T2

    that is the paper Im referring to, it already shows the free testosterone levels, so I dont need to calculate it, just using this paper as part of my project. So when talking about the results you see, it is best to talk more about free test or total test,

    Im still not entirely sure what they mean, Ill research it and get back thanks

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    Atlas Tatyana's Avatar
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    If you check the method, as this is a research paper and obviously done in a research lab, they measured the free test.

    Most diagnostic labs would calculate.

    Adverse experiences, blood counts and chemistries, PSA, plasma lipids, total and free testosterone, luteinizing hormone (LH), sex steroid-binding globulin (SHBG), and insulin-like growth factor I (IGF-I) levels were measured periodically during control and treatment periods. Serum total testosterone was measured by an immunoassay (8-11); free testosterone by equilibrium dialysis (43); LH, SHBG, and PSA by immunoradiometric assays (9-11); and IGF-I by acid-ethanol extraction and immunoassay (28). The sensitivities and intra- and interassay coefficients of variation for hormone assays were as follows: total testosterone (0.6 ng/dl), 8.2 and 13.2%; free testosterone (0.22 pg/ml), 4.2 and 12.3%; LH (0.05 U/l), 10.7 and 13.0%; SHBG (6.25 nmol/l), 4 and 6%; PSA (0.01 ng/ml), 5.0 and 6.4%; and IGF-I (80 ng/ml), 4 and 6%, respectively. These assays have been validated previously (8-11).


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    Atlas Tatyana's Avatar
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    Quote Originally Posted by ukstrongman View Post
    thanks for the reply tatyana, youre a star


    http://ajpendo.physiology.org/cgi/co...281/6/E1172/T2

    that is the paper Im referring to, it already shows the free testosterone levels, so I dont need to calculate it, just using this paper as part of my project. So when talking about the results you see, it is best to talk more about free test or total test,

    Im still not entirely sure what they mean, Ill research it and get back thanks

    Oh, sorry, I didn't really answer your question.

    It is only the free testosterone that is biologically active, the rest is sort of a reservoir in the blood, bound to albumin and SHBG.


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    Quote Originally Posted by Tatyana View Post
    Oh, sorry, I didn't really answer your question.

    It is only the free testosterone that is biologically active, the rest is sort of a reservoir in the blood, bound to albumin and SHBG.

    Yeah I just read in a book that only 2% os serum test circulates freely from protein binding, the rest is bound to SHBG or albumin, 2% seems so tiny!!! so for all the test we have in our body as males we dont use much of it!!!

    or even when injecting steroids, the same applies

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