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List All Test Names Beginning With:
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Testosterone, Free

Source Blood
Mnemonic FTESTO
Specimen Requirements

Free Testosterone is NO CHARGE.

1 x 3.5 mL gold top SST tube AND 1 x 3.0 mL light green (mint) top PST tube

1 mL serum AND 0.5 mL plasma

Specimen Handling
Additional Information The concentration of Free Testosterone is derived from a mathematical expression based on constants for the binding of Testosterone to Sex Hormone Binding Globulin and Albumin.

Indicate gender of the patient on the requisition.

Testosterone exhibits diurnal variation in adult males. Values are highest in the morning, with decreases up to 25% later in the day. Reference intervals were established on specimens collected in the morning (07:00 - 10:00), thus it is suggested to collect specimens within this timeframe. The amplitude of diurnal variation decreases with age, with patients aged >70 showing an approximate 10% decrease.
Diurnal variation of testosterone in females is not well defined in the literature, but similar variation may be expected in pre-menopausal women.
Reference:
Brambilla, DJ, Matsumoto, AM, Araujo, AB, McKinlay, JB. The Effect of Diurnal Variation on Clinical Measurement of Serum Testosterone and Other Sex Hormone Levels in Men. J. Clin. Endocrinol. Metab. 2009. 94(3):907-913.
Testing Location Immunochemistry
Testing Frequency Weekdays
Alternate Name(s) Free Testosterone
Reference Interval

Adult male

175-700 pmol/L

Adult female

2-30 pmol/L