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Pre-analytical factors that affect testosterone levels in replacement therapy

June 14, 2012
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Total testosterone but not free testosterone (especially analog based free testosterone method) is recommended to monitor testosterone levels in patients who receive testosterone replacement therapy by the American Endo Society. It is also recommended to evaluate the patient 3 to 6 months after treatment initiation, aiming at achieving serum testosterone levels in the mid-normal range. After the targeted serum level is archived, annual check of testosterone level is necessary to assess whether symptoms have responded to treatment and whether the patient is suffering any adverse effects, and to check compliance.

There are a few major pre-analytical factors contributing to fluctuation in testosterone levels: dosage, time of dosing and drug formulation. These factors actually share one root: the pharmacokinetics of testosterone.

American Endo Society provided specific strategy for various testosterone formulations as following:

Injectable testosterone: Patients who are on intramuscular testosterone often have a “saw tooth” pattern of testosterone levels which are higher than optimal soon after injection and decrease to lower than optimal before the next injection.

 • Injectable testosterone enanthate or cypionate: Measure serum testosterone level midway between injections.

 • Injectable testosterone undecanoate: Measure serum testosterone level just prior to each subsequent injection.

 If a patient seems to be having too much variation in levels please confirm the consistency of the time interval between last dosage and blood collection.

 Transdermal patches: Assess testosterone level 3–12 h after application of the patch.

Patches keep testosterone levels stable and with less variation than injections. Transdermal testosterone patches are often placed nightly. Testing an early morning testosterone in patients on transdermal testosterone patches falls into the 3-12h window and is a good strategy. The important point to remember to prevent fluctuation of testosterone levels again is the consistency of the patch placing time and blood collection time.

Buccal testosterone bioadhesive tablet: Assess level immediately before or after application of fresh system.

Transdermal gels: Assess testosterone level any time after patient has been on treatment for at least 1 wk.

However, fluctuation of testosterone levels was observed in patients using transdermal gel. Testosterone levels may appear too low if obtained immediately before gel is applied and too high if it is measured within the hour or two afterwards. It is better to measure a total testosterone after levels have plateaued, about 6 to 8 hours after application.

If levels are consistently too low in a patient on testosterone gel, often the explanation is poor application technique. Applying over as large a surface area as possible maximizes absorption.

Testosterone pellets: Measure testosterone levels at the end of the dosing interval.

Oral testosterone undecanoate: Monitor serum testosterone level 3 to 5 h after ingestion. 

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