🧊 On an Aromatase Inhibitor

What this panel can settle, and by what logic

Nine markers for the man who feels worse on an aromatase inhibitor than he did without one, and cannot tell whether that is the estradiol or the testosterone.

1. The assay is the panel. Direct immunoassay estradiol is unreliable at the low male concentrations an aromatase inhibitor produces, which is the subject of an Endocrine Society position statement Rosner 2013 and of accuracy-based proficiency testing that measured how far apart methods actually sit Tim Cao 2023. Only the LC-MS/MS assay is on this requisition, and that single choice is most of what makes the result usable.
2. Total Testosterone and Free Testosterone with SHBG (Sex Hormone-Binding Globulin) give the other half of the ratio. The testosterone to estradiol ratio has been reviewed as a measurement, including how much of its apparent variation is assay rather than biology Swislocki 2024, and free testosterone cannot be interpreted without SHBG beside it.
3. LH & FSH says what the drug is actually doing. In a man not on exogenous testosterone, blocking aromatase releases pituitary feedback and raises LH, FSH and testosterone, which is the mechanism behind its use as a testosterone-raising strategy and was demonstrated in randomized work in older men Leder 2004. In a man on TRT the gonadotropins are already suppressed and that mechanism is gone, so the only thing the drug does is subtract estradiol.
4. Vitamin D (25-Hydroxy) and the calcium on the Comprehensive Metabolic Panel (CMP) are the half of the bone question you can act on now. Aromatase inhibition lowers estradiol and has measurable effects on bone mineral density and bone turnover in men Burnett-Bowie 2009, and in postmenopausal women a steroidal inhibitor produced measurable bone density change over years Cheung 2012.
5. The Lipid Panel (Cholesterol, HDL, LDL, Triglycerides) with ApoB (Apolipoprotein B) and hs-CRP (High-Sensitivity C-Reactive Protein) is the metabolic cost. Aromatase inhibition in men has been studied against lipids and inflammatory cardiovascular markers directly Dougherty 2005, and ApoB is the lipid measurement that tracks residual risk better than the cholesterol-based ones Johannesen 2021.

What it cannot settle, and what would

It cannot measure your bone density, which is the cost that matters most. Bone loss from a sustained low estradiol takes years and is measured by DEXA Burnett-Bowie 2009Cheung 2012. If you have run an aromatase inhibitor continuously for more than a couple of years, that scan is the measurement worth buying and no blood marker replaces it.

It cannot tell you that estradiol is the reason you feel bad. Low libido, low mood and aching joints have a long differential, and a mid-range estradiol with those symptoms means the search continues somewhere else. This panel can rule the crash in or out; it cannot rule everything else out Swislocki 2024.

It cannot make existing breast tissue regress. Gynecomastia that has become fibrotic stops responding to hormonal manipulation regardless of what the estradiol does, so lowering estradiol further is not a treatment for tissue that is already established.

And it cannot be compared across laboratories. Estradiol methods disagree enough at male concentrations that a value from one laboratory and a value from another are not a trend Tim Cao 2023Rosner 2013. Use the same laboratory and the same assay every time.

Draw conditions that decide whether the money is wasted

Trough timing and steady state, and the two are different conditions.

1. Draw immediately before your next testosterone injection and before the day's inhibitor dose. The same protocol reads completely differently at peak and at trough Swislocki 2024.
2. Not within 2 weeks of starting, stopping or changing the inhibitor. Anastrozole is a reversible inhibitor reaching steady state in about a week Leder 2004; exemestane inactivates the enzyme irreversibly, so its effect outlasts the last tablet by considerably longer Cheung 2012.
3. Write the exact drug, dose and schedule on the requisition. The drugs in this class are not interchangeable at the same milligram number, and a result read against the wrong assumption is worse than no result.
4. Morning, fasted 9 to 12 hours for the Lipid Panel (Cholesterol, HDL, LDL, Triglycerides), ApoB (Apolipoprotein B) and Comprehensive Metabolic Panel (CMP).

How you would know it answered your question, and what each pattern means next

Four patterns, and the marker that should move if you change something.

• Low or undetectable Estradiol, Sensitive (LC/MS-MS) with joint pain, low libido and low mood: the crash. Less inhibitor rather than more testosterone, and the confirmation is estradiol rising into the male range at the same trough timing with the symptoms following it Leder 2004.
• Mid-range estradiol with the same symptoms: estradiol is not the explanation, and lowering it further will make things worse Swislocki 2024.
• HDL falling and ApoB (Apolipoprotein B) rising across two draws: the metabolic cost is showing Dougherty 2005Johannesen 2021. Recheck 8 to 12 weeks after any dose reduction.
• Risen LH & FSH and testosterone in a man NOT on exogenous testosterone: the drug is doing what it was chosen to do Leder 2004, and the question becomes whether the estradiol has been taken too low in the process.

Sources read for these sections

• Leder BZ, Rohrer JL, Rubin SD, Gallo J, Longcope C. Effects of aromatase inhibition in elderly men with low or borderline-low serum testosterone levels.. J Clin Endocrinol Metab 2004 · PMID 15001605
• Burnett-Bowie SA, McKay EA, Lee H, Leder BZ. Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels.. J Clin Endocrinol Metab 2009 · PMID 19820017
• Dougherty RH, Rohrer JL, Hayden D, Rubin SD, Leder BZ. Effect of aromatase inhibition on lipids and inflammatory markers of cardiovascular disease in elderly men with low testosterone levels.. Clin Endocrinol (Oxf) 2005 · PMID 15670201
• Cheung AM, Tile L, Cardew S. Bone density and structure in healthy postmenopausal women treated with exemestane for the primary prevention of breast cancer: a nested substudy of the MAP.3 randomised controlled trial.. Lancet Oncol 2012 · PMID 22318095
• Rosner W, et al. Challenges to the measurement of estradiol: an endocrine society position statement. Journal of Clinical Endocrinology and Metabolism 2013 · PMID 23463657
• Swislocki ALM, et al. A Review on Testosterone: Estradiol Ratio-Does It Matter, How Do You Measure It, and Can You Optimize It?. World Journal of Men's Health 2024 · PMID 39344113
• Johannesen CDL, et al. Apolipoprotein B and Non-HDL Cholesterol Better Reflect Residual Risk Than LDL Cholesterol in Statin-Treated Patients. Journal of the American College of Cardiology 2021 · PMID 33736827
• Tim Cao Z, et al. Accuracy-based proficiency testing for estradiol measurements. Clinical Biochemistry 2023 · PMID 38043696