Is it likely that my hypogonadism was present but not noticeable before given my sudden onset of erectile dysfunction and low libido with a total testosterone level of 40 and SHBG of 90 nmol?

Sudden Onset Hypogonadism: Likely Acquired, Not Pre-existing

Your hypogonadism with total testosterone of 40 ng/dL (1.4 nmol/L) and SHBG of 90 nmol/L is almost certainly a recently acquired condition, not a longstanding problem that was previously asymptomatic. The sudden onset of symptoms 6 months ago, combined with your well-controlled diabetes and hypothyroidism, strongly suggests a new endocrine disturbance rather than unmasking of pre-existing hypogonadism.

Why This is Likely New-Onset Hypogonadism

Your testosterone level is severely low—far below the diagnostic threshold of 300 ng/dL (10.4 nmol/L) used in most guidelines. 1, 2 This degree of deficiency would have caused noticeable symptoms earlier if it had been longstanding. Men with testosterone levels this profoundly suppressed typically experience:

• Progressive loss of libido and erectile function over time
• Gradual changes in body composition (muscle loss, fat gain)
• Declining energy levels
• Mood changes

1

The fact that you felt completely normal until 6 months ago—with good erections, high libido, and normal semen volume—makes it highly unlikely this severe deficiency existed previously.

The SHBG Factor: A Critical Clue

Your SHBG of 90 nmol/L is significantly elevated (normal range typically 20-60 nmol/L), which further supports recent onset. 1, 3 While elevated SHBG can mask hypogonadism by lowering total testosterone while free testosterone remains normal, your total testosterone is so profoundly low that even accounting for high SHBG, your free testosterone must be severely deficient. 3, 4

In obesity-related hypogonadism (which can occur with diabetes), SHBG is typically low, not high. 1 Your elevated SHBG suggests a different mechanism:

• Thyroid dysfunction (though you report this is well-controlled)
• Liver disease
• Aging-related increases (SHBG rises with age, especially after 60)
• Medication effects
• HIV infection (less likely given your history)

3, 4

Essential Next Steps for Diagnosis

You need immediate repeat morning testosterone measurement (between 8-10 AM) plus additional hormonal evaluation to determine the cause. 1, 2 The diagnostic workup should include:

Confirmatory Testing

• Second morning total testosterone (diagnosis requires two low measurements) 2, 5
• Free testosterone by equilibrium dialysis (most accurate method, essential with your elevated SHBG) 1, 3, 4
• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to distinguish primary testicular failure from secondary (pituitary/hypothalamic) hypogonadism 1, 2

Additional Evaluation Based on LH/FSH Results

If LH/FSH are low or inappropriately normal (secondary hypogonadism):

• Prolactin level (pituitary adenoma screening) 1, 2
• MRI of pituitary if prolactin elevated or other pituitary dysfunction suspected 1
• Iron saturation (hemochromatosis can cause hypogonadism) 1
• Review all medications for testosterone-suppressing drugs (opioids, glucocorticoids, anabolic steroids) 1

If LH/FSH are elevated (primary testicular failure):

• Testicular examination for masses, atrophy, or trauma
• Karyotype if Klinefelter syndrome suspected (though unlikely with your previous normal function)

1

Diabetes and Hypothyroidism Considerations

Your well-controlled diabetes and hypothyroidism are relevant but unlikely sole causes of this acute change. 1

• Diabetes is associated with lower testosterone levels, but this is typically gradual and related to obesity/metabolic syndrome, not sudden onset. 1 Diabetes-related hypogonadism usually presents with low SHBG, not elevated. 1

• Hypothyroidism, if undertreated, can lower testosterone, but you report this is well-controlled. Conversely, hyperthyroidism or overtreatment with thyroid hormone can elevate SHBG. 3 Verify your thyroid function tests are truly optimal.

Critical Pitfalls to Avoid

Do not accept a diagnosis based on a single testosterone measurement, even one this low. 2, 5 Guidelines require two separate morning measurements for confirmation.

Do not rely solely on total testosterone given your elevated SHBG. 3, 4 Free testosterone measurement is essential in your case—up to 17% of men with ED have normal total testosterone but low free testosterone, especially with elevated SHBG. 3

Do not delay evaluation for secondary causes. 1 Sudden-onset severe hypogonadism can indicate:

• Pituitary tumor (prolactinoma or other adenoma)
• Hemochromatosis
• Medication effects
• Acute illness or critical illness
• Infiltrative diseases (sarcoidosis, histiocytosis)

These require specific treatment beyond testosterone replacement.

Treatment Implications

Once confirmed and the etiology is determined, testosterone replacement therapy is indicated for your severe symptomatic hypogonadism. 1 Benefits include:

• Improved sexual function (libido and erectile function)
• Increased muscle mass and strength
• Improved bone density
• Better quality of life and well-being

1, 6

However, treatment of the underlying cause takes priority over testosterone replacement if a reversible etiology is identified. 1 For example, if a pituitary adenoma is found, neurosurgical evaluation is needed. If medication-induced, stopping the offending agent may restore normal testosterone production.

The sudden onset of your symptoms strongly argues against this being a longstanding condition that simply became symptomatic—your testosterone level is too low and your previous function was too normal for that explanation to fit.