Can This Patient Start HRT Without LH/FSH?
No, a patient with suspected hypogonadism should not start testosterone replacement therapy without first measuring LH and FSH levels, as these tests are essential to determine the etiology of testosterone deficiency and guide appropriate treatment selection. 1
Why LH/FSH Measurement is Mandatory
The AUA explicitly states that clinicians should measure serum luteinizing hormone levels in all patients with low testosterone as a Strong Recommendation (Evidence Level: Grade A). 1 This is not optional—it is a foundational step in the diagnostic algorithm.
Critical Diagnostic Information from LH/FSH
LH/FSH levels distinguish between primary testicular failure (high gonadotropins) and secondary/central hypogonadism (low or inappropriately normal gonadotropins). 1
Low or low-normal LH with low testosterone indicates hypothalamic-pituitary dysfunction, which fundamentally changes management options. 1, 2
Patients with low/low-normal LH are candidates for alternative therapies like selective estrogen receptor modulators (SERMs) or gonadotropin therapy, particularly if fertility preservation is desired. 1, 2
Additional Required Testing Before Starting HRT
Prolactin Measurement is Mandatory in Specific Cases
Serum prolactin must be measured in patients with low testosterone combined with low or low-normal LH levels (Strong Recommendation; Evidence Level: Grade A). 1
Persistently elevated prolactin may indicate pituitary tumors such as prolactinomas, requiring endocrinology referral before initiating testosterone therapy. 1
Men with testosterone <150 ng/dL and low/low-normal LH should undergo pituitary MRI regardless of prolactin levels, as non-secreting adenomas may be present. 1
Why This Matters for Treatment Selection
Starting testosterone without knowing LH/FSH status can lead to inappropriate treatment that suppresses fertility or misses underlying pituitary pathology. 1
Exogenous testosterone provides negative feedback to the hypothalamus and pituitary, suppressing gonadotropin secretion and potentially causing azoospermia. 1
In hypogonadotropic hypogonadism (low LH/FSH with low testosterone), gonadotropin therapy (hCG plus FSH) can initiate spermatogenesis and achieve pregnancies, whereas testosterone monotherapy will suppress this. 1
Patients with functioning pituitary glands but low testosterone may benefit from SERMs, aromatase inhibitors, or hCG to increase endogenous testosterone production while preserving fertility. 1
The Diagnostic Algorithm
The proper sequence is: 1
Confirm low testosterone with two early morning measurements (<300 ng/dL) using the same laboratory and method
Document symptoms consistent with testosterone deficiency (reduced energy, diminished physical performance, fatigue, depression, reduced libido, erectile dysfunction)
Measure LH levels in all patients with confirmed low testosterone
If LH is low or low-normal, measure prolactin
Consider pituitary MRI if testosterone <150 ng/dL with low/normal LH
Only after this workup should treatment be initiated, with the choice guided by LH/FSH results and fertility goals
Common Pitfalls to Avoid
Do not assume "mildly decreased" testosterone automatically warrants standard testosterone replacement. 1
The threshold for treatment requires both laboratory confirmation (<300 ng/dL on two occasions) and clinical symptoms—laboratory values alone do not justify treatment. 3, 2
Skipping LH/FSH testing may result in missing reversible causes of hypogonadism (hyperprolactinemia, pituitary adenomas) or inappropriately suppressing fertility in men with secondary hypogonadism. 1
In men with low/normal LH (functional or secondary hypogonadism), lifestyle modifications including weight loss and exercise can improve testosterone levels by 1-2 nmol/L and should be considered as part of the treatment approach. 2