What laboratory tests should be drawn for a patient being considered for testosterone replacement therapy?

Laboratory Testing for Testosterone Replacement Therapy

Before initiating testosterone replacement therapy, you must obtain two early morning (8-10 AM) total testosterone measurements showing levels consistently <300 ng/dL, combined with serum luteinizing hormone (LH) to differentiate primary from secondary hypogonadism. 1, 2

Mandatory Baseline Laboratory Panel

Core Hormonal Assessment

• Two separate morning total testosterone levels (drawn between 8-10 AM, preferably using the same laboratory and methodology) with both values <300 ng/dL required for diagnosis 1, 3, 4
• Serum luteinizing hormone (LH) in every patient with confirmed low testosterone—this is the single most important test to distinguish primary (testicular) from secondary (hypothalamic-pituitary) hypogonadism 1, 2
  • Low or low-normal LH with low testosterone indicates secondary hypogonadism and triggers additional pituitary evaluation 1, 2
  • Normal or elevated LH with low testosterone indicates primary testicular failure 1

Secondary Hypogonadism Workup

• Serum prolactin should be measured only when testosterone is low AND LH is low or low-normal to screen for hyperprolactinemia and possible prolactinoma 1, 2, 3

  • If prolactin is persistently elevated, refer to endocrinology for evaluation of pituitary tumors 1
  • Critical pitfall: Do not measure prolactin in patients with normal or elevated LH—this wastes resources and provides no diagnostic value 2

• Pituitary MRI is mandatory when total testosterone is <150 ng/dL combined with low or low-normal LH, regardless of prolactin levels, as non-secreting adenomas may be present 1, 2, 3

Safety Monitoring Labs

• Hemoglobin and hematocrit at baseline before initiating therapy to monitor for polycythemia risk during treatment 2, 4

  • Recheck at 3-6 months after starting treatment, then annually 4

• Prostate-specific antigen (PSA) in all men over 40 years before starting testosterone therapy to screen for occult prostate cancer 2, 3, 4

• Liver function tests for baseline assessment and periodic monitoring 4

Conditional Laboratory Testing Based on Clinical Presentation

Fertility Concerns

• Follicle-stimulating hormone (FSH) in men interested in fertility preservation, as elevated FSH with low testosterone indicates impaired spermatogenesis 2

Breast Symptoms or Gynecomastia

• Serum estradiol only in patients presenting with breast symptoms or gynecomastia prior to commencing testosterone therapy 1, 2
  • Elevated baseline estradiol requires endocrinology referral 2

Metabolic and Cardiovascular Risk Assessment

• Fasting glucose and/or HbA1c, as testosterone deficiency is highly prevalent in men with diabetes and metabolic syndrome 1, 3
• Fasting lipid panel for cardiovascular risk assessment 1, 3

Obesity-Specific Considerations

• Free testosterone by equilibrium dialysis and sex hormone-binding globulin (SHBG) in patients with obesity, as obesity-related decreases in testosterone are frequently attributable to low SHBG concentrations 1
  • Men with obesity may have low total testosterone due solely to low SHBG but normal free testosterone levels 1
  • Treatment should only be considered when morning free testosterone is frankly low on at least two separate assessments 1

Common Pitfalls to Avoid

• Never skip LH measurement—it is the single most important test to differentiate primary from secondary hypogonadism and guides appropriate treatment selection 2, 3

• Never rely on screening questionnaires as substitutes for laboratory testosterone measurement—they have variable sensitivity/specificity and are not appropriate diagnostic tools 1, 3

• Never measure testosterone at random times of day—morning samples are essential for accurate diagnosis due to diurnal variation 1, 3

• Never diagnose hypogonadism based on symptoms alone—biochemical confirmation with low testosterone on two separate occasions is mandatory 1, 3

• Never delay pituitary MRI when testosterone is <150 ng/dL with low/low-normal LH, as non-secreting adenomas may be present even with normal prolactin 2, 3

• Never measure prolactin in patients with normal or elevated LH—this provides no diagnostic value 2

Ongoing Monitoring During Treatment

Once testosterone replacement therapy is initiated, monitor serum testosterone levels at approximately 14 days and 28 days after starting treatment or following dose adjustment, then periodically thereafter 4. Continue monitoring PSA, hemoglobin, hematocrit, liver function tests, and lipid concentrations periodically throughout treatment 4.