What laboratory tests should be ordered to diagnose male hypogonadism?

Laboratory Tests for Diagnosing Male Hypogonadism

The diagnosis of male hypogonadism requires at least two early morning total testosterone measurements below 300 ng/dL combined with symptoms and/or signs of testosterone deficiency. 1

Primary Laboratory Testing

Essential Tests

• Total testosterone:

  • Must be measured in early morning (when levels are highest) 1
  • At least two separate measurements are required 1
  • A level below 300 ng/dL is considered diagnostic cut-off 1
  • Should be measured using an accurate and reliable assay 1, 2

• Luteinizing hormone (LH):

  • Essential to determine the etiology of testosterone deficiency 1
  • Helps distinguish between primary (testicular) and secondary (pituitary/hypothalamic) hypogonadism 1
  • Elevated LH indicates primary hypogonadism
  • Low or normal LH with low testosterone suggests secondary hypogonadism

When Total Testosterone is Borderline

• Free testosterone:
  • Indicated when total testosterone is close to lower limit of normal 1
  • Best measured by equilibrium dialysis (gold standard) 1, 2
  • Can be calculated using total testosterone, sex hormone binding globulin (SHBG), and albumin 1
  • Note: Free testosterone assays using analog methods have limited reliability 1

Additional Testing Based on Initial Results

For Low/Low-Normal LH with Low Testosterone

• Prolactin level:

  • Essential to screen for hyperprolactinemia 1
  • Persistently elevated levels require endocrinology referral 1
  • May indicate pituitary tumors such as prolactinomas 1

• Pituitary MRI:

  • Indicated if total testosterone <150 ng/dL with low/normal LH 1
  • Helps identify non-secreting pituitary adenomas 1

For Specific Symptoms

• Estradiol:
  • Measure in patients with breast symptoms or gynecomastia 1
  • Elevated levels require endocrinology referral 1

For Men Interested in Fertility

• Follicle-stimulating hormone (FSH):

  • Important for assessing reproductive health status 1
  • Elevated FSH with low testosterone indicates impaired spermatogenesis 1

• Semen analysis:

  • Consider in men with elevated FSH 1
  • Essential if fertility is a concern 1

Pre-Treatment Evaluation

Once hypogonadism is confirmed, additional tests are needed before initiating testosterone therapy:

• Hemoglobin/hematocrit:

  • Baseline measurement required 1
  • Hematocrit >50% may warrant withholding therapy 1

• PSA (Prostate-Specific Antigen):

  • Required in men over 40 years 1
  • Helps exclude occult prostate cancer 1

• Cardiovascular risk assessment:

  • Evaluate for ASCVD risk factors 1
  • Both fixed (age, male gender) and modifiable factors (dyslipidemia, hypertension, diabetes, smoking) 1

Common Pitfalls to Avoid

1. Single testosterone measurement: A single low measurement is insufficient for diagnosis; at least two measurements are required 1

2. Afternoon testing: Testosterone levels have diurnal variation with highest levels in the morning; afternoon measurements may falsely diagnose hypogonadism 1

3. Relying on symptoms alone: Symptoms of hypogonadism are nonspecific; laboratory confirmation is essential 1

4. Using questionnaires for diagnosis: Screening questionnaires have variable specificity and sensitivity and should not replace laboratory testing 1

5. Ignoring SHBG abnormalities: Conditions that alter SHBG (obesity, diabetes, liver disease) can affect total testosterone without affecting free testosterone 1

6. Using unreliable free testosterone assays: Many commercial direct free testosterone assays lack reliability; equilibrium dialysis or calculated free testosterone is preferred 1, 2

Algorithm for Diagnosing Male Hypogonadism

1. Initial evaluation: Measure early morning total testosterone
2. If low (<300 ng/dL): Repeat measurement on a separate morning
3. If confirmed low: Measure LH to determine etiology
   • If LH elevated: Primary hypogonadism (testicular failure)
   • If LH low/normal: Secondary hypogonadism (pituitary/hypothalamic disorder)
     • Measure prolactin
     • Consider pituitary MRI if testosterone <150 ng/dL
4. If total testosterone borderline: Measure free testosterone
5. Before treatment: Check hemoglobin/hematocrit and PSA (if >40 years)

This systematic approach ensures accurate diagnosis of male hypogonadism and appropriate identification of its underlying cause.