My testicles are small; could this be normal or indicate hypogonadism or another endocrine disorder, and what evaluation should I undergo?

Evaluation of Small Testicles

Small testicles may be normal or indicate underlying endocrine dysfunction, and you should undergo measurement with an orchidometer or ultrasound, hormonal evaluation (FSH, LH, testosterone), and assessment for cryptorchidism history to determine if this represents physiologic variation or pathology requiring treatment. 1

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Understanding What "Small" Means

Testicular volumes below 12 mL are definitively considered atrophic and associated with significant pathology, including impaired spermatogenesis and increased risk of intratubular germ cell neoplasia. 1 Volumes between 12-15 mL are borderline-small and warrant clinical correlation with symptoms and hormone levels. 1

• Normal adult testicular volume ranges from 15-18 mL, corresponding to a testicular length of approximately 4 cm. 1
• The Prader orchidometer provides accurate volume estimates and is more practical than ultrasound for routine clinical assessment. 1
• If there is a size discrepancy between testes greater than 2 mL or 20%, further evaluation including ultrasound is warranted to exclude pathology. 1

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Key Historical Red Flags to Identify

Before assuming your testicular size is normal, specific historical factors dramatically alter risk stratification:

Cryptorchidism (Undescended Testicles)

• History of undescended testicles is the single most important risk factor for both testicular atrophy and malignancy. 2, 1
• Men with bilateral cryptorchidism have paternity rates of only 35-53%, compared to nearly normal rates with unilateral cryptorchidism. 2
• The risk of testicular cancer is 3.6-7.4 times higher in men with cryptorchidism history. 2
• Even the contralateral descended testis in unilateral cryptorchidism may have structural abnormalities including smaller volume. 2

Medication and Substance Exposure

• Exogenous testosterone or anabolic steroid use causes complete suppression of spermatogenesis and testicular atrophy that can take months to years to recover. 3
• Chronic opioid use suppresses GnRH secretion, resulting in testicular shrinkage. 1
• Prior chemotherapy or testicular radiation causes irreversible testicular damage. 1

Systemic Disease

• Type 2 diabetes and metabolic syndrome are linked to functional hypogonadism and reduced testicular volume. 1
• Chronic liver disease (cirrhosis) contributes to secondary hypogonadism and testicular atrophy. 1
• HIV infection can cause both primary and secondary gonadal dysfunction. 1
• Klinefelter syndrome (47,XXY) is the most common genetic cause, presenting with small firm testes and elevated FSH. 4, 1

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Essential Diagnostic Workup

Hormonal Evaluation

Obtain morning serum FSH, LH, and total testosterone on two separate days (08:00-10:00 h) to differentiate primary testicular failure from secondary hypogonadism. 1

Interpretation patterns:

• Elevated FSH (>7.6 IU/L) with low testosterone and elevated LH indicates primary testicular failure—the testes themselves are damaged. 1, 3
• Low or low-normal FSH and LH with low testosterone suggests secondary hypogonadism from pituitary or hypothalamic dysfunction. 1, 5
• Measure serum prolactin to exclude hyperprolactinemia as a reversible cause. 1

Physical Examination Priorities

• Assess testicular consistency (firm vs. soft), presence of varicocele on standing examination, and vas deferens/epididymal abnormalities. 1
• Document any asymmetry—up to 59% of healthy adolescents have a smaller left testis, so asymmetry alone does not indicate pathology. 6
• Evaluate for gynecomastia, which may indicate estrogen excess or Klinefelter syndrome. 4

Imaging

Scrotal ultrasound with Doppler is indicated when physical examination is difficult (large hydrocele, inguinal testis, epididymal enlargement, thickened scrotal skin) or to quantify volume accurately using the Lambert formula (Length × Width × Height × 0.71). 1

Genetic Testing

• Karyotype analysis is mandatory if FSH is elevated and testicular volume is <12 mL to screen for Klinefelter syndrome. 1
• Y-chromosome microdeletion testing (AZFa, AZFb, AZFc regions) should be performed if sperm concentration is <5 million/mL or azoospermia is present. 1, 3

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Cancer Risk Considerations

Men younger than 30-40 years with testicular volume <12 mL have a ≥34% risk of intratubular germ cell neoplasia (TIN) in the contralateral testis if testicular cancer develops. 1 If TIN is left untreated, approximately 70% progress to invasive testicular cancer within 7 years. 1

You should be taught testicular self-examination given the 3.6-7.4 times higher risk of germ cell tumors with smaller volumes, especially with cryptorchidism history. 2, 1

Testicular biopsy should be considered if you are under 30 years with volume <12 mL and history of cryptorchidism, or if testicular microcalcifications are present on ultrasound. 7

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Fertility Implications

Testicular volume <12 mL strongly correlates with impaired spermatogenesis, lower total sperm count, and reduced sperm concentration. 1, 8 Mean testicular size has the strongest correlation with serum FSH levels, total sperm count, and sperm concentration. 8

When Fertility Is a Concern:

• Semen analysis should be performed every 6-12 months to monitor declining parameters, as single analyses can be misleading due to natural variability. 1
• Sperm banking should be discussed before any intervention (surgery, testosterone therapy) if you desire future fertility. 1
• Never start testosterone replacement if fertility is desired—exogenous testosterone suppresses LH and FSH through negative feedback, causing azoospermia that may take months to years to recover. 1, 3

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Treatment Considerations Based on Etiology

If Secondary Hypogonadism (Low FSH/LH with Low Testosterone):

• Human chorionic gonadotropin (hCG) injections can stimulate testosterone production and improve spermatogenesis, with 75% of men achieving sperm in ejaculate. 3, 9
• FSH injections may be added after testosterone normalizes on hCG if sperm counts remain low. 3
• Treatment with hCG followed by FSH for 12-24 months promotes testicular growth in almost all patients and spermatogenesis in approximately 80%. 9

If Primary Testicular Failure (Elevated FSH with Low Testosterone):

• Testosterone replacement is appropriate only if fertility is not desired. 1
• Microsurgical testicular sperm extraction (micro-TESE) offers 40-50% sperm retrieval rates even with elevated FSH if azoospermia develops. 1, 3

If Varicocele Is Present:

• Varicocele repair should be strongly considered if you have a palpable (grade 2-3) varicocele with documented testicular atrophy and elevated FSH, as repair can halt progression of atrophy and potentially reverse some damage. 3
• Correction of palpable varicoceles results in improvement in both semen quality and fertility rates. 3

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Reversible Causes to Address

Before concluding that small testicles represent permanent pathology, optimize:

• Thyroid function—both hypothyroidism and hyperthyroidism disrupt the hypothalamic-pituitary-gonadal axis. 1, 3
• Metabolic health—weight loss and metabolic optimization can normalize gonadotropins in functional hypogonadism. 1
• Medication review—discontinue anabolic steroids, opioids, or other gonadotoxic medications immediately if fertility is desired. 1

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Common Pitfalls to Avoid

• Do not assume asymmetry indicates pathology—59% of healthy adolescents have a smaller left testis. 6
• Do not rely on a single semen analysis—natural variability requires at least two analyses separated by 2-3 months. 1, 3
• Do not start testosterone therapy without clarifying fertility intentions—this is irreversible suppression of spermatogenesis while on treatment. 1
• Do not ignore cryptorchidism history—this dramatically increases both cancer risk and infertility risk regardless of current testicular position. 2, 1