I am an adult male whose testicular ultrasound measured a volume of approximately 10 mL using the ellipsoid formula (length × width × height × 0.52); is this size normal and what further evaluation or management is recommended?

Testicular Volume Assessment: 10 mL Measurement Using 0.52 Formula

Your testicular volume of 10 mL calculated with the 0.52 formula is artificially low and does not reflect your true testicular size—when recalculated using the correct 0.71 formula (Lambert equation) recommended by the European Association of Urology, your actual testicular volume is approximately 13.7 mL, which falls within the borderline-normal range and does not indicate severe atrophy. 1, 2

Why Your Measurement Is Misleading

The 0.52 ellipsoid formula systematically underestimates testicular volume by 20-30% because it assumes a perfect ellipsoid shape and doesn't account for actual testicular geometry. 1, 2 Multiple ultrasound systems still use this outdated formula in their built-in software, leading to inappropriate classification of testicular atrophy. 2

The European Association of Urology explicitly recommends using the Lambert formula (Length × Width × Height × 0.71) as the clinical standard for testicular volume calculation. 1, 2

When the same testicular measurements are calculated with different formulas (0.71 vs. 0.52), they produce a 26.76% difference in volume. 2 This means your "10 mL" measurement would be approximately 13.7 mL using the correct formula—a clinically significant difference that changes the interpretation entirely.

Clinical Significance of Your Actual Volume (13.7 mL)

Normal vs. Atrophic Thresholds

• Testicular volumes less than 12 mL are definitively considered atrophic and associated with impaired spermatogenesis, increased risk of intratubular germ cell neoplasia, and potential infertility. 1, 3
• Volumes between 12-15 mL are considered borderline-small, warranting clinical correlation but not automatically pathological. 3
• Your corrected volume of 13.7 mL places you in the borderline-small category, not the severely atrophic category. 3

What This Means for Fertility

Testicular volume strongly correlates with total sperm count and sperm concentration. 3 At 13.7 mL, you likely have oligospermia (reduced sperm count) rather than azoospermia (complete absence of sperm). 4

Recommended Next Steps

1. Confirm Accurate Measurement

Request a repeat scrotal ultrasound with explicit instructions to the radiologist to calculate volume using the Lambert formula (0.71 coefficient). 1, 3 Specify that measurements should include three perpendicular dimensions (length, width, height) using high-frequency probes (>10 MHz) to maximize resolution and accurate caliper placement. 1, 3

2. Obtain Semen Analysis

Proceed with semen analysis to assess sperm concentration, motility, and morphology, as testicular volume alone cannot definitively predict fertility status. 1, 3 The American Family Physician recommends semen analysis when testicular volume is less than 20 mL total or individual testis is less than 10 mL (using the 0.52 formula), which would correspond to approximately 13.7 mL using the correct formula. 1

3. Hormonal Evaluation

Measure serum FSH, LH, and testosterone to distinguish primary testicular failure from hypogonadotropic hypogonadism. 1, 3 This is particularly important if semen analysis shows abnormalities, especially sperm concentration less than 10 million/mL. 5, 1

• FSH >7.6 IU/L with borderline-small testes indicates reduced testicular reserve, meaning impaired but not absent spermatogenesis. 3, 4
• The pattern of gonadotropins helps distinguish primary testicular dysfunction from secondary causes. 3

4. Check for Size Discrepancy Between Testes

If there is a size discrepancy between testes greater than 2 mL or 20%, further evaluation including ultrasound is warranted to exclude pathology such as varicocele, testicular masses, or structural abnormalities. 3

High-Risk Scenarios Requiring Additional Workup

You need closer surveillance and potentially testicular biopsy if you have any of these features:

• Age under 30-40 years with history of cryptorchidism (undescended testicles): This combination carries a ≥34% risk of intratubular germ cell neoplasia in the contralateral testis if testicular cancer develops. 3
• Presence of testicular microcalcifications on ultrasound: This increases testicular cancer risk 18-fold in patients with small testicular volumes. 3
• Severe oligospermia (<5 million sperm/mL) or azoospermia: This mandates karyotype testing and Y-chromosome microdeletion analysis, as chromosomal abnormalities occur in 10% of these patients. 1, 4

Common Pitfalls to Avoid

Don't Accept the 0.52 Formula for Clinical Decision-Making

Many ultrasound systems (Siemens Sonoline S2000, Philips EPIQ5, GE Logiq E9, Hitachi Aloka prosoundα7) use the 0.52 formula in their built-in software, producing discordant values compared to the guideline-recommended 0.71 formula. 2 Only Mindray DC-8 and Mindray Resona7 systems use the correct formula. 2

Don't Rely on Single Measurements

Technical error in caliper placement during ultrasound can lead to incorrect measurements. 3 The same sonographer should perform serial measurements when possible, or measurements should be remeasured on previous scans by the current operator to minimize inter-scan variability. 3

Don't Ignore Clinical Context

Even "normal-sized" testes should prompt semen analysis in the context of infertility concerns, as testicular volume alone cannot definitively predict fertility status. 3 The assessment of combined ejaculate parameters (concentration, motility, morphology, total count) is more predictive of testicular function than any single parameter. 4

Monitoring Recommendations

If your semen analysis shows abnormalities:

• Repeat semen analysis every 6-12 months to detect early decline in sperm parameters, as single analyses can be misleading due to natural variability. 3, 4
• Avoid exogenous testosterone or anabolic steroids, which will completely suppress spermatogenesis through negative feedback and can cause azoospermia that takes months to years to recover. 3, 4
• Consider sperm banking immediately if any sperm are present in ejaculate and you have concerns about future fertility, preferably 2-3 separate collections with 2-3 days abstinence between collections. 3
• Learn testicular self-examination given the increased cancer risk associated with smaller testicular volumes, particularly if you have a history of cryptorchidism. 3