What does low testosterone in a teenage female indicate?

Low Testosterone in Teenage Females: Clinical Significance

Low testosterone in a teenage female most commonly indicates Relative Energy Deficiency in Sport (RED-S) or inadequate energy availability, particularly in athletic adolescents, though it can also signal underlying endocrine disorders affecting the hypothalamic-pituitary-gonadal axis. 1

Primary Diagnostic Considerations

Energy Deficiency States

• RED-S represents the most critical diagnosis to consider in adolescent females with low testosterone, as this syndrome affects multiple body systems and can cause irreversible bone loss during the critical period of peak bone mass acquisition (around age 19 in females). 1
• Low energy availability alters metabolic hormones including testosterone, along with insulin, cortisol, growth hormone, and thyroid hormones, creating a cascade of endocrine dysfunction. 1
• In both males and females, testosterone has anabolic effects on bone, stimulating osteoclasts and increasing calcium absorption—when testosterone is low during adolescence, the bones benefit less from the osteogenic effects of exercise, potentially causing irreversible bone loss. 1

Normal Physiological Context

• Healthy young women normally produce approximately 300 micrograms of testosterone daily, with roughly half derived from the ovaries and half from the adrenal glands. 2
• Testosterone levels in females naturally decline with age, even before menopause, with a steep age-related decline beginning in the reproductive years. 3
• However, in a teenage female, low testosterone is NOT a normal physiological finding and warrants investigation. 1, 2

Clinical Manifestations to Assess

Reproductive and Sexual Health

• Functional hypothalamic amenorrhea (absent or irregular menses) frequently accompanies low testosterone in the setting of energy deficiency. 1
• Decreased libido and reduced sense of well-being may occur, though these symptoms are more commonly studied in adult women. 4, 5
• Irregular or absent menses may create anxiety about normalcy and can confound conception later in life. 1

Musculoskeletal Effects

• High-risk stress fractures (including femoral neck fractures) occur in adolescent athletes with RED-S and can have serious long-term consequences. 1
• Decreased bone mineral density during the critical period of peak bone mass acquisition (around age 19) may be irreversible. 1
• Reduced muscle protein synthesis occurs even at moderately low energy availability. 1

Metabolic and Systemic Effects

• Chronic fatigue, increased risk of infections and illnesses, and nutrient deficiencies (including anemia) commonly develop. 1
• Psychological stress and depression can both cause and result from low energy availability states. 1
• Abnormalities in glucose utilization, fat mobilization, and metabolic rate occur. 1

Diagnostic Workup Algorithm

Initial Assessment

• Evaluate for signs of energy deficiency: rapid or significant fat mass reduction (even over 1 month), restrictive eating patterns, excessive exercise, or disordered eating behaviors. 1
• Assess menstrual history for functional hypothalamic amenorrhea or oligomenorrhea. 1
• Screen for athletic participation, particularly in gravitational sports, aesthetic sports, or weight-class sports where energy restriction is common. 1

Laboratory Evaluation

• Measure morning total testosterone levels on at least two separate occasions to confirm low levels. 1
• Measure LH and FSH to distinguish primary (ovarian) from secondary (hypothalamic-pituitary) causes of low testosterone. 1, 6
• If LH/FSH are low or low-normal, measure prolactin to screen for hyperprolactinemia and potential pituitary pathology. 1, 6
• Consider measuring other metabolic hormones affected by energy deficiency: insulin, cortisol, thyroid hormones (T3), and IGF-1. 1

Advanced Evaluation When Indicated

• If prolactin is persistently elevated or testosterone is severely low (<150 ng/dL equivalent for females) with low/normal LH, consider pituitary MRI to evaluate for non-secreting adenomas or other structural abnormalities. 1, 6
• Evaluate for other causes of testosterone deficiency: adrenal disease, premature ovarian failure, Turner's syndrome, or use of high-dose corticosteroids. 2

Critical Management Priorities

Addressing Energy Deficiency

• The primary intervention for RED-S is restoring adequate energy availability, as this addresses the root cause of hormonal dysfunction including low testosterone. 1
• Nutritional rehabilitation must be sufficient to restore normal metabolic hormone levels and menstrual function. 1
• Failure to address energy deficiency during adolescence can result in irreversible bone loss that persists despite later normalization of hormones. 1

Monitoring for Complications

• Screen for stress fractures, particularly high-risk locations like the femoral neck. 1
• Assess bone mineral density if amenorrhea has been prolonged or stress fractures have occurred. 1
• Monitor for psychological complications including depression, anxiety, and eating disorders. 1

Common Pitfalls to Avoid

• Do not dismiss low testosterone as "normal variation" in a teenage female—this finding warrants thorough evaluation for underlying pathology, particularly energy deficiency states. 1, 2
• Do not delay intervention while waiting for "spontaneous recovery"—the adolescent period represents a critical window for bone mass acquisition that cannot be recaptured. 1
• Avoid focusing solely on menstrual dysfunction while overlooking the broader metabolic consequences of low testosterone and energy deficiency. 1
• Do not assume athletic amenorrhea is benign—RED-S has serious short-term and long-term health consequences affecting multiple organ systems. 1
• Recognize that testosterone deficiency in adolescent females is fundamentally different from age-related decline in adult women and requires different diagnostic and therapeutic approaches. 1, 3