FSH Reference Ranges in Children by Age
Prepubertal Children (Ages 2-12 years)
FSH levels in prepubertal children remain consistently low, with mean serum concentrations below 3.0 IU/L until approximately age 10 years in girls and age 12 years in boys. 1, 2
Infancy (0-6 months)
- FSH levels are transiently elevated during the first 6 months of life 1, 3
- Female infants demonstrate higher FSH concentrations compared to male infants during this period 1
- After 6 months, FSH levels decline and remain low throughout childhood 3
Early Childhood (6 months to 2 years)
- FSH concentrations drop to low but measurable levels following the initial postnatal surge 1
- These levels remain relatively stable throughout the prepubertal years 3
Late Childhood (2-12 years)
- Mean prepubertal FSH levels stay below 3.0 IU/L in both sexes 2
- Urinary FSH excretion in prepubertal children (ages 2-6 years) averages 2.2 U per liter 4
- FSH remains detectable but at very low concentrations using sensitive immunoassays 1, 5
Pubertal Children (Ages 10-18 years)
During puberty, FSH levels increase approximately 3-fold from prepubertal baseline, with mean concentrations rising to about 5 IU/L in boys and 10 IU/L in girls. 2
Early Puberty (Tanner Stages 2-3)
- FSH begins to rise earlier than LH in the pubertal transition 1
- Peak GnRH-stimulated FSH is highest in prepubertal females compared to males 1
- The increase in FSH is more gradual compared to the dramatic rise in LH 5
Mid to Late Puberty (Tanner Stages 4-5)
- FSH values reach adult levels, with urinary concentrations approximately 5 IU/L in boys and 10 IU/L in girls 2
- The FSH:LH ratio decreases from 5:1 in childhood to approximately 1:1 in adulthood 4
Clinical Evaluation Thresholds
Failure to initiate puberty by age 13 years in girls (no Tanner stage 2 breast development) requires laboratory evaluation of FSH and estradiol levels. 6, 7
When to Measure FSH
- Prepubertal females age ≥11 years with delayed puberty should undergo FSH evaluation 6
- Girls with no signs of puberty by age 13 years require FSH measurement 6, 7
- Primary amenorrhea by age 16 years necessitates FSH testing 6
- Failure of pubertal progression for ≥12 months warrants FSH assessment 8, 7
Interpretation Considerations
- FSH measurement should use sensitive immunochemiluminometric assays (ICMA) or time-resolved immunofluorometric assays for accurate detection of low prepubertal levels 1, 5
- Normal ranges vary significantly by age, sex, and pubertal stage, requiring age-appropriate reference values 6, 3
- Two elevated FSH levels in the menopausal range (based on laboratory-specific thresholds) combined with amenorrhea ≥4 months defines premature ovarian insufficiency in females under age 40 years 8, 6
Important Caveats
- Older radioimmunoassay methods lack sensitivity for accurate measurement of low prepubertal FSH levels; modern ICMA or immunofluorometric assays are essential 1
- FSH levels should be interpreted in conjunction with LH and estradiol/testosterone to fully assess gonadotropin axis function 6, 1
- In menstruating females, FSH should ideally be measured during the early follicular phase (days 2-5) for accurate interpretation 8, 6
- Random FSH measurement is acceptable in amenorrheic patients 6