Hormone Priming Before Growth Hormone Stimulation Testing
Sex steroid priming involves administering testosterone or estradiol before GH stimulation testing to improve diagnostic accuracy in prepubertal adolescents, but it is NOT mandatory—it should be selectively used in older prepubertal children (boys >11 years, girls >10 years) with delayed puberty to prevent false-positive GHD diagnoses. 1
What Is Hormone Priming?
Hormone priming is the administration of sex steroids prior to growth hormone provocation testing (GHPT) to mimic the physiologic effects of puberty on GH secretion. The rationale is that sex steroids naturally enhance GH secretion during puberty, and their absence in late prepubertal children can lead to falsely low GH responses on stimulation tests—resulting in overdiagnosis of GHD in children who simply have constitutional delay of growth and puberty.
How Is It Performed?
The Pediatric Endocrine Society (PES) suggests the following priming protocols 1:
For Girls:
- 2 mg of β-estradiol (NOT ethinyl-estradiol) orally
- 1 mg if body weight <20 kg
- Given on 2 consecutive evenings immediately before the stimulation test
For Boys:
- 50-100 mg testosterone (depot preparation)
- Administered intramuscularly 1 week prior to GH stimulation testing
Important caveat: These protocols are endorsed but NOT standardized—multiple regimens have been used in practice with varying testosterone doses (62.5-125 mg/m²) showing similar efficacy 2. The lack of standardization reflects ongoing controversy in the field.
Is It Mandatory?
No, priming is NOT mandatory and remains highly controversial. 1, 3, 4
When to Consider Priming:
The PES specifically recommends priming for:
- Prepubertal boys older than 11 years
- Prepubertal girls older than 10 years
- Adult height prognosis within -2 SDs of reference mean
- Purpose: To prevent unnecessary treatment of children with constitutional delay of growth and puberty 1
The Controversy—Two Sides of the Evidence:
- Increases GH response during stimulation testing, improving test specificity
- Reduces false-positive diagnoses (up to 54-60% of "GHD" patients normalize after priming) 2
- Studies show that treatment based on primed tests may improve final height outcomes compared to unprimed tests 3
- Mimics the physiologic pubertal state more accurately
Arguments AGAINST priming 4, 5:
- May lead to underdiagnosis of children who could benefit from GH treatment
- Lack of standardized protocols (dose, timing, type of steroid)
- No consensus on whether to adjust GH cutoff values after priming
- Concern that priming only temporarily augments GH secretion while spontaneous secretion remains insufficient for normal pubertal growth
Current Practice Reality:
Outside of adolescence with delayed puberty, the use of priming varies widely 1. The decision remains with the individual clinician, as there is no clear consensus. The ideal age to recommend priming is undefined, and data are lacking on whether GH diagnostic cutoffs need adjustment after priming 1.
Common Pitfalls to Avoid:
Using ethinyl-estradiol instead of β-estradiol in girls—the guideline specifically recommends β-estradiol 1
Priming younger prepubertal children routinely—this is not recommended and increases risk of overdiagnosis 5
Assuming priming is always necessary—many situations don't require GH stimulation testing at all (pituitary abnormalities, multiple pituitary hormone deficiencies, severe congenital GHD with IGF-I <-2 SD) 1
Not considering bone age context—priming decisions should factor in bone age delay, which itself suggests constitutional delay 1
Failing to recognize that normal IGF-I doesn't exclude GHD—but it does make provocative testing mandatory if pursuing diagnosis 6
Practical Algorithm for Decision-Making:
Step 1: Determine if stimulation testing is even needed
- Skip testing if: pituitary abnormality + auxologic criteria, ≥3 other pituitary deficiencies, or severe congenital GHD presentation 1, 6
Step 2: If testing needed, assess pubertal status and age
- Prepubertal boy >11 years OR prepubertal girl >10 years → Consider priming
- Younger prepubertal children → Do NOT prime routinely
- Already in puberty → Priming not needed
Step 3: Assess for constitutional delay features
- Delayed bone age, family history of late puberty, adult height prognosis reasonable → Stronger indication for priming
- These children are at highest risk for false-positive diagnosis without priming
Step 4: Choose protocol if priming
- Girls: 2 mg β-estradiol × 2 evenings before test
- Boys: 50-100 mg testosterone IM 1 week before test
The evidence suggests that a targeted, selective approach to priming in older prepubertal adolescents with features of constitutional delay is most reasonable 4, 5, rather than universal application or complete avoidance.