IGF-1 Z-Score (Age and Sex Adjusted)
Hormones marker
IGF-1 Z-Score
IGF-1 Z-Score (Age and Sex Adjusted)
Age- and sex-adjusted standardised score for IGF-1, expressed in standard deviations from the population mean. A z-score of 0 represents the age-matched median, +1 represents one standard deviation above the mean, and -1 represents one standard deviation below. Removes the age-decline confounder that complicates raw IGF-1 interpretation across the lifespan.
PED Notes
The cleanest way to interpret IGF-1 on GH or peptide protocols. Raw IGF-1 ng/mL or nmol/L values cannot be compared across age groups because endogenous IGF-1 falls roughly 1-2% per year after age 30. A 250 ng/mL value at age 25 is high-normal; the same value at age 65 is supraphysiological. The z-score normalises against the age-matched reference, making it the right number to monitor when running tesamorelin, CJC-1295 plus ipamorelin, MK-677, or exogenous HGH. The FDA tesamorelin label uses z-score (SDS) thresholds: dose reduction at z >2 SDS sustained, discontinuation at z >3 SDS. Bidlingmaier et al. (PMID 24432983) published the largest IGF-1 reference dataset (n=15,014) for z-score calculation by Roche immunoassay; LabCorp, Quest, and Mayo all derive their reference ranges from comparable population datasets.
When high
Understanding the z-score:
- 0 SD: at the age-matched median
- +1 SD: approximately 84th percentile for age and sex
- +2 SD: approximately 97.7th percentile (FDA tesamorelin dose-reduction threshold if sustained)
- +3 SD: approximately 99.9th percentile (FDA tesamorelin discontinuation threshold)
- Negative z-scores: below age-matched median; can occur off GH or peptide therapy or with malnutrition, liver disease, or hypopituitarism
When elevated on GH or peptide therapy (z >+2 SD):
- 47% of EGRIFTA Phase 3 patients hit IGF-1 >2 SDS by week 26 (FDA label data)
- 36% hit >3 SDS
- Reduce GH or peptide dose
- For tesamorelin: drop from 2 mg to 1 mg, recheck IGF-1 at week 4 of new dose
- For exogenous HGH: reduce by 0.5 to 1 IU/day, recheck IGF-1 at 4 to 6 weeks
- For MK-677: reduce to 10 mg/day or hold; this compound is the most prone to sustained IGF-1 elevation
Hard stop at z >+3 SD sustained:
- Discontinue GH or peptide
- Approaches the IGF-1 levels seen in untreated acromegaly
- Sustained IGF-1 above population +3 SD is associated with increased all-cause mortality, cancer risk, and insulin resistance in epidemiological data
Monitoring cadence on GH or peptide protocols:
- Baseline IGF-1 with z-score
- Week 4 if baseline z-score >+1 SD
- Every 12 weeks thereafter
- Pull at trough (12 to 16 hours post-injection, fasted morning) for the most reproducible read
When low
When z-score is LOW (z <-2 SD):
- Off GH or peptide therapy: indicates relative GH deficiency, malnutrition, liver disease, or systemic illness
- Investigate underlying cause: pituitary imaging, liver enzymes, nutritional assessment, chronic disease screen
- A low z-score in a young athlete eating adequate protein and sleeping well warrants endocrine workup
Pharmacological options for genuinely low z-score:
- Sermorelin -- 200-300mcg subQ before bed; GHRH analog, restores pulsatile GH and IGF-1 release at lowest pharmacological risk
- CJC-1295 (no DAC) plus Ipamorelin -- 100mcg plus 100mcg subQ 1-3x/day; stronger pulsatile rise without continuous GH bleed
- Tesamorelin -- 1.4-2mg subQ daily; FDA-approved GHRH analog with proven visceral fat reduction; raises IGF-1 by 30-50% in healthy users
- Recombinant HGH (somatropin) -- 1-2 IU/day; physician-prescribed; reserved for confirmed adult GH deficiency
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
VitalMetrics Range