Thank you Corb.
I agree with the text you quote at beginning of your post which I guess is from HERE. Indeed ref. ranges comparison is a common problem and also the reference 36 above clearly had to study percentiles of IGF-1 rather than absolute values:
“…Different immunoassays are used to measure IGF-I levels, each assay having specific reference ranges, which precludes a direct comparison of absolute IGF-I values (23). For this reason, the analyses were based on percentiles of IGF-I, assuming that different IGF-I assays reflect the same underlying distribution of IGF-I levels….”
http://press.endocri...10/jc.2011-1377
Herewith is what the Life Extension Foundation (LEF) reports as (age-dependent) reference range for IGF-1 (I think they work with LabCorp):
20 years 127–424 ng/mL 51–55 years 87–238 ng/mL
21–25 years 116–358 ng/mL 56–60 years 81–225 ng/mL
26–30 years 117–329 ng/mL 61–65 years 75–212 ng/mL
31–35 years 115–307 ng/mL 66–70 years 69–200 ng/mL
36–40 years 109–284 ng/mL 71–75 years 64–188 ng/mL
41–45 years 101–267 ng/mL 76–80 years 59–177 ng/mL
46–50 years 94–252 ng/mL 81–85 years 55–166 ng/mL
http://www.lef.org/P...Testing/Page-04
I do not know what to do with some of the Anti-Aging community recommendation to keep "youthful” levels of hormones. Is this the right approach? It is not clear as I do not understand on which evidence you can base this strategy. The AA community gives “optimal” values in some cases, not for all hormones. LEF gives them for e.g. DHEA HERE but not for IGF-1 and I suspect because it is more dangerous to target the IGF-1 level you had in your 30's at say your 60’s or 70’s due to the U-curve and increased cancer risk. Others in the community do, e.g.:
Dr. Claude Dalle (President of the French Anti-Aging Medicine) gives in one of his books:
ref: 115-490 and optimal for men: 200-380 ng/ml
and Dr. Philip Miller in his “Life Extension Revolution” book:
ref: 114-492 and optimal: 200-300 ng/ml