Matrix what do you think bro I hear 17.8 and under is considered deficient not low and 21 is close to it.A endo gave me a blood test due to being tired,cold intolerance,brain fog low libido delayed orgasm and very little ejaculate.He tested my igf-1,testosterone,thyroid,white cell blood count,cortisol vitamin d prolactin and hematocrit.And they said everything was normal except for my vitamin d and they gave me a 50,000 unit vitamin d supplement.