Patient type Lower limit Upper limit Unit Normal adult 0.7,[14] 0.8[2] 1.4,[14] 1.5,[12] 1.8[15] ng/dL 9,[16][17] 10,[6] 12 [13] 18,[16][17] 23[13] pmol/L Infant 0–3 d 2.0[14] 5.0[14] ng/dL 26[17] 65[17] pmol/L Infant 3–30 d 0.9[14] 2.2[14] ng/dL 12[17] 30[17] pmol/L Child/Adolescent 31 d – 18 y 0.8[14] 2.0[14] ng/dL 10[17] 26[17] pmol/L Pregnant 0.5[14] 1.0[14] ng/dL 6.5[17] 13[17] pmol/L