Adult: 1.0—2.8 umol/L
1 - 6 y.o: 0.7—1.5 umol/L
Vitamin A is measured as retinol by HPLC-UV. Retinol levels below 0.7 umol/L are diagnostic of Vitamin A deficiency, while levels of 0.7—1.0 umol/L are borderline deficient. Retinol levels above 2.6 umol/L have been associated with an increased risk of fracture (N Engl J Med 348:287-294, 2003).