(Normal range: 10-85 mg/dL (0.19-1.58 mmol/L
Comment: Low from dietary deficiency, malabsorption and liver disease and in association with Vitamin A deficiency to give rise to “night blindness” and keratomalacia. Raised in high carotene intake, hypothyroidism, diabetes mellitus and hyperlipidaemia
Sample: Serum, protect from light, fasting