Results of the relative dose response, in the absence of malabsorption or with intravenous dosing, correlate with vitamin A stores and with dark adaptation.
Dose given: retinyl palmitate, either 1 mg as water miscible solution IV over 30 minutes or 0.45 mg in corn oil given po.
relative dose response, as percentage =
= 100% ( 1 - ((plasma vitamin A prior to dose) / (plasma vitamin A 5 hrs after dose)))
where:
• Vitamin A is expressed in µg/dL in conventional units (µmol/L for SIU)
Interpretation:
• The normal relative dose response is < 10%.
• Values > 15% indicate depleted liver vitamin A stores.
• Decreased levels are seen with: malabsorption, cirrhosis, chronic cholestasis, hepatocellular disease, protein-caloric malnutrition, zinc deficiency.
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