Determination of vitamin A in blood. Some practical considerations on the time of collection of the specimens and the stability of the vitamin.

The stability of vitamin A and retinol-binding protein (RBP) in serum separated from the clot at different times after blood extraction and the effect of ingesting a vitamin A-rich breakfast on postprandial serum levels of retinol, carotenoids, and RBP were investigated. In the stability trials, venous blood was drawn from 12 well-nourished young adult subjects and sample aliquots were maintained, respectively, at 4 degree C or at room temperature (26 to 28 degrees C). The serum was separated from the clot either immediately after blood clotting or at 2, 4, 6, 12, and 24 h after blood extraction. Serum retinol and RBP were stable either at 4 degrees C or at room temperature, even if the serum was separated from the clot 24 h after blood extraction. In the breakfast experiment, seven young adult subjects ingested a meal containing 291 microgram of retinol equivalents. The serum levels of retinol, carotenoids, and RBP were measured pre- and postprandially up to a period of 4 h. The ingestion of the breakfast meal did not alter significantly the postprandial serum levels of retinol, carotenoids, or RBP. These results are of practical importance for the performance of vitamin A nutrition surveys involving field work, when as is common, blood specimens cannot be collected under fasting and, in addition, they have to be transported from far away localities to the laboratory.