Micronutrient assay for cancer prevention clinical trials: serum retinol, retinyl palmitate, alpha-carotene, and beta-carotene with the use of high-performance liquid chromatography.

Assay of serum levels of retinol, retinyl palmitate, alpha-carotene, and beta-carotene to assess nutritional status, to trials of retinol and/or beta-carotene to assess nutritional status, to monitor compliance with medication schedules, and to conduct toxicity surveillance. The optimal assay method for clinical trial use represents a balance between analytical power and speed/simplicity. Three such methods were evaluated by means of shared samples between two laboratories. Each method required less than 15 minutes per assay and detected all of the analytes of interest. Careful evaluation of calibration materials and procedures permitted different laboratories using different methods to produce results with an interlaboratory variability smaller than the within-laboratory variability for each separate method. Typical precisions for the analytes in serum samples are: retinol, 0.06 relative standard deviation (RSD; standard deviation divided by mean value); retinyl palmitate, 0.08 RSD; alpha-carotene, 0.15 RSD; and beta-carotene, 0.11 RSD. Application of these methods to several hundred samples indicated that retinyl palmitate and beta-carotene levels were indicative of administered retinol and beta-carotene, whereas retinol itself was not. Population variability in pretreatment serum levels of these micronutrients expressed as RSD (retinol, 0.24; alpha-carotene, 1.11; and beta-carotene, 0.98) far exceeded the analytical imprecision in these determinations, confirming that the present assays could meet the needs of current clinical intervention trials.