PICR = (A₀ - A₂) / A₀ × 100%

Normal value should be < 15%

Measure fasting serum zinc concentration A₀ as the baseline level, then provide a standard diet (calculated as 20% of the total daily caloric intake, with 10%~15% protein, 30%~35% fat, and 50%~60% carbohydrates). Recheck serum zinc A₂ after 2 hours and calculate according to the formula. If PICR > 15%, it indicates zinc deficiency.