Plasma vitamin A levels--a diagnostic indicator of hepatitis in an institutionalized mentally retarded population

Based on hepatitis-associated antigen carrier status as a model liver disease, level of vitamin A can be a useful diagnostic indicator in mentally retarded individuals. It was found that vitamin A levels and age were linearly related by the equation A = (B + CD), where A is the plasma vitamin A in mugms per 100 mls of plasma, B is the sex dependent constant of 25.9 for males and 28.4 for females, C is a sex dependent constant of 0.64 for males and 0.77 for females, and D is age in years. Above age 20, D becomes a constant with a value of 20. With this equation, if the observed vitamin A value is less than 79 percent of the predicted value, then liver damage should be suspected. This information presented graphically allows one to predict liver damage by observing the plasma vitamin A levels and then locating the point on the appropriate graph.