Tryptophan load test helps in the evaluation of deficiency of the Vitamin
Folic acid
Niacinamide
Pyridoxine
Cyanocobolamine
The synthesis of niacin coenzymes (NAD+ and NADP+) from tryptophan is dependent on PLP The enzyme kynureninase requires PLP. In B6 deficiency, 3-hydroxy anthranilic acid is diveed to xanthurenic acid Increased excretion of xanthurenic acid in urine is an indication of B6 deficiency. ref satyanarayana 4th ed page 145
vitamins