You are seeing a 32 yo PTC with a history of disordered eating. The patient says that they have been experiencing difficulty seeing at night when they try to drive. What vitamin deficiency might they be experiencing and how would you test?
a) Vitamin A; serum retinol
b) Vitamin D; serum 25-OH vitamin D
c) Vitamin E; serum tocotrienols
d) Vitamin K; clotting time