Catalyzes the reduction of D-erythrulose to D-threitol with the concomitant oxidation of NAD(P)H to NAD(P)(+). NADH is less effective than NADPH. May also catalyze the reduction of L-xylulose. D-threitol + NADP(+) = D-erythrulose + H(+) + NADPH NADP(+) + xylitol = H(+) + L-xylulose + NADPH Homotetramer. Highly expressed in kidney, and also found in high amounts in liver and testis. Low expression seen in all other tissues tested. The N-terminus is blocked. Belongs to the short-chain dehydrogenases/reductases (SDR) family.