Catalyzes the reduction of 3-ketodihydrosphingosine (KDS) to dihydrosphingosine (DHS). NADP(+) + sphinganine = 3-oxosphinganine + H(+) + NADPH Lipid metabolism; sphingolipid metabolism. Expressed in all tissues examined. Highest expression in placenta. High expression in lung, kidney, stomach and small intestine, low expression in heart, spleen and skeletal muscle. Weakly expressed in normal hematopoietic tissues. Higher expression in some T-cell malignancies and PHA-stimulated lymphocytes. A chromosomal aberration involving KDSR is a cause of follicular lymphoma; also known as type II chronic lymphatic leukemia. Translocation t(2;18)(p11;q21) with a Ig J kappa chain region (PubMed:8417785). The disease is caused by variants affecting the gene represented in this entry. Belongs to the short-chain dehydrogenases/reductases (SDR) family.