Dr. Kumar's research is engaged in examining the structure and function of hormones and signaling petides and receptors.

Dr. Kumar's group has recently identified novel proteins, the "phosphatonins", secreted frizzled realted protein 4 and fibroblast growth factor 23, that control phosphate homeostasis and renal phosphate exccretion. His primary focus is in determining the physiological role of these factors and the role of newly discovered intestinal phosphatonins.

Dr. Kumar and his associates are examining the structure and function of the calcium-sensing receptor, an important G-protein coupled receptor, the vitamin D-dependent calcium binding proteins and other calcium binding proteins such as KChIP-3/DREAM, and the vitamin D receptor. In addition, he is interested in the metabolism and mechanism of action of 1,25-dihydroxyvitamin D.

His laboratory is also engaged in the examination of calcium pumps in osteoblastic cells with the intent of finding the mechanism of mineralization in human and animal bone.

Dr. Kumar is interested in the physiology of vasopressin receptors. Additional areas of research include the examination of the mechanism of action of "polycystin," a protein mutation in polycystic kidney disease