Bone and mineral status of patients beginning total parenteral nutrition

Total parenteral nutrition (TPN) is commonly used to provide nutrition in the seriously ill. Osteomalacia has been described with long-term TPN and the administered solutions and/or vitamin D metabolites have been blamed for the occurrence of osteomalacia. These studies however were performed on patients on long-term TPN programs. We in contrast measured the serum calcium (Ca), ionized calcium (Ca2+), phosphate (Pi), bone GLA protein (BGP), alkaline phosphatase (ALK-P), 25(OH)D, 1,25(OH)2D, the iPTH (carboxyl terminal) in 25 malnourished patients just beginning TPN therapy. The patients ranged from 25 to 80 yr of age and suffered from a variety of diseases. No patient had symptoms, recent fractures, or radiographic evidence of osteomalacia. The results of our study revealed significantly lower 25(OH)D (p less than 0.001), Pi (p less than 0.01), and Ca (p less than 0.01), but higher iPTH (p less than 0.002) values when compared to normals. BGP, 1,25(OH)2D and Ca2+ and ALK-P were not significantly different. We conclude that patients requiring TPN have low serum 25(OH)D values reflecting their nutritional status with a compensatory increase in PTH secretion to maintain their serum Ca2+ levels. The normal BGP levels may indicate depressed bone formation and skeletal resistance to PTH in the very ill patient. The cause of osteomalacia in these patients may therefore be multifactorial and not only related to the TPN infusions.