title: Bone isoenzyme of serum alkaline phosphatase and serum inorganic phosphate in metabolic bone disease of prematurity.
abstract: We wanted to improve detection of low bone mineral density in preterm infants by combining serum measurements of total alkaline phosphatase, its bone-type isoenzyme and serum inorganic phosphate in a prospective design. The subjects were 43 preterm infants. Total and bone isoenzyme activity of alkaline phosphatase was determined at 3 wk chronological age and at 3 and 6 mo corrected age. The main outcome measure, apparent bone mineral density (BMAD) at the distal forearm and forearm shaft, was assessed by dual energy X-ray absorptiometry at 3 and 6 mo corrected age. An apparent density below 95 mg/cm3 at 3 mo corrected age was considered to indicate bone disease, based on the distribution of BMAD values of children with non-complicated courses of prematurity. At 3 mo corrected age, total alkaline phosphatase activities exceeding 900 IU/l revealed low bone mineral density with 88% sensitivity and 71% specificity. Measurements of bone isoenzyme activity did not improve diagnostic performance. Serum inorganic phosphate levels below 1.8 mmol/l reflected low bone density with high specificity (96%), but the sensitivity was only 50%.
  
  
  CONCLUSIONS
  A combination of the criteria "serum total alkaline phosphatase activity above 900 IU/l" and "serum inorganic phosphate concentrations below 1.8 mmol/l" yielded a sensitivity of 100% at a specificity of 70%. This was the best available screening method for low bone mineral density in preterms.
authors.affiliation: Department of Paediatrics, Tampere University Hospital, Finland. maria.backstrom@pp.qnet.fi
authors.forename: M C
authors.initials: MC
authors.lastname: Backström
authors.forename: T
authors.initials: T
authors.lastname: Kouri
authors.forename: A L
authors.initials: AL
authors.lastname: Kuusela
authors.forename: H
authors.initials: H
authors.lastname: Sievänen
authors.forename: A M
authors.initials: AM
authors.lastname: Koivisto
authors.forename: R S
authors.initials: RS
authors.lastname: Ikonen
authors.forename: M
authors.initials: M
authors.lastname: Mäki
mesh_terms: D015502:Absorptiometry, Photon; D000367:Age Factors; D000469:Alkaline Phosphatase / Q000097:blood*; D015519:Bone Density; D001851:Bone Diseases, Metabolic / Q000175:diagnosis*; D002130:Calcium Phosphates / Q000097:blood*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D007527:Isoenzymes / Q000097:blood; D011446:Prospective Studies; D012044:Regression Analysis; D012680:Sensitivity and Specificity
chemical_list: D002130:Calcium Phosphates; D007527:Isoenzymes; D000469:Alkaline Phosphatase