title: Significance of the ionized calcium measurement to assess calcium status in osteopenic/osteoporosis postmenopausal outpatients.
abstract: BACKGROUND
  Evaluation of calcium status is important in the osteoporotic risk assessment. Although guidelines indicate total calcium (tCa) as first-line measurement, directly measured ionized calcium (m-iCa), considered as the gold standard, is more and more often required. Aim of this study is to evaluate the agreement between m-iCa, tCa and iCa calculated from a formula based on total calcium and albumin (c-iCa) in osteopenic/osteoporotic postmenopausal outpatients.
  
  
  METHODS
  A total of 140 postmenopausal outpatients, 41 osteopenic (OPN) and 99 osteoporotic (OP) were enrolled. Levels of tCa, m-iCa, c-iCa, total protein and albumin, vitamin D (25-OHD), parathyroid hormone 1-84 (PTH), bone alkaline phosphatase, osteocalcin and serum collagen type 1 cross-linked C-telopeptide (CTX) were also measured.
  
  
  RESULTS
  There were no statistically significant differences between OPN and OP groups regarding values of tCa, m-iCa, and c-iCa, 25-OHD and PTH. However, OP women had lower levels of CTX (p < 0.05). A significant direct correlation between m-iCa and tCa (r = 0.60, p < 0.001) and c-iCa (r = 0.61, p < 0.001) was found. Women with isolated hyper-m-iCa had similar DEXA parameter levels respect to the other patients. However, one patient with confirmed primary hyperparathyroidism presented hyper-m-iCa versus normal tCa and c-iCa values.
  
  
  CONCLUSIONS
  The use of tCa could be sufficient to characterize the calcium status in postmenopausal outpatients, but reflexive calcium testing strategy for m-iCa test is necessary to women presenting the low or high extremes of tCa levels, or in women with suspected PHPT.
authors.affiliation: a Institute of Clinical Physiology, CNR National Research Council , Pisa , Italy and.
authors.forename: Letizia
authors.initials: L
authors.lastname: Guiducci
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Maffei
authors.affiliation: a Institute of Clinical Physiology, CNR National Research Council , Pisa , Italy and.
authors.forename: Laura
authors.initials: L
authors.lastname: Sabatino
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Luc
authors.initials: L
authors.lastname: Zyw
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Debora
authors.initials: D
authors.lastname: Battaglia
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vannucci
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Di Cecco
authors.affiliation: b Fondazione CNR-Regione Toscana G Monasterio , Pisa , Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Vassalle
mesh_terms: D000368:Aged; D001851:Bone Diseases, Metabolic / Q000097:blood*; D002118:Calcium / Q000032:analysis / Q000097:blood*; D005260:Female; D006801:Humans; D007477:Ions / Q000032:analysis / Q000097:blood; D007558:Italy; D008875:Middle Aged; D009752:Nutritional Status; D015663:Osteoporosis, Postmenopausal / Q000097:blood; D010045:Outpatients; D017698:Postmenopause / Q000097:blood*
chemical_list: D007477:Ions; D002118:Calcium
keywords: Calculated ionized calcium; measured ionized calcium; osteoporosis; postmenopausal women; total calcium