title: Fasting and postprandial spot urine calcium-to-creatinine ratios do not detect hypercalciuria.
abstract: CONCLUSIONS
  Clinicians can diagnose high urine calcium by asking patients to collect urine for 24 h or to provide a random urine specimen. In this study, random urine calcium levels were not as accurate as those from the 24-h collection. Clinicians should only use 24-h collections to diagnose high urine calcium.
  
  
  BACKGROUND
  Clinicians diagnose hypercalciuria using a 24-h urine calcium (24HUC) or a spot urine-calcium-to-creatinine ratio (SUCCR) specimen. The SUCCR is reportedly interchangeable with the 24HUC. However, studies to date show mixed results when comparing SUCCR and 24HUC values. We systematically compared fasting and postprandial SUCCR measurements to 24HUC measurements using Bland-Altman analysis.
  
  
  METHODS
  Twenty-one postmenopausal women aged 58 ± 7 years came to the research ward for three 24-h inpatient stays. At each study visit, research nurses collected fasting morning (n = 62) and postprandial (n = 62) spot urine specimens along with carefully timed and complete 24-h urine specimens (n = 63) from each woman.
  
  
  RESULTS
  Hypercalciuria was present in 13 24HUC samples (21%) using an upper limit of 250 mg/24-h. The fasting SUCCR underestimated the 24HUC (Bland-Altman bias -71 mg/24-h), with a sensitivity and specificity for diagnosing hypercalciuria of 0% and 98%, respectively. The postprandial SUCCR overestimated the 24HUC (Bland-Altman bias +61 mg/24-h), with a sensitivity and specificity of 77% and 61%, respectively. The average of fasting and postprandial SUCCR measurements had a lower Bland-Altman bias of -3 mg/24-h but demonstrated a sensitivity and specificity of only 42% and 78%, respectively.
  
  
  CONCLUSIONS
  The SUCCR is not interchangeable with the 24HUC. The fasting SUCCR systematically underestimates, and the postprandial SUCCR systematically overestimates, 24HUC. The average SUCCR demonstrates low sensitivity and specificity for hypercalciuria. Clinicians must use the 24HUC to diagnose hypercalciuria in postmenopausal women.
authors.affiliation: Department of Medicine, University of Wisconsin School of Medicine and Public Health, 600 Highland Avenue, Madison, WI 53792, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Jones
authors.forename: M M
authors.initials: MM
authors.lastname: Shafer
authors.forename: N S
authors.initials: NS
authors.lastname: Keuler
authors.forename: E M
authors.initials: EM
authors.lastname: Crone
authors.forename: K E
authors.initials: KE
authors.lastname: Hansen
mesh_terms: D000368:Aged; D002118:Calcium / Q000652:urine*; D003404:Creatinine / Q000652:urine*; D005215:Fasting / Q000652:urine*; D005260:Female; D006801:Humans; D053565:Hypercalciuria / Q000175:diagnosis*; D008875:Middle Aged; D019518:Postprandial Period; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059349:Urine Specimen Collection / Q000379:methods
chemical_list: D003404:Creatinine; D002118:Calcium