Adjustment for body mass index and calcitrophic hormone levels improves the diagnostic accuracy of the spot urine calcium-to-creatinine ratio

• Published in: Osteoporosis international Vol. 21; no. 8; pp. 1417 - 1425
• Main Authors: Jones, A. N, Blank, R. D, Lindstrom, M. J, Penniston, K. L, Hansen, K. E
• Format: Journal Article
• Language: English
• Published: London London : Springer-Verlag 01.08.2010; Springer-Verlag; Springer; Springer Nature B.V
• Subjects: Aged; Biological and medical sciences; Body Mass Index; Calcium; Calcium - urine; Creatinine - urine; Diagnosis; Diseases of the osteoarticular system; Endocrinology; Epidemiologic Methods; Female; Hormones; Humans; Hypercalciuria; Hypercalciuria - complications; Hypercalciuria - diagnosis; Medical diagnosis; Medical sciences; Medicine; Medicine & Public Health; Middle Aged; Nephrology. Urinary tract diseases; Original Article; Orthopedics; Osteoporosis; Osteoporosis. Osteomalacia. Paget disease; Parathyroid Hormone - blood; Postmenopause - urine; renal calculi; Rheumatology; Specimen Handling - methods; Urinalysis; Urinary lithiasis; Urinary system involvement in other diseases. Miscellaneous; Urinary tract. Prostate gland; urine; Vitamin D Deficiency - complications; Urine; Osteoporosis; Hypercalciuria; Diagnosis; Nephrolithiasis; Calcium; Kidney disease; Creatinine; Hormone; Urinary system disease; Diseases of the osteoarticular system; Rheumatology; Urinary tract disease; Urinary stone; Body mass index; Accuracy; Renal lithiasis
• ISSN: 0937-941X; 1433-2965
• DOI: 10.1007/s00198-009-1058-z

Summary Providers diagnose hypercalciuria using a 24-hour or random urine samples. We compared calcium measurements from paired 24-hour and morning urine samples; measurements correlated poorly. We developed a formula to correct random urine calcium levels. Corrected levels showed excellent agreement with 24-hour measurements. Until validation, providers should diagnose hypercalciuria using 24-hour tests. Introduction Hypercalciuria is a risk factor for osteoporosis and nephrolithiasis. The 24-hour urine calcium (24HUC) measurement is the gold standard to diagnose hypercalciuria, but the spot urine calcium-to-creatinine ratio (SUCCR) is more convenient. Although authors claim they are interchangeable, we observed inconsistencies during the conduct of a clinical trial. Therefore, we systematically evaluated agreement between the tests. Methods During a 28-inpatient calcium absorption studies in 16 postmenopausal women, we simultaneously collected paired fasting morning and 24-hour urine specimens. Results We found moderate correlation between paired SUCCR and 24HUC specimens (r = 0.57, p = 0.002), but the SUCCR underestimated 24HUC by a mean of 83 mg (Bland-Altman). We diagnosed hypercalciuria (24HUC >250 mg) in eight specimens using the 24HUC, but only in two specimens using the SUCCR (25% sensitivity). We developed a regression model to predict 24HUC using SUCCR, parathyroid hormone, body mass index, and 1,25(OH)₂D. The model improved diagnostic sensitivity to 100% and decreased Bland-Altman bias of the SUCCR to +0.06 mg/kg/24-hour. Conclusions We conclude that the SUCCR underestimates urine calcium loss and does not reliably diagnose hypercalciuria. A formula derived from multivariate regression incorporating other readily measurable variables greatly improved the SUCCR's accuracy. Future studies must verify this correction before clinical implementation.