The 5-year reproducibility of calcium-related biochemical variables in postmenopausal women

Abstract

A total of 19 measured and derived bone-related biochemical variables were determined in 307 postmenopausal volunteers on two occasions, 5 years apart. The plasma variables with the highest coefficients of determination (r²) were plasma globulins, alkaline phosphatase, creatinine and calculated ionized and ultrafiltrable calcium. In the urine, the highest r² values were in respect of fasting urine calcium excretion corrected for urine sodium, hydroxyproline excretion, and the maximal renal tubular reabsorption of calcium and phosphate (TmCa/GFR and TmP/GFR). The components of variance of TmCa/GFR and TmP/GFR show marked individuality but their methods determination meet the criterion for acceptable analytical goals. We conclude that most of the measured and derived bone-related biochemical variables in fasting plasma and urine are sufficiently reproducible in postmenopausal women to be useful for ranking individuals for a period up to 5 years.

Key Words:

• biochemistry
• bone markers
• menopause
• reproducibility