Abstract

Variability of bone marker measurements is a major problem in their clinical application. Most studies on marker variability have been performed in healthy subjects and over relatively short intervals of time. We prospectively evaluated the long-term variability of bone markers in 102 postmenopausal women diagnosed with primary breast cancer. During follow up (8-48, median 30 mo.), no patient developed bone metastases or other skeletal disease. Patients were seen every 3 months and exactly timed blood/ urine specimens were obtained. All analyses were performed after study end by the same technician, using a single batch of reagents per analyte. The coefficient of variation was calculated. as CV(%) = \(\sqrt{\sum(CV^2_i)/n}\) (CVi= SD/mean x 100; n = n of CVi). The least significant change (LSC) was then LSC (%)= Z x CV x \(\sqrt{2}\). Z= 1.96 for a 95% confïdence interval (LSC-95). In a subset of n = 10 patients with no potential interference during follow-up, lowest CVs were recorded for serum (s) calcium (5%), sTAP (12%) and sBAP (14%). The LSC-95 for these markers were 14%, 33% and, 39%, respectively. Highest CVs were seen with urine (56%) and serum (42%) CTX (LSC-95: 155%,117% resp.). We conclude that in breast cancer patients without bone metastases, long-term variability varied greatly between markers. For certain markers, the LSC seems considerably higher than previously reported. (Clin. Lab.2002;48:579-582)

DOI: Clin. Lab. 2002;48:579-582