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Abstract ObjectivesInvestigating factors that contribute to bone loss and accretion across populations in remote settings is challenging, particularly where diagnostic tools are scarce. To mitigate this challenge, we describe validation of a commercial ELISA assay to measure osteocalcin, a biomarker of bone formation, from dried blood spots (DBS). MethodsWe validated the Osteocalcin Human SimpleStep ELISA kit from Abcam (ab1951214) using 158 matched plasma and DBS samples. Passing‐Bablok regression analysis assessed the relationships between plasma and DBS osteocalcin concentrations. Dilutional linearity and spike and recovery experiments determined if the DBS matrix interfered with osteocalcin measurement, and intra‐ and inter‐assay coefficients of variation (CVs) were calculated. Limit of detection, analyte stability, and specific forms of osteocalcin measured by the kit were also investigated. ResultsMean plasma osteocalcin value was 218.2 ng/mL (range 64.6‐618.1 ng/mL). Linear relationships existed between plasma and DBS concentrations of osteocalcin, with no apparent bias in plasma vs DBS concentrations. There was no apparent interference of the DBS matrix with measurement of osteocalcin in DBS. Intra‐assay CV for DBS was ~8%, while average inter‐assay CV was 14.8%. Limit of detection was 0.34 ng/mL. Osteocalcin concentrations were stable in DBS stored at −28°C and room temperature, but not those stored at 37°C. This ELISA kit detects total osteocalcin. ConclusionsOsteocalcin, a bone formation biomarker, can be measured from DBS. Combined with a previously validated DBS assay for TRACP‐5b, a bone resorption biomarker, these assays have the potential to help researchers disentangle the many factors contributing to bone strength. 

Abstract ObjectivesA number of basic questions about bone biology have not been answered, including population differences in bone turnover. In part, this stems from the lack of validated minimally invasive biomarker techniques to measure bone formation and resorption in field‐based population‐level research. The present study addresses this gap by validating a fingerprick dried blood spot (fDBS) assay for tartrate‐resistant acid phosphatase 5b (TRACP‐5b), a well‐defined biomarker of bone resorption and osteoclast number. MethodsWe adapted a commercially available enzyme‐linked immunosorbent assay (ELISA) kit from MyBiosource for the quantitative determination of TRACP‐5b levels in serum and plasma for use with DBS. We used a rigorous process of assay modification and validation, including the use of a matched set of 189 adult plasma, fDBS, and venous DBS (vDBS) samples; parameters evaluated included precision, reliability, and analyte stability. ResultsPlasma and DBS TRACP‐5b concentrations showed a linear relationship. There were no systematic differences in TRACP‐5b levels in fDBS and vDBS, indicating no significant differences in TRACP‐5b distribution between capillary and venous blood. Parallelism and spike‐and‐recovery results indicated that matrix factors in DBS do not interfere with measurement of TRACP‐5b levels from DBS using the validated kit. Intra‐ and interassay CVs were 5.0% and 12.1%, respectively. DBS samples should preferably be stored frozen but controlled room temperature storage for up to a month may be acceptable. ConclusionsThis DBS‐based ELISA assay adds to the methodological toolkit available to human biologists and will facilitate research on bone turnover in population studies.