Assessment of Dried Plasma Spots (DPS) as an Appropriate Sample Matrix for the Measurement of Circulating Calretinin, a Biomarker for Mesothelioma-A Proof-Of-Concept Study.

BACKGROUND: Microsampling using filter cards for dried blood spots (DBS) and dried plasma spots (DPS) is a well-established technique offering practical advantages for blood collection and subsequent processing. For DBS/DPS, only a small sample volume is required it enables transport and storage at ambient temperature, and it is well suited for decentralized sample collections and resource-limited settings, as well as collection from elderly individuals, when venous blood collection might be problematic. Many protein-based biomarker assays like enzyme-linked immunosorbent assays (ELISA) depend on blood, plasma, or serum as sample matrix. Calretinin is an established biomarker for the early detection of mesothelioma. Herein, we investigated whether DPS are suitable for the determination of calretinin protein by ELISA in comparison to commonly used plasma samples.

METHODS: Plasma samples of 47 mesothelioma patients and 47 matched asbestos-exposed controls were spotted onto filter cards. After drying, calretinin was reconstituted and determined using ELISA.

RESULTS: It was revealed that the use of filter cards, i.e., DPS as sample matrix, was comparable to and in good agreement with the use of plasma. Calretinin could be determined reliably and comparably even after storage for 5 days at ambient temperature. Additionally, the performance of calretinin as biomarker using DPS is improved in comparison to the use of plasma, resulting in a slightly increased sensitivity at constant specificity.

CONCLUSION: The findings of this proof-of-concept study suggest that filter cards represent a valuable alternative sampling method to determine calretinin for the detection or monitoring of mesothelioma.