RADAR study article published in Scientific Reports.

Above image excerpt from publication shows Bland-Altman analysis comparing the measurement of CRP using two different sampling methods across n=100 RADAR study participants. The graph shows agreement between a reference immunoturbidimetry analysis of whole blood (Ref. Hosp.) and ELISA testing of dried blood spot samples (DBS EL).

We have published a paper in Scientific Reports reporting a concordance study of dried blood spot (DBS) samples to measure C-reactive protein (CRP; a blood based inflammatory marker) in patients with actively flaring arthritis.

The study revealed that DBS CRP measures across 100 RADAR study participants correspond well with conventional venous blood CRP measures. Importantly the study also provides evidence that indicates flare ups could be accurately identified remotely in the majority of weekly sampled participants who experienced flares during a 6 week follow up. 

The abstract of the publication is below and full article can be accessed at the link.  

Rheumatoid arthritis (RA) is characterised by painful, stiff and swollen joints. RA features sporadic ‘flares’ or inflammatory episodes—mostly occurring outside clinics—where symptoms worsen and plasma C-reactive protein (CRP) becomes elevated. Poor control of inflammation results in higher rates of irreversible joint damage, increased disability, and poorer quality of life. Flares need to be accurately identified and managed. A method comparison study was designed to assess agreement between CRP values obtained by dried blood spot (DBS) versus conventional venepuncture sampling. The ability of a weekly DBS sampling and CRP test regime to detect flare outside the clinic was also assessed. 

Matched venepuncture and finger lancet DBS samples were collected from n = 100 RA patients with active disease at baseline and 6 weeks (NCT02809547). A subset of n = 30 RA patients submitted weekly DBS samples over the study period. Patient demographics, including self-reported flares were recorded. DBS sample CRP measurements were made by enzyme-linked immunosorbent assay, and venepuncture samples by a reference immunoturbometric assay. Data was compared between sample types by Bland–Altman and weighted Deming regression analyses. Flare detection sensitivity and specificity were compared between ‘minimal’ baseline and 6 week sample CRP data and the ‘continuous’ weekly CRP data. 

Baseline DBS ELISA assay CRP measures yielded a mean positive bias of 2.693 ± 8.640 (95% limits of agreement − 14.24 to 19.63%), when compared to reference assay data. Deming regression revealed good agreement between the DBS ELISA method and reference assay data, with baseline data slope of 0.978 and intercept -0.153. The specificity of ‘continuous’ area under the curve (AUC) CRP data (72.7%) to identify flares, was greater than ‘minimal’ AUC CRP data (54.5%). 

This study indicates reasonable agreement between DBS and the reference method, especially at low to mid-range CRP values. Importantly, longitudinal CRP measurement in RA patients helps to clearly identify flare and thus could assist in remote monitoring strategies and may facilitate timely therapeutic intervention.