Finger prick test has potential to monitor adalimumab response
medwireNews: Patients with inflammatory arthritis who are treated with adalimumab could monitor their blood levels of the drug using a finger prick test in place of full intravenous blood draws, researchers report.
“[T]herapeutic drug monitoring (TDM) can help to identify causes for insufficient response” to adalimumab treatment, but currently used TDM methods rely on blood collection by venipuncture, which “requires qualified personnel and flexibility of the patient,” explain the study authors, led by Karien Bloem (Sanquin Diagnostic Services Amsterdam, the Netherlands).
In a cross-sectional analysis of 161 patients with inflammatory arthritis, of whom 60% had rheumatoid arthritis, 21% had ankylosing spondylitis, and 19% had psoriatic arthritis, the team found that adalimumab concentrations measured using dried blood spots obtained from a finger prick “correlated well” with corresponding serum measurements taken with venipuncture from the same patient (correlation coefficient=0.93).
Levels of adalimumab, anti-adalimumab antibody, and total immunoglobulin G antibody measured from dried blood spots were systematically lower than those measured from blood draws. Bloem and colleagues found that this discrepancy was “consistently observed” when testing dried blood spot samples spiked with a range of adalimumab concentrations, “suggesting a slightly different protein composition of blood collected via finger prick vs venipuncture.”
Therefore, the researchers calculated that dried blood spot measurements from finger prick tests should be multiplied by a correction factor of 1.19 based on the average decrease in antibody concentrations in dried blood spot versus venipuncture measurements.
After converting finger prick test measurements using this correction factor, the slope of the regression line between the two measurements of adalimumab concentration became “close to 1,” suggesting “good correlation between [dried blood spot] and the [venipuncture]-serum values,” explain the authors in the British Journal of Clinical Pharmacology.
Taken together, these findings suggest that serum concentrations of adalimumab “can be satisfactorily estimated by measuring concentrations in [dried blood spot] eluates, collected by finger prick,” which “offers great opportunity to simplify TDM of adalimumab,” says the team.
And Bloem told the press that “[e]asy home sampling at different time points will benefit patients and could help to prescribe biologics optimally.”
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