MicroRNA‐122 can be measured in capillary blood which facilitates point‐of‐care testing for drug‐induced liver injury

AIMS: Liver‐enriched microRNA‐122 (miR‐122) is a novel circulating biomarker for drug‐induced liver injury (DILI). To date, miR‐122 has been measured in serum or plasma venous samples. If miR‐122 could be measured in capillary blood obtained from a finger prick it would facilitate point‐of‐care testing, such as in resource‐limited settings that have a high burden of DILI. METHODS: In this study, in healthy subjects, miR‐122 was measured by polymerase chain reaction in three capillary blood drops taken from different fingers and in venous blood and plasma (n = 20). miR‐122 was also measured in capillary blood obtained from patients with DILI (n = 8). RESULTS: Circulating miR‐122 could be readily measured in a capillary blood drop in healthy volunteers with a median (interquartile range) cycle threshold (Ct) of 32.6 (31.1–34.2). The coefficient of variation for intraindividual variability across replicate blood drops was 49.9%. Capillary miR‐122 faithfully reflected the concentration in venous blood and plasma (Pearson R = 0.89, P < 0.0001; 0.88, P < 0.0001, respectively). miR‐122 was 86‐fold higher in DILI patients [median value 1.0 × 10(8) (interquartile range 1.89 × 10(7)–3.04 × 10(9)) copies/blood drop] compared to healthy subjects [1.85 × 10(6) (4.92 × 10(5)–5.88 × 10(6)) copies/blood drop]. Receiver operator characteristic analysis demonstrated that capillary miR‐122 sensitively and specifically reported DILI (area under the curve: 0.96, P = 0.0002). CONCLUSION: This work supports the potential use of miR‐122 as biomarker of human DILI when measured in a capillary blood drop. With development across DILI aetiologies, this could be used by novel point‐of‐care technologies to produce a minimally invasive, near‐patient, diagnostic test.