Painless Capillary Blood Collection: A Rapid Evaluation of the Onflow Device

Abstract

Blood-based diagnostics are critical for many medical decisions, but mostly rely on venepuncture, which can be inconvenient and painful. The Onflow Serum Gel (Loop Medical SA, Vaud, Lausanne, Switzerland) is a novel blood collection device that utilises needle-free technology to collect capillary blood. In this pilot study, 100 healthy participants were enrolled and provided two Onflow collected specimens and one venous blood specimen. Five chemistry analytes (AST, ALT, LDH, potassium, creatinine) and haemolysis were measured per specimen, and laboratory analyte results were compared. Onflow was found to be more acceptable than venepuncture with lower pain ratings, and 96.5% of participants would use the Onflow method again. All phlebotomists (100%) found Onflow intuitive and user-friendly, with ~1 mL of Onflow blood successfully collected from 99% of participants in <12 min (mean: 6 min, 40 s) and 91% collected on the first attempt. ALT and AST analytes showed no difference in performance, while creatinine generated a negative bias (-5.6 µmol/L), and increased variability was noted with potassium (3.6%CV) and LDH (6.7%CV), although none were clinically relevant. These differences may be due to 35% of Onflow collected specimens having "mild" haemolysis. Onflow is a promising alternative blood collection device that should now be evaluated in participants with expected abnormal chemistries and as an option for self-collection.

Keywords: capillary blood collection; onflow serum gel; pain-free; serum chemistry; upper arm collection device; venous-comparable blood specimen.

Figure 1

Examples of the Onflow device placed on the upper arm.

Figure 2

Measure of haemolysis (haemoglobin (g/L)) for each specimen collected by venepuncture and Onflow. Specimen results are sorted by increasing venous haemoglobin on the horizontal axis. The shaded areas represent the haemolysis classification [22], which are also tabulated alongside the graph. g/L: grams per litre.

Figure 3

Percentage similarity analysis. (a) Scatter plots for Onflow 1 and Onflow 2 device test results compared to venous blood test results for all analytes from each specimen listed in sequence. Black circles highlight two results for LDH which would be clinically relevant, but both had the presence of haemolysis on venous blood. (b) Split-violin plots representing the percentage similarity for each Onflow device result compared to the venous blood result across the five analytes. The dotted line marks the 100% similarity reference line. %: percentage; ALT: alanine transaminase; AST: aspartate transaminase; LDH: lactate dehydrogenase.

Figure 4

Scatter plots showing (a) Onflow specimen haemolysis by Onflow specimen collection time and absolute bias for the Onflow results compared to venous results for all analytes srted by specimen collection time and stratified by haemolysis ((b) ALT, (c) AST, (d) Creatinine, (e) potassium, (f) LDH). ALT: alanine transaminase; AST: aspartate transaminase; LDH: lactate dehydrogenase; µmol/L: micromoles per litre; mmol/L: millimoles per litre; n: number; U/L: units per litre.

Figure 5

Usability and acceptability of the Onflow device compared to venepuncture (a) Participant pain rating for venepuncture and onflow, (b) Participant likelihood of using venepuncture and Onflow again, (c) Participant-perceived ease-of-use, and (d) Time taken for Onflow specimen collection.