Comparison between point-of-care testing from capillary samples and conventional laboratory testing from venous samples for white blood cells and C-reactive protein in a pediatric outpatient setting

Background: Studies on the accuracy of point-of-care (POC) testing using capillary samples are scarce. Therefore, this study aimed to assess the analytical accuracy of POC testing for white blood cell (WBC) and C-reactive protein (CRP) using capillary samples compared with conventional central laboratory testing using venous samples in a pediatric ambulatory care setting.

Methods: This was a retrospective study including patients younger than 18 years who underwent concurrent WBC and CRP evaluations via capillary and subsequent venous sampling within a 2-h window. Capillary and venous blood samples were collected using finger prick and standard venipuncture techniques, respectively. Capillary blood analysis was performed using a Microsemi CRP device. Venous samples were measured in the hospital's central laboratory. The agreement between the capillary POC and venous laboratory results was evaluated using Bland-Altman analysis.

Results: A total of 277 pediatric patients were included in this study. The median age of the participants was 1 year (interquartile range: 0-2 years). The mean difference between the capillary and venous measurements for WBC was -18 × 100/μL with 95% limits of agreement of -73 × 100/μL to 37 × 100/μL. The mean difference between the capillary and venous measurements for CRP was -0.25 mg/dL with 95% limits of agreement of -2.1 mg/dL to 1.6 mg/dL.

Conclusions: POC CRP testing via capillary sampling by finger prick demonstrated sufficient accuracy. POC CRP testing has the potential to be a valuable instrument for clinical decision making, particularly in screening febrile outpatient children.