Use of a capillary specimen in the laboratory to verify a point‐of‐care international normalized ratio: Avoidance of a venipuncture in a pediatric setting

• Published in: International journal of laboratory hematology Vol. 41; no. 1; pp. 55 - 59
• Main Author: Williams, Vaughan K.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01-02-2019
• Subjects: Blood Specimen Collection - standards; Capillaries; capillary; Citric acid; Clinical Laboratory Techniques - methods; finger‐stick; Humans; international normalized ratio; International Normalized Ratio - methods; Laboratories; Observer Variation; pediatric; Pediatrics; Point-of-Care Systems; point‐of‐care; Trauma; Veins; finger-stick; capillary; international normalized ratio; point-of-care; pediatric
• ISSN: 1751-5521; 1751-553X
• DOI: 10.1111/ijlh.12920

Introduction
Point‐of‐care (POC) international normalized ratio (INR) values above an institutional cutoff are confirmed in the laboratory using a gold standard venous specimen. This can be problematic in a pediatric setting.
Method
In this study, 449 consecutive POC INR results were compared to an INR performed in the laboratory on a capillary citrate specimen collected from the same finger‐stick. The results were statistically analyzed.
Results
The mean INR values from the CoaguChek XS and laboratory were 2.85 ± 1.19 and 2.63 ± 1.11, respectively. There was a good correlation between the methods with r = 0.97. Bland–Altman analysis indicated a bias of 0.22 favoring the CoaguChek XS, with 95% limits of agreement −0.29 to 0.72. Passing and Bablok method comparison resulted in a slope of 0.91 (y = 0.91x + 0.02). An INR of ≤0.5 was found between the methods in 89% of cases and 84% agreement was noted (κ = 0.69).
Conclusion
Comparing the capillary INR laboratory results to studies involving a venous specimen, the capillary specimen performed with equivalence. Thus, a capillary citrate specimen can be collected from the same finger‐stick used to perform the POC INR for confirmation in the laboratory. This avoids the trauma of a venous collection in such a situation.