Offer children alternative to venepuncture to confirm INR

Haematologists in South Australia have come up with a simple method that allows children to avoid the trauma of venepuncture to confirm an abnormal Point-of-care (POC) INR test result.

To avoid taking a venous specimen to confirm any raised INR results in children, the haematology department at the Women’s and Children’s Hospital, Adelaide collects a capillary citrate specimen from the same finger-stick used to collect the POC INR.

Specimens from a 0.5-mL 3.2% citrate tube produce INR values in the laboratory that are comparable to the gold standard venous specimen, according to Dr Vaughn Williams.

In a study published in the International Journal of Haematology, Dr Williams  compared 449 consecutive POC INR results to an INR performed in the laboratory on a capillary citrate specimen collected from the same finger-stick.

The mean difference in INR values from the CoaguChek XS and laboratory was 0.22 (2.85 vs 2.63). There was a good correlation between the methods with r = 0.97.

An INR of ≤0.5 was found between the methods in 89% of cases and 84% agreement was noted (κ = 0.69).

“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,” he concludes.

Dr Williams notes that that in paediatric settings, most anticoagulated patients are cardiac patients, postsurgery.

“These children have already undergone considerable trauma as a result of these procedures. Therefore, when their INR exceeds an INR of 3.5 (up to INR 5 at some institutions), there is an expectation of further insult through a venepuncture being performed to allow for a laboratory confirmation of the raised INR.”

Based on his results, he recommends that it should be standard practice for paediatric institutions to collect a capillary citrate specimen for laboratory confirmation of POC INR values.

“This removes the requirement for a venous specimen, which may be problematic, particularly in very young patients, and at the same time, reducing the stress for both the patient and caregiver should a confirmatory specimen be required.”

And while the method was been tested in a paediatric setting, it may also be applicable to all patients particularly those with poor venous access,” he adds.

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