Importance of good capillary sampling

Point-of-care (POC) testing is one of the fastest-growing areas in medical diagnostics, and so capillary blood (fingerstick) sampling is increasingly being used worldwide as a means of quickly and easily obtaining small amounts of blood for such tests. Anaemia is the most widespread disorder of the blood, affecting approximately 25% of the global population, with iron deficiency being the most common cause. In turn, iron deficiency is the commonest nutritional disorder globally and the only nutrient deficiency with significant prevalence in industrialised countries, as well as developing countries. Consequently, haemoglobin (Hb) is the most frequently performed test in POC haematology.1

In hospitals POC haemoglobin testing is used in a variety of settings, such as dialysis units, A&E, O&G, critical care and operating theatres. By using blood obtained by skin puncture, rather than venepuncture, it can deliver fast and accurate results, supporting immediate clinical decision making. However, Hb values are prone to being affected by pre-analytical errors, with incorrect capillary blood sampling being the most common reason leading to inaccurate POC haemoglobin results.2 Therefore, personnel drawing blood must adhere to strict and standardised blood sampling techniques to ensure accurate and consistent POCT results that are fully comparable to laboratory techniques. 

For this reason, detailed capillary blood sampling guidelines have been published by a number of organisations, including the Clinical and Laboratory Standards Institute and World Health Organization (WHO).3,4 This article provides an overview of the factors that can affect the measurement of haemoglobin and a guide to capillary blood sampling best practice.