![]() ![]() 7 In real terms this goal is a trade-off between imprecision and bias, with the lower the method bias, the wider the allowable imprecision. The Laboratory Working Group of the National Kidney Disease Education Program (NKDEP) stated that the combination of systematic bias and random error should not give rise to an error in eGFR calculation of >10%. 7, 13 Westgard has recently updated the desirable analytical goals for serum creatinine to 8.2% for total error, 3.8% for imprecision and 2.7% for bias. 12 Analytical goals derived from biological variation allow for a minimum total error goal of 11.4% (comprising a goal for imprecision of 3.2% and a goal for bias of 5.1%), desirable total error of 7.6% (2.2% for imprecision and 3.4% for bias) and optimal total error of 3.8% (1.1% for imprecision and 1.7% for bias). However, as PoCT methods should strive to be of equivalent analytical standard to those of the laboratory, it is appropriate to apply currently accepted specifications for laboratory measurement of creatinine to PoCT. To the author’s knowledge, there are no analytical performance standards that relate specifically to PoCT creatinine methods and devices. ![]() Apart from the StatSensor which is a discrete whole blood creatinine measuring device, all other instruments can test for a range of other analytes. All have good connectivity to laboratory or clinical information systems. The i-STAT and NovaStat devices both work off battery as well as mains power. The ABL and Dri-Chem systems are heavier again (more than 20 kg) and more suited to the hospital or satellite laboratory environment than the community-based screening setting for example. The i-STAT and StatSensor are hand-held devices while the remainder are benchtop, weighing 5 kg or more. Some devices such as the ABL, Reflotron and StatSensor can provide an automatic calculation of eGFR, using aligned and non-aligned Modification of Diet in Renal Disease (MDRD) formulae. Measuring ranges are generally very wide. All devices have rapid turnaround times for results varying from 30 seconds to 5 minutes, except the Piccolo which takes 8.5 minutes for the first result and 40 seconds thereafter for each subsequent result. Sample volumes range from 1 to 30 μL generally, but the i-STAT requires 65 μL of venous whole blood and the ABL systems even more, depending on sample type. Preferred sample types vary from whole blood to serum/plasma or both. Measurement consumables range from strips to cassettes and cartridges to a rotor system. In terms of calibration, the ABL is IDMS-aligned while others are traceable to IDMS through Standard Reference Material (SRM) products. Method principles are based on a cascade of enzymatic reactions, followed by either photometric or electrochemical detection. ![]() ![]() Table 3 summarises the non-analytical specifications of those devices currently in Australasia. The i-STAT and ABL devices are examples of the former category that are available in Australasia, while the Reflotron, Dri-Chem, StatSensor and Piccolo are Australasian examples of the latter category. PoCT creatinine devices can be conveniently divided into two types: those that are primarily blood gas analysers that offer creatinine as one of the metabolites that they measure and those that are ‘non blood gas’ analysers. NIST = National Institute of Standards and Technology, SRM = Standard Reference Material A = arterial, V = venous, C = capillary. ![]()
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