Evaluation of analytical performances of a serum acetaminophen assay designed for round-the-clock use

Abstract

Acetaminophen (paracetamol) voluntary (or not) intoxications are a major cause of life-threatening liver damage. Most of available assays on the market show an upper range measurement level that is close to thresholds considered as toxic levels. Therefore, high concentration samples must be further diluted in to accurately measure paracetamol levels. This study aims at assessing the performances of a Cambridge life sciences (CLS) test for acetaminophen determination in human serum, which solves this issue. Indeed, the particularities of this test consist in (i) an extended announced upper limit of quantitation, and (ii) in the use of a genetically unique enzyme (Aryl acylamidase). This evaluation encompasses comparison of results with those obtained using the acetaminophen Thermofisher test currently used in the University Hospital of Lille, and here after referred to as “reference method”. Analytical performance was evaluated on a Beckman Coulter AU480 chemistry analyzer. Within-run precision was determined by assaying 3 serum samples at 3 concentration levels (low, medium, high) in 10 replicates and between-run precision in running 5 samples on 6 days, twice a day. Linearity was assessed against a set of standards covering the entire claimed linearity range. Fifty-two fresh serum samples form patients were prospectively assessed for correlation to the reference method. The within-run and between-run precision (%CV) was respectively < 1% and < 3%. The assay showed good linearity with very low CV < 2% at concentrations up to 859 mg/L, consistent with the analytical range announced by the manufacturer. The regression equation against the reference method was Y = 1.133 x + 0.145, r2 = 0.99988. However, the lower limit of quantification (LLOQ) appears to be slightly higher than the manufacturer's stated (3 mg/L). Comparison to reference method showed that values given by the CLS assay were overestimated especially in the low range of concentration values (< 50 mg/L). The CLS acetaminophen assay has proven to have good analytical performance. Non-correlation to reference method does not affect the ability of the test to detect and to guide the management of paracetamol poisoning. The major advantage of CLS acetaminophen assay is the broad linearity range covering high acetaminophen concentrations. The use of this assay eliminates the need for dilution of highly positive samples and is particularly designed for round-the-clock use.