A rapid point-of-care assay for acetaminophen-related liver toxicity had a sensitivity of 100% and a specificity of 86%, compared with etiologic diagnosis, based on the results of a multicenter study published in the April issue of Clinical Gastroenterology and Hepatology.

The test might help guide treatment decisions for these patients in the emergency department and intensive care unit, said Dean W. Roberts, PhD, of the University of Arkansas, Little Rock, and his associates.

About 45% of acute liver failure cases in the United States stem from acetaminophen toxicity, but the diagnosis can be hard to confirm because the drug has a short half-life and patients often cannot or will not report an overdose, which also may consist of multiple exposures, limiting the interpretability of the Rumack nonogram. High-pressure liquid chromatography with electrochemical detection (HPLC-EC) accurately detects acetaminophen-protein adducts (3-[cysteine-S-yl] acetaminophen) released by lysed hepatocytes into the peripheral circulation, but this test requires specialized equipment and skilled personnel, the researchers noted (Clin Gastroenterol Hepatol. 2016 Sep 15. doi: 10.1016/j.cgh.2016.09.007 ).

Therefore, they developed AcetaSTAT, a competitive lateral flow immunoassay designed to detect acetaminophen-protein adducts in 27 minutes. To compare its performance with that of clinical diagnosis and HPLC-EC results, they evaluated charts and serum samples from 19 healthy adults, 33 adults with acetaminophen-induced liver failure from the Acute Liver Failure Study Group , and 29 registry members of similar age and sex who were considered to have nonacetaminophen acute liver failure. Based on past research, the investigators set a positive HPLC-EC test threshold of 1.0 nmol or greater, which corresponded to a band intensity of 1,200 on AcetaSTAT.

The point-of-care assay was positive in all 33 patients diagnosed with acetaminophen toxicity, for a test sensitivity of 100%, the researchers reported. The median band amplitude for cases was 584 (range, 222-1,027), significantly lower than that for patients with nonacetaminophen acute liver failure (3,678; range, 394-8,289; P less than .001) or for controls (8,971; range, 5,151-11,108; P less than .001). Band amplitude correlated inversely with adduct levels because AcetaSTAT is a competitive immunoassay – the presence of adducts decreases reactions at the test band, the investigators reported.

AcetaSTAT results were negative for 25 of 29 patients who were initially diagnosed with nonacetaminophen liver failure, for a test specificity of 86%, a positive predictive value of 89%, and a negative predictive value of 100%. Among the remaining four “false positives,” three tested near or above the toxicity threshold on HPLC-EC and were considered positive after further review, the investigators said. The fourth false-positive case was HPLC-EC–negative autoimmune hepatitis.

AcetaSTAT might not catch cases very early after acetaminophen overdose or that have only mild toxicity, the researchers noted. Nonetheless, it can help guide treatment decisions “at the point of clinical care,” they said. “Because the survival rate of acetaminophen acute liver failure is more favorable than that of other causes of acute live failure, assay results could impact future physician referral patterns and reduce medical costs associated with additional tests to determine the etiology of liver injury.”

The National Institute of Diabetes and Digestive and Kidney Diseases funded the study. Dr. Roberts and two coinvestigators are part owners of Acetaminophen Toxicity Diagnostics and have submitted a patent application for the AcetaSTAT serum assay used in this study. There were no other disclosures.