The predictive value of hospital admission serum alanine transaminase activity in patients treated for paracetamol overdose

Background: Paracetamol is a major cause of poisoning. Treatment decisions are predominately based on the dose ingested and a timed blood paracetamol concentration because most patients present to hospital soon after overdose, before hepatotoxicity can be confirmed/excluded using serum alanine transaminase (ALT). Nonetheless, ALT is measured at hospital presentation; we investigated its value in predicting hepatotoxicity. Methods: From March 2011 to May 2012, patients admitted to the Royal Infirmary of Edinburgh for paracetamol overdose treatment were identified. We determined the value of admission ALT (below or above our upper limit of normal-50 IU/l) at predicting three endpoints: 1-doubling of ALT; 2-peak ALT > 1000 IU/l; 3-peak international normalized ratio (INR) > 2. Results: From 500 patients, 410 met the entry criteria; 264 presented within 8 h of overdose, 54 between 8 and 24 h, 53 after 24 h and 39 were staggered ingestions. Admission ALT was increased in 71. For endpoint 1 (ALT doubling), the positive predictive value (PPV) of admission ALT was 19% [95% confidence interval (CI) 12-30] with a negative predictive value (NPV) of 98% (95% CI 96-99); endpoint 2 (ALT > 1000 IU/l: PPV 23% (95% CI 14-34) and NPV 100% (95% CI 99-100) and for endpoint 3 (INR > 2): PPV 14% (95% CI 7-25) and NPV of 100% (95% CI 99-100). The NPV remained high when only late presenters were included. Conclusion: Admission ALT within the normal range has a high NPV and could be used, alone or in combination with newer biomarkers, to identify lower risk patients at hospital presentation.