Phosphate level in acetaminophen-induced acute liver failure

Case: A patient is transferred from a nearby community hospital with acetaminophen-induced acute liver failure. ALT / AST reported in thousands and the last PT-INR of 2.7. On clinical exam, the patient is alert and oriented. Hemodynamics are stable. You alerted the hepatology team and sent STAT labs. After 45 minutes you received a call from the lab with a 'critical value' of phosphate with 0.9 mg/dl. It is a? (select one) (select one)

A) bad sign

B) good sign

Answer: B

Hypophosphatemia in the setting of acetaminophen-induced acute liver failure is a good sign. It indicates the regeneration of hepatocytes and the reversal of acute liver failure. You may have to replace it aggressively. Conversely, hyperphosphatemia suggests impaired regeneration and is a poor prognostic sign. It is also a sign of impending hepato-renal failure due to the kidney's lost ability to lower serum phosphate.

Said that experts warn against relying exclusively on this marker (see reference 3).

#hepatology

#electrolytes

References:

1. Schmidt LE, Dalhoff K. Serum phosphate is an early predictor of outcome in severe acetaminophen-induced hepatotoxicity. Hepatology. 2002 Sep;36(3):659-65. doi: 10.1053/jhep.2002.35069. PMID: 12198658.

2. Yoon E, Babar A, Choudhary M, Kutner M, Pyrsopoulos N. Acetaminophen-Induced Hepatotoxicity: a Comprehensive Update. J Clin Transl Hepatol. 2016 Jun 28;4(2):131-42. doi: 10.14218/JCTH.2015.00052. Epub 2016 Jun 15. PMID: 27350943; PMCID: PMC4913076.

3. Ng KL, Davidson JS, Bathgate AJ. Serum phosphate is not a reliable early predictor of outcome in paracetamol induced hepatotoxicity. Liver Transpl. 2004 Jan;10(1):158-9. doi: 10.1002/lt.20022. Erratum in: Liver Transpl. 2004 Feb;10(2):329. PMID: 14755796.