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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Critical Care Medicine

Decoding the Numbers: Labs and Scoring Systems

At a Glance

Acute liver failure is monitored using key labs like INR, ammonia, bilirubin, and creatinine. Doctors use these lab results to calculate the King's College Criteria and MELD score, which determine if the liver can recover or if an emergency transplant is needed.

In the ICU, you will be presented with a constant stream of lab results. These numbers are the “dashboard” doctors use to monitor the liver’s function, the brain’s safety, and the necessity of a transplant. Understanding which numbers matter most can help you follow the medical team’s logic and ask more targeted questions.

The Diagnostic “Must-Haves”

To be officially diagnosed with Acute Liver Failure (ALF), a patient must have two specific clinical findings:

  1. INR ≥ 1.5: This confirms the liver is no longer making enough proteins to clot the blood. While this is a critical marker of the liver’s declining function (synthetic failure), the body often naturally rebalances its clotting system, making spontaneous bleeding relatively rare [1][2][3].
  2. Encephalopathy: This is the presence of mental confusion or altered consciousness. Without this mental change, the condition is called “Acute Liver Injury” rather than “Failure” [4][2].

Key Labs to Watch

While doctors look at dozens of values, these five are often the most critical in ALF:

  • INR (International Normalized Ratio): The most sensitive measure of how the liver is currently functioning [3]. A rising INR often signals worsening failure.
  • Ammonia: A toxin normally cleared by the liver. High levels (especially above 150-200 µmol/L) are strongly linked to brain swelling (cerebral edema) and worsening encephalopathy [5][6][7].
  • Bilirubin: A waste product from old blood cells. High levels cause jaundice (yellowing) [3]. In non-acetaminophen cases, very high bilirubin is a major warning sign for mortality [8].
  • Creatinine: A measure of kidney function. Because ALF often triggers multi-organ failure, rising creatinine tells doctors the kidneys are struggling—a key factor in deciding if a transplant is needed [8][9].
  • ALT and AST (Liver Enzymes): These “leak” into the blood when liver cells die. Interestingly, very high numbers (in the thousands) aren’t always bad; they may just show a sudden hit (like Tylenol). If these numbers drop while the INR stays high, it may mean there are very few healthy liver cells left to even leak enzymes [4].

Scoring Systems: How Doctors Decide

Doctors use “calculators” called prognostic scores to predict if the liver can recover on its own or if the patient needs a transplant.

1. King’s College Criteria (KCC)

This is the “gold standard” for deciding when a patient needs an emergency transplant [10]. It uses different rules depending on the cause:

For Acetaminophen (Tylenol) For All Other Causes (Non-Tylenol)
Blood is too acidic (pH < 7.3) INR > 6.5
OR all three of: OR three of the following:
1. High INR (> 6.5) 1. Age <10 or >40
2. Kidney failure (Creatinine > 3.4) 2. Jaundice >7 days before brain symptoms
3. Severe brain dysfunction (Grade III/IV HE) 3. INR > 3.5
4. Bilirubin > 17.5 mg/dL
5. Unfavorable cause (e.g., drug reaction or unknown cause) [11][12].

2. MELD Score (Model for End-Stage Liver Disease)

Originally for chronic disease, MELD is now frequently used in ALF [13]. It uses a mathematical formula (including bilirubin, creatinine, INR, and sodium) to assign a score from 6 to 40 [14][15]. In the ICU, a rapidly rising MELD score often triggers the need for “Status 1A” transplant listing, the highest priority in the country [13][16].

Lab Checklist for Caregivers

You can ask the nurse or doctor if the following have been checked recently:

  • [ ] Arterial pH and Lactate: To check for blood acidity (critical for Tylenol cases) [8].
  • [ ] Ammonia: To assess the risk of brain swelling [17].
  • [ ] Phosphate: Low phosphate can actually be a good sign, suggesting the liver is trying to regenerate and using up phosphorus to build new cells [4].
  • [ ] Acetaminophen Level: Even if the family doesn’t suspect an overdose, this is standard to rule out a hidden cause [18].

Common questions in this guide

How is acute liver failure officially diagnosed?
Doctors diagnose acute liver failure when a patient has an INR of 1.5 or higher, indicating the liver cannot clot blood properly, combined with encephalopathy, which is mental confusion or altered brain function.
What does a high ammonia level mean in liver failure?
Ammonia is a toxin normally cleared by the liver. In acute liver failure, high ammonia levels are dangerous because they are strongly linked to brain swelling and worsening confusion or altered consciousness.
What are the King's College Criteria?
The King's College Criteria is a scoring system used by doctors to determine if a patient with acute liver failure needs an emergency liver transplant. It evaluates specific lab results like blood acidity, INR, kidney function, and brain dysfunction.
Why might liver enzymes (ALT and AST) drop suddenly?
While dropping liver enzymes can sometimes mean the liver is healing, it can also be a warning sign. If enzymes drop while the INR stays high, it may indicate that there are very few healthy liver cells left to release enzymes into the blood.
What is the MELD score used for in the ICU?
The MELD score is a mathematical formula that uses lab values like bilirubin, creatinine, INR, and sodium. In the ICU, doctors use a rapidly rising MELD score to prioritize a patient for a high-priority emergency liver transplant.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does the patient currently meet the King's College Criteria for a liver transplant?
  2. 2.What is the patient’s current MELD score, and how has it changed in the last 24 hours?
  3. 3.What was the patient's most recent ammonia level, and are you considering continuous renal replacement therapy (CRRT) to lower it?
  4. 4.Are the liver enzymes (ALT/AST) trending down because the liver is healing, or because there are few healthy liver cells left to release them?
  5. 5.Is the patient's kidney function (creatinine) stable, and how does that affect their overall prognosis?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (18)
  1. 1

    Managing the patient with acute liver failure.

    Cardoso FS, Karvellas CJ

    Clinical liver disease 2017; (9(4)):89-93 doi:10.1002/cld.628.

    PMID: 30992967
  2. 2

    Editorial: Severe Acute Liver Injury: Cause Connects to Outcome.

    Argo CK, Caldwell SH

    The American journal of gastroenterology 2017; (112(9)):1397-1399 doi:10.1038/ajg.2017.221.

    PMID: 28874859
  3. 3

    EASL Clinical Practical Guidelines on the management of acute (fulminant) liver failure.

    , , Wendon, J, et al.

    Journal of hepatology 2017; (66(5)):1047-1081 doi:10.1016/j.jhep.2016.12.003.

    PMID: 28417882
  4. 4

    Acute Liver Failure (ALF) in Pregnancy: How Much Is Pregnancy Related?

    Casey LC, Fontana RJ, Aday A, et al.

    Hepatology (Baltimore, Md.) 2020; (72(4)):1366-1377 doi:10.1002/hep.31144.

    PMID: 31991493
  5. 5

    Hyperammonemia and Hepatic Encephalopathy in Pediatric and Adult Liver Intensive Care Unit.

    Ocak I, Colak M, Battal M

    Sisli Etfal Hastanesi tip bulteni 2023; (57(1)):68-72 doi:10.14744/SEMB.2022.78872.

    PMID: 37064852
  6. 6

    Continuous renal replacement therapy is associated with reduced serum ammonia levels and mortality in acute liver failure.

    Cardoso FS, Gottfried M, Tujios S, et al.

    Hepatology (Baltimore, Md.) 2018; (67(2)):711-720 doi:10.1002/hep.29488.

    PMID: 28859230
  7. 7

    Cerebral edema and liver disease: Classic perspectives and contemporary hypotheses on mechanism.

    Liotta EM, Kimberly WT

    Neuroscience letters 2020; (721()):134818 doi:10.1016/j.neulet.2020.134818.

    PMID: 32035166
  8. 8

    Acute liver failure: A practical update.

    Fernández J, Bassegoda O, Toapanta D, Bernal W

    JHEP reports : innovation in hepatology 2024; (6(9)):101131 doi:10.1016/j.jhepr.2024.101131.

    PMID: 39170946
  9. 9

    The Pathology of Acute Liver Failure.

    Lefkowitch JH

    Advances in anatomic pathology 2016; (23(3)):144-58 doi:10.1097/PAP.0000000000000112.

    PMID: 27058243
  10. 10

    Absolutely FABulous? FABP-1 in Non-acetaminophen-related Acute Liver Failure.

    Cavazza A, McPhail MJ

    Digestive diseases and sciences 2021; (66(1)):10-11 doi:10.1007/s10620-020-06256-9.

    PMID: 32328891
  11. 11

    Liver Transplantation for Acute Liver Failure- Indication, Prioritization, Timing, and Referral.

    Biswas S, Shalimar

    Journal of clinical and experimental hepatology 2023; (13(5)):820-834 doi:10.1016/j.jceh.2023.01.008.

    PMID: 37693253
  12. 12

    Prognostic Scores in Acute Liver Failure Due to Viral Hepatitis.

    Biswas S, Kumar R, Acharya SK, Shalimar

    Diagnostics (Basel, Switzerland) 2023; (13(6)) doi:10.3390/diagnostics13061035.

    PMID: 36980341
  13. 13

    Novel predictors for liver transplantation or death in drug-induced acute liver failure.

    Weber S, Woischke C, Denk G, Gerbes AL

    European journal of gastroenterology & hepatology 2022; (34(4)):422-425 doi:10.1097/MEG.0000000000002272.

    PMID: 34432679
  14. 14

    The Evolution of the MELD Score and Its Implications in Liver Transplant Allocation: A Beginner's Guide for Trainees.

    Trivedi HD

    ACG case reports journal 2022; (9(5)):e00763 doi:10.14309/crj.0000000000000763.

    PMID: 35919673
  15. 15

    The outcomes and prognostic factors of patients with hepatocellular carcinoma and Child-Turcotte-Pugh class B.

    Fu CC, Chen YJ, Su CW, et al.

    Journal of the Chinese Medical Association : JCMA 2023; (86(10)):876-884 doi:10.1097/JCMA.0000000000000975.

    PMID: 37537726
  16. 16

    Proteomics Indicates Lactate Dehydrogenase Is Prognostic in Acetaminophen-Induced Acute Liver Failure Patients and Reveals Altered Signaling Pathways.

    Vazquez JH, Kennon-McGill S, Byrum SD, et al.

    Toxicological sciences : an official journal of the Society of Toxicology 2022; (187(1)):25-34 doi:10.1093/toxsci/kfac015.

    PMID: 35172013
  17. 17

    Ammonia Level and Mortality in Acute Liver Failure: A Single-Center Experience.

    Niranjan-Azadi AM, Araz F, Patel YA, et al.

    Annals of transplantation 2016; (21()):479-83 doi:10.12659/aot.898901.

    PMID: 27480786
  18. 18

    Acetaminophen (APAP or N-Acetyl-p-Aminophenol) and Acute Liver Failure.

    Bunchorntavakul C, Reddy KR

    Clinics in liver disease 2018; (22(2)):325-346 doi:10.1016/j.cld.2018.01.007.

    PMID: 29605069

This guide to acute liver failure labs and scoring systems is for informational purposes only. Always consult the intensive care team or hepatologist regarding your loved one's specific lab results and transplant prognosis.

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