Liver Function Tests Explained: Bilirubin, Albumin, PT/INR
1. Introduction
A liver function panel blood test has many different values; some show liver irritation or injury (like AST and ALT), while others show how well your liver is actually working.
This chapter focuses on three of the most important liver function tests:
Bilirubin: how well your liver processes waste
PT/INR: how well your liver produces clotting factors
Albumin: your liver’s ability to make essential proteins
Together, these tests give a realistic picture of your liver’s overall health and reserve, especially in conditions like MASLD/MASH, alcohol-related liver disease, viral hepatitis, or cirrhosis.
A mild elevation in one test doesn’t always mean something serious. But persistent abnormalities, especially in bilirubin, albumin, or INR, can signal that the liver is under strain or not performing at full capacity.
In this guide, we break down each test and by the end, you’ll understand what these numbers really mean and how they fit into the bigger picture of your metabolic and liver health.
2. Bilirubin
Bilirubin is a yellow-brown pigment produced when old red blood cells are broken down, primarily in the spleen. The liver processes and excretes this bilirubin, making it a direct measure of the liver’s excretory function.
Normal Ranges: (Kwo et al 2017) - Total bilirubin: 0.3-1.2 mg/dL (5-21 μmol/L) - Direct (conjugated) bilirubin: 0-0.3 mg/dL (0-5 μmol/L) - Indirect (unconjugated) bilirubin: 0.2-0.8 mg/dL (3-14 μmol/L)
Clinical Significance:
Elevated bilirubin levels typically indicate either impaired liver function or bile duct obstruction. Importantly, in MASLD/MASH patients, rising bilirubin is often a late finding that suggests progression to significant liver dysfunction or decompensated cirrhosis.
An elevation in conjugated bilirubin specifically implies hepatocellular disease or cholestasis (Kwo et al., 2017). Normal bilirubin levels can be maintained even in the presence of significant liver disease until the disease becomes quite advanced.
Bilirubin is what makes bruises turn yellow-green as they heal and gives bile its characteristic color. When your liver is healthy, it efficiently processes and eliminates bilirubin. If bilirubin builds up in your blood, your skin and eyes may turn yellow, a condition called jaundice. This is a sign that your liver isn’t working properly or that bile isn’t flowing as it should.
3. International Normalized Ratio (INR) and Prothrombin Time (PT)
The liver produces clotting factors essential for blood coagulation. PT measures how long it takes for blood to clot, while INR is a standardized way of reporting PT results that allows for comparison across different laboratories.
Normal Ranges: - Prothrombin Time: 10.9-12.5 seconds - INR: 0.8-1.2
Clinical Significance:
Elevated INR/PT indicates decreased synthesis of clotting factors and represents true impairment of liver synthetic function. This parameter is particularly valuable in assessing the severity of liver disease and is a component of the Model for End-Stage Liver Disease (MELD) score used to prioritize liver transplant candidates (Kamath et al., 2001). In MASLD patients, a rising INR often signals progression to decompensated cirrhosis.
Your liver makes proteins that help your blood clot when you get cut. The INR and PT tests measure how well your blood clots. If these numbers are high, it means your liver isn’t making enough clotting factors, which is a sign of serious liver damage. This is why people with advanced liver disease bruise easily and may have trouble stopping bleeding.
4. Albumin
Albumin is the most abundant protein in blood plasma, synthesized exclusively by the liver. It maintains oncotic pressure and transports various substances throughout the body.
Normal Range: - Serum albumin: 3.5-5.5 g/dL (35-55 g/L)
Clinical Significance: Low albumin (hypoalbuminemia) indicates decreased liver synthetic capacity and is associated with advanced liver disease. Because albumin has a relatively long half-life (approximately 20 days), it reflects chronic liver dysfunction rather than acute changes. Declining albumin levels in MASLD patients suggest progression to cirrhosis and increased mortality risk (Kwo et al., 2017).
Albumin is like a delivery truck in your bloodstream—it carries hormones, vitamins, and other substances where they need to go and helps keep fluid from leaking out of blood vessels. Your liver is the only organ that makes albumin, so when levels drop, it’s a sign your liver has been struggling for a while. Low albumin can cause swelling in your legs (edema) and abdomen (ascites) as fluid leaks out of blood vessels.
5. Next Steps
Your bilirubin, albumin, and PT/INR levels are pieces of a larger puzzle. They help estimate how well your liver is performing and whether additional imaging or non-invasive tests are needed. Now that you understand these numbers, the next step is exploring how clinicians assess liver structure and stiffness using tools like Ultrasound, FibroScan, and MRI. These chapters will help you understand what to expect and how each test fits into your care journey.
Note: If you have jaundice, unexplained weight loss, abdominal swelling, confusion, or bleeding issues, these require urgent medical review, go to the nearest ER without waiting for a hepatologist referral.
6. References
Caraceni P, Tufoni M, Bonavita ME. Clinical use of albumin. Blood Transfus. 2013 Sep;11 Suppl 4(Suppl 4):s18-25. doi: 10.2450 /2013.005s. PMID: 24333308; PMCID: PMC3853979. https://pubmed.ncbi.nlm.nih.gov/24333308/.
Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017;112(1):18-35. doi:10.1038/ajg.2016.517. https://pubmed.ncbi.nlm.nih.gov/27995906/. Comprehensive ACG guideline on evaluation of abnormal liver tests. Provides systematic approach to interpreting patterns of elevation (hepatocellular vs. cholestatic). Discusses when imaging and biopsy are indicated. Establishes normal ranges for all standard liver function tests.
Kamath PS, Wiesner RH, Malinchoc M, et al. A model to predict survival in patients with end-stage liver disease. Hepatology. 2001;33(2):464-470. doi:10.1053/jhep.2001.22172 https://aasldpubs.onlinelibrary.wiley.com/doi/10.1053/jhep.2001.22172 This is the original description of the MELD score for predicting mortality in patients with end-stage liver disease.