Which laboratory test is crucial for assessing the severity of liver failure?

The International Normalized Ratio (INR) is a critical laboratory test for assessing the severity of liver failure because it directly measures the liver's ability to synthesize clotting factors, primarily factors II, VII, IX, and X, which are produced by the liver. When liver function declines, the production of these clotting factors decreases, resulting in an elevated INR. This increase indicates a prolonged prothrombin time, which reflects the liver’s impaired synthetic function. Clinicians often use the INR as a marker for liver function and to help evaluate the severity of liver disease, guiding management decisions.

In contrast, blood urea nitrogen (BUN) levels are more indicative of kidney function rather than liver health. A complete blood count (CBC) provides information about the overall blood cell status and can indicate various conditions but does not provide specific insight into liver function. An arterial blood gas (ABG) analysis measures the acidity and levels of oxygen and carbon dioxide in the blood, which are important for assessing respiratory and metabolic conditions, but it does not specifically reflect liver function. Thus, INR is the most relevant test in this context for evaluating liver failure severity.