Alcoholic Liver Disease: This is a common cause of liver function test (LFT) derangement in young adults, even if they are otherwise healthy. The justification lies in the prevalence of alcohol consumption in this demographic and the potential for underreported or underestimated alcohol intake.

Viral Hepatitis (A, B, C, E): These infections are prevalent and can cause LFT derangements. Hepatitis A and E are typically acute and self-limiting, while hepatitis B and C can be chronic.
Non-Alcoholic Fatty Liver Disease (NAFLD): Although more commonly associated with obesity and metabolic syndrome, NAFLD can occur in lean individuals and is a significant cause of LFT abnormalities.
Drug-Induced Liver Injury (DILI): Many prescription and over-the-counter medications, as well as herbal supplements, can cause liver injury, making this a broad and likely category.
Autoimmune Hepatitis: Although less common, autoimmune hepatitis can present in young adults without a significant past medical history and can cause significant LFT derangements.

Wilson's Disease: A genetic disorder leading to copper accumulation in the liver, which can present with LFT derangements and is potentially treatable if diagnosed early.
Hemochromatosis: Genetic iron overload can lead to liver damage and is critical to diagnose early to prevent long-term complications.
Alpha-1 Antitrypsin Deficiency: A genetic disorder that can cause liver disease and lung disease, diagnosis of which is crucial for management and family screening.
Budd-Chiari Syndrome: Hepatic vein thrombosis, which can present with acute liver dysfunction and is a medical emergency.

Primary Biliary Cholangitis (PBC): An autoimmune disease of the bile ducts that can cause LFT derangements, more commonly seen in middle-aged women but can occur in younger males.
Primary Sclerosing Cholangitis (PSC): A chronic liver disease characterized by inflammation and scarring of the bile ducts, often associated with inflammatory bowel disease.
Mitochondrial Liver Diseases: A group of rare genetic disorders affecting the mitochondria within liver cells, leading to liver dysfunction.
Vascular Liver Diseases (e.g., portal vein thrombosis): Conditions affecting the blood vessels of the liver, which can lead to liver dysfunction and are important to diagnose due to their potential for treatment and prevention of complications.