Liver Function Tests: A Comprehensive Guide

Have you ever wondered how a simple blood test can reveal the secrets of your liver's health?

The liver is a powerhouse organ, playing a crucial role in digestion, detoxification, and metabolism. It processes the nutrients from the food we eat, filters toxins from the blood, and produces vital proteins necessary for various bodily functions. Given its importance, maintaining liver health is critical for preserving health and well-being. But how do we know if our liver is functioning correctly? This is where liver function tests (LFTs) come into play.

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What Are Liver Function Tests?

Liver function tests are a series of blood tests that measure specific enzymes, proteins, and substances the liver produces. They help evaluate how well the liver is working and can indicate potential liver damage or disease.

LFTs assist healthcare providers in diagnosing and monitoring various liver conditions, such as:

• Hepatitis: Inflammation of the liver, often caused by viral infections
• Fatty Liver Disease: Accumulation of fat in liver cells, which can lead to inflammation and scarring
• Cirrhosis: Severe scarring of the liver, often resulting from long-term liver damage
• Liver Cancer: Malignant growths in the liver
• Gallstones: Hardened deposits in the gallbladder that can affect liver function

Why Are They Done?

Reasons your doctor may order LFTs include: 

• Routine Health Checks: As part of a comprehensive metabolic panel during regular health examinations.
• Symptom Evaluation: When experiencing symptoms like jaundice (yellowing of the skin and eyes), fatigue, abdominal pain, or unexplained weight loss.
• Monitoring Existing Conditions: For individuals with known liver diseases or those taking medications that can affect liver health.
• Pre-Surgical Assessments: To ensure the liver is functioning properly before undergoing surgery.
• Monitor Drug-Induced Side Effects: Certain medications can affect liver function. LFTs help ensure that drugs are not causing liver damage.

Key Components of a Liver Function Test

Liver function tests (also called a liver panel) use a blood sample to measure various substances made by the liver. Many of these tests are included in a broader blood test called the comprehensive metabolic panel (CMP), which assesses overall metabolic health.

Main Markers and Their Meanings

Some of the most common liver function tests include: 

• Alanine Transaminase (ALT): An enzyme predominantly made by the liver that helps it convert proteins into energy. Sometimes, you might see this test called SGPT. 
• Aspartate Transaminase (AST): An enzyme made by the liver and other tissues, such as those in the heart, pancreas, and skeletal muscles, that helps convert proteins into energy. This test is also called SGOT. 
• Alkaline Phosphatase (ALP): An enzyme in the liver and bone that assists various physiological processes, including detoxification, fat metabolism, and bone formation.
• Albumin: A protein made by the liver that accounts for 50% of the blood's total protein content. Albumin is responsible for transporting substances, such as hormones and vitamins, through the blood and keeping fluid inside the blood vessels. 
• Bilirubin: A substance produced during the breakdown of red blood cells that is processed by the liver to be eliminated by the body.
• Prothrombin Time (PT): A measure of how long it takes your blood to clot. It is named after prothrombin, a protein made by the liver that is involved in blood clotting.

Interpreting Results

The table below outlines the standard normal ranges for each of the above LFTs. Normal ranges may vary slightly depending on the performing laboratory and the patient's sex and age. 

Levels outside of the normal reference ranges may suggest liver inflammation or disease:

• High ALT and AST levels may indicate liver inflammation or damage. Possible causes include viral hepatitis, excessive alcohol consumption, and certain medications. 
• High ALP can be associated with bile duct blockage (such as gallstones), cirrhosis, and hepatitis. 
• Low albumin might suggest the liver isn't producing enough proteins, which can occur in chronic liver disease or malnutrition.
• Elevated bilirubin may cause jaundice and can result from liver disease, bile duct obstruction, or excessive red blood cell breakdown.
• Prolonged PT means your blood is taking longer than usual to clot. If you're not taking warfarin, this could suggest that the liver isn't producing enough clotting factors. 

Abnormal LFT levels do not definitively indicate a liver problem. Liver function tests are one component of a comprehensive medical evaluation and should be interpreted in the context of the patient's medical history and symptoms. Abnormal results typically warrant further testing to determine the underlying cause.

The Procedure for Liver Function Testing

Liver function tests require a blood draw. A healthcare professional collects a small blood sample from a vein, usually in the arm, using a tourniquet and a small needle. Once the needle is inserted, blood is collected into a vial. This procedure is quick, typically lasting less than five minutes, and relatively painless. You may feel a little pinch or discomfort as the needle is inserted and taken out of the vein. 

Before the Test

Here are some general tips to follow the day before your blood test:

• Follow your doctor's instructions. While LFTs don't generally require fasting (avoid eating and drinking anything except water), your doctor may advise you to refrain from taking certain medications or supplements that can influence liver enzyme levels, such as acetaminophen, ibuprofen, or kava.
• Avoid drinking alcohol, which has been linked to higher levels of AST and bilirubin. 
• If you don't have an appointment at the lab, call ahead to ask about when they are the least busy to avoid long wait times.

These are some general tips to follow on the day of your blood test:

• Stay hydrated by drinking plenty of water to help make your veins more accessible for the blood draw.
• If you don't need to fast, eat 1-2 hours before your blood draw. Bring a small snack and a bottle of water with you to have after the appointment.
• Wear a comfortable shirt that has sleeves that can be easily rolled up.
• If you tend to feel nervous or anxious about blood draws, practice meditation techniques like deep breathing to help you relax. Inform the healthcare professional performing the blood draw about your anxiety so they can assist in making the experience more comfortable.
• Bring your insurance card and a form of identification with you to the lab. 

After the Test

You won't need to follow special instructions and can resume normal activities immediately after your blood draw. You may have mild soreness or a small bruise at the site of the blood draw, which should resolve within a few days.

Your blood sample will be sent to a lab for analysis, which may be located on-site or at a different facility. The location of the lab will influence how quickly your results are available. If the analysis is performed on-site, results may be accessible within a few hours. Otherwise, getting your results might take a few days if they are processed off-site.

Factors Affecting Liver Function Test Results

LFTs are valuable tools for assessing liver health, but various factors can influence their results. 

In some cases, repeating liver function tests may be necessary:

• To confirm abnormal findings and rule out temporary factors affecting the results.
• Monitor the effectiveness of treatments for individuals undergoing therapy for liver disease and adjust treatments as needed.
• Track disease progression and manage complications in chronic liver conditions.

Here's a closer look at what can affect your liver test results:

Lifestyle Factors

Alcohol Consumption: Alcohol is toxic to the liver and will elevate liver enzymes. If alcohol abuse is suspected to contribute to abnormal LFTs, a doctor may order an additional test called gamma-glutamyl transferase (GGT), which tends to elevate with heavy drinking. 

Smoking: Smoking has been shown to increase GGT levels and decrease serum proteins, including albumin. There is evidence suggesting an association between cigarette smoking and the progression of liver disease.

Body Mass Index (BMI): Higher BMI is associated with elevated ALT and AST levels. 

Physical Activity: Intense exercise can sometimes increase liver enzyme levels because AST and ALT are also found in skeletal muscles. This rise is typically temporary and resolves with rest. 

Genetic Factors

Your family genes can cause differences in the proteins measured by liver tests. Genetics are responsible for about 20-77% of these differences. For example, Gilbert syndrome is a genetic condition passed down through families that affects the liver's ability to break down bilirubin. People with Gilbert syndrome have chronic elevations of serum bilirubin. 

Liver enzyme levels can also vary with age and sex.

Medical Conditions

It is expected that certain medical conditions will influence LFT levels, including:

• Metabolic dysfunction-associated steatotic liver disease (MASLD), previously called non-alcoholic fatty liver disease (NAFLD)
• Infection: viral hepatitis and mononucleosis induce liver inflammation, causing measurable elevations in liver enzymes
• Metabolic conditions, such as diabetes, metabolic syndrome, and thyroid disorders

Various medications and supplements can also cause liver enzyme elevations. Examples include, but are not limited to:

• Statins, used to lower high cholesterol
• Certain antibiotics, such as amoxicillin-clavulanic acid and ceftriaxone
• Anticonvulsants, including carbamazepine, phenytoin, valproic acid, and gabapentin
• Medications used to treat tuberculosis
• Acetaminophen, when taken in large doses (greater than 4,000 mg daily)
• Prolonged consumption of vitamin A in doses higher than 8,000 RAE daily.

Please consult your healthcare provider for personalized advice and interpretation of your liver function test results.

Maintaining Liver Health

Taking proactive steps can keep your liver functioning optimally:

• Balanced Diet: Eat an anti-inflammatory diet, incorporating plenty of fruits, vegetables, lean proteins, and omega-3 fatty acids while limiting saturated fats, sugars, and processed foods.
• Limit Alcohol: Excessive alcohol consumption can lead to liver damage. If you drink alcohol, do so in moderation. General guidelines suggest no more than two drinks per day for men and one drink per day for women.
• Coffee: Some studies suggest that moderate coffee consumption may support liver health. For instance, research has indicated that individuals who regularly consume coffee may have better liver enzyme profiles. Specifically, people with preexisting liver conditions who drank more than two cups of coffee daily were less likely to develop fibrosis, cirrhosis, and liver cancer.
• Avoid Toxins: Minimize exposure to harmful chemicals and environmental pollutants, such as cigarette smoke, pesticides, and aflatoxins, that can strain the liver.
• Exercise: Incorporate more physical activity into your daily routine. Even modest increases in activity, such as walking an additional 2,500 steps per day, have been associated with significant reductions in the risk of chronic liver disease and the development of MASLD.
• Vaccinations: Get vaccinated against hepatitis A and B to protect your liver from viral infections.

Before making significant changes to your diet, exercise, or lifestyle habits, it is advised that you speak with your healthcare provider to ensure it is safe for you to do so.

Warning Signs to Watch For

If you begin experiencing any symptoms associated with liver disease, consult your doctor to discuss the possibility of testing your liver function.

Early symptoms of liver disease can include:

• Upper abdominal pain
• Fatigue
• Nausea
• Loss of appetite

As liver disease progresses, you may begin experiencing additional symptoms, such as:

• Jaundice (yellowing of the skin and the whites of the eyes)
• Dark-colored urine
• Light-colored stool
• Weight loss
• Itchy skin
• Small red dots on your skin
• Fatty deposits on your skin or eyelids
• Changes in the appearance of your nails
• Easy bleeding and bruising 
• Ascites (abdominal swelling)
• Edema (swelling in the feet, hands, and face)

These symptoms can be indicative of various health conditions, not exclusively liver disease. Always seek professional medical advice for accurate diagnosis and appropriate treatment.

The Role of Regular Monitoring

Regular, periodic liver function testing can facilitate the early detection of liver issues, enabling timely intervention and preventing potential complications. Healthcare professionals may recommend incorporating LFTs into routine health check-ups, especially for individuals with risk factors such as heavy alcohol use, obesity, or a family history of liver disease.

Consult your healthcare provider to determine the appropriate frequency of liver function testing based on your health profile and risk factors.

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Key Takeaways

• Liver function tests are indispensable tools in assessing liver health. They offer insights into the liver's ability to perform its vital functions. 
• Common liver function tests include ALT, AST, ALP, albumin, bilirubin, and PT. Many of these tests can be ordered together on a comprehensive metabolic panel, typically ordered during a general health screening.
• While LFTs alone cannot definitively diagnose liver disease, they serve as preliminary tests to screen for potential liver dysfunction. They are also useful for monitoring the progression of liver diseases and assessing the efficacy of treatments in individuals with diagnosed liver conditions.
• Take charge of your liver health today! If you have concerns about your liver health or questions regarding liver function tests, consult your healthcare provider for personalized advice and recommendations.