Albumin vs. Prealbumin

Attribute	Albumin	Prealbumin
Function	Transport of hormones, fatty acids, and drugs	Transport of thyroid hormones and retinol-binding protein
Location	Synthesized in the liver	Synthesized in the liver and intestine
Half-life	Approximately 20 days	Approximately 2 days
Normal Range	3.5 - 5.5 g/dL	15 - 35 mg/dL
Diagnostic Value	Indicates liver and kidney function, nutritional status, and inflammation	Indicates nutritional status and response to nutritional therapy

Introduction

Albumin and prealbumin are two important proteins found in the human body. They play crucial roles in various physiological processes and are often used as biomarkers to assess nutritional status and overall health. While both proteins are involved in transporting substances in the blood, they differ in terms of their structure, functions, and clinical significance.

Structure

Albumin, also known as serum albumin, is a globular protein composed of a single polypeptide chain. It is synthesized in the liver and accounts for approximately 60% of the total protein content in the blood plasma. Albumin has a molecular weight of about 66 kDa and consists of three homologous domains. These domains are responsible for binding various substances such as fatty acids, hormones, drugs, and metals.

On the other hand, prealbumin, also known as transthyretin, is a tetrameric protein composed of four identical subunits. It is primarily synthesized in the liver and is smaller in size compared to albumin, with a molecular weight of about 55 kDa. Prealbumin gets its name from its migration pattern on electrophoresis gels, where it migrates faster than albumin.

Functions

Albumin serves multiple functions in the body. Its primary role is to maintain oncotic pressure, which helps regulate the distribution of fluid between the blood vessels and tissues. Albumin also acts as a carrier protein, transporting various substances such as fatty acids, bilirubin, and drugs. Additionally, albumin plays a crucial role in buffering pH and binding and detoxifying harmful substances.

Prealbumin, on the other hand, is involved in the transport of thyroxine (T4) and retinol-binding protein (RBP). It acts as a carrier protein for these hormones, facilitating their transport in the blood. Prealbumin also plays a role in the regulation of thyroid hormone availability and metabolism. It is worth noting that prealbumin has a shorter half-life compared to albumin, making it a more sensitive indicator of recent changes in nutritional status.

Clinical Significance

Albumin is widely used as a biomarker to assess nutritional status, liver function, and overall health. Low levels of albumin in the blood, known as hypoalbuminemia, can indicate malnutrition, liver disease, kidney disease, or inflammation. Hypoalbuminemia is associated with increased morbidity and mortality in various medical conditions. Additionally, albumin is often used in clinical settings to evaluate the severity of burns, as burn injuries can lead to a significant decrease in albumin levels.

Prealbumin, on the other hand, is considered a more sensitive marker of nutritional status compared to albumin. Its levels decrease rapidly in response to acute illness or malnutrition, making it useful in monitoring patients' response to nutritional interventions. Prealbumin levels are commonly measured in individuals with critical illnesses, such as sepsis or trauma, to assess their nutritional status and guide appropriate interventions.

Measurement and Interpretation

Albumin levels are typically measured using a simple blood test called serum albumin assay. Normal albumin levels range between 3.5 and 5.5 g/dL. However, it is important to consider that albumin levels can be influenced by various factors, including hydration status, liver function, and inflammation. Therefore, interpretation of albumin levels should be done in conjunction with other clinical parameters.

Prealbumin levels are measured using a similar blood test, often referred to as transthyretin assay. Normal prealbumin levels range between 15 and 35 mg/dL. As prealbumin has a shorter half-life compared to albumin, its levels can change rapidly in response to nutritional changes or acute illness. Serial measurements of prealbumin over time can provide valuable information about a patient's nutritional status and response to treatment.

Conclusion

Albumin and prealbumin are two important proteins with distinct structures, functions, and clinical significance. While albumin primarily serves as a carrier protein and maintains oncotic pressure, prealbumin is involved in the transport of specific hormones. Both proteins are used as biomarkers to assess nutritional status, but prealbumin is considered more sensitive to recent changes. Understanding the attributes of albumin and prealbumin can aid healthcare professionals in diagnosing and managing various medical conditions, as well as monitoring patients' response to treatment.