Special Protein Testing in The Clinical Laboratory - Part One

Special Protein Testing in The Clinical Laboratory - Part One

Welcome to part one of our look into the world of special protein testing in a clinical laboratory setting.

Over the coming weeks we will be posting excerpts from an article written by Bob Janetschek, MS, MT (ASCP), our Immunologicals Business Manager for the USA East Coast and Canadian territories.

Join us as we provide an overview of the proteins most commonly considered in clinical testing.


The proteins found within the human machine are, quite literally, the building blocks of life: individual cells contain more than 5000 individual proteins. The variety of proteins is seemingly infinite; so too, is their function, composition, distribution and makeup.

Proteins in the body form the structure of cells; make up enzymes and hormones that regulate bodily functions; transport analytes, nutrients, and drugs throughout the body; remove metabolic waste; and provide defenses against infection. Among the classes of molecular analytes found inside the body, proteins provide a unique combination of broad clinical significance and accessibility. The analysis of proteins and clinical diagnostic tests for proteins are widely accepted in medical technology.

Varying concentrations of proteins are found in blood and its liquid components, plasma and/or serum, and are also present in urine, spinal fluid, feces, amniotic fluids, saliva and pleural fluid, to name a few. Applications involving protein detection and analysis thus have tremendous diagnostic potential.

Total protein concentration in the body comprises two main components - albumin and globulin. Albumin is relatively straightforward in composition, while globulin contains alpha-1-, alpha-2-, beta- and gammaglobulin fractions. These fractions can be further broken down into individual diagnostic assays, commonly referred to as special protein tests. Along with other patient data, these unique analytes can provide a wealth of clinical information such as definitive diagnosis of acute events, prediction of disease risk and detection of disease recurrence.


Picture: Technician using automated instrumentation for analysis of special proteins

The most widely used special protein tests are described below:

Albumin: This single-chain protein occurs primarily in plasma and other bodily fluids, albeit at lower concentrations. Its primary functions are the maintenance of osmotic pressure and the binding/transport of substances throughout the body. Albumin is synthesized in the liver and constitutes approximately 60% of the total serum protein. Both increased and decreased levels can be observed with environmental, nutritional, toxic and traumatic stresses to the body.

Alpha (α)-1-acid glycoprotein: Also known as orosomucoid, α-1-acid glycoprotein (AGP) is one of the major acute-phase proteins and is important in drug binding. Elevated AGP levels are found in acute and chronic inflammatory conditions and infections. Low levels of AGP are seen when there is a reduction in synthesis, as in chronic liver disease, or an increased excretion of AGP, as in nephrotic syndrome.

Alpha (α)-1-antitrypsin: This serine protease inhibitor protects the lungs from degradation by neutrophil elastase. Reduced levels are associated with liver disease, but can also occur in early childhood and old age, and with hereditary deficiency. This can cause an imbalance between the neutrophil elastase in the lung and the anti-elastases that are responsible for protecting the lungs, and can potentially lead to emphysema.

Alpha (α)-2-macroglobulin: α-2-Macroglobulin is almost exclusively found and distributed within the intravascular pool. As such, its measurement aids in the diagnosis of blood clotting, or clot lysis, disorders. Levels of α-2-macroglobulin are reported to increase in nephrotic syndrome, liver cirrhosis and diabetes mellitus, where lower-molecular-weight proteins leak from the kidneys into the urine.

In part 2 we look at Complement proteins along with many others.

Excerpt taken from the article "Special Protein Testing in the Clinical Laboratory: Overview of Available Assays" published in American Laboratory magazine, August 2016.

Reference link: http://www.americanlaboratory.com/