Serum Proteins

albumin, globulins, and associated test methods

What is the pathway of amino acids in the body after ingestion?

1. enzymes in the GI tract free amino acids from our food

2. amino acids are absorbed into circulation

3. amino acids are filtered through the renal glomeruli but are reabsorbed in the tubules

4. amino acids are stored in “pools” to be used for synthesizing proteins

   1. pools exist in cells that produce proteins

Where are most serum proteins produced?

in the liver

Where are immunoglobulins, hemoglobin, and protein-based hormones created?

• immunoglobulins

  • B lymphocytes and plasma cells

• hemoglobin

  • nRBCs in the bone marrow

• hormones

  • pituitary gland

List the various functions of protein (7)

• forms into digestive enzymes to facilitate enzymatic reactions in the GI tract

• immune function

• supporting muscle contraction and support

• basis of hormones

• transports essential molecules

• part of fibrin in the blood

• maintaining colloidal osmotic pressure

What is colloidal osmotic pressure?

• pressure exerted mostly by serum proteins

• blood with high or normal solute concentration keeps water in the circulatory system

• decreased proteins (or other solutes) can lead to water moving out into peripheral tissues, causing low COP and edema

total protein (albumin and globulins) reference range

6.0 - 8.3 g/dL

serum albumin reference range

3.5 - 5.5 g/dL

serum globulin reference range

2.0 - 3.0 g/dL

What is the albumin/globulin reference range and how is it calculated?

• 0.8 - 2.2

• albumin result is divided by the globulin result

What is the primary test method for determining total protein?

• Biuret reaction

  • colorimetric and spectrophotometric

  • protein combines with cupric ions in an alkaline medium

  • a purple color results and is read spectrophotometrically

  • interferences: hemolysis (increase in proteins from RBCs), lipemia, and icterus

Causes of hyperproteinemia

• dehydration (hemoconcentration)

  • not drinking water, excessive sweating, vomiting, diarrhea, DKA, salt-losing syndromes

• increases in globulin concentration

  • multiple myeloma, Waldenstrom’s, chronic inflammatory conditions, HIV/AIDS

Causes of hypoproteinemia

• hemodilution (increased water volume)

  • water intoxication, salt-retention syndromes, massive IV infusion

• increased protein loss

  • nephrotic syndrome, trauma, burn patients

• decreased intake of proteins

  • malnutrition, malabsorption

• decreased protein synthesis

  • liver disease, immunodeficiency disorders

What is the main test used for determining albumin concentrations?

• dye-binding test

  • albumin binds to specific dyes, resulting in a measurable color change

  • bromcresol purple is used as a pH indicator

What are the 4 requirements for the albumin dye-binding test?

• the dye must be specific to albumin (bromcresol purple)

• the dye and pH indicator must have high binding affinity

• there should be a substantial change in absorbance when albumin combines with the dye

• test must be measured at a specific wavelength to prevent interference from hemolysis, lipemia, and icterus

the rate of albumin production depends on:

• protein intake in the diet

• feedback from plasma albumin and osmotic pressure

  • if there is low COP, the liver is alerted to produce albumin

What are all the functions of albumin?

• maintaining colloidal osmotic pressure

• bind to and transport molecules such as bilirubin, hormones, or drugs

• acts as an endogenous source of amino acids

• promotes acid-base balance

• coagulation

Causes of hyperalbuminemia

• decreased plasma volume due to dehydration

• prolonged tourniquet application

Causes of hypoalbuminemia

• low COP

• increased protein catabolism

  • tissue damage or inflammation

• impaired synthesis

  • liver disease, decreased intake, malnutrition, malabsorption

• increased loss of protein

  • nephrotic syndrome, glomerulonephritis, diabetes, burns

• analbuminemia - rare genetic disorder

Causes of increased and decreased A/G ratio

• increased

  • underproduction of globulins

• decreased

  • decreased albumin (low production due to liver disease or increased loss in urine due to nephrotic syndrome)

  • increased production of globulins (MM or autoimmune disorders)

What is the main function of globulin proteins?

• to act as acute phase reactants

  • inflammation and infection markers that assist in immune response and transport hormones

List 5 alpha-1 globulins?

• alpha-1 antitrypsin

• alpha-1 acid glycoprotein

• alpha-1 antichymotrypsin

• alpha-1 lipoprotein (HDL)

• alpha-1 fetoprotein

alpha-1 antitrypsin

• acute phase reactant

• deficiency associated with lung disease, liver disease, cancer, cirrhosis, or early emphysema

alpha-1 acid glycoprotein

• major glycoprotein acute phase reactant

• increased in RA, cancer, pneumonia, and acute MIs

alpha-1 antichymotrypsin

• acute phase reactant

• increased in inflammation

• decreased in asthma, emphysema, and liver disease

alpha-1 fetoprotein

• major serum protein produced by the fetal liver

  • increased levels in serum indicate fetal distress (spina bifida or anencephaly)

  • decreased levels in serum indicate Down syndrome and Trisomy 18

• elevated levels in pregnancy, liver cancer, and germ cell tumors

List 3 alpha-2 globulins

• haptoglobin

• alpha-2 macroglobulin

• ceruloplasmin