Clinical Chemistry: Proteins Part 2 Overview

Prealbumin

A more sensitive indicator of nutrition, synthesized mainly in the liver, and migrates ahead of albumin on electrophoresis.

Albumin

The protein present in the highest concentration in plasma, synthesized in the liver, and functions to maintain colloid osmotic pressure, buffer pH, and bind substances in the blood.

Globulins

A group of proteins consisting of α1, α2, β, and γ fractions, synthesized in the liver.

α1-Globulins

Nonspecific indicators/markers of inflammation, known as acute phase reactants.

α2-Globulins

One of the fractions of globulins, involved in various physiological functions.

β-Globulins

One of the fractions of globulins, involved in various physiological functions.

γ-Globulins

The largest fraction of globulins, synthesized by activated B cells or plasma cells instead of the liver.

Hypoproteinemia

A condition characterized by low levels of protein in the blood.

Hyperproteinemia

A condition characterized by high levels of protein in the blood.

Total Protein

The total amount of protein present in the blood, including albumin and globulins.

A/G Ratio

The ratio of albumin to globulin in the blood, used to assess protein levels.

Hepatic damage

A condition that can lead to decreased levels of all proteins except for γ-Globulins.

Chronic renal failure

A condition that primarily decreases albumin levels due to leakage in urine.

Malnutrition/Malabsorption

A condition that can lead to decreased albumin levels.

Dehydration

A condition that can falsely increase albumin levels due to hemoconcentration.

Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE)

A technique used to separate proteins based on their size.

Acute Phase Reactant

Substances that increase in concentration during inflammation.

C-reactive Protein (CRP)

A specific acute phase reactant that increases during inflammation.

Immunoglobulins

Proteins that make up most of the globulin fraction of serum proteins.

Electrophoresis

A method used to separate proteins based on their charge and size.

Colloid osmotic pressure

The pressure that keeps water inside blood vessels to prevent edema.

Negative acute phase reactant

A substance that decreases in concentration during inflammation.

Transport protein for thyroid hormones and retinol

The function of prealbumin in the body.

Marasmus

A condition where prealbumin and albumin levels decrease.

Spina bifida

A birth defect where there is incomplete closing of the backbone and membranes around the spinal cord.

Anencephaly

A severe birth defect in which a baby is born without parts of the brain and skull.

Fetal distress

A condition indicating that the fetus is not well, often due to lack of oxygen.

α2-Globulins

A class of globulins that includes proteins such as haptoglobin and ceruloplasmin.

Haptoglobin

A protein that binds and carries hemoglobin.

Ceruloplasmin

A protein that binds to copper in the blood.

Wilson's Disease

A genetic disorder that leads to copper accumulation in the body due to decreased ceruloplasmin.

Kayser Fleischer Rings

Copper deposits in the cornea associated with Wilson's Disease.

α2-Macroglobulin

A protease inhibitor that prevents the breakdown of proteins.

Hypergammaglobulinemia

A condition characterized by excessive antibodies due to multiple myeloma.

Monoclonal Antibodies

Antibodies produced from a single clone of cells, used to treat diseases.

Transferrin

A protein that transfers iron in the blood.

Ferritin

A protein that binds to iron during infection.

IDA

Iron deficiency anemia, a condition resulting from insufficient iron.

Hemopexin

A protein that binds heme, but not entire hemoglobin.

Lipoprotein

A protein that transports lipids, mainly low-density lipoprotein (LDL).

Low Density Lipoprotein (LDL)

Often referred to as bad cholesterol, associated with increased risk of heart disease.

High Density Lipoprotein (HDL)

Known as good cholesterol, involved in reverse cholesterol transport.

Fibrinogen

A clotting factor that is a precursor of fibrin clot.

Complement

Part of the nonspecific/innate immune response.

Hypoproteinemia

A condition where the total protein level is less than 6.4 g/dL, often due to negative nitrogen balance.

Total protein

Measures all of the protein in the plasma, reflecting nutritional status, kidney disease, and liver disease.

IgG

The most numerous antibody that persists in plasma.

IgM

An antibody produced by plasma cells once activated.

IgA

An antibody found in secretions such as sweat and plasma.

IgE

An antibody associated with allergic reactions.

IgD

An antibody that is not diagnostic but is involved in infections.

Excessive Loss

Caused by Renal Disease, Blood Loss, and Burns.

Decreased Intake

Caused by Malnutrition and Intestinal Malabsorption.

Decreased Synthesis

Caused by Liver Disease and Inherited Immunodeficiency.

Acceleration of Catabolism of Proteins

Caused by Burns and Trauma.

HYPERPROTEINEMIA

The total protein level is > 8.3 g/dL.

Dehydration

Excessive water loss leads to an increased concentration of protein.

Examples of Dehydration

Vomiting, Diarrhea, Diabetic Acidosis, and Hypoaldosteronism.

Excessive Production of γ-Globulins

Caused by Multiple Myeloma and Waldenstrom's Macroglobulinemia.

HABA (2,4'-hydroxyazobenzene - benzoic acid)

Albumin binds to dye; causes shift in absorption maximum.

BCG (Bromocresol Green)

Sensitive; overestimates low albumin levels; most commonly used dye.

Total Protein

Normal or Decreased: Decreased in Hepatic Damage, Burns, Trauma.

Electrophoresis

Proteins separated based on electric charge.

A/G RATIO

Can be determined by dividing the albumin concentration by the calculated globulin.

Globulin Calculation

Globulin concentration can be calculated by subtracting the albumin from the total protein.

Reference interval for Total Protein

6.4 - 8.3 g/dL.

Kjeldahl

Digestion of protein; measurement of nitrogen content.

URINARY PROTEIN

When proteins appear in the urine, they have not been reabsorbed by the renal tubules.

Screening Test for Urinary Protein

Urine Dipstick.

Quantitative Assay for Urinary Protein

12 or 24 hour Urine.

Biuret Method

Formation of violet colored chelate between Cu2+ ions and peptide bonds.

Turbidimetric Methods

Routine method; requires at least 2 peptide bonds and an alkaline medium.

Sulfosalicylic Acid (SSA)

Most commonly used due to ease; will precipitate proteins, hence the urine will turn turbid if proteins exist.

CRP (C-Reactive Protein)

Acute phase reactant associated with inflammatory processes.

Complement

Part of the immune response involved in inflammation and hemolytic anemia.

Dye Binding

Protein binds to dye and causes spectral shift in the absorbance maximum of the dye.

Albumin Determination

Methods to quantify albumin levels in a sample.

Biuret

Proteins are concentrated by precipitation, redissolved in alkali, then reacted with Cu2+.

Cu2+ complex formation

Cu2+ forms colored complex with peptide bonds.

Folin-Lowry

Initial biuret reaction; Oxidation of tyrosine, tryptophan, and histidine residues by Folin phenol reagent.

Folin phenol reagent

A mixture of phosphotungstic and phosphomolybdic acids used in the Folin-Lowry method.

Dye Binding (Coomassie blue, Ponceau S)

Protein binds to dye, causes shift in absorption maximum.

Hyperproteinemia

A total protein level of > 8.3 g/dL.

Hypoproteinemia

Due to a negative nitrogen balance; one cause is dehydration.

Physiological Causes of Transient Proteinuria

Includes exercise, emotional stress, fever, pregnancy, and orthostatic/postural changes.

Pathologic Causes of Proteinuria

Includes glomerular nephritis, pyelonephritis, increased permeability of glomerulus, and systemic disorders.

CSF Proteins

Total CSF protein reference range is 15-45 mg/dL.

Increased Total CSF Proteins

Caused by bacterial, viral, fungal meningitis, traumatic tap, multiple sclerosis, and neoplasm.

Transferrin

Transports iron while hemopexin binds to hemoglobin.

Primary function of albumin

Maintains colloid osmotic pressure.

Folin-Lowry method sensitivity

Became more sensitive by incorporating a biuret reaction as its initial step.

Turbidimetric and dye binding methods

Have the issue of reagents not reacting equally with each protein fraction.

Act as an enzyme

Function of certain proteins that catalyze biochemical reactions.

Transport thyroid hormones

Role of proteins in carrying thyroid hormones throughout the bloodstream.

Maintain colloid osmotic pressure

Function of proteins in regulating the pressure that keeps fluid in the bloodstream.

Serve as coagulation factor

Role of proteins in the blood clotting process.

A decrease in serum albumin is commonly seen in

Conditions such as dehydration, nephrotic syndrome, multiple myeloma, and hyperproteinemia.

Salt precipitation method for albumin determination

A method that precipitates albumin from serum.

Biuret method for total protein measurement

A method based on the reaction of peptide bonds with copper ions.

Troponin

Heart marker for Myocardial Infarction.