Chapter 4 — Proteins, Protein Status and Protein Methods
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103 Terms
What percentage of plasma is water?
About 93%.
What percentage of plasma is mainly proteins?
About 7%.
What are functions of plasma proteins?
Enzymes, antibodies, coagulation factors, transport proteins, nutrition, oncotic pressure and acid-base balance.
Which plasma protein is most important for oncotic pressure?
Albumin.
What is oncotic pressure?
Pressure created by plasma proteins that keeps water inside blood vessels.
What happens when albumin is very low?
Water moves into tissues, causing edema.
How does serum differ from plasma?
Serum lacks fibrinogen because fibrinogen is consumed during clotting.
Why is serum usually used for total protein measurement?
Fibrinogen contributes only a small fraction compared with total protein.
What is hyperproteinemia?
Increased plasma protein concentration.
Why does dehydration cause hyperproteinemia?
Water decreases, so protein concentration increases even if total protein amount is unchanged.
What disease can cause marked hyperproteinemia?
Multiple myeloma.
What are paraproteins?
Monoclonal immunoglobulins produced in multiple myeloma.
What is hypoproteinemia?
Decreased plasma protein concentration.
Name causes of hypoproteinemia.
Nephrotic syndrome, burns, wounds, hemorrhage, ulcerative colitis, malnutrition and malabsorption.
Why does nephrotic syndrome cause hypoproteinemia?
Large amounts of albumin are lost in urine.
What is basic protein status?
Total protein, albumin and calculated globulins.
How are globulins calculated?
Globulins = total protein − albumin.
Which method measures total protein?
Biuret method.
Which method measures albumin?
Bromocresol green method.
What is the Biuret reaction?
Proteins react with Cu²⁺ in alkaline solution to form a purple complex.
What do copper ions bind in the Biuret method?
Peptide bonds.
What does the Biuret method measure?
Total protein concentration.
What is the hidden idea of the Biuret method?
More peptide bonds mean more purple complex and higher absorbance.
What is the BCG method?
Albumin reacts with bromocresol green in acidic buffer to form a colored complex.
What does the BCG method measure?
Albumin concentration.
Why is BCG more specific than Biuret?
BCG mainly binds albumin, while Biuret reacts with all proteins.
What is the normal adult total protein range?
6.6–8.7 g/dL or 66–87 g/L.
What is the normal albumin range?
3.8–5.1 g/dL or 38–51 g/L.
What can interfere with total protein and albumin methods?
Hemolysis, lipemia and icterus.
What is an antigen-antibody reaction?
Specific binding of an antigen with its antibody, often forming immune complexes.
What happens when soluble antigen and antibody react?
A precipitate or immune complexes can form.
What are the three zones of immunoprecipitation?
Antibody excess, equivalence and antigen excess.
What is the antibody excess zone?
Zone where increasing antigen produces increasing precipitate and free antibodies remain.
What is the equivalence zone?
Zone of maximal precipitation with no free antigen or antibody.
What is the antigen excess zone?
Zone where excess antigen forms small soluble immune complexes.
Why must immunoassays measure in the antibody excess zone?
To avoid ambiguity where one signal could represent two different antigen concentrations.
What is turbidimetry?
Measuring decreased transmitted light caused by turbidity.
What is nephelometry?
Measuring scattered light caused by immune complexes.
What is the difference between turbidimetry and nephelometry?
The reaction is the same, but turbidimetry measures transmitted light and nephelometry measures scattered light.
Why can a spectrophotometer be used for turbidimetry?
Because turbidimetry measures transmitted light similar to photometry.
What is latex-enhanced immunoturbidimetry?
Immunoturbidimetry using latex particles to amplify immune complex formation.
What is a nephelometer?
An instrument specialized for measuring scattered light.
What wavelength does the MININEPHplus laser use?
670 nm.
What is CRP?
C-reactive protein, an acute-phase protein synthesized by the liver.
What is the reference value of CRP?
Up to about 10 mg/L.
When does CRP increase?
Inflammation, infection, trauma and tissue necrosis.
Why is CRP clinically useful?
It rises quickly and decreases quickly after the cause resolves.
What CRP values suggest mild inflammation or viral infection?
About 10–40 mg/L.
What CRP values suggest acute inflammation or bacterial infection?
About 40–200 mg/L.
What is hsCRP used for?
Cardiovascular risk assessment in patients without inflammation.
What is rheumatoid factor?
Autoantibodies directed against the person’s own immunoglobulins.
In which disease is RF especially relevant?
Rheumatoid arthritis.
What is transferrin?
An iron-binding and iron-transport plasma protein.
When does transferrin increase?
Low plasma iron, pregnancy and estrogen therapy.
When does transferrin decrease?
Chronic infections, malignant disease, liver or kidney disorders.
What is haptoglobin?
A plasma protein that binds free hemoglobin.
Why is haptoglobin important?
It prevents free hemoglobin loss through kidneys and protects from renal damage.
When is haptoglobin decreased?
Hemolytic anemia and liver disease.
What is beta2-microglobulin?
A low molecular mass protein found on nucleated cells.
Why is urinary beta2-microglobulin useful?
It is a marker of tubular proteinuria.
What is CRP agglutination?
A qualitative or semiquantitative latex particle antigen-antibody reaction.
What does visible agglutination in CRP testing mean?
Positive CRP result.
How can CRP agglutination become semiquantitative?
By testing serial dilutions of the sample.
What is fibrinogen?
A plasma protein and precursor of fibrin in coagulation.
What else is fibrinogen besides a coagulation protein?
An acute-phase protein.
When does fibrinogen increase?
Inflammation, infection, trauma and pregnancy.
When does fibrinogen decrease?
DIC, systemic fibrinolysis and severe hepatic dysfunction.
What is the Clauss method?
A fibrinogen activity method measuring clotting time after excess thrombin addition.
How is fibrinogen concentration related to clotting time in the Clauss method?
Inversely proportional.
Which sample is used for fibrinogen determination?
Citrated plasma.
Why must citrate tubes be filled correctly for coagulation tests?
To maintain the correct blood-to-anticoagulant ratio.
What is proteinuria?
Urine protein concentration above reference values.
What is normally the main plasma protein excreted in urine?
Albumin.
What is Tamm-Horsfall protein?
A normal urinary glycoprotein secreted in the loop of Henle.
What is the normal urine protein excretion at rest?
About 50–80 mg/24 h.
What is often used as a practical urine protein reference limit?
How much can protein excretion rise with physical exertion?
Up to about 300 mg/24 h.
What is the first sign of increased glomerular permeability?
Increased albumin in urine.
What indicates loss of glomerular selectivity?
High molecular mass proteins in urine.
What indicates impaired tubular reabsorption?
Low molecular mass proteins in urine.
What are the main types of proteinuria?
Glomerular, tubular, overload and postrenal proteinuria.
What is glomerular proteinuria?
Proteinuria caused by increased permeability of the glomerular basement membrane.
Why is glomerular proteinuria often called albuminuria?
Because most excreted protein is albumin.
What is functional proteinuria?
Benign glomerular proteinuria caused by altered glomerular blood flow.
What can cause functional proteinuria?
Intense exercise, fever, cold exposure, heart failure and hypertension.
What is orthostatic proteinuria?
Proteinuria related to upright body position.
What is tubular proteinuria?
Urinary loss of low molecular mass proteins due to impaired proximal tubular reabsorption.
What is overload proteinuria?
Proteinuria due to high plasma concentration of a low molecular mass protein.
Name examples of overload proteinuria.
Hemoglobinuria, myoglobinuria and Bence-Jones proteinuria.
What is postrenal proteinuria?
Proteinuria caused by urinary tract inflammation or carcinoma after the kidney.
How do urine protein test strips work?
By protein error of an indicator, mainly detecting albumin.
Which indicator is often used on urine protein strips?
Tetrabromophenol blue.
What color change occurs in urine albumin strips?
Yellow to green or green-blue.
What type of method is the urine albumin strip?
Semiquantitative.
What can cause false-positive urine protein strip results?
Alkaline urine pH >9 or detergent/disinfectant contamination.
What is the sulfosalicylic acid test?
A qualitative protein test where turbidity indicates proteins.
What does sulfosalicylic acid detect?
Albumins, globulins and Bence-Jones protein.
What can cause false-positive sulfosalicylic acid test results?
Urates.
What is the pyrogallol red method?
A quantitative urine protein method measuring a blue-violet protein complex at 600 nm.
Which sample is used for quantitative urine protein by pyrogallol red?
24-hour urine without preservative.