MLT GlobeChemistry: Proteins & electrophoresis – page 5
125 Chemistry MCQs on Proteins & electrophoresis with answers and explanations.
An increased CSF/serum albumin quotient is mainly used to assess:
Albumin is made only in the liver, so a raised CSF/serum albumin ratio means more albumin is crossing into CSF, indicating barrier damage. Intrathecal IgG synthesis is judged by the IgG index or oligoclonal bands.
Transthyretin (prealbumin) is preferred over albumin for monitoring short-term nutritional support mainly because it:
Transthyretin's half-life of about 2 days lets it reflect recent changes, while albumin's half-life is about 3 weeks. Transthyretin is still lowered by inflammation, a key limitation.
Which serum marker is part of the International Staging System for multiple myeloma along with albumin?
The ISS uses serum beta-2 microglobulin and albumin; higher beta-2 microglobulin reflects tumour burden and renal function. The revised ISS adds LD and cytogenetics, not CRP.
A monoclonal protein that migrates in the beta region rather than the gamma region on serum electrophoresis is most often of which class?
IgA monoclonal proteins commonly migrate in the beta region and can be hidden behind transferrin or C3, so immunofixation is important. IgG usually migrates in the gamma region.
In capillary zone electrophoresis of serum, separated proteins are usually detected by:
Capillary systems pass proteins through a detector that reads UV absorbance of peptide bonds, so no gel staining is needed. Staining and densitometry apply to agarose gel electrophoresis.
A blood sample is sent to test for cryoglobulins. How should it be handled?
Cryoglobulins precipitate in the cold, so the sample must be kept at 37 °C during clotting and separation; cooling early loses the protein in the clot. The serum is then stored at 4 °C to look for precipitation.
A 70-year-old with blurred vision, bleeding gums and a large IgM monoclonal protein most likely has:
An IgM monoclonal protein with hyperviscosity symptoms (visual changes, mucosal bleeding) is typical of Waldenström macroglobulinemia (lymphoplasmacytic lymphoma). MGUS has a small M-protein without symptoms.
The plasma half-life of albumin is approximately:
Albumin has a half-life of about 15–20 days, so its level changes slowly and is a poor marker of acute changes in nutrition or liver synthesis. 120 days is the red cell lifespan.
A protein with an isoelectric point (pI) of 5.0 is placed in a buffer at pH 8.6. It will:
When buffer pH is above the pI, the protein loses protons and becomes negatively charged, so it moves toward the positive electrode (anode). At its pI it has no net charge.
A woman with iron deficiency anemia has an increased beta-1 band on serum protein electrophoresis. Which protein explains this?
Transferrin is the main beta-1 protein and rises in iron deficiency as the liver increases its synthesis. C3 forms the beta-2 band; ferritin is present in too small an amount to be seen.
A 2-year-old boy with repeated bacterial infections has an almost absent gamma band, very low IgG, IgA and IgM, and no circulating B cells. The most likely diagnosis is:
X-linked (Bruton) agammaglobulinemia is a BTK defect that stops B-cell maturation, so all immunoglobulins are very low. DiGeorge syndrome mainly affects T cells.
Total serum protein is 8.0 g/dL (80 g/L). Densitometry shows the monoclonal spike is 18% of the total area. What is the M-protein concentration?
M-protein = total protein × fraction = 8.0 × 0.18 = 1.44 g/dL. The spike is quantified by densitometry, while immunofixation is used to type it.
Total protein is 7.5 g/dL (75 g/L) and albumin is 3.0 g/dL (30 g/L). What is the albumin/globulin (A/G) ratio?
Globulin = 7.5 − 3.0 = 4.5 g/dL, so A/G = 3.0 ÷ 4.5 = 0.67. A reversed ratio (below 1) is seen with low albumin and/or high globulins, as in cirrhosis or myeloma.
A 60-year-old has an IgG-kappa M-protein of 1.2 g/dL (12 g/L), 5% clonal marrow plasma cells, and no hypercalcemia, renal damage, anemia or bone lesions. By IMWG criteria this is:
MGUS requires M-protein below 3 g/dL, fewer than 10% clonal plasma cells and no myeloma-defining events. Smoldering myeloma has M-protein ≥3 g/dL or 10–60% plasma cells.
A child with minimal change disease has highly selective proteinuria. The urine protein consists mainly of:
In selective glomerular proteinuria, only intermediate-size proteins such as albumin and transferrin pass the filter; large proteins like IgG are held back. Beta-2 microglobulin indicates tubular proteinuria.
A urine sample gives a negative protein dipstick but a positive sulfosalicylic acid test. This most suggests the presence of:
The dipstick protein pad reacts mainly with albumin, while sulfosalicylic acid precipitates all proteins, including Bence Jones light chains. Such a result calls for urine protein electrophoresis.
For cardiovascular risk assessment (AHA/CDC), which hs-CRP level indicates high risk in a person without acute illness?
hs-CRP below 1 mg/L is low risk, 1–3 mg/L average risk and above 3 mg/L high risk. Values above 10 mg/L suggest acute inflammation, and the test should be repeated later.
Which marker is most useful for distinguishing bacterial from viral lower respiratory tract infection and for guiding when to stop antibiotics?
Procalcitonin rises strongly in bacterial infection and is suppressed by interferon-γ in viral infection. A falling level supports stopping antibiotics. ESR and ferritin are non-specific.
Which method is commonly used on automated analyzers for the low protein concentrations in urine and CSF?
Pyrogallol red–molybdate (or turbidimetric methods such as benzethonium chloride) can detect milligram-per-deciliter protein levels. Biuret and refractometry are not sensitive enough.
Proteins absorb ultraviolet light at 280 nm mainly because of which amino acids?
The aromatic rings of tryptophan and tyrosine absorb strongly near 280 nm. Peptide bonds absorb at around 200–220 nm; aliphatic and basic amino acids do not absorb at 280 nm.