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Compendium Chemistry > Proteins > Flashcards

Proteins Flashcards

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1
Q

Albumin

  • amount in serum
  • analbuminemia results in
  • albumin alleles
  • clinical utility
A
  • Most abundant serum protein
  • Analbuminemia results in mild edema and hyperlipidemia
  • Several albumin alleles (most common = albumin A); variant alleles may result in bisalbuminemia (benign)
  • Clinical utility:
    1. Assessing nutritional status: halflife of albumin is 17 days
    2. Assessing hepatic synthetic function
    3. Assessment of renal glomerular function
    4. Negative acute phase reactant
    5. Diabetic control: glycated albumin is indicator of short term glycemic control
    6. Maintains serum oncotic pressure
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2
Q

Prealbumin

  • SPEP
  • function
  • clinical utility
A
  • AKA transthyretin
  • Not normally seen on SPEP
  • Functions in serum to bind
    • thyroxine
    • retinol binding protein: vitamin A complex
  • Clinical utility
    • Assessment of nutritional status
    • Negative acute phase reactant
    • Prealbumin band is a hallmark of CSF protein electrophoresis
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3
Q

Alpha1-antitrypsin

  • SPEP appearance
  • genetics (number of alleles, most common alleles)
  • clinical utility of SPEP
A
  • Major component of the alpha1 band
  • AAT gene (SERPINA1) highly polymorphic with > 100 alleles
  • Most common allele is PiM
  • Most common genotype is PiMM
  • SPEP can detect AAT deficiency (homozygotes for PiZZ) showing a diminished alpha1 band
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4
Q

Electrophoretic band

alpha1-alpha2 interface

A
  • Gc globulin: binds vitamin D
  • alpha1-antichymotrypsin: positive acute phase reactant
  • alpha1-acid glycoprotein: minor component of alpha1 band normally but major component of the increased alpha1 band in acute inflammatory states
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5
Q

alpha2 electrophoretic band

A
  • alpha2-macroglobulin:
    • relative concentration elevated in liver and renal disease
    • large size prevents its loss in nephrotic syndrome, leading to a relative 10 fold rise in concentration
  • Haptoglobin:
    • binds free hemoglobin
    • rapidly depleted in intravascular hemolysis
    • does not bind myoglobin
    • positive acute phase reactant
  • Ceruloplasmin
    • binds copper
    • low ceruloplasmin not detectable with SPEP
    • positive acute phase reactant
    • decreased in Wilson disease
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6
Q

alpha2-beta interface electrophoretic band

A
  • Usually empty
  • Hemoglobin, usually absent from serum, may be present here when there is hemolysis (a possible pseudo M spike)
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7
Q

Beta1 electrophoretic band

A

Transferrin

  • Transports ferric (Fe3+) iron
  • Normally 30% saturated
  • Markedly increased in iron deficiency
  • Asialated transferrin (tau protein) and a double transferrin peak are hallmarkes of CSF electrophoresis
  • Carbohydrate deficient transferrin a marker for alcohol use
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8
Q

beta1-beta2 interface

A

Beta-lipoprotein

  • LDL
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9
Q

Beta2 electrophoretic band

A
  • IgA
  • Fibrinogen, usually absent from serum
    • May be present in the beta-gamma interface when there is incomplete clotting (a possible pseudo M spike)
  • C3
    • positive acute phase reactant
    • C3 breakdown products may produce a pseudo M spike
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10
Q

gamma1 electrophoretic band

A

gamma globulins

  • positive acute phase reactants
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11
Q

gamma2 electrophoretic band

A

CRP

  • Marker of inflammation
  • produces a small band
  • high sensitivity assays can detect CRP as little as <0.5 mg/L resulting in 3 tiers of CRP
    • Normal CRP: <2-3 mg/L
    • High level CRP elevation: >10 mg/L usually indicates active inflammation such as collagen vascular disease, infection, etc.
    • Low level CRP elevation: 3-10 mg/L; indicates cellular stress and correlated with higher all cause mortality, poor outcome following cardiovascular events
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12
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16
Q

What does a normal serum electrophoresis look like

A
  • Nearly invisible prealbumin band
  • Large albumin band
  • Small peaked alpha1
  • Broad alpha2
  • Biomodal beta
  • Broad gamma
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17
Q

Bisalbuminemia

A
  • Heterozygotes for albumin alleles
  • SPEP shows double albumin spike
  • No clinical consequence
18
Q

alpha1-antitrypsin deficiency electrophoresis

A

Can be detected with SPEP (but not the most S and S assay)

19
Q

Nephrotic syndrome electrophoresis

A
  • Loss of small serum proteins, particularly albumin
  • Large protein molecules retained
  • Decrease of all bands except alpha2 band that contains alpha2 macroglobulin
20
Q

Beta-gamma bridging

A
  • Indicative of cirrhosis and caused by increased serum IgA
  • Hypoalbuminemia
  • Blunted alpha1 and alpha2 bands
21
Q

Monoclonal gammopathy

A
  • Immunochemically homogeneous immunoglobulin M protein in the serum
  • SPEP shows a prominent, discrete, dark band within gamma, beta, or rarely alpha2
  • M protein usually intact immunoglobulin, composed of 2 heavy and 2 light chains
    • Sometimes light chain only
    • Rarely a heavy chain only
    • Biclonal gammopathy in 3-4% of cases (if IgA, more likely due to the appearance of both monomers and dimers, especially if IgA light chain)
  • 10% of patients show only hypogammaglobulinemia
  • Immunofixation or immunosubtraction is indicated to characterize the M protein
    • urine should be screened for monoclonal free light chains
    • serum free light chain levels should be evaluated
  • M spike is most commly the result of PCN, Waldenstrom macroglobulinemia (lymphoplasmacytic lymphoma) or CLL
22
Q

Pseudo M spikes

A
  1. Fibrinogen (incompletely clotted sample)
  2. Hemoglobin (hemolyzed sample)
  3. Elevated CRP
  4. Elevated transferrin
  5. Antibiotics
  6. Radiocontrast agents
  7. Serum tumor markers (e.g., CA19-9)
  8. C3
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29
Q

CSF protein electrophoresis

A
  • CSF normally contains proteins in serum, but in smaller quantities
  • Prominent prealbumin band and a double beta (transferrin) band
  • Electrophoresis used to support a diagnosis of multiple sclerosis by finding oligoclonal bands, which should be absent in the serum
30
Q

Urine Protein Electrophoresis

A
  • Glomerular proteinuria pattern:
    • strong albumin alpha1 and beta bands
    • large proteins (persistence of some filtering function) absent
    • small proteins (tubular reabsorption) absent
    • Intermediate proteins are left in urine
      • Albumin
      • AAT
      • Transferrin
  • Tubular proteinuria
    • Weak albumin band
    • strong alpha1 and beta bands
  • Overflow proteinuria pattern
    • Monoclonal light chain (Bence Jones proteinuria) usually
    • Could also be myoglobin or hemoglobin
31
Q

Cryoglobulins

  • define
  • detection
A
  • Immunoglobulins that precipitate reversibly at low temperature
  • Detection
    • Draw blood at 37 degrees until clotted
    • Centrifuge at 37 degrees
    • Place serum at 4 degrees for 3 days
    • Centrifuge at 4 degrees
    • Any precipitate can be washed and electrophoresed and immunofixed
32
Q

Type I, II, and III cryoglobulins

A
  1. monoclonal immunoglobulins associated with MM or Waldenstrom
  2. Mixture of monoclonal IgM and polyclonal IgG
    • IgM has RF activity (anti IgG)
    • most common type of cryoglobulin
  3. Mixture of 2 polyclonal immunoglobulins, typically IgG and IgM; IgM has RF activity
33
Q

Mixed cryoglobulinemia

A
  • Associated with
    • Lymphoproliferative disorders
    • Chronic infection
    • Chronic liver disease
    • Autoimmune disease
    • HCV is most common cause
  • Systemic immune complex disease
    • palpable purpura (leukocytoclastic vasculitis)
    • arthralgias
    • HSM
    • LAD
    • anemia
    • sensorineural deficits
    • glomerulonephritis
  • Renal involvement:
    • Nephrotic syndrome or nephritic syndrome
    • Associated with severe hypocomplementemia
    • MPGN type II most common
      • +/- thrombotic microangiopathy
      • electron microscopy: subendothelial immune complex deposits with a fibrillary or tubular structure in a fingerprint like pattern
34
Q

Lab method of protein electrophoresis

A
  • Performed at pH 8.6 for serum, resulting in 5 bands: alpha1, alpha2, beta, and gamma
  • bands are measured by densitometry
35
Q

Immunoelectrophoresis (IEP)

A
  • No longer commonly used
  • Patient serum placed in every other of a series of wells
  • Remaining wells contain normal serum
  • Gel undergoes EP
  • Antiserum added to each trough
  • Precipitation arcs form between antisera in the troughs and the electrophoresed proteins in the gel
  • Interpretation depends on visual comparison of the arcs formed with patient serum
36
Q

Immunofixation electrophoresis

A
  • Patient serum placed into 6 wellsin agarose gel
  • Gel undergoes EP
  • 5 different antisera applied to gel: anti IgG, IgA, IgM, kappa, and lambda
37
Q

Immunotyping

A

IT, immunosubtraction

  • Often used in conjunction with capillary EP
  • Serum sample incubated with different solid phase sepharose beads attached to antibodies against gamma, alpha, mu, kappa, or lambda
  • supernatants undergo EP to determine which reagent resulted in removal of the abnormal spike
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Compendium Chemistry (13 decks)

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