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Clinical Chemistry > Porphyrins and Hemoglobin > Flashcards

Porphyrins and Hemoglobin Flashcards

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1
Q

Hemoglobin and myoglobin are chemically similar molecules that contain what chemical groups?

A

Porphyrin groups

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2
Q

Porphyrin structure

A

Cyclic structure made of 4 pyrrole rings joined by methine bridges

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3
Q

What produces heme?

A

Chelation of ferrous iron to protoporphyrin

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4
Q

Heme

A

Prosthetic group of Hgb responsible for binding O2

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5
Q

Porphyrias

A

Group of rare disorders that result from disturbances in heme synthesis

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6
Q

Hemoglobinopathies caused by

A
  • Qualitative defects in Hgb (aa mutations)
  • Structural defects
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7
Q

Thalassemias are caused by

A
  • Quantitative defects in Hgb production (less Hgb made)
  • Rate and quantity made affected
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8
Q

Myoglobin

A

Simple heme protein found in cardiac and skeletal muscles

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9
Q

Porphyrins

A

Chem intermediates in Hgb synthesis, Mgb, and other respiratory pigments called cytochromes

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10
Q

What indicates metabolic block of heme synthesis?

A

Excessive amounts of porphyrin intermediates in blood, urine, or feces

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11
Q

Porphyrinogens

A
  • Reduced compounds that are intermediates in heme synthesis
  • Non-protein, iron-containing prosthetic group of Hgb
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12
Q

How are porphyrinogens converted to porphyrins?

A

Oxidation upon air exposure

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13
Q

Which of the 4 porphyrin isomers generates heme?

A

Type III isomer

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14
Q

Which of the 4 porphyrin isomers occur naturally?

A

Types I and III

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15
Q

Porphyrin photoactive properties (color, absorbance wavelength)

A
  • Dark red color
  • 400 nm
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16
Q

Aqueous solubility of porphyrins varies with number of what functional group?

A

Carboxylic acid

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17
Q

Number of carboxylic acid functional groups in:
Uroporphyrin
Coproporphyrin
Porphyrin

A

Uroporphyrin = 8
Coproporphyrin = 4
Porphyrin = 2

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18
Q

Which cells of the human body contain hemoproteins that can synthesize heme?

A

All cells

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19
Q

Primary organ sites of heme synthesis

A

Bone marrow and liver

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20
Q

___ molecule(s) of heme is produced from ____ molecules of ____

A
  • One
  • 8
  • delta-aminolevulinic acid (ALA)
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21
Q

The first and last steps of heme synthesize occurs where? Requires what?

A
  • Mitochondria
  • Requires lots of energy
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21
Q

What is the last step of heme synthesis

A

Protoporphyrin converts to heme through action of ferrochelatase adding ferrous iron

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22
Q

Heme formation regulated by which mechanism? How?

A

Negative feedback whereby less heme stimulates more ALAS production

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23
Q

Rate-limiting enzyme of heme synthesis

A

ALAS

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24
Q

Most heme biosynthesis disorders display what kind of inheritance pattern?

A

Autosomal dominant

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25
Q

Neuropsychiatric symptoms

A
  • Abdominal pain
  • Nausea
  • Constipation
  • Hypertension
  • Psychiatric symptoms
  • Fever
  • Paresthesia
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26
Q

Cutaneous symptoms

A
  • Photosensitivity
  • Blisters
  • Excess facial hair
  • Hyperpigmentation
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27
Q

List porphyrias that feature neuropsychiatric symptoms

A
  • ALA dehydratase deficiency porphyria (ADP)
  • Acute intermittent porphyria (AIP)
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28
Q

List porphyrias that feature cutaneous symptoms

A
  • Congenital erythropoietic porphyria (CEP)
  • Porphyria cutanea tarda (PCT)
  • Erythropoietic protoporphyria (EPP)
  • X- linked protoporphyria (XLPP)
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29
Q

Which specific cutaneous symptoms are featured in CEP and PCT?

A

Increased fragility of light-exposed skin

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30
Q

Which specific cutaneous symptoms are featured in EPP and XLPP?

A

Burning of light-exposed skin

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31
Q

Photosensitizing effects of porphyrins attributed to what factor?

A

Light absorption

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32
Q

List porphyrias that feature
neurocutaneous symptoms

A
  • Hereditary coproporphyria (HCP)
  • Variegate porphyria (VP)
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33
Q

Most common acute porphyria

A
  • Acute intermittent porphyria (AIP)
  • 80% asymptomatic
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34
Q

Secondary porphyrinuria

A
  • Acquired condition associated with increased excretion of urinary porphyrins
  • Not due to inherited defect, but is rather caused by another disorder or toxin
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35
Q

Specific causes of secondary porphyrinuria

A
  • Liver disease
  • Heavy metal poisoning (Pb)
  • Inherited bilirubin metabolism disorder
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36
Q

How to test for acute porphyria?

A
  • Initial: determine if there’s porphobilinogen in urine
  • If positive: measure deficient PBG deaminase to ID AIP, analyze fecal porphyrins to differ btwn AIP, VP, and HCP
37
Q

How to test for cutaneous porphyria?

A
  • Initial: measure porphyrins in random or timed urine
  • Increased excretion of porphyrins in certain pattern diagnostic for PCT and CEP
  • EPP and XLPP tested using plasma or whole blood
38
Q

List analytic methods for porphyrias

A
  • Watson Schwartz
  • HPLC with fluorescence
  • Chromatographic analysis
  • Fecal HPLC with fluorescence
39
Q

Watson-Schwartz assay

A

Add Ehrlich’s reagent to make rose red color in presence of porphyrins, absorbance 555 nm

40
Q

Which analytical method helps to ID CEP?

A

Chromatographic analysis

41
Q

Specimen requirements

A
  • Protect from light
  • Unpreserved urine must be in fridge for 48 hr or -20C for many weeks
  • Fecal frozen many months -20C
  • Whole blood in EDTA, protect from light, 4°C
42
Q

Hemoglobin function

A
  • Oxygen transport to tissue and CO2 transport back to lungs
  • Major buffering system
43
Q

Hemoglobin structure

A

2 alpha globins + 2 beta globins with central heme

44
Q

Hgb A1 structure

A

2 alpha + 2 beta chains

45
Q

Hgb A2 structure

A

2 alpha + 2 delta chains

46
Q

Hgb F structure (fetal)

A

2 alpha + 2 gamma chains

47
Q

Alpha genes on which chromosome?

A
  • 16
  • Duplicated on this chromosome (alpha 1 and 2)
48
Q

Non-alpha genes on which chromosome?

A
  • 11
  • Non-homologous crossover -> fused/hybrid globin chains
49
Q

Hemoglobinopathies divided into which 4 groups based on genetics of globin chain production?

A
  1. Amino acid substitutions (Hgb S, C, D, E ,O, G)
  2. Aa deletions (Hgb Gun Hill)
  3. Elongated globin chains resulting from chain termination, frame shift, or other mutations (Hgb Constant Spring)
  4. Fused/hybrid chains (Hgb Lepore and Kenya)
50
Q

Which chain is affected in approx 2/3 of hemoglobinopathies?

A

Beta

51
Q

Normal heme synthesis requires which 3 things?

A
  1. Heme synthesis in mitochondria
  2. Globin synthesis in cytoplasm
  3. Adequate iron supply
52
Q

Newly made heme exits the ____ to the _____ to complex with 4 globin molecules

A
  • Mitochondria
  • Cytoplasm
53
Q

Most common hemoglobinopathy in the US, which causes sickle cell trait, and is most common in Blacks

A

Hgb S

54
Q

Hgb S testing

A
  • Solubility test
  • Cellulose acetate alkaline pH Hgb electrophoresis (Hgb S between Hgb A and A2
55
Q

Hemoglobinopathy found in West Africa-Ghana, microscopic target cells and crystalloid structures

A

Hgb C

56
Q

Hgb C testing

A
  • Cellulose acetate electrophoresis (moves with Hgb A2)
  • Negative solubility test
57
Q

Most common mixed hemoglobinopathy, microscopic target cells, occasional sickle cells, Hgb C crystal or combos

A

Hgb SC

58
Q

Hgb SC testing

A
  • Solubility test (positive)
  • Cellulose acetate electrophoresis (equal amounts of Hgb S and C)
59
Q

Hemoglobinopathy found in Asia, microscopic microcytosis and target cells

A

Hgb E

60
Q

Hgb E testing

A
  • Cellulose acetate
  • Citrate agar (migrates with A)
61
Q

Hemoglobinopathy with rare homozygous state usually found in Northwest India, slight anisocytosis

A

Hgb D

62
Q

Hgb D testing

A
  • Cellulose acetate (migrates with Hgb S)
  • Citrate agar (migrates with Hgb A)
63
Q

Inheritance pattern of thalassemias

A

Autosomal dominant

64
Q

Thalassemia minor

A
  • Heterozygous
  • Asymptomatic
  • Resembles iron deficiency
65
Q

Thalasemia major

A
  • Usually lethal before birth or in childhood
  • Early/continuous treatment allows survival into young adulthood with many complications
66
Q

List the 4 types of alpha thalassemias

A
  1. Hydrops fetalis (total absence of alpha chains)
  2. Hgb H (3/4 alpha chains missing)
  3. Alpha-thal trait (2/4 alpha chains missing)
  4. Silent carrier (1/4 alpha chains missing) -> normal Hgb production
67
Q

Hydrops fetalis

A

Most clinically severe form that feature Hgb Barts and stillborn/death at birth

68
Q

Two major subtypes of beta-thal

A
  1. Beta+ (Beta chains made in reduced amounts)
  2. Beta null (complete absence of beta chains)
69
Q

Beta thal major

A
  • Homozygous
  • Crippling childhood disease
  • Microcytic/hypochromic anemia
  • BM compensates by expanding in size, thus causing bone abnormalities
70
Q

Beta thal minor

A
  • Heterozygous
  • Inheritance of one thal gene
  • RBC survival not shortened
  • Asymptomatic
  • Mild microcytic anemia
  • Lab values resemble IDA
71
Q

Most hemoglobinopathies and thalassemias can be diagnosed by:

A
  • CBC
  • Blood smear
  • Solubility test
  • Cellulose acetate electrophoresis
72
Q

Additional tests to diagnose hemoglobinopathies and thalassemias

A
  • Citrate agar electrophoresis
  • Serum ferritin
  • Newer HPLC
  • Isoelectric focusing
73
Q

Principle of solubility test

A

Sickled Hgb are insoluble in the deoxygenated state and thus precipitate when placed in high molarity buffer solution -> can’t read lines on card thru tube

74
Q

Solubility test false negatives

A
  • Recent transfusion
  • Infants with Hgb F anemia
75
Q

Solubility test false positive

A

Whole blood vs packed RBCs

76
Q

Does solubility test distinguish between sickle cell trait and disease?

A

No, so it’s just a screening test, not a diagnostic test

77
Q

Order of Hgb electrophoretic mobility from slowest to fastest

A

Accelerated, Fast, Slow, and Crawl

78
Q

Universal newborn screening for ___ is now the norm

A

Hemoglobinopathies

79
Q

List Hgb-based analytic methods

A
  • Citrate agar electrophoresis
  • Hgb A2 quantitation (HPLC)
  • Acid elution for Hgb F
  • Hgb F quantitation (HPLC)
80
Q

Citrate agar electrophoresis

A
  • pH 6.0-6.2
  • Used after cellulose acetate detects abnormal Hgb
  • uses solubility in determining mobility
81
Q

Acid elution of Hgb F staining results for adult and fetal cells

A

Adult cells = ghost
Fetal cells = Red with eosin

82
Q

Why use DNA technology?

A

Definitive diganosis of some hemoglobinopathies and thalassemias include combos of genetic defects that may require DNA analysis

83
Q

DNA technology advantages

A
  • Increased sensitivity and specificity
  • Prenatal diagnosis of thal major
84
Q

DNA technology disadvantages

A

Higher cost and lack of availability in routine labs

85
Q

Myoglobin role

A

Reversibly binds oxygen but only releases under low oxygen tension from muscle membrane to muscle cell cytoplasm

86
Q

Myoglobin structure

A

1 polypeptide chain + 1 heme with iron

87
Q

How does muscle damage affect myoglobin?

A

Increased serum and urine Mgb

88
Q

Which molecule features fast renal clearance and may cause acute renal failure in high concentrations?

A

Myoglobin

89
Q

T/F
Myoglobin in urine cross-reacts with Hgb on dipstick and cause positive reaction

A

True

90
Q

Myoglobin measured to test for

A
  • rhabdomylosis
  • myocardial infarction
  • aid diagnosis of hereditary progressive muscular dystrophy
91
Q

Myoglobin analytical methods

A
  • Fluorescence
  • Chemiluminescence
  • Immunochromatic

Clinical Chemistry (21 decks)

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