hemoglobins

Normal nonsmoker level of CO

0.4‐2%

average lifespan of sickled red blood cells

17 days

Normal smoker level of CO

2‐6%

Sickle cell trait (SA) electrophoresis

35% to 45% HbS, <1% HbF, 1% to 3% HbA2, and 50% to 55% HbA.;The roughly 60:40 ratio of A:S is due to a greater affinity of α chains for βA chains over βS chains.

Hemoglobin C disease (homozygous CC) electrophoresis

90% HbC, 7% HbF, 3% HbA2, 0% HbA. T Hemoglobin C disease (homozygous CC) - symptoms there is mild hemolytic anemia, splenomegaly, and numerous target cells. Hexagonal or rod‐shaped crystals may be found in the red cells, especially after splenectomy.

The electrophoresis in SS shows

>80% HbS, 1‐20% HbF, 1‐4% HbA2, and 0% HbA.

Fast hemoglobins

A fast hemoglobin is one that migrates beyond A on the alkaline gel, -HbH or HbBarts.

Unstable hemoglobins

A group of hemoglobins that are associated with characteristic peripheral smear findings of Heinz bodies and bite cells. Oxidative stresses may precipitate hemolytic crisis.

Altered oxygen affinity hemoglobins

A group of hemoglobins with shifted oxygen dissociation curves, due to mutations that effect conformation sensitive amino acids in the globin chains.

The α thal 1 gene is prevalent in

Asians, and it is they who are at risk for the very severe kinds of αthalassemia (hemoglobin Bart's and hemoglobin H diseases).

β gene (HBB) abnormality categorization

Based upon their impact on β globin chain production, these alleles can be categorized as βº alleles, β+ alleles, silent alleles

Carboxyhemoglobin (HbCO)

CO binds tightly (with 200 times the affinity of oxygen) to hemoglobin forming carboxyhemoglobin (Hb‐CO), thus reducing the available binding sites for oxygen.

Carboxyhemoglobin (HbCO) and fetal hemoglobin

CO has even greater avidity for fetal hemoglobin, placing infants (and fetuses) at great risk. Furthermore, CO is directly toxic to intracellular oxidative mechanisms and appears to enhance production of nitric oxide (NO).

Splenic sequestration crisis - susceptible patients

Children (whose spleens have not yet undergone fibrosis) and adults with SC disease or sickle cell‐β+ are most susceptible.

sickle cell disease- other liver abnormalities

Chronic nonspecific hepatomegaly and liver dysfunction, thought to be related to centrilobular congestion. Chronic hepatitis C, related to multiple infections, is also a problem. Gallstones (pigmented type) are ubiquitous in sickle cell disease, and may be present in patients as young as 3 years.

Hb‐CO levels >50% - symptoms

Coma and death

Hb Lepore

Common near the Mediterranean, especially Italy; the result of a fusion between δ and β genes

Sulfhemoglobin (SHb)- cyanosis

Cyanosis manifests at around 3% to 4% or 0.5 g/dL. Normally, SHb is less than 1% of total Hb.

Migration of hemoglobins in acid electrophoresis from cathode to anode

F; [A,D,G,E,A2,M]; [Origin, O];[A, Charlem]; C

Low oxygen affinity hemoglobins -Examples

Hb Beth Israel, Kansas, and Providence.

Hb Constant Spring (CS)

Hb CS is another cause of thalassemic indices. Hb CS results from a mutation in the α gene stop codon, producing an abnormally long transcript that is unstable. The αCS gene is thus inefficient, producing thalassemia.

High oxygen affinity hemoglobins- Examples

Hb Chesapeake, J‐Capetown, Malmo, Yakima, Ypsilanti, Rainier and Hemoglobin Denver.

Why aren't the manifestations of sickle cell disease apparent at birth?

Hb F, present at birth, has an inhibitory effect on Hemoglobin S polymerization; there are no symptoms until Hb S levels increase beyond 50% ‐ usually at about 6 months of age. Likewise, in patients with combined sickle cell disease hereditary persistence of fetal hemoglobin (SS‐HPFH) clinical manifestations are milder than in SS.

Hb M -examples

Hb M‐Iwate, M‐Boston, M‐Saskatoon, and M‐Hyde Park.

Type II envelope cells- diseases

HbC, sickling disorders, thalassemia

Acid electrophoresis does not help to separate

HbD from HbG and HbLepore or HbE from HbO‐Arab.

Methemoglobin (Hi, hemiglobin) and cyanide toxicity

Hi has a very high affinity for cyanide, so part of the treatment for cyanide toxicity involves administration of nitrites to generate Hi which will chelate cyanide.

The acid elution technique

In an acid buffer, HbA elutes from red cells, but HbF does not. Cells with persistent eosinophilia following acid elution contain HbF.

Methemoglobin (Hi, hemiglobin)- cause

Large quantities of Hi may be the result of hereditary and acquired states.

Beta thal is most common in what populations?

Mediterranean populations, and manifestations do not become evident until 6 to 9 months of age.

Hb‐CO levels 10‐20% - symptoms

Mild symptoms: dyspnea on exertion

Hb M -electrophoresis

Most M hemoglobins run with Hb A on routine gels.

Beta thal minor - electropheresis

On hemoglobin electrophoresis, one of several patterns emerges. In most common situation, one sees high HbA2 (over 2.5%, usually 4% to 8%) and normal HbF. In the second most common situation, the electrophoresis may show normal A2 (because the patient is also iron deficient). This electrophoresis may be erroneously interpreted as consistent with alpha thalassemia. When the electrophoresis is done for a CBC with thalassemic indices, many labs perform parallel iron studies to exclude this possibility. If the results of these indicate iron deficiency and the percent A2 is normal, electrophoresis should be repeated following iron repletion.

Bone symptoms in sickle cell disease

Osteonecrosis is a common complication and may affect the vertebrae, hands, feet, and femoral and humeral heads.

Aplastic crises -causes in children

Parvovirus B19 accounts for nearly 70% of aplastic crises.

Males with sickle cell disease

Priapism has been reported in up to 40% of.

Hb‐CO levels 20‐50%- symptoms

Severe symptoms: intoxication, with headache, lethargy, loss of consciousness

Heme synthesis

Succinylcoenzyme A condenses + glycine → α-amino β-ketoadipic acid →readily decarboxylated to δ-aminolevulinic acid (ALA) (vitamin B6, occurs in mitochondria)→ porphobilinogen, catalyzed by the enzyme ALA-dehydrase → uroporphyrinogen III or I. The type III isomer → protoporphyrin by way of coproporphyrinogen III and protoporphyrinogen → Iron is inserted into protoporphyrin by the mitochondrial enzyme ferrochelatase →heme

Hb Lepore - electrophoresis

Suspect Hb Lepore whenever around 15% of 'hemoglobin S' is present on the electrophoresis. Actual HbS is rarely present in this quantity, unless aggressively transfused. Hb Lepore runs with HbS on cellulose acetate but is inefficiently produced so that it only comprises 8% to 15% of total Hb. HbF may be as high as 20%.

Thalassemia and hemoglobin electrophoresis

Thalassemia is a quantitative defect in production of entirely normal hemoglobins and does not produce abnormal bands on the electrophoresis.

Hereditary persistence of fetal hemoglobin (HPFH) in beta thal

The HbF in this condition, as in most things other than HPFH (below) is present in a heterocellular distribution (some cells with and some cells without on the Kleihauer‐Betke stain). Hereditary persistence of fetal hemoglobin (HPFH) results from a delayed switch from gamma to beta or delta chains. This can result from deletion of the beta and delta genes. Hemoglobin F is present in a pancellular distribution. Combined sickle cell‐HPFH is found in about 1 in 100 of those with homozygous HbSS. These individuals have a pancellular distribution of about 25% Hb F and suffer from neither anemia nor vasoocclusive episodes.

What techniques may be used to detect red cells containing HbF, in support of a diagnosis of hereditary persistence of fetal hemoglobin (HPFH) or fetomaternal hemorrhage?

The acid elution technique and the alkali denaturation technique

Methemoglobin (Hi, hemiglobin)- measurement

The co‐oximeter is capable of measuring methemoglobin directly. Recall that both pulse oximetry and arterial blood gas analyzers, however, estimate oxygen saturation by emitting a red light (wavelength of 660 nm) absorbed mainly by reduced hemoglobin and an infrared light (wavelength of 940 nm) absorbed by oxyhemoglobin. Since methemoglobin absorbs equally at both of these wavelengths, it is essentially undetectable by these modalities; in fact, increasing levels of methemoglobin result in regression of the measured oxygen saturation towards 85%. This is a form of oxygen saturation gap.

Rapid detection of hemoglobin S

The hemoglobin solubility (dithionate) test and the sickling (metabisulfite) test

Pulse oximetry - hemoblogin identification

The pulse oximeter can identify only oxyHb and deoxyHb; it cannot measure carboxyhemoglobin, methemoglobin, or sulfhemoglobin and will therefore over‐estimate the oxygen saturation in these settings. Carboxyhemoglobin has an absorbance peak at approximately the same wavelength as oxyhemoglobin; therefore, the oxyhemoglobin saturation may be reported as quite artificially high. In contrast, while also over‐estimating the percent saturation, methemoglobin tends to produce a reading of around 85%.

SC complications

The various SS‐associated complications are about half as frequent in SC, but avascular necrosis of bone and proliferative retinopathy are equally common or more common in SC. The peripheral smear is remarkable for mild sickling and abundant target cells.

β gene (HBB) abnormalities

There are a large number of possible abnormal alleles at the HBB gene locus (more than 200). The vast majority of these consist of point mutations. Large deletions, such as those that underlie α‐thalassemia, are rarely seen in the HBB gene.

alpha genes

There are two copies of the alpha genes on each chromosome 16, for a total of 4 alpha chain‐producing gene loci in each normal cell.

Pregnancy sickle cell disease

There is certainly an increased risk of pregnancy induced hypertension (preeclampsia), but there is also an increased incidence of intrauterine growth retardation, intrauterine fetal demise, and prematurity.

β gene (HBB)

There is one copy of ;the β gene (HBB) on each chromosome 11, for a total of two productive genes in normal cells;Nearby (within the HBB gene cluster) are the genes for the delta (δ) globin chain, gamma (γ) globin chains, and a pseudo‐HBB gene.

Hb D & G

Those with Hb D or G are clinically normal. On cellulose acetate there is a band that runs with HbS and runs with HbA on citrate. Often D & G can be distinguished because HbD is a β chain defect, while HbG is an α chain defect; thus, HbG may produce two HbA2 bands (one normal, the other abnormal) separated by a distance equal to that separating HbA from HbG.

Acquired methemoglobinemia - treatment

Treatment for methemoglobinemia is methylene blue, which reduces Hi to Hb.

The acid elution technique - patterns

Two patterns may be seen: heterocellular (some RBCs contain HbF but others do not) and pancellular (all RBCs contain HbF). The pancellular pattern is characteristic of most types of hereditary persistence of fetal hemoglobin (HPFH). Other examples of elevated HbF are heterocellular (e.g., thalassemia).

Methemoglobin (Hi, hemiglobin)- normal metabolism

Under normal circumstances, there is a small degree of hemoglobin oxidation, and up to 1.5% of total Hb is Hi. The small amount of Hi that normally forms is reduced in the erythrocyte by the NADH‐dependent methemoglobin reductase system.

Unstable hemoglobins -clinical severity

Variable clinical severity is seen, ranging from severe hemolysis (Hb Hammersmith, Ann Arbor, Koln) to mild (most other examples). Note that Hb Barts and Hb H (severe alpha thal) are also associated with Heinz body anemia.

S bands

When a band is present in the S region, its identity can be confirmed by the sickle screen; if negative, this may indicated D, G, or Lepore.

Hemoglobin A2' (hemoglobin A2 prime)- electrophoresis

When heterozygotes for this variant undergo gel electrophoresis, A2' is barely detectable. This may lead to under‐estimation of the A2 and therefore under‐diagnosis of β thal trait. In looking for an elevated A2 as part of excluding β thal trait HbA2 and HbA2' levels must be added. A2' is easily detectable by HPLC, in which it produces a minor peak in the S area.

S‐α thal

When α‐thalassemia is coinherited with sickle cell trait, there is a decreased percentage of hemoglobin S;the degree to which HbS is decreased is relative to the number of α‐globin genes deleted. In single gene alpha gene deletion (‐α/αα), there is about 30‐35% Hb S. In two alpha gene deletions (‐‐/αα or ‐α/‐α) there is 25‐30% Hb S.

Migration of hemoglobins in alkaline electrophoresis from cathode to anode

[C, A2, E, O, Charlem]; [S, D, G, Lepore]; F; [A, M], [H, Barts]

Hemoglobin A2' (hemoglobin A2 prime)

a clinically insignificant δ‐chain variant that occurs in 1% to 2% of African Americans.

Hb M

a group of hemoglobins that, due to various amino acid substitutions, prefer the ferric (methemoglobin) state, which binds oxygen poorly. Cyanosis appears at 6 months of age, unless there is M fetal hemoglobin in which case cyanosis abates at about 6 months.

Alpha thalassemia alleles usually result from

a large structural deletion within the translated portion of the gene, but occasionally result from a point mutation in the untranslated region (e.g. Hb Constant spring).

The alkali denaturation technique

a quantitative assay for HbF based upon the principal that HbF is resistant to alkali denaturation (in 1.25 Molar NaOH). HbA is denatured and precipitated out; the optical density of the remaining supernatant reflects the quantity of HbF.

A2 or F

a quantitative assay should be performed to obtain an exact amount.

silent alleles

almost no impact on chain production - mutation of the promoter's CACCC box or the 5' untranslatedregion

CBC findings typical of thalassemia ('thalassemic indices')

an elevated RBC count (>5.5 °x1012 in men, >5.0 °x1012 in women), low MCV (65 to 75 fL in α thal, 55 to 65 fL in β thal), low hematocrit, and normal to slightly increased RDW. An MCV/RBC count ratio <13 favors thalassemia, while a ratio >15 favors iron deficiency.

Pulse oximetry

based upon two wavelengths of light‐emitting diodes (LEDs), one that emits light at 660 nm (red) and another that emits at 940 nm (infrared). Deoxy Hb has an absorption peak at 660 nm, while oxyHb has a peak at 940 nm. By simultaneously measuring at these wavelengths, the pulse oximeter can estimate arterial oxygen saturation (SaO2).

The α thal 2 gene is most prevalent in what populations?

blacks

β thalassemia -diagnosis

by the presence of 'thalassemic indices' (low hematocrit, increased RBC count, low MCV) and a quantitatively increased Hb A2.

Arterial blood gas analyzers

calculate the percent saturation after directly measuring the pH, pCO2, and PO2. The calculation assumes a normal Hb‐O2 saturation curve, normal 2,3‐DPG, and an absence of abnormal hemoglobins.

S‐β thal -disease manifestations

can be quite severe, depending upon the type of β thal defect.

Hereditary methemoglobinemia

can result from either deficiency in this system or abnormal hemoglobins (HbM) upon which this enzyme cannot act.

Altered oxygen affinity hemoglobins- detection

cannot be resolved on either gel electrophoresis or HPLC, but the Hb02 dissociation curve (P50) is diagnostic.

Clinically, sickle cell disease is characterized by

chronic hemolytic anemia and recurrent crises.

An adult hemoglobin electrophoresis with Hb S, F, and A2 has two possible

combined sickle cell‐HPFH and combined sickle cell‐β‐thalassemia. These can be distinguished by the pancellular distribution in the former and heterocellular in the latter.

βº alleles

complete absence of β chain production - usually nonsense or frameshift mutations

Reduced synthesis of either α or β chains results in

decreased total hemoglobin production, leading to hypochromasia and microcytosis.

The hemoglobin solubility (dithionate) test

detects insoluble forms of hemoglobin within a lysate of blood. Red cells are lysed in sodium dithionate buffer with saponin, the development of marked turbidity indicating a positive screen. Note that this test detects free hemoglobin with altered solubility; it may be positive in SS, SA, SC, SD, and C‐harlem. This test may be negative when the concentration of HbS is too small; e.g. in neonates.

The sickling (metabisulfite) test

detects red cells with sickling hemoglobins. In this test, whole blood is subjected to metabisulfite, which encourages cells containing HbS to sickle. A smear is then examined microscopically for sickling. Like the solubility test, this test may be positive in SS, SA, SC, SD, and C‐harlem. The test requires at least 10% HbS to be positive. Thus, it may not be falsely negative in neonates or those very aggressively transfused.

Erythrocyte survival

determined by removing a sample of blood, labeling the erythrocytes with chromium-51 (51Cr), inactivating the excess 51Cr remaining in the plasma, and reinjecting the labeled erythrocytes into the patient. The 51Cr is bound to the β-chain of the hemoglobin molecule and for the most part is not released until the red cell is removed from the circulation and the hemoglobin is degraded. Measurements of radioactivity in the red cells are made at 2 hours or 24 hours (the zero time, or 100% level) and at 1- to 3-day intervals until over 50% of the activity has disappeared. The results are usually expressed as the 51Cr half-survival time.

The oxygen gap

difference between pulse oximetry co‐oximetry; reflects the level of Hb‐CO

β+ alleles

diminished β chain production - mutations in the promoter sequence, LCR, or 5' untranslated region

Aplastic crises- pathogenesis

due to a transient arrest of erythropoiesis and are characterized by an abrupt drop in hemoglobin, reticulocytes, and red cell precursors in the marrow. Although these episodes typically last only a few days, the level of anemia may be severe.

CO elimination

eliminated by slowly being replaced by oxygen on hemoglobin molecules. The half‐life of CO depends on the oxygen tension. The T1/2 on room air is about 6 hours, while the T1/2 on 100% O2 is 1 hour.

Carboxyhemoglobin (HbCO)

endogenous production from only one source: the breakdown heme, resulting in Hb‐CO levels ≤ 1%.

Hb Bart disease (hydrops fetalis)-electropheresis

fast-migrating Hb Barts. Hb Barts = γ4 tetramers.

HbH disease-electrophoresis

fast-migrating Hb H, Hb H = β4 tetramers.

What are the types of sickle cells?

filamentous and oat cell

Which type of sickle cell is irreversible upon oxygenation?

filamentous cell

Sulfhemoglobin (SHb)

formed when hemoglobin is oxidized in the presence of sulfur. If further oxidized, SHb precipitates to form Heinz bodies. SHb cannot transport oxygen. Unlike, Hi, SHb cannot be reduced to Hb.

The seven classic sickle cell nephropathies

gross hematuria, papillary necrosis, nephrotic syndrome, renal infarction, isosthenuria, pyelonephritis, and renal medullary carcinoma. The risk of the latter is also increased in sickle cell trait and SC.

α thalassemia-diagnosis

has 'thalassemic indices' and normal Hb A2.

Hemoglobin C trait (heterozygous AC)

has about 40% to 50% of hemoglobin in the in C band (HbA2 + HbC); generally asymptomatic, but the peripheral smear has scattered target cells.

SC red cells

have an average lifespan of 27 days (compared with 17 days for SS and 120 days for normal red cells).

Hb Bart disease (hydrops fetalis)-CBC

hypochromia nRBCs

In what other hemoglobinopathies might sickled cells be seen?

in S‐ β thal, S‐C, S‐D, C‐Harlem, Hb C-Georgetown, HB I, large amounts of Hb Barts

Double heterozygosity for beta thal and an abnormal beta chain results

in an increased percentage of the abnormal beta chain; e.g., in S‐beta thal, there is >50% Hb S with 1‐15% Hb F.

Unstable hemoglobins -Examples

include Hb Hasharon, Koln, Seattle, Tacoma, Ann Arbor, & Zurich.

HbC- crystals

intraerythrocytic tetragonal crystals; after partial drying or hemolysis; conc must be >44%

The prevalence of sickle cell trait (genotype SA)

is about 10%

Screening for unstable hemoglobins

is carried out by incubating lysed red cells with 17% isopropanol which causes precipitation of unstable hemoglobins.

Hemoglobin E

is common in Southeast Asia; The CBC shows thalassemic indices and the peripheral smear numerous target cells.

Routine hemoglobin electrophoresis

is performed by placing a sample of lysed blood on cellulose acetate at pH 8.6 (alkaline electrophoresis). The gel is subjected to electromotive force, fixed, and stained. The normal adult has mostly hemoglobin A which is a fast‐moving hemoglobin found near the anode. A small amount (less than 3%) of slower‐moving hemoglobin A2 is detectable, seen in the C band.

Acute pain crisis (acute painful episode)

is thought to be due to a vaso‐occlusive event within bone. These episodes often follow exposure to cold, dehydration, infection, or alcohol consumption.

Alkaline electrophoresis- hemoglobins unable to separate

it does not separate HbS from HbD, HbG, and Hb‐Lepore nor does it resolve HbC, HbA2, HbO‐Arab, and HbE.

HPLC- technique

it employs a pump to provide the high pressure needed to push a sample (the 'mobile phase') through a column at a much greater rate than could be obtained by gravity alone. A column is a steel cylinder into which are packed numerous small particles (the 'stationary phase') such as silica gel beads. Individual molecules exit the column (elute) at different rates, depending upon their properties. As a molecule elutes, a light source produces a deflection on a spectrophotometer that is proportional to the concentration of that molecule in the original sample. Thus, HPLC can give information about the identity of a hemoglobin molecule (when correlated with known rates of elution) and its percentage in the sample.

Sickle cell disease and thrombosis

it is known that patients with SS, even in inter‐critical periods, have elevated levels of prothrombin fragments 1+2, d‐dimer, fibrinopeptide A, and factor V. Similarly, their platelets are hypersensitive in vitro.

Infections in sickle cell disease

made worse by the functional asplenia that is so common in. S. pneumoniae infections, including pneumococcal sepsis, pneumonia, meningitis, and arthritis, are the most common overall. Other common infections include Salmonella, Haemophilus (HITB), and M pneumoniae. Neurologic complications of sickle cell disease transient ischemic attacks (TIAs), cerebral infarcts, cerebral hemorrhage, cord infarction, sensorineural hearing loss, and meningitis.

Acute hepatic cell crisis (right upper quadrant syndrome) in sickle cell disease

manifests as progressive jaundice, elevated LFTs, and a tender, enlarged liver. This usually resolves within 2 weeks, it may progress to liver failure.

Alpha thal trait

manifests as thalassemic indices and an electrophoresis with normal A and A2 bands. A2 is not increased. In the absence of iron deficiency, this can be interpreted as consistent with alpha thalassemia trait. Unlike βthalassemia, the manifestations of α thal are present at birth.

Sulfhemoglobin- elevations

may increase after exposure to sulfonamides and in the presence of C. perfringens bacteremia (enterogenous cyanosis).

Additional laboratory testing in support of the patient with CO poisoning may include

measurement of lactate, calculation of the anion gap, myocardial markers, and cyanide levels (smoke inhalation also poses a risk of cyanide inhalation, depending upon the materials present in the fire).

Thalassemia -Peripheral smear findings

microcytic hypochromic cells, occasional target cells (more in β thal than α thal), and basophilic stippling.

α-thal trait- electrophoresis

normal

What genotypes show the clinical manifestations associated with sickle cell disease

not limited to those with the SS genotype;being more or less similar in sickle cell‐β0‐thalassemia, sickle cell‐β+‐thalassemia, and SC disease (Hb SC).

The peripheral smear in SS shows

numerous sickled cells

Which type of sickle cell is reversible upon oxygenation?

oat cell

Ocular complications (proliferative retinopathy) in sickle cell disease

occurs with greater frequency in SC disease and sickle cell‐β+‐thalassemia than in SS.

Hyperhemolytic crisis

presents as a sudden exacerbation of anemia in association with profound reticulocytosis and hyperbilirubinemia. This complication has been associated in many patients with concomitant G6PD deficiency.

Splenic sequestration crisis

presents as worsening of anemia in association with an enlarged, tender spleen. These episodes often occur during a viral illness.

The acute chest syndrome

presents with dyspnea, cough, chest pain, and fever. One may find tachypnea, leukocytosis, a pulmonary infiltrate on chest x‐ray, and progressive hypoxia. This syndrome is thought to be related to either vaso‐occlusive events or bacterial pneumonia.

Worsening of anemia in a more slowly progressive fashion than that seen in aplastic and sequestration crises may be due to

progressive renal insufficiency (with decreasing erythropoietin) or supervening iron/folate/B12 deficiency.

α thal 2 (α+ thal)

refers to a genotype in which chromosome 16 has one normal and one deleted alpha gene (‐α/). This is the most common genotype in African‐Americans.

Α thal 1 (α0 thal)

refers to a genotype in which chromosome 16 has two deleted alpha genes (‐‐/). Alpha thal 1 genotype is prevalent in Asians.

Thalassemia

refers to a quantitative abnormality of structurally normal globin chain synthesis. This is distinguished from hemoglobinopathy, which refers to the production of a structurally abnormal globin chain. Thalassemia- worldwide distribution most prevalent in the Mediterranean, Africa and Southeast Asia, paralleling the prevalence of malaria.

Continued synthesis of normal amounts of the unaffected chain leads to

relative abundance of those chains and precipitation of these chains in the red cell, reducing the cell's lifespan. Thus, in α thal, β4 and γ4 tetramers form, while in β thal, α4 tetramers form.

Sickled red blood cells- cause

result from the abnormal polymerization of deoxygenated hemoglobin S.

High oxygen affinity hemoglobins

result in a leftward shift in the curve and erythrocytosis

Low oxygen affinity hemoglobins

result in a rightward shift in the curve, anemia, and cyanosis.

Acquired methemoglobinemia

results from exposure to drugs or chemicals that increase the formation of Hi, common examples being nitrites, quinones, phenacetin, and sulfonamides.

Beta thal major

results from inheritance of two abnormal β genes such as β0β0, β+medβ+med, or β0β+med. Anemia develops by one year of age. The hemoglobin electrophoresis shows increased HbF (50% to 95%), normal to elevated HbA2, and little to no HbA.

Double heterozygosity for HbS and HbC

results in about 50% HbS and clinical manifestations intermediate in severity between SS and SA.

Methemoglobin (Hi, hemiglobin)- Cyanosis

results when Hi reaches 10% of total Hb or around 1.5 g/dL. In such cases the blood is grossly chocolate brown.

moyamoya disease

segmental arterial stenoses with 'puff of smoke' collaterals; approximately 1 in 3 patients with sickle cell disease

HbC- PBS

target cells, microspherocytes, envelope cells

β+ Mediterranean

tends to be more severe than in β+American, the latter found in American blacks.

α-thal trait- CBC

thalassemic

HbH disease-CBC

thalassemic; Heinz bodies

Hb‐CO can be measured by

the co‐oximeter, and venous blood is as good as arterial for this determination.

Beta thal intermedia and major (Cooley's anemia) are distinguished by

the dependence of Beta thal major on transfusions.

Methemoglobin (Hi, hemiglobin)

the form of hemoglobin in which iron is in the oxidized ferric (Fe+++) state instead of the usual ferrous (Fe++), often resulting from oxidation of hemoglobin. It is incapable of combining with oxygen.

Hb Constant Spring (CS) in the heterozygote

the hemoglobins produced are: α‐β (HbA), αCS ‐β (HbCS), α‐δ (HbA2), αCS ‐δ (four bands are seen in the adult on cellulose acetate electrophoresis)

δ‐β thal (deletion of both the δ and β genes)

there is a normal quantity of HbA2 and elevated HbF (5% to 20%);

In heterozygous Hb Lepore (fusion of δ and β)

there is a normal quantity of HbA2, slightly elevated HbF, and a band in the S region comprising 6% to 15% (Hb Lepore).

S‐β thal

there is an increased proportion of HbS (S usually >50%).

Alpha thalassemia is most common in

those of sub‐Saharan African and southeast Asian descent.

Types of envelope rbcs

type I: rbc folded on itself- "clamshell"; type II: hb conc to one side- flap-like

Beta thal minor

typically results from inheritance of one abnormal β gene, either β+ or β0.

Sickle cell trait (SA)- symptoms

usually asymptomatic. Those affected may manifest mild isosthenuria, are at risk for splenic infarcts at high altitudes, and have a risk for renal medullary carcinoma. The peripheral blood smear shows no sickle cells.

The co‐oximeter

utilizes multiple wavelengths of light and can specifically measure carboxyhemoglobin and methemoglobin (in addition to oxyHb and deoxyHb).

Hb F

Α2γ2; Major late fetal Hb

Hb A

α2β2; Major adult Hb

Hb A2

α2δ2; Minor adult Hb

Hb Gower2

α2ε2 ;Minor early fetal Hb

Alpha chain- normal genotype

αα/αα

Hb Constant Spring (CS) in the newborn

α‐γ (HbF), and αCS‐γ

HbC- molecular changes

β chain has lysine instead of glutamic acid in the 6th position

Hb S- molecular changes

β chain has valine instead of glutamic acid in the 6th position

β-thalassemia minor- genotype

β/β+ ; β/β°

β-thalassemia major- genotype

β/β°; β+/β+ ;β+/β°

HbE mutation

β26glu→lys

HbC mutation

β6glu→lys

HbS- mutation

β6glu→val

Hb Gower1

ζ2ε2 ;Major early fetal Hb

Alpha Thalassemia silent carrier genotype

−α/αα

α-thal trait- genotype

−α/−α or −−/αα;

HbH disease- genotype

−−/−α or −−/αCSα

Hb Bart disease (hydrops fetalis)- genotype

−−/−−