Page 2623 - Hematology_ Basic Principles and Practice ( PDFDrive )

e4 Part XIII Consultative Hematology

Haptoglobin
Summary points • Binds free hemoglobin in plasma
• Haptoglobin-hemoglobin complex removed by reticuloendothelial system
• Often used to evaluate for intravascular hemolysis but has low sensitivity and specificity
• Acute-phase reactant
Methodology Immunoassay
Specimen requirements Lithium heparin, EDTA, or plain tube
Indications Evaluation of hemolysis, especially intravascular
Reference range Table 162.6
Interpretation • Levels low in neonates and young infants, severe extravascular hemolysis, liver disease, massive tissue hemorrhage,
and congenital deficiency states
• High levels occur with pregnancy, steroids, estrogen, and acute-phase responses. Preexisting high levels may mask
hemolysis
Related tests Plasma-free hemoglobin concentration, LDH, bilirubin, reticulocyte count
Interfering substances Lipemia
Reference Owen JA, Better FC, Hoban J: A simple method for the determination of serum haptoglobins. J Clin Pathol 13:163, 1960.

EDTA, Ethylenediaminetetraacetic acid; LDH, lactate dehydrogenase.

Hemoglobin F and Hemoglobin A 2
Summary points • Hemoglobin F is composed of two α and two γ chains—the dominant hemoglobin during gestation and early infancy
• Hemoglobin A 2 is composed of two α and two δ chains—a normal minor hemoglobin in adulthood
• Hemoglobin A 2 present at very low levels at birth, gradually increasing to adult levels over the first 1–2 years of life
Methodology Gel electrophoresis or high-performance liquid chromatography
Specimen requirements Whole blood: EDTA
Indications • Assess for β-thalassemia (including trait) or other hemoglobinopathy
• Evaluate for bone marrow failure syndromes or juvenile myelomonocytic leukemia (elevated hemoglobin F); evaluate
patients being treated with hydroxyurea for hemoglobin F response (e.g., sickle cell anemia)
Reference range Tables 162.7 and 162.8
Interpretation • Hemoglobin F is elevated in β-thalassemia, δβ-thalassemia, hereditary persistence of fetal hemoglobin, sickle cell
anemia, other hemoglobin disorders, some bone marrow failure syndromes, and juvenile myelomonocytic leukemia
• Hemoglobin A 2 is elevated in β-thalassemia, unstable β-chain variants, megaloblastic anemia, thyrotoxicosis
• Hemoglobin A 2 is decreased in δβ-thalassemia and at times in iron deficiency, lead poisoning, anemia of chronic
disease, sideroblastic anemia, and hypothyroidism
• Infants with suspected β-thalassemia disorders may require repeat testing at 6 months to 1 year of age to reliably
evaluate hemoglobin A 2 levels
Related tests Complete blood count, peripheral smear review, molecular diagnostic testing for β-chain mutations
EDTA, Ethylenediaminetetraacetic acid.

Sickle Cell Screen (Hemoglobin S Solubility Test)
Summary points • Rapid test to evaluate for the presence of hemoglobin S >30%
• Also known as a sickle prep or by the brand name of a commonly used test kit—Sickledex
Methodology Differential solubility
Specimen requirements Whole blood: EDTA, some laboratories accept heparin or ACD anticoagulants
Indications Suspected hemoglobin S disorder
Reference range Negative
Interpretation • Positive when hemoglobin S >30%, negative when hemoglobin S <20%
• Hemoglobin S between 20% and 30% may be positive or negative
• False positive with cryoglobulinemia, multiple myeloma, dysglobulinemia, certain rare hemoglobinopathies (C Harlem
or C Georgetown); false negative with severe anemia, high hemoglobin F, infants under 6 months
• Recent transfusion may give false-positive or false-negative results
• Does not distinguish between sickle cell trait and sickle cell disease or compound heterozygotes for hemoglobin S and
another hemoglobinopathy
• Positive results should be confirmed by another method
Related tests Hemoglobin fractionation/electrophoresis
Interfering substances Hemolyzed sample
References Lange RD, Minnich V, Moore CV: Effect of oxygen tension and of pH on the sickling and mechanical fragility of
erythrocytes from patients with sickle cell anemia and sickle cell trait. J Lab Clin Med 37:789, 1951.
Nalbandian RM, Nichols BM, Camp FR Jr, et al: Dithionite tube test—a rapid, inexpensive technique for the detection
of hemoglobin S and non-S sickling hemoglobin. Clin Chem 17:1028, 1971.

ACD, Acid citrate dextrose; EDTA, Ethylenediaminetetraacetic acid.