Sorted By Test Name - Mayo Medical Laboratories

THEVP
84158
TLU
8603
Thalassemia and Hemoglobinopathy Evaluation
Clinical Information: The thalassemias are a group of autosomal recessive disorders of hemoglobin
(Hb) synthesis. Normal adult Hb consists of 2 alpha globin chains (encoded by 2 pairs of alpha globin
genes, each pair located on 1 of the chromosomes 16), and 2 beta globin chains (encoded by 2 beta globin
genes, each located on 1 of the chromosomes 11). Thalassemia syndromes result from an underproduction
of 1 or 2 types of globin chains and are characterized by the type (alpha, beta, delta) and magnitude of
underproduction (number of defective genes) and the severity of clinical symptoms (minor, major). The
severity of the clinical and hematologic effects is directly related to the number of genes deleted or
affected. The most common form of thalassemia is heterozygous alpha thalassemia 2, with 1 affected
alpha globin gene. In heterozygous alpha thalassemia 2, there is no clinical effect and the blood count,
including the mean cell volume, is normal. Heterozygous alpha thalassemia 1 and homozygous alpha
thalassemia 2 (both with 2 affected genes) have the typical thalassemic picture (eg, hypochromic
microcytic anemia, pallor, fatigue, shortness of breath, jaundice, and splenomegaly). Hemoglobin H (Hb
H) disease, having a deletion of 3 alpha chains, is a moderate-to-severe hemolytic disease. The severity of
Hb H disease is related to the amount of Hb H in the red cells. The morphology of the red cells is often
very bizarre due to denatured Hb found within the red cells. The deletion of all 4 alpha chains is
incompatible with life. Affected fetuses are hydropic and die in utero or shortly after premature birth. The
blood smears show large hypochromic red cells, nucleated red cells, target cells, and red cell fragments.
Hb Barts, Hb H, and Hb Portland are present in significant quantities. It is the most common cause of
hydrops fetalis in southeast Asia and southern China. This consultative study tests for the detection of
alpha-thalassemias, beta-thalassemias, delta-beta-thalassemia, and for Hb variants that are commonly
accompanied by thalassemias: Hb H, Hb Lepore, Hb Barts, unstable Hb, hemolytic anemias, Hb E,
hereditary persistence of high fetal Hb (several varieties), and combinations of Hb S with alpha- or
beta-thalassemia, Hb E/beta-O-thalassemia, and many other complex thalassemic disorders. Some of the
alpha-thalassemias (eg, Hb H disease) can be reliably identified by Hb electrophoresis alone; some require
DNA probe studies. Since iron deficiency can mimic thalassemias, ferritin levels are measured to evaluate
this possibility.
Useful For: Diagnosis of thalassemia
Interpretation: A hematopathologist expert in these disorders evaluates the case, appropriate tests are
performed, and an interpretive report is issued.
Reference Values:
Definitive results and an interpretive report will be provided.
Clinical References: Hoyer JD, Hoffman DR: The thalassemia and hemoglobinopathy syndromes.
In Clinical Laboratory Medicine. 2nd edition. Edited by KD McMlatchey. Philadelphia, Lippencott
Williams and Wilkins, 2002, pp 866-892
Thallium, 24 Hour, Urine
Clinical Information: Thallium is found in some depilatories and rodenticides. Accidental ingestion
may lead to vomiting, diarrhea, and leg pains followed by a severe and sometimes fatal sensorimotor
polyneuropathy and renal failure. Alopecia (hair loss) may occur 3 weeks after poisoning. The fatal dose
is approximately 1 g.
Useful For: Detecting toxic thallium exposure
Interpretation: Normal daily output is 10
mcg/day. The long-term consequences of such an exposure are poor.
Reference Values:
0-1 mcg/specimen
Reference values apply to all ages.
Clinical References: 1. Bank WJ, Pleasure DE, Suzuki K, et al: Thallium poisoning. Arch Neurol
Current as of January 4, 2013 7:15 pm CST 800-533-1710 or 507-266-5700 or MayoMedicalLaboratories.com Page 1722