Laboratory Data

1. Peripheral smear. Note size and shape of RBCs and WBCs, and presence of platelets.

2. Reticulocyte count. The most important laboratory test after peripheral smear.

a. Increased. Indicates either an appropriate response to anemia or shortened RBC survival through blood loss or hemolysis.

b. Low. With anemia, indicates that marrow is responding inappropriately to nutritional deficiency, marrow failure, or marrow replacement.

c. Very low (< 0.2%). Seen with congenital pure red cell aplasia and transient erythroblastopenia of childhood.

3. Iron and total iron-binding capacity (TIBC) or transferrin. Consider checking ferritin (reflects iron stores or an inflammatory process) in patients with microcytic anemia. Patients with iron deficiency anemia have low iron and normal or elevated TIBC or transferrin; ferritin is generally low but can be normal or high in response to inflammation. Very low MCV (< 70) and normal iron and TIBC suggest thalassemia. Increased hemoglobin A2 on hemoglobin electrophoresis occurs with 0-thalassemia trait.

Acute and chronic illnesses can dramatically affect iron and TIBC, making their utility in diagnosis of anemia low. If the question of iron deficiency requires definite diagnosis, a bone marrow exam with iron stains is indicated in children 4 years of age or older (by which time they have accumulated stainable iron in bone marrow). A trial of iron therapy can be both diagnostic and therapeutic in many patients.

4. Guaiac test for occult blood. Stool may reveal occult GI bleeding.

5. Vitamin B12 and folate. Order these tests prior to transfusion if deficiency is suspected. In folate deficiency secondary to malnutrition, serum folate may be normal after one or two well-balanced meals; consider checking RBC folate level.

6. Haptoglobin and urine hemosiderin. Low haptoglobin indicates acute hemolysis. A positive urine hemosiderin, which tests for heme in shed renal tubular cells, indicates hemolysis; this may have occurred weeks earlier.

7. Direct and indirect Coombs test. Indicates that hemolysis is mediated by antibody. Direct Coombs test measures presence of antibody or complement, or both, on the RBC; indirect Coombs test detects antibody in plasma directed at the RBC. The direct Coombs test is more valuable in evaluating immuno-hemolytic disease; the indirect Coombs is of value as a blood-banking procedure. Detection of an antibody in plasma but not on the RBC suggests an alloantibody (usually IgG) rather than an autoantibody.

8. Platelet count. Elevated in early iron deficiency or transient ery-throblastopenia of childhood. Decreased in folate and vitamin B12 deficiency, severe iron deficiency, and with marrow replacement.

Radiographic and Other Studies. Order as clinically indicated.

0 0

Post a comment