G7

Normal serum Normal serum Patient serum Patient cells Dilute acid Dilute acid

Patient cells Patient cells

Trace hemolysis 3+ Hemolysis 2+ Hemolysis

Tube 4

Tube 5

Tube 6

Tube 7

Tube 4

Heat inactivated serum Dilute acid Patient cells

Figure 7.11 Ham's test. Note varying degrees of hemolysis in tubes 1, 2, and 3. Hemolysis occurs in tubes containing patient cells, patient serum, and acidified serum. Hemolysis does not occur in tubes with heat-inactivated serum and control cells, because heat inactivates complement.

Heat inactivated serum Dilute acid Patient cells

No hemolysis

Tube 5

Normal serum Normal cells

Normal serum Normal cells

No hemolysis

Tube 6

Normal serum Dilute acid Normal cells

Normal serum Dilute acid Normal cells

No hemolysis

Heat inactivated serum Dilute acid Normal cells

No hemolysis

Flow Cytometry in the Diagnosis of PNH

Currently, flow cytometry procedures are available that can test white cells for the presence or absence of GPI-linked proteins. White cells can be examined for reactivity to anti-CD48, CD55, and CD59, all of which are anchored proteins.34 A new diagnostic procedure, FLAER (fluorescent-labeled aerolysin) has proved effective in detecting smaller populations of abnormal leukocytes in PNH.35 This technique may prove useful in determining PNH cell clones in individuals presenting with varying levels of bone marrow failure.

Cold Agglutinin Syndrome

Cold agglutinin syndrome (CAS) is another of the rare hemolytic disorders that affect primarily individuals over 50 years of age. Also known as cold hemagglutinin disease (CHAD), the hemolysis in this disorder is caused by an IgM autoantibody of wide thermal range. Complement is fixed on the red cells during cold temperatures, 0° to 5°C and then red cells agglutinate and hemolyze as body temperature rises, 20° to 25°. Patients experience acrocyanosis or numbness and a bluish tone to the fingertips and toes and will experience weakness, pallor, and weight loss. The lysis is intravascular with a positive direct antiglobulin test (with polyclonal antihuman globulin reagent or anti-C3d). Some hemoglobinuria may be present. If the antibody is strong, the CBC will need correcting because the antibody coats the red cells, causing agglutination and falsely elevated red cell indices and hematocrit. The sample should be warmed at 37°C for 15 to 30 minutes and then recycled through the instrument for accurate results. After warming, all parameters should be accurate. Treatment is circumstantial, depending on the level of hemolysis; many individuals change loca-

108 Part II • Red Cell Disorders tion and opt for warmer climates to avoid hemolytic episodes altogether.

Paroxysmal Cold Hemoglobinuria

Paroxysmal cold hemoglobinuria (PCH) is a rare hemolytic anemia caused by anti-P, which attaches to the red blood cells at lower temperature and then activates complement at warmer temperatures. Lysis occurs at body temperature. The lysis is intravascular and severe, with hemoglobinemia, hemoglobinuria, and increased bilirubin. The symptoms are similar to a hemolytic transfusion reaction with back pain, fever, chills, and abdominal pain. Some patients may require transfusion.33 The screening test for PCH is the Donath-Landsteiner test, which is rarely performed in the clinical laboratory

The Donath-Landsteiner Test

The patient's anticoagulated blood sample is split into two parts. The first aliquot is the control and should be incubated at 37°C for 1 hour. The second aliquot is placed at 4°C for 30 minutes and then incubated at 37°C for 30 minutes. Both aliquots should be cen-trifuged and then observed for hemolysis. The control should show no hemolysis. If the second aliquot shows hemolysis, that is evidence for PCH.

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