Hematology: Hemolytic anemias & hemoglobinopathies – page 5

Sudden pooling of sickled cells in a still-functioning spleen causes rapid anemia with splenic enlargement while the marrow keeps responding. In an aplastic crisis the reticulocyte count falls to near zero and the spleen does not enlarge.

The hypoxic, acidic, hypertonic renal medulla causes sickling even in trait, leading to hyposthenuria and papillary hematuria. Carriers do not have chronic hemolysis, crises or autosplenectomy.

Adult hemoglobins are denatured and precipitated by alkali, while HbF stays in solution and is measured in the filtrate. Precipitation in reducing phosphate buffer is the principle of the sickle solubility test.

Target cells have extra membrane relative to volume, so they can swell more before lysis and resist hypotonic saline. The other conditions produce spherocytes, which lyse easily.

Unstable hemoglobins denature and precipitate in isopropanol or on heating, forming Heinz bodies. With normal G6PD activity, the Heinz bodies are not from an enzyme defect; PK deficiency does not cause Heinz bodies.

Methylene blue reduces methemoglobin using NADPH, which G6PD produces. Without enough NADPH it is ineffective and can itself cause oxidant hemolysis.

G6PD converts glucose-6-phosphate and reduces NADP+ to NADPH, which absorbs at 340 nm; the rate of absorbance rise equals activity. p-Nitroaniline at 405 nm is used in chromogenic coagulation assays.

Warm autoantibodies usually react with nearly all cells and often target Rh-related proteins. Anti-I and anti-P are cold-reacting autoantibodies seen in cold agglutinin disease and PCH.

Penicillin binds firmly to the red cell membrane, and IgG anti-penicillin attaches to the coated cells, so the eluate reacts only with drug-treated cells. A true autoantibody, as with methyldopa, reacts with untreated cells.

Complement destroys PNH red cells and transfused normal cells dilute the rest, so red cells underestimate the clone. Granulocytes and monocytes, tested with FLAER and CD24/CD14, give a truer clone size.

PNH has a high rate of venous thrombosis in unusual sites such as the hepatic (Budd–Chiari), portal and cerebral veins, which is the major cause of death. Iron is lost in urine rather than overloaded.

Ongoing mechanical intravascular hemolysis causes loss of iron in urine as hemoglobin and hemosiderin, leading to iron deficiency. B12 is not lost in hemolysis.

Repeated foot strike damages red cells in the sole, causing intravascular hemolysis with pink plasma and low haptoglobin. Myoglobin does not color plasma or lower haptoglobin, and hematuria shows many red cells.

More bilirubin reaches the gut and is converted to urobilinogen, so more is reabsorbed and excreted in urine. Urine bilirubin stays negative because unconjugated bilirubin is not filtered.

About three-quarters of HS cases are autosomal dominant, which is why a parent is often affected. The rest are recessive or new mutations.

When alpha chains are severely lacking in fetal life, the extra gamma chains form γ4 (Hb Bart's). In adults the extra beta chains form β4 (HbH).

Ineffective erythropoiesis drives huge marrow expansion, which widens the skull bones and gives the hair-on-end pattern. Regular transfusion prevents it.

The α chain has 141 amino acids, while β, γ and δ chains have 146. The difference helps explain chain-specific mutation numbering.

Washed cells are lysed with water, then shaken with an organic solvent that pulls out membrane lipids and stroma, which are removed by centrifugation to give a clear hemolysate.

Each chromosome 16 carries two α genes (four per cell), and each chromosome 11 carries one β gene (two per cell). This explains why α-thalassemia has four severity grades.