Hematology: Hemolytic anemias & hemoglobinopathies – page 4

Normal G6PD converts NADP to NADPH, which fluoresces under long-wave UV light; deficient samples produce little NADPH and show no fluorescence. Turbidity is the endpoint of the sickle solubility test, not the G6PD screen.

The block at pyruvate kinase causes upstream accumulation of 2,3-BPG, which lowers hemoglobin oxygen affinity and improves oxygen delivery to tissues. ATP is decreased, not raised, in this enzyme defect.

Filtered hemoglobin is taken up by renal tubular cells and stored as hemosiderin, which stains blue with Prussian blue; cells shed into urine show this a few days after hemolysis starts. Myoglobin does not form Prussian blue-positive granules in tubular cells.

Warm AIHA is usually caused by IgG autoantibodies that react at 37°C, sometimes with complement fixation, and cells are removed in the spleen. A C3-only pattern is typical of cold agglutinin disease.

Mycoplasma pneumoniae infection often triggers polyclonal IgM anti-I cold agglutinins. Anti-i is linked with infectious mononucleosis, not Mycoplasma.

PCH is caused by a biphasic IgG anti-P antibody that binds in the cold and fixes complement, causing lysis on warming; it is typical in children after viral infections. PNH is an acquired stem cell defect, not antibody-mediated.

Methyldopa induces IgG autoantibodies, often with Rh specificity, that react with untreated red cells even without the drug. Penicillin causes hemolysis by the drug-adsorption mechanism, needing drug-coated cells to show reactivity.

This picture suggests thrombotic thrombocytopenic purpura, which is confirmed by severely reduced ADAMTS13 activity (usually below 10%). The DAT is useful for immune hemolysis but is negative in TTP.

In TTP, platelet-rich microthrombi form without major consumption of clotting factors, so PT, aPTT and fibrinogen stay near normal. Prolonged clotting times and low fibrinogen point to DIC.

Before about 6 months of age, HbF is still high and HbS is too low to produce turbidity, giving false negatives. Newborn and infant screening therefore uses electrophoresis or HPLC instead.

Lipemia or very high plasma proteins make the solution turbid even without HbS. Severe anemia, recent transfusion and deteriorated reagent tend to cause false negatives, not false positives.

Both HbAS and HbSS (and HbSC) give turbidity, so the amount and type of each hemoglobin must be measured to make the diagnosis. The test works in adults; its weakness is in infants, not adults.

In sickle cell trait HbA is greater than HbS, with HbS usually 35–40% and normal indices. In sickle-beta+ thalassemia HbS exceeds HbA and the cells are microcytic.

Roughly equal HbS and HbC with target cells and SC crystals is typical of HbSC disease. Sickle cell trait shows HbA and HbS, with no HbC band.

Absence of HbA with HbS present suggests HbSS or sickle-beta0 thalassemia, which must be confirmed on a repeat sample. Sickle cell trait in a newborn gives an 'FAS' pattern, with HbA present.

HbH (beta-4 tetramers) is unstable and precipitates with brilliant cresyl blue as many small inclusions. This occurs when three of four alpha genes are lost; beta-thalassemia trait does not produce HbH.

At birth HbF (alpha2 gamma2) is the main hemoglobin and does not need beta chains; when gamma production falls, the beta chain defect appears. Alpha chains are already made from fetal life, so they do not start after birth.

With no beta chains produced, HbA is absent and HbF forms most of the hemoglobin, with severe anemia. HPFH gives high HbF but little or no anemia and normal red cell indices.

Alpha-thalassemia trait does not raise HbA2 or HbF in adults, so it is confirmed by molecular methods such as gap-PCR. Repeating HbA2 will not detect an alpha-gene deletion.

Bone infarcts and poor splenic function make Salmonella a characteristic cause of osteomyelitis in sickle cell disease. N. meningitidis causes sepsis and meningitis, not typical osteomyelitis.