The differential diagnosis of hemolytic anemias.

The differential diagnosis of haemolytic anaemias is difficult. It requires a wide clinical knowledge, complete command of a wide range of laboratory techniques and imagination. However, it is possible to base a system for differential diagnosis on no more than five basic tests. These are:i. Examination of a properly stained thin blood film, stained so that the cells are orange, but show polychromasia as a greyish tinge. This requires a buffered diluting fluid which has been carefully tested. Smears too thick, or stained dull grey, are quite useless, and it is usually much easier to obtain good staining with Leishman's stain (from British Drug Houses) than from any other brand, or from other Romanowsky stains such as Giemsa or Wright's stain (Discombe, 1950). A well-stained film may indicate spherocytosis, target cells, hypochromic cells, burr cells, or other odd forms. One should remember that severe carbon dioxide retention, or other acidosis, will make cells increase in diameter by as much as I IA, while obstructive jaundice causes target cells to appear. 2. Examination of blood spread out between two coverslips coated with brilliant cresyl blue. In this the reticulocytes can be counted (and it is unusual'for an anaemia to be due solely to haemolysis unless the reticulocytes exceed 2 per cent.), Heinz bodies searched for, Haemoglobin H precipitates seen, and some indication of the shape of the erythrocytes obtained. It is imperative that the blood be examined wet, after at least 20 min. incubation, and that the stain should be known to be effective in staining reticulocytes. This examination is so important that it should never be deputed entirely to a technician, unless he is exceptionally experienced. From this examination may be obtained the clues which lead to a diagnosis of several acute haemolytic episodes, such as those due to some poisons, drugs, favism and changes in the thickness of red cells. 3. Examination of urine for haemosiderin is easy, for the deposit is mixed with equal parts of 2 per cent. potassium ferrocyanide and N hydrochloric acid, and after io min. centrifuged again and the deposit examined wet. Profuse green granules, especially within cells or casts, indicate a chronic process in whieh haemoglobin has been liberated into the blood stream and leaked into the unne; this is usually paroxysmal nocturnal haemoglobinuria (P.N.H.). Of course, stringent precautions must be taken against contaXnination, but contaminating iron is usually in irregular lumps, not the tiny spherical granules of haemosiderin. 4. The direct antiglobulin test should be performed on cells which have been allowed to' cool to about 40C. in contact with their serum, and the washed cells should be tested with antiglobulin serum at one, two, four and possibly eight times the concentration normally used for the demonstration of Rhesus antibodies. If positive, the test should be repeated using cells which have been taken in a warm syringe and at once washed with large volumes of saline previously warmed to 370C., and with normal cells incubated in the patient's serum obtained from blood which has never been allowed to cool below 370C., so that the quality and quantity of the antibody may be further assessed. 5. The only common haemoglobinopathies are those causing sickling and thalassaemia. The former is quickly detected by mixing cells with