[The hematological laboratory of clinical practice].

The spectrum of analyses of a hematological laboratory comprises the counts of erythrocytes, leukocytes and platelets, the determinations of the hemoglobin concentration and of the hematocrit, the calculation of the red cell indices and the microscopic examination of the blood film. The determination of white blood cells, platelets, hematocrit and MCV as well as staining of the blood film should be performed within two hours after blood sampling. The hemoglobin concentration, red-cell count and MCH value remain constant for five days, provided that the blood samples is stored at 4 degrees C. The recognition of morphologically 'minor' pathological findings is important in view of the possible clinical significance that they might have. In the case of thrombotic-thrombocytopenic purpura, for instance, it is very important that the fragmentocytes are recognized and recorded. The grading of pathological findings by use of +, ++, is based on strict limits of ranges. Quality control and quality assurance are integral parts of the daily laboratory performance; moreover, the importance of external quality control in morphological hematology is stressed as being a challenge to the hematological laboratory technologist.