Table of contents :

  • RBC inclusions
  • poikilocytes
  • erythroblastosis
  • reticulocytosis
  • reticulocytopenia
  • basophilia
  • anemia
  • hypoproliferative anemias
  • myelophthisis
  • impaired DNA synthesis
  • impaired HSC
  • aplastic anemia
  • congenital dyserythropoietic anemias (CDA)
  • erythroblastopenia
  • anemia of chronic diseases (ACD)
  • megaloblastic anemias
  • pernicious anemia
  • folic acid deficiency
  • impaired hemoglobin synthesis
  • iron deficiency (sideropenic anemia) 
  • sideroblastic anemia
  • porphyrias
  • myelodysplastic syndromes (MDS)
  • thalassemias
  • hemolytic anemia
  • hemoglobinopathies
  • sickle cell disease
  • structural protein defects
  • microangiopathic hemolytic anemia
  • polycythemia
  • absolute
  • relative

  • An examination of the blood smear (or film) may be requested by physicians or initiated by laboratory staff. With the development of sophisticated automated blood-cell analyzers, the proportion of blood-count samples that require a blood smear has steadily diminished and in many clinical settings is now < 10-15%. Nevertheless, the blood smear remains a crucial diagnostic aid. The proportion of requests for a complete blood count that generate a blood smear is determined by local policies and sometimes by financial and regulatory as well as medical considerations. For maximal information to be derived from a blood smear, the examination should be performed by an experienced and skilled person, either a laboratory scientist or a medically qualified hematologist or pathologist. In Europe, only laboratory-trained staff members generally "read" a blood smear, whereas in the USA, physicians have often done this. Increasingly, regulatory controls limit the role of physicians who are not laboratory-certified. Nevertheless, it is important for physicians to know what pathologists or laboratory hematologists are looking for and should be looking for in a smear. In comparison with the procedure for an automated blood count, the examination of a blood smear is a labor-intensive and therefore relatively expensive investigation and must be used judiciously. A physician-initiated request for a blood smear is usually a response to perceived clinical features or to an abnormality shown in a previous CBC. A laboratory-initiated request for a blood smear is usually the result of an abnormality in the CBC or a response to "flags" produced by an automated instrument. Less often, it is a response to clinical details given with the request for a CBC when the physician has not specifically requested examination of a smear. For example, a laboratory might have a policy of always examining a blood smear if the clinical details indicate lymphadenopathy or splenomegaly. The International Society for Laboratory Hematology (ISLH) has published consensus criteria for the laboratory-initiated review of blood smears on the basis of the results of the automated blood count. The indications for smear review differ according to the age and sex of the patient, whether the request is an initial or a subsequent one, and whether there has been a clinically significant change from a previous validated result (referred to as a failed delta check). All laboratories should have a protocol for the examination of a laboratory-initiated blood smear, which can reasonably be based on the criteria of the International Society for Laboratory Hematology. Regulatory groups should permit the examination of a blood smear when such protocols indicate that it is necessary. There are numerous valid reasons for a clinician to request a blood smear, and these differ somewhat from the reasons why laboratory workers initiate a blood-smear examination. Sometimes it is possible for a definitive diagnosis to be made from a blood smear. Clinical indications for examination of a blood smear :

    Occasionally, a blood smear leads to a fortuitous diagnosis that can be very important to the patient. As an example, the detection of features of unexpected hyposplenismmay suggest a congenital absence of the spleen, splenic atrophy, deposition of amyloid in the spleen, infiltration of neoplastic cells (e.g., in leukemia, lymphoma, or carcinoma) in the spleen, previous splenic infarction, or even a splenectomy of which the patient was unaware — in each case putting the patient at risk for complications of hyposplenism. Conversely, the failure to observe expected hyposplenism in a blood smear from a patient who has undergone splenectomy for the treatment of autoimmune thrombocytopenic purpura may indicate that there is functioning residual splenic tissue, either from splenosis or from accessory spleens, that may be responsible for a relapse of the disease. Sometimes the blood smear provides the primary or the only evidence of a specific diagnosis, such as myelodysplastic syndrome, leukemia, lymphoma, or hemolytic anemia. It is important that, if possible, such blood smears be stored over the long term, just as a tissue that provides a histologic diagnosis is stored over the long term. In practice, such storage is easily achieved if a patient has also had a bone marrow aspirate (since a blood smear should always be stored with an aspirate), but it is harder to achieve if the peripheral blood smear alone has provided the diagnosis. Individual laboratories should have a mechanism to make possible the retention of such smears or an image derived from them. Some laboratories retain all smears that have been reviewed by a laboratory hematologist or pathologist; this can create a storage problem, and it is likely that, increasingly, digital images of important abnormal smears will be stored. The continuing importance of the blood smear is highlighted by the recent introduction of photographs of blood smears as a regular feature in both the journal Bloodref and the British Journal of Haematology, by ongoing efforts to develop image-recognition technology for the automated examination of blood smears, and by the development of telehematology to permit the remote interpretation or second opinions of blood smearsref1, ref2. Even in the age of molecular analysis, the blood smear remains an important diagnostic tool. Physicians should request a blood smear when there are clinical indications for it. Members of the laboratory staff should make and examine a blood smear whenever the results of the complete blood count indicate that a blood smear is essential for the validation or the further elucidation of a detected abnormality. If error is to be avoided, sophisticated modern investigations of hematologic disorders should be interpreted in the light of peripheral-blood features as well as the clinical contextref Alterations from prolonged storage of RBCs : increased in lactic acid and ammonium, reduction in ATP and 2,3-DPG.

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