The next concept—scale, proportion, and quantity—concerns the sizes of things and the mathematical relationships among disparate elements. The next four concepts—systems and system models, energy and matter flows, structure and function, and stability and change—are interrelated in that the first is illuminated by the other three. Each concept also stands alone as one that occurs in virtually all areas of science and is an important consideration for engineered systems as well. Regardless of the labels or organizational schemes used in these documents, all of them stress that it is important for students to come to recognize the concepts common to so many areas of science and engineering.
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: The presence of unexplained jaundice, particularly if unconjugated hyperbilirubinemia is also present, is an additional reason for a blood-smear examination.
Laboratory-initiated examinations of blood smears for patients with anemia are usually the result of a laboratory policy according to which a blood smear is ordered whenever the hemoglobin concentration is unexpectedly low.
This policy should be encouraged, since the consideration of the blood smear and the red-cell indices is a logical first step in the investigation of any unexplained anemia ref.
Initiating a smear as a reflex test also means that a further blood sample does not have to be taken for this purpose.
Modern automated instruments impart valuable information about the nature of anemia. These variables usually include the RDW, which correlates on a blood smear with anisocytosis, and they may also include the hemoglobin-distribution width and the percentages of hypochromic and hyperchromic cells, which correlate with anisochromasia, hypochromia, and hyperchromia.
A variety of histograms and scatterplots give a visual representation of red-cell characteristics. It may be possible to detect increased numbers of hyperchromic cells spherocytes or irregularly contracted cellssmall hyperchromic cells microspherocyteshypochromic microcytic cells, large normochromic cells normally hemoglobinized macrocytesand hypochromic macrocytes either reticulocytes or dysplastic red cells.
Despite this wealth of information, there are still morphologic abnormalities that are critical in the differential diagnosis of anemia and that can be determined only from a blood smear. Some types of hemolytic anemia yield such a distinctive blood smear that the smear is often sufficient for diagnosis.
This is true of hereditary elliptocytosis which is only infrequently associated with anemia; numerous elliptocytes and smaller numbers of ovalocyteshereditary pyropoikilocytosis striking poikilocytosis, with elliptocytes, ovalocytes, and fragmentsand Southeast Asian ovalocytosis moderate poikilocytosis, with the poikilocytes including several macro-ovalocytes.
The presence of spherocytes is not diagnostically specific, since this may result from hereditary spherocytosis numerous spherocytes hyperchromatic cells with a regular outlineor immune hemolytic anemia.
Nevertheless, consideration of the clinical features, together with the results of a direct antiglobulin test, in patients with spherocytes will generally indicate the correct diagnosis. Microangiopathic hemolytic anemia resulting from cyclosporine therapy shows numerous red-cell fragments.
Microspherocytes may be present in low numbers in patients with a spherocytic hemolytic anemia but are also characteristic of burns and of microangiopathic hemolytic anemia. In microangiopathic hemolytic anemia, examination of the blood smear is also important to validate the platelet count, since red-cell fragments and platelets may be of similar size.
Most automated instruments cannot make this distinction. A minority of automated instruments that measure both the size and the refractive index of small particles in the blood sample can make this distinction and can be used to exclude red-cell fragmentation; however, although the fragment "flag" on such instruments is sensitive, it is not specific.
Hence, a blood smear is still advised for validation ref. Blood-smear features similar to those seen in microangiopathic hemolytic anemia are also a feature of mechanical hemolytic anemia, such as that associated with a leaking prosthetic valve, and provide important evidence of this cause of hemolytic anemia.
A blood smear is particularly important in the diagnosis of acute hemolysis induced by oxidant damage. The characteristic feature is the presence of keratocytes, or "bite" cells, "blister" cells, and irregularly contracted cells; the latter must be distinguished from spherocytes because of the quite different diagnostic significance.
These irregularly contracted cells share with spherocytes the lack of central pallor but differ in that they have an irregular outline.
Oxidant-induced hemolysis is most often seen in glucosephosphate dehydrogenase G6PD deficiency but can also occur with other defects in the pentose shunt or in glutathione synthesis and when oxidant exposure overwhelms normal protective mechanisms.Investigative Reporting. In the seventeenth century the puritans lived through relationships, religion, community, discipline and punishment in a way that would bring honor and glory to God.
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