Blood smear

BLOOD SMEARSRAJESH MOHESS, CLT

BLOOD SMEARS• Peripheral blood smear is a very important tool in the

hematology lab

• It provides rapid, reliable access to information about a variety of hematologic disorders

• Examination of the peripheral blood smear is an inexpensive but powerful diagnostic tool in both children and adults

• The smear offers a window into the functional status of the bone marrow

• Review of the smear is an important adjunct to other clinical data; in some cases, the peripheral smear alone is sufficient to establish a diagnosis

BLOOD SMEARS• An examination of the blood smear (or film) may be

requested by physicians based on medical history or initiated by laboratory staff as part of their protocol

• Majority of cases for blood smears are from laboratory protocol

• 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 to 15 percent or less.

• Nevertheless, the blood smear remains a crucial diagnostic aid

BLOOD SMEARS• For a true morphological interpretation, a trained

person is required to review the smear, as automation in hematology will normally generalize the morphology

• 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

BLOOD SMEARS• Not all hematological disorder requires a

peripheral blood smears for diagnosis.

• Some conditions can be diagnosed by other laboratory data also.

• For example, Iron deficiency anemia can be diagnosed by MCV, iron and ferritin levels

BLOOD SMEARS• 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.

• More often, the smear is an important tool in the provision of a differential diagnosis and the indication of further necessary tests.

• The blood smear can have an important part in the speedy diagnosis of certain specific infections.

• Otherwise, its major roles are in the differential diagnosis of anemia and thrombocytopenia and in the identification and characterization of leukemia and lymphoma.

BLOOD SMEARSAnemia:

• In patients with anemia, physician-initiated examinations of blood smears are usually performed in response to clinical features or to a previously abnormal complete blood count

• 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

BLOOD SMEARSHemolytic Anemia:

• In the hemolytic anemias, red-cell shape is of considerable diagnostic importance.

• 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, and ovalocytosis.

• The presence of bite cells points to a Heinz body hemolytic anemia

BLOOD SMEARSMacrocytic Anemia:

• Patients with vitamin B12 or folic acid deficiency, the blood smear shows macrocytes.

• It may also show oval macrocytes and hypersegmented neutrophils.

• When the anemia is more severe, there may be marked poikilocytosis, with teardrop and red-cell fragments

BLOOD SMEARS

Microcytic Anemia:

• Blood smear not very significant in diagnosis, although very useful.

• Most common cause is iron deficiency anemia which can be diagnosed by other blood tests

Sickle cells/Thalassemia:

• A blood smear is useful. Usually shows target cells sickle cells

BLOOD SMEARSThrombocytopenia/Thrombocytosis:

• A blood smear should always be examined for patients with thrombocytopenia.

• This is done to both confirm the thrombocytopenia and to look for the underlying cause.

• Falsely low platelet counts may be the result of small clots, platelet clumping, platelet satellitism or abnormally large platelets

BLOOD SMEARSWhite Cell Disorders

(Leukemia/Lymphoma/Bone Marrow Failure):

• The precise disease classification may rely upon evaluation of abnormal circulating cells.

• Blood smears must always be examined when there is unexplained leukocytosis, lymphocytosis, or monocytosis or when the flagging system of an automated instrument suggests the presence of blast cells

• For example, the presence of Auer rods in a blast form in patients with acute myeloid leukemia

BLOOD SMEARSThe role of the blood smear in the diagnosis of leukemia and lymphoma is to suggest:

• A likely diagnosis or range of diagnoses

• To indicate which additional tests should be performed

• To provide a morphologic context without which immunophenotyping and other sophisticated investigations cannot be interpreted

BLOOD SMEARSSummary

• The blood smear remains an important diagnostic tool, even in this age of molecular analysis

• Physicians may and should request a blood smear when there are clinical indications for it.

• The Laboratory technologist should make and examine a blood smear whenever the results of the CBC indicate that a blood smear is necessary for the validation or to further investigate an abnormality

• To avoid errors and miss any diagnoses, hematological disorders should be investigated by both clinical data and the peripheral smear

PREPARATION OF A BLOOD SMEARPrinciple:

• A peripheral smear may be requested by the clinician. • It may also be performed as part of the laboratory

protocol from reflex or if there are discrepancies from prior results.

• We will discuss the ‘Wedge Smear’• Smears are prepared by placing a drop of blood on a

clean glass slide and spreading the drop using another glass slide at an angle.

• The slide is then stained and observed microscopically, mainly to determine differential count and morphology study

PREPARATION OF A BLOOD SMEARPrinciple:

• A well-stained peripheral smear will show the red cell background as red orange.

• White cells will appear with blue purple nuclei with red purple granules throughout the cytoplasm.

• A well made, well distributed peripheral smear will have a counting area at the thin portion of the wedge smear which is approximately 200 red cells not touching.

• A good counting area is an essential ingredient in a peripheral smear for evaluating the numbers of and types of white cells present and evaluating red cell and platelet morphology.

PREPARATION OF A BLOOD SMEARPrinciple:

• Functions of the peripheral blood smear are:

- provide information for diagnosis

- provide information for further testing or to establish diagnosis

- used as a guide for therapy

- Used as an indicator to monitor the harmful effects for chemotherapy and radiation therapy

PREPARATION OF A BLOOD SMEARMaterials:

- Glass slides

- Applicator sticks

- Capillary tubes

- EDTA specimen (smear should be made within 4 hours of blood collection)

- Capillary blood specimen collected in heparinized tubes

BLOOD SMEAR PROCEDURE• Mix blood properly

• Place a small drop of blood (about 2-3 mm) about 1 cm from the frosted end of a clean slide (slide must be completely clean)

• Using a spreader (another slide), draw backwards into the drop of blood (while applying pressure) – maintain an angle of 30-45 degrees

BLOOD SMEAR PROCEDURE• When the spreader touches the blood, allow the

blood to spread across the edge of the spreader

• Move the spreader forward on the slide (in one smooth motion), so a smear is made approximately 3 to 4 cm in length.

• The smear should be half the size of the slide, with no ridges, and a “feather edge” should be toward the end of the smear.

BLOOD SMEAR PROCEDURE

BLOOD SMEAR PROCEDURE• Label the frosted end of the slide with the

patient’s last name and first initial, specimen number, and the date

• Allow the smear to air dry completely (about 5 minutes)

• Specimen can now be stained

BLOOD SMEAR PROCEDURE

BLOOD SMEARGood smear

A good smear should have the following appearance:

• Appear smooth and uninterrupted

• Start thick and gradually thinning out (feather-edge)

• The film should take up ½ to ¾ the length of the slide

BLOOD SMEAR LIMITATIONS

• The angle between the slides is dependent upon the size of the blood drop and viscosity of the blood. The optimal angle is 45 degrees

• The larger the drop of blood and lower the hematocrit, the higher the angle needs to be so the blood smear is not too long

• Blood with a higher hematocrit needs to have a lower angle so the smear is not too short and thick

• Glass slides must be clean; otherwise, this results in imperfect distribution of cells and improper staining

• Smears should not be made from blood remaining on the tube stopper as the lubricant on the stoppers can interfere with the drying process

BLOOD SMEAR LIMITATIONS• Once the drop of blood has contact on the slide, the smear

needs to be made immediately.

• Otherwise, the blood will clump and dry, again resulting in uneven distribution of WBC and platelets (granulocytes will accumulate at the edges)

POOR SMEARSPoor smears can results from a number of reasons, such as:

• Too large or small blood drop

• Not pushing the spreader in an even motion

• Pressing down heavily on the spreader

• Too great or small an angle of the spreader

• Speed of stroke used to move the spreader

• Clots in the blood

• Dirty (oily) slides

BLOOD SMEAR

BLOOD SMEAR

BLOOD SMEAR

THE END