Direct smear Information and Courses from MediaLab, Inc.

Particle smears are also made from the unanticoagulated sample. The bone marrow particles are removed from the watchglass and placed on a coverslip. One of the following items: Pasteur pipet, capillary tube or broken end of a wooden applicator stick, may be used to transfer the particles. A second coverslip is placed over the first and the particles are crushed between the coverslips as they are pulled apart. Some practice is needed to perfect this technique. As mentioned previously, this type of preparation provides a more accurate assessment of marrow architecture and cellularity than the direct smear. Morphological detail is preserved on well made slides. The remaining sample may be added to a tube containing EDTA anticoagulant and additional smears may be made if needed.

The sample in the first syringe is quickly delivered into a watchglass or onto a slide. After the technologist verifies the presence of white-gray marrow particles in the sample, push smears and/or coverslip smears from this unanticoagulated sample are made immediately. All films should be rapidly air dried. The appearance of fat as irregular holes in the films also give the assurance that marrow and not just blood has been obtained. This type of smear is referred to as a direct smear and is usually used to evaluate morphology. Although some evaluation of cellularity and M:E ratio is possible, particle smears or biopsy sections provide a more accurate representation of these factors.

The Gram stain reaction and appearance can be used to identify most cellular material seen in a direct smear. Identification of cellular elements present in a direct clinical smear is important because most of these elements play an important role in the disease process. For example, the quality of a sputum sample can be assessed by determining the relative numbers of squamous epithelial cells and polymorphonuclear leukocytes (segmented neutrophils) present.

Identification of bacteria in direct smears may be of lifesaving importance. For example, a rapid diagnosis of bacterial meningitis, made after examining a gram stained smear of the patient's cerebrospinal fluid, allows the physician to begin treatment immediately. The appearance of bacteria on gram stained smears is suggestive of a certain species, but identification may not be made on the basis of the stain alone. An exception to this rule is the presence of gram negative intracellular diplococci from a male urogenital specimen, which is presumptive identification of Neisseria gonorrhoeae. In addition, culture results can be correlated with the direct smear report.

View control smears under oil immersion. If the control smears stained correctly, read the remainder of the smears.Look at the direct smear macroscopically to locate the stained area.Examine the direct smear under oil immersion and find an area that is properly decolorized.Examine at least ten fields in an area that is properly decolorized.Identify the following nonbacterial cell types: epithelial cells, white blood cells, red blood cells, yeast and hyphae.Look for microorganisms and record their characteristics.Quantitate each type of element found and record on the work card.Interpret the direct smear result.Report the direct smear finding.

Epithelial cells in large numbers within sputum smears means that the specimen is predominantly oral saliva, rather than true sputum from the lung. Epithelial cells in urine smears indicate that the sample has been contaminated by organisms found on the vulva or distal urethra. Bacteria found near or on epithelial cells are usually normal contaminating bacterial flora.White blood cells indicate inflammation and possible infection. The direct smear examination should focus within and around these cells.Red blood cells in a direct smear are not usually significant.Yeast may be present as normal flora in upper respiratory tract or genital tract. They may be significant if they predominate, or if budding yeast forms are seen.Hyphae are more likely to indicate the presence of fungal infection, but this determination requires correlation with clinical findings.Bacteria found in spinal fluid, blood, tissue and specimens from other sterile sites are always significant.Body fluids which are normally sterile must be examined carefully. If only one organism per oil immersion field is identified, then there are about 105 organisms per mL present in the sample! Bacteria observed in specimens from the throat, genital tract and other areas containing normal flora suggest infection only if their composition and type varies significantly from the norm.

Direct smear results are generally reported in the same way that they are read, except that bacterial cell arrangement (ex: clusters, chains, pairs) may be misleading and is generally not reported except in the case of intracellular diplocci in genital smears.