Blood smear evaluation is perhaps the most important yet often overlooked aspect of a point-of-care CBC. With the point-of-care CBC, a blood smear examination is as diagnostically valuable as numerical cell counts. It is thus imperative that a properly prepared diagnostic blood smear be a component of the in-house CBC.
In busy practices, both clinicians and the technical staff may feel that they do not always have the time to prepare and examine blood smears from their patients. However, both clinicians and technicians can easily be trained to make diagnostic blood smears with little time and effort. Mastering a proper blood smear technique enables the clinician to offer additional in-house diagnostic patient care. Even clinicians who do not personally plan to microscopically examine blood smears should not discount the benefits of knowing how to produce a smear. This knowledge is especially handy if, for example, the diagnostic laboratory requests a fresh, unstained blood smear in addition to the original anticoagulated blood sample.
Several techniques have been described-the following step-by-step process illustrates a routine version of the procedure. Remember, the learning process can be frustrating, so practice as much as possible, and the procedure will eventually become second nature.
Before you make the blood smear, have everything you need handy to expedite the process. Smears should be made as soon as possible after blood collection (ideally within an hour) to preserve the quality of the blood cells. Waiting too long to prepare the smear may lead to blood cell deterioration, platelet clumping, excessive erythrocyte sedimentation, and potential loss of blood cell parasites.
What You Will Need
• Anticoagulated blood sample (EDTA preferable) • Plain microhematocrit tubes without anticoagulant • Clean, noncoated microscopic glass slides (frosted end preferable) • Gauze sponges or similar material • Wright or modified Wright cytologic stain, such as Diff Quik • Gloves to avoid exposure to blood proteins (optional but good practice) • Blood tube mixer (optional) • Blood tube rack (optional)
Before handling the blood sample, place two to four (or more if you are practicing) glass slides and one to two microhematocrit tubes on a clean surface for easy availability. It is also a good idea to have gauze and a blood tube rack readily accessible.
How to Obtain a Diagnostic Blood Smear