How Do I Obtain a Valid White Count When My Patient's White Count Is Outside of the Linearity Range?
Consider the case study presented earlier in this chapter. The white count is 199 X 109/L, which is out of the linearity range. Special techniques must be used by the technologist to obtain a valid white count on this sample. The technologist will notice that the white count is seen as a vote out + + + + on the automated screen, and this is the first alert that the count may be too high (out of the linearity range) to be recorded by the instrument. The first step is to dilute a small amount of the patient's sample, usually 1:2 dilution, and re-run it to see if a number can be obtained. If this dilution is still out of range then several more dilutions are tried until a reading can be obtained. Once a reading is obtained, then the technologist must remember to multiply by the dilution factor to obtain an accurate white count. The white count will be a critical value and must be called and reported to a responsible party. Additionally, each of the other parameters of the CBC must be examined to evaluate whether they are credible. The troubleshooting case in Chapter 11 outlines each of the steps necessary to resolve the total CBC on a troublesome patient such as this, examining each CBC parameter and the resolution steps. Although each of these procedures seems exhaustive, they are necessary to give the physician an accurate account of this patient's CBC.
WORD KEY Gout • Arthritic disorder marked by crystal formation
^ r i n (usually uric acid) in the joints or tissues
Clonal • Disease arising from a single cell
Deep vein thrombosis • Formation of a blood clot in the Hyperplasia • Increase in the number of cells in the bone deep veins of the legs, arms, pelvis, etc. marrow
202 Part III • White Cell Disorders
Myelofibrosis • Increase in the reticulin or fibrotic tissue in the bone marrow.
Myeloproliferative • Disease that results in the uncontrolled overproduction of normal-appearing cells in the absence of an appropriate stimulus
Organomegaly • Enlargement of the organs
Osteosclerosis • Abnormal increase in the thickening or density of bone
Plethora • Excess blood volume Pruritus • Itching
Therapeutic phlebotomy • Withdrawing blood for a medical purpose
Transient ischemic attack • Neurological defect, having a vascular cause, producing stroke symptoms that resolve in 24 hours
Trisomy • In genetics, having three homologous chromosomes instead of two
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