Wintrobe's Clinical Hematology 14e SC

Part 1 LABORATORY HEMATOLOGY

Section 1 Chapter 1  ■ 

Examination of the Blood and Bone Marrow

KRISTI J. SMOCK

INTRODUCTION

Thus, data such as patient age, gender, and time of specimen collection

as well as pertinent correlative clinical information should be noted.

Most often, blood is collected by venipuncture into vacuum collection tubes containing anticoagulant. 7 The three most commonly used antico-

Since the advent of microscopy several hundred years ago, there have been

continual advances in our ability to identify and quantify the components

agulants are tripotassium or trisodium salts of ethylenediaminetetraacetic

of blood and bone marrow. One important advance was the invention

acid (EDTA), trisodium citrate, and heparin. EDTA is the preferred anti-

of the Coulter counter in the 1950s, which allowed accurate automated

coagulant for blood counts because it produces complete anticoagulation

counting of large numbers of cells. In the present time, evaluation of blood

with minimal morphologic and physical effects on cells. Heparin causes

and bone marrow counts and morphology, along with important ancillary

a bluish colorati n of the background when a blood smear is stained

studies, are essential for accurate diagnosis of hematologic disorders and

with Wright-Giemsa, but does not affect cell size or shape. Heparin is

for monitoring disease progression and response to therapy. This chapter

often used for red cell testing and functional or immunologic analysis of

introduces the fundamental concepts and limitations that underlie labora-

leukocytes. Trisodium citrate is the preferred anticoagulant for platelet

tory evaluation of the blood and bone marrow and introduces additional

and coagulation studies. Anticoagulated blood may be stored at 4°C for

testing that may aid in evaluating hematologic disorders.

a 24-hour period without significantly altering cell counts or cellular morphology. 4 However, it is preferable to perform hematologic analysis

Blood elements include erythrocytes (red blood cells [RBCs]), leu-

kocytes (white blood cells [WBCs]), and platelets. RBCs are the most

Laboratory Hematology

as soon as possible after the blood is obtained.

numerous cells in the blood and are required for tissue respiration. RBCs

lack nuclei and contain hemoglobin (Hg), an iron-containing protein that

RELIABILITY OF TESTS

transports oxygen and carbon dioxide. WBCs include a variety of cell

types that have specific immune functions and characteristic morphologic

appearances. WBCs are nucleated and include neutrophils, lymphocytes,

In addition to proper acquisition of specimens, data reliability requires

monocytes, eosinophils, and basophils. Platelets are cytoplasmic fragments

accurate and precise testing methods. Both manual and automated testing

derived from bone marrow megakaryocytes that functio in hemostasis.

of hematologic specimens must be interpreted in light of expected test

Blood evaluation requires quantification of the cellular elements

accuracy and precision (reproducibility), particularly when evaluating

by either manual or automated methods. Automated methods are more

the significance of small changes. Accuracy is the difference between

commonly used, are more precise than manual procedures, and provide

the measured value and the true value, which implies that a true value is

additional data regarding cellular characteristics. Automated methods

known. Clearly, this may present difficulties when dealing with biologic

also require less technical time and minimize the possibility of human

specimens. The Clinical and Laboratory Standards Institute (CLSI),

error. However, the automated measurements describe average cellular

formerly the National Committee for Clinical Laboratory Standards, has

characteristics, but do not adequately describe the variability of individual

developed standards to assess the performance characteristics of auto- mated blood cell analyzers. 8 Automated instrumentation requires careful

values. For example, a bimodal population of small (microcytic) and

large (macrocytic) RBCs might be reported as average normal cell size.

calibration and regular quality control and quality assurance procedures

Therefore, a thorough blood examination also requires microscopic eval-

to reach expected performance goals for accuracy and reproducibility.

uation of a stained blood film to complement hematology analyzer data.

CELL COUNTS

SPECIMEN COLLECTION

As previously mentioned, cell counts are obtained manually or by au-

Proper specimen collection is essential for acquisition of accurate labo-

tomated hematology analyzers. Because blood contains large numbers

ratory data for hematologic specimens. Before a specimen is obtained,

of cells, sample dilution is required for accurate analysis. The type

careful thought as to what studies are needed will aid in optimal collec-

of diluent depends on the cell type to be enumerated. RBC counts

tion of samples. Communication with laboratory personnel is helpful

require dilution with an isotonic medium, whereas for WBC or platelet

in ensuring proper handling and test performance.

Copyright © 2019 Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. Anumber of preanalytical factors may affect hematologic measure- ments, and specimens should be collected in a standardized manner to reduce data variability. For example, patient activity, level of hydration, counts, a diluent that lyses the more numerous RBCs is used to simplify counting and avoid errors. The highest degree of precision occurs when a large number of cells are evaluated. Clearly, automated methods are

superior to manual methods for counting large numbers of cells and

medications, gender, age, race, smoking, and anxiety level may signifi- cantly affect hematologic parameters. 1-3 Similarly, the age and storage conditions of the specimen may affect the quality of the data collected. 4-6

minimizing statistical error. A recent comparison of five common he-

matology analyzers showed good between-instrument concordance for

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