血常规-英文

Complete blood count

From Wikipedia, the free encyclopedia

A

complete blood count

(

CBC

), also known as a

complete blood cell count

,

full blood

count

(

FBC

),

or

full

blood

exam

(

FBE

),

is

a

blood

panel

requested

by

a

doctor

or

other

medical professional

that gives

information about the cells

in a patient's

blood

, such

as

the

cell

count

for

each

cell

type

and

the

concentrations

of

various

proteins

and

minerals.

A

scientist

or

lab

technician

performs

the

requested

testing

and

provides

the

requesting medical professional with the results of the CBC.

Blood counts of various types have been used for clinical purposes since the 19th century.

Automated equipment to

carry out complete blood counts was

developed

in

the

1950s

and 1960s.

[1]

The

cells

that

circulate

in

the

bloodstream

are

generally

divided

into

three

types:

white

blood

cells

(

leukocytes

),

red

blood

cells

(

erythrocytes

),

and

platelets

(

thrombocytes

).

Abnormally high or low counts may indicate the presence of many forms of disease, and

hence blood counts are amongst the most commonly performed

blood tests

in medicine,

as they can provide an overview of a patient's general health status. A CBC is routinely

performed during annual

physical examinations

in some jurisdictions.

Medical uses

[

edit

]

Complete blood counts are done to monitor overall health, to

screen

for some diseases, to

confirm a diagnosis of some medical conditions, to monitor a medical condition, and to

monitor changes in the body caused by medical treatments.

[2]

For patients who need

blood transfusion

, a blood count may be used to get data which

would help plan an amount of treatment.

[3]

In such cases, the person should have only one

blood

count

for

the

day,

and

the

transfusion

of

red

blood

cells

or

platelets

should

be

planned

based

on

that.

[3]

Multiple

blood

draws

and

counts

throughout

the

day

are

an

excessive use of phlebotomy and can lead to unnecessary additional transfusions, and

the extra unnecessary treatment would be outside of

medical guidelines

.

[3]

Procedure

[

edit

A

phlebotomist

collects

the

sample

through

venipuncture

,

drawing

the

blood

into

a

test

tube

containing

an

anticoagulant

(

EDTA

,

sometimes

citrate

)

to

stop

it

from

clotting

.

The

sample is then transported to a

laboratory

. Sometimes the sample is drawn off a finger

prick using a

Pasteur pipette

for immediate processing by an automated counter.

In the past, counting the cells in a patient's blood was performed manually, by viewing a

slide

prepared

with

a

sample

of

the

patient's

blood

(a

blood

film

,

or

peripheral

smear)

under

a

microscope

.

Presently,

this

process

is

generally

automated

by

use

of

an

automated analyzer

, with only approximately 10

–

20% of samples now being examined

manually.

CBC being performed in a hospital using an

Abbott

Cell-Dyn 1700 automatic analyzer.

Complete blood count performed by an

automated analyser

. Differentials not seen here.

Automated

[

edit

]

Most blood counts today include a CBC count and leukocyte differential count (LDC) (that

is, not just the total WBC count but also the count of each WBC type, such as neutrophils,

eosinophils,

basophils,

monocytes,

and

lymphocytes).

More

sophisticated

modern

analyzers

can

provide

extended

differential

counts,

which

include

hematopoietic

progenitor cells, immature granulocytes, and erythroblasts.

[4]

The blood is well mixed (though not shaken) and placed on a rack in the analyzer. This

instrument has flow cells, photometers and apertures that analyze different elements in

the blood. The cell counting component counts the numbers and types of different cells

within the blood. The results are printed out or sent to a computer for review.

Blood counting machines aspirate a very small amount of the specimen through narrow

tubing followed by an aperture and a laser flow cell. Laser eye sensors count the number

of cells passing through the aperture, and can identify them; this is

flow cytometry

. The two

main

sensors

used

are

light

detectors

and

electrical

impedance

.

The

instrument

measures the type of blood cell by analyzing data about the size and aspects of light as

they

pass

through

the

cells

(called

front

and

side

scatter).

Other

instruments

measure

different characteristics of the cells to categorize them.

Because an automated cell counter samples and counts so many cells, the results are

very precise. However, certain abnormal cells in the blood may not be identified correctly,

requiring manual review of the instrument's results and identification of any abnormal cells

the instrument could not categorize.

In addition to counting, measuring and analyzing red blood cells, white blood cells and

platelets, automated hematology analyzers also measure the amount of

hemoglobin

in the

blood and within each red blood cell. This is done by adding a diluent that lyses the cells

which is then pumped into a spectro-photometric measuring

cuvette

. The change in color

of the

lysate

equates to the hemoglobin content of the blood. This information can be very

helpful to a physician who, for example, is trying to identify the cause of a patient's

anemia

.

If the red cells are smaller or larger than normal, or if there is a lot of variation in the size of

the

red

cells,

this

data

can

help

guide

the

direction

of

further

testing

and

expedite

the

diagnostic process so patients can get the treatment they need quickly.

Manual

Hemocytometers

(counting

chambers that hold a specified

volume

of diluted blood

and

divide it with grid lines) are used to calculate the number of red and white cells per litre of

blood. (The dilution and grid lines are needed because there are far too many cells without

those aids.)

To identify the numbers of different white cells, a

blood film

is made, and a large number

of white blood cells (at least 100) are counted. This gives the percentage of cells that are

of each type. By multiplying the percentage with the total number of

white blood cells

, the

absolute number of each type of white cell can be obtained.

Manual

counting

is

useful

in

cases

where

automated

analyzers

cannot

reliably

count

abnormal cells, such as those cells that are not present in normal patients and are only

seen

in

peripheral

blood

with

certain

haematological

conditions.

Manual

counting

is

subject

to

sampling

error

because

so

few

cells

are

counted

compared

with

automated

analysis. A manual count will also give information about other cells that are not normally

present in peripheral blood, but may be released in certain disease processes.

Medical technologists examine blood film via a microscope for some CBCs, not only to

find

abnormal

white

cells,

but

also

because

variation

in

the

shape

of

red

cells

is

an

important

diagnostic

tool.

Although

automated

analysers

give

fast,

reliable

results

regarding the number, average size, and variation in size of red blood cells, they do not

detect

cells'

shapes.

Also,

some

normal

patients'

platelets

will

clump

in

EDTA

anticoagulated blood, which causes automatic analyses to give a falsely low platelet count.

The person viewing the slide in these cases will see clumps of platelets and can estimate

if there are low, normal, or high numbers of platelets.

Manual blood counts use a

light microscope

, usually with a specialized

microscope slide

, which is

called a

hemocytometer

.