3. PERIPHERAL BLOOD SMEAR
• DEFINATION:- A blood film or peripheral blood smear is a thin layer of
blood smeared on a microscope slide and then stained in such a way
to allow the various blood cells to be examined microscopically.
4. AIM OF BLOOD SMEAR
• Blood films are usually examined to investigate hematological
problems and, occasionally, to look for parasites within the blood
such as malaria and filarial.
• Examination of thin blood films is important in the investigation and
management of anemia, infections, and other conditions which
produce changes in the appearance of blood cells and differential
white cell count.
• A blood film report can provide rapidly and at low cost, useful
information about a patient’s condition.
5. The peripheral blood film is of two types:
• Thin blood film
• Thick blood film
• THREE BASIC STEPS TO MAKE BLOOD FILM
• Preparation of blood smear
• Fixation of blood smear
• Staining of blood smear
6. BLOOD FILM PREPARATION
• Blood films are made by placing a drop of blood on one end of a
slide,and using a spreader slide to disperse the blood over the slide’s
length.
• The aim is to get a region, called a mono layer, where the cells are
spaced far enough apart to be counted and differentiated.
• The monolayer is found in the “feathered edge” created by the
spreader slide as it draws the blood forward.
• The slide is left to air dry, after which the blood is fixed to the slide by
immersing it briefly in methanol.
• The fixative is essential for good staining and presentation of cellular
detail.
7. BLOOD FILM PREPARATION
• After fixation, the slide is stained to distinguish the cells from each
other.
• Routine analysis of blood in medical laboratories is usually performed
on blood films stained with Romanowsky, wright’s, or Giemsa stain.
• This stains allow for the detection of white blood cell, red blood cell,
and platelet abnormalities.
• After staining, the mono layer is viewed under a microscope using
magnification up to 1000X. Individual cells are examined and there
morphology is characterized and recorded.
13. MANTOUX TEST
• The mantoux test is the standard method of determining whether a
person is infected with mycobacterium tuberculosis.
• The local skin reaction to tuberculin purified protein derivative[PPD]
injected into the skin is used to asses the individual’s sensitivity to
tuberculin protein.
14. PROCEDURE
• A standard dose of 5 tuberculin units [TU-0.1ml] is injected
intradermally. This intradermal injection is termed the mantoux
technique.
• The reaction is read by measuring the diameter of induration
[hardened area] across the forearm in millimeters.
• If there is no induration, the result should be recorded as ”0 mm”.
• Erythema[redness] should not be measured.
15. Classification of the tuberculin reaction
5mm or more is classified as positive in:
• HIV- positive persons.
• Recent contacts of TB case.
• Persons with fibrotic changes on chest x-ray consistent with old
healed TB.
• Patients with organ transplants and other immunosuppressed
patients.
16. Classification of the tuberculin reaction
10mm or more is classified as positive in:
• Injection drug users .
• Residents and employees of high risk settings .
• Persons with clinical conditions that place them at high risk.
15mm or more is classified as positive in:
• Persons with no unknown risk factors for TB.
17. Classification of the tuberculin reaction
False negative :
• Anergy ,
• Acute TB,
• Live virus vaccination,
• Immunological compromise- those on immuno –suppressive treatment or
those with HIV and low CD4 T cell counts, frequently show negative results
from the PPD test.
False positive:
• BCG vaccination ,
• Non tuberculosis mycobacteria infection.
19. QBC TEST
• The QBC test, developed by Becton and Dickenson Inc., is a new
method for identifying the malarial parasite in the peripheral blood. It
involves staining of the centrifuged and compressed red cell layer
with acridine orange and its examination under uv light source.
• The buffy coat is the fraction of an anticoagulated blood sample that
contains most of the white blood cells and platelets following density
gradient centrifugation of the blood .
20. METHOD
• The QBC tube is a high precision glass hematocrit tube , pre coated
internally with acridine orange and potassium oxalate. It is filled with
55 to 65 microliters of blood from a finger.
• The tube is centrifuged at . 12,000 rpm for 5minutes.
• After centrifugation, one can distinguish a layer of clear fluid [the
plasma],a layer of red fluid containing most of the red blood cells , a
thin layer in between. Making up less than 1% of the total volume of
blood sample, the buffy coat, contains most of the WBCs and
platelets.
• The fluorescing parasites can then be observed under uv light at the
interface between RBCs and buffy coat.
22. DIAGNOSTIC USE OF BUFFY COAT
• QBC is a laboratory test to detect infection with malaria or other
blood parasites.
• The buffy coat is used, for example, to extract DNA from the blood of
mammals.
23. REFERENCES AND TEXT BOOKS
https://www.google.co.in/search?client=safari&channel=mac_bm&biw
=999&bih=671&q=diagnostic+testing+and+remedial+teaching+in+mat
hematics&revid=1040878865&sa=X&ved=0ahUKEwjBnaSNsOrKAhXFRI
4KHZbTDP8Q1QIIcigE.
Clinical lab techniques by K .M. Samuel
