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Course: Clinical Analysis
Lecturer: Dr. Weam Saad
Lecture: Blood Tests
Blood Tests
Collection of whole blood:
Whole blood usually collected by venipuncture mainly from the vein in the
arm using a needle of syringes, if only drops of blood are needed, then blood
sample can be collected from finger. Then blood should be transformed into
tubes with anticoagulant (EDTA, heparin) and mixed gently.
Tests that use whole Blood:
1.
Total WBCs Count:
This test can be done manually using whole blood and special slide called
Hemocytometer. The whole blood should be diluted by a special diluting
fluid made from mixing D.W. with a dye usually crystal violet and glacial
acetic acid, the dye is for WBCs nucleolus staining and glacial acetic acid is
for destroying RBCs.
Counting chambers hold a specified volume of diluted
blood, by multiplying the dilution factor by the total number of white blood
cells then divided on volume, the total number of white blood cells can be
obtained.
Normal range for adult: 5,000-10,000.
Total WBCs (cell/ml)= cell count (mean of 4 squares)x dilution factor
0.1
= cell count (mean of 4 squares) x dilution factor x10
= No.x 20 x10
2.
Differential WBCs count:
Also called complete blood picture or blood film. This test can be done
using whole blood, a small drop of blood is placed on a clean slide and by
another slide called spreader, spreading that drop making fingerprint like
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shape, blood should be left to dry at room temperature for the next step of
staining. Leishman's or Gemsa stains are commonly used for staining, then
after slides dry they must be examined by 40 X then oil lenses. Counting
100 WBCs and determining each type percentage, platelets are also
counted and if there is any abnormalities must be mentioned.
3.
Blood Type Test
This test mainly performed for patients receiving blood transfusion,
pregnant women, tests before marriage and pregnant women. This test
includes ABO system and Rh test. These tests depend on antigens
(proteins) on the surface of red cells, A, B, Rh.
4.
Erythrocyte Sedimentation Rate(ESR)
The erythrocyte sedimentation rate (ESR) is the rate of the red blood cells
sediment in a period of one hour. It is a common hematology test, and is a
non-specific measure of inflammation. To perform the test, anticoagulated
blood is placed in an upright tube, known as a Westergren tube, and the rate
at which the red blood cells fall was measured and reported in mm/h.
The ESR depends on the balance between sedimentation factors,
mainly fibrinogen, and those factors resisting sedimentation, ). When an
inflammatory process stats, the high levels of fibrinogen in the blood causes
red blood cells to stick to each other. The red cells form stacks called
'rouleaux,' which settle faster. The ESR is increased in pregnancy,
inflammation, anemia or rheumatoid arthritis.
5.
Hemoglobin % (Hb %)
This test represents the amount of hemoglobin in the blood, expressed
in grams per deciliter (dl). The low level of Hemoglobin is a sign of anemia.
Normal range: Male: 13.5 - 17.5 g/dl and Female: 12.0 - 16.0 g/dl.
6.
Hematocrit value or Packed cell volume (PCV) or erythrocyte
volume fraction (EVF):
The hematocrit (Ht or HCT), also known as packed cell volume (PCV) or
erythrocyte volume fraction (EVF), is the volume percentage (%) of red
blood cells in blood. It is normally about 45% for men and 40% for women.
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It is considered as a part of a person's complete blood count results, with
hemoglobin concentration, white blood cell count, and platelet count. Usually
gives an indicator for hemoglobin concentration and mainly ordered for
anemia cases.
This test can be done using fresh heparinized blood loaded in capillary
tube (also known as a microhematocrit tube or pcv tube) and special
instrument called microcenterfuge at 10,000 rpm for five minutes.
This
instrument will separate the blood into layers RBCs layer and plasma layer.
The volume of packed red blood cells divided by the total volume of the
blood sample gives the PCV. Because a tube is used, this can be calculated
by measuring the lengths of the layers.
7.
Erythrocytes count and Erythrocytes indices (MCV, MCH and
MCHC):
These indices with erythrocytes number are used as clues for the classification of
anemia types as rotten laboratory tests
MCV or Mean cell volume, the average volume of the red cells, detects conditions
that can affect MCV include thalassemia, reticulocytosis, alcoholism,
chemotherapy, vitamin B12, and/or Folic acid deficiency.
MCH or Mean cell hemoglobin, the average amount of hemoglobin per red blood
cell, in picograms.
MCHC or Mean cell hemoglobin concentration, the average concentration of
hemoglobin in the cells.
8.
Prothrombin Time or clotting time:
Prothrombin time (PT) is a blood test that measures how long it takes
blood to clot. A prothrombin time test can be used to check for bleeding
problems liver function because the liver is responsible for the production of
coagulation factors (prothrombin). This test is usually ordered for patients
before operations as a checkup step. Normal range for adult: 9.9-13 seconds.
This test can be done using capillary tube(or pcv tube) loaded with fresh
blood and breaking one centimeter every couple of seconds while recording
time the time when the clott appears it is the PT.
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9.
Blood culture
Blood culture usually ordered to detect infections that are spreading
through the bloodstream (such as bacteremia, septicemia). No micro
organisims should be found in blood because bloodstream is usually a sterile
environment.
When a patient shows signs or symptoms of a systemic infection, results
from a blood culture can confirm that an infection is present, and they can
identify the type (or types) of microorganism that is responsible for the
infection to give inappropriate treatment. For example, blood tests can
identify the causative organisms in severe pneumonia, puerperal fever, pelvic
inflammatory disease, sepsis, and fever of unknown origin. Also, negative
growths do not mean that there is no infection.
Method of blood culture involves 5-10 ml of blood is taken through
venipuncture and injected into two or more "blood bottles" with specific
media for aerobic and anaerobic organisms. A common media used for
anaerobes is thioglycollate broth. The blood is collected using aseptic
technique. This requires that both the tops of the culture bottles and the
venipuncture site of the patient are cleaned prior to collection with cotton and
70% isopropyl alcohol. Ordering multiple sets of cultures increases the
probability of discovering a pathogenic organism in the blood and reduces the
probability of having a positive culture due to the flora of skin contaminants.
After inoculating the culture vials, they are entered into incubator which
incubates the specimens at body temperature (37
ₒ
C). The blood culture
instrument reports positive blood cultures (cultures with bacteria present, thus
indicating the patient has "bacteremia"). Most cultures are kept for 5 days for
negative vials removing.
If a vial is positive, a microbiologist will perform a Gram Stain on the
blood for a rapid, general identification of the bacteria. The blood is also
subcultured or "subbed" onto agar plates to isolate the pathogenic organism
for culture and susceptibility testing, which takes up to 3 days. This culture &
sensitivity (C&S) process identifies the species of bacteria. Antibiotic
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sensitivities are then assessed on the bacterial isolate to inform physician
about the appropriate antibiotics for treatment.
Cases that request blood culture:
1. Septicemia or bacterimia cases: when infection with any bacteria
succeeded to inter blood stream and circulating system causing
spreading of pathogen to all body organs and tissues. Examples:
Pseudomonas aeroginosa or Escherichia coli.
2. Meningitis: suspecting for example with bacteria e.g. Hemophilus
influenza, Neisseria meningitides, Streptococcus pneumoniae,
Listeria monocytogens and fungi e.g. Cryptococcus neoformans.
3. Endocaditis: suspecting for example with Staphylococcus aureus
and Streptococcus pyogens.
4. Recurrent cases of typhoid fever (Salmonella typhi and Salmonella
paratyphi) and Malta fever (Brucella melatanses).
5. Unknown causative pathogen for fever cases: for example post
delivery infections when pregnant women getting birth and suffer
from fever due to spreading of pathogens to maternal blood during
delivery process e.g. Streptococcus pyogens and Mycoplasma
hominis