VENOUS BLOOD
CAPILLARY BLOOD.
Collection of blood sample by Venipuncture : It is one
of the most critical phases of obtaining accurate
laboratory test result
Prepared by: Mahmoud Ramlawi
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 1. Syringes :
 In the past syringes were the only practical way blood could be
collected . They were made of :
 A. Glass : and after each use ,they were placed in paper bags or
cloth wraps and sterilized(by boiling )for reuse. These have
been replaced By:
 B. Plastic , disposable syringes
 C. Evacuated System :tubes and needle holders
 Syringes are still used for collecting types of samples:
 A. Arterial blood Gases
 B. Blood cultures
 C. various body fluids
 These are best for patients with small veins , veins that easily
collapse ( when exposed to the pressure in the evacuated tubes )
 They may also be the best choice when other collecting devices
are used ,such as Butterfly infusion sets and intravenous infusion
sets .
 Two advantages for syringes use :
 1. Blood usually appear in the hub of the syringe as a vein is
penetrated , which is helpful for the phlebotomist and when
collecting blood from arms with fragile , deep or mobile veins .
 2.Blood –flow rate and withdrawal pressure is easily controlled by
the phlebotomist , so that collapse of thin walled veins can be
avoided . Large amounts of blood (up to 60 mL ) can be withdrawn
using a small diameter needle and syringe.
2- Capillary Blood Capillary blood is used for infants under 1 year of age and
when it is not possible to obtain venous blood. Common sites for drawing
capillary blood are the heel and the ball of the middle finger.
Areas to Avoid When Choosing a Site for Blood Draw:
Certain areas are to be avoided when choosing a site for blood draw:
1- Extensive scars from burns and surgery - it is difficult to puncture the
scar tissue and obtain a specimen.
2- Hematoma - may cause erroneous test results. If another site is not
available, collect the specimen distal to the hematoma.
3- Intravenous therapy (IV) / blood transfusions - fluid may dilute the
specimen, so collect from the opposite arm if possible.
4-Cannula/fistula/heparin lock - hospitals have special policies regarding
these devices. In general, blood should not be drawn from an arm with a
fistula or cannula without consulting the attending physician.
5- Edematous extremities - tissue fluid accumulation alters test results.
Techniques to Prevent Hemolysis (which can interfere with many tests):
1- Mix all tubes with anticoagulant additives gently (vigorous shaking can
cause hemolysis) 5-10 times.
2- Avoid drawing blood from a hematoma; select another draw site.
3- Make sure the venipuncture site is dry before proceeding with draw.
4-Avoid milking the site when collecting capillary samples
5- Do not use a small diameter needle if not needed.
6-Avoid a probing, traumatic venipuncture.
7-Avoid prolonged tourniquet application (no more than 2 minutes; less than 1
minute is optimal).
8-Avoid massaging, squeezing, or probing a site.
9-Avoid excessive fist clenching.
10- If blood flow into tube slows, adjust needle position to remain in the center
of the lumen
 The most common blood collecting system use: 1.A disposable
needle . 2.A needle holder .3. An evacuated tube
 The needle screw into the holder and each end of the needle is
pointed ; one to enter the vein ; the other is to puncture a
collecting tube . The vein is entered first , and then any number
of collecting tubes can be added to the other end . Each tube is
punctured through the rubber cap and blood flows into it due
to the partial vacuum . (gradually loss of vacuum from the tubes
that have been stored on shelf a few years .
 Collecting tubes are available in many sizes and the tube walls are
made of soda lime glass or borosilicate glass. Some tubes also
employ a special material that separates serum from the blood clot
. Many tubes are coated with silicon to minimize clotting and
hemolysis . The collecting tubes may contain additives such as
anticoagulant and preservatives , which are usually denoted by a
stopper color code :
 1. Lavender (purple ) : contains EDTA
 2.Red : has NO additives (plain )
 3. Blue : contains Na citrate .
 4. Green :contains Heparin
 Advantages of the Evacuated System :
 1. One needle holder can replace many bulky syringes saving
space on Phlebotomy trays .
 2. A number of collecting tubes with various additives can be used
sequentially (some patients experience anxiety at the sight of a 30
mL syringe being filled with their blood whereas 5-6 tubes may not
seem as threatening )
 3. Blood enters each tube and mixes rapidly with a specific
anticoagulant , whereas blood in a syringe must either forgo
anticoagulion until the phlebotomy is complete , or the syringe
must be coated with anticoagulant , thus limiting the variety of
additives used.
 4. Blood collection is faster with the evacuated tubes than with the
syringes especially if several tubes are to be filled .
22 ،‫ أيلول‬17
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 Coagulation of blood requires about 15 clotting factors ,most of
them are proteins which are activated into enzymes when
injury occurs : the last steps for clot formation:
 Prothrombin
Prothrombinase Thrombin
(Ca + Plasma thromboplastin )
 Fibrinogen
Thrombin
Fibrin (Clot)
 Most procedures used in hematology require whole blood or
plasma . Anticoagulants prevent blood clotting by enhancing the
action of natural inhibitors (as antithrombin ,by Heparin ) or by
removing (chelating ) Calcium (most other anticoagulants ).
Selection of the anticoagulant depends on the requirements of the
procedure . Some used in hematology includes the following :
 1.Heparin : inactivates Fx and FII(thrombin).
 Available as Sodium , Potassium and Ammonium salts , It inhibits
Thrombin action .About 20 units of heparin are required to
anticoagulate 1 mL of blood .
 Advantages :1. minimum interference in most chemical tests .2.
Available as a liquid or a powder . 3. can be used in Phosphorous
test.
 Disadvantages : 1. Relatively expensive . 2. Produces blue
background on Wright –Stained smear .3.Inhibits acid Phosphatase
activity .4.Causes clumping of WBCs & Platelets .
 2. EDTA (ethylene diaminetetraacetic acid ) (sequestrene,
Versene):
 It is used as a disodium or dipotassium salt that prevent
coagulation by chelating or binding Calcium in the plasma .
Calcium is required in many steps of the coagulation process.
About 1-2 mg of EDTA is needed for each mL of blood . EDTA is
the most common anticoagulant used in routine hematological
studies .
 Advantages : a. Prevents Platelet clumping .
 b. Preserves cellular morphology.
 c. Prevents artifacts in preparing blood films .
 d. Little effect on chemistry tests
 e. EDTA blood stored at 4c for 24hrs . If tested again show no
changes in results compared to the previous results .
 Disadvantages : a. Inhibits Alkaline phosphatase
 b. Not useful for Calcium and Iron testing
 c. If in excess : shrink RBCs ,so dec . Hematocrit , False ESR
results and MCHC . , Degenerates WBCs & platelets so inc.
platelet count.
 3.Sodium Citrate : this is the anticoagulant of choice for the
coagulation studies . A concentration of 3.2% is used , mixing 1
part of Na citrate with 9 parts of blood . Calcium is chelated ,
which is easily reversed by the addition of ionized Ca since it is
required to clot the plasma in coagulation tests .
 Advantages :a. Maintain stability of coagulation factors
(V&VIII&platelets)
 Disadvantages : a. Not suitable for many chemistry tests . b.
Inhibits Alkaline Phosphatase . c. Cause distortion of cells
morphology .
 The Gauge (diameter ) and Length of the needle used on a
syringe or evacuated system depends on :
 1.Amount of blood to be drawn .
 2.Type of analysis to be performed
 3.Condition of potential phlebotomy sites
 Its gauge number gives the bore size , or diameter of a needle .
The smaller the number , the greater the diameter, For ex:
G24&G26 indicates small needle Lumen(diameter) while ,
G16&G18 indicates needles with large lumen.
 Most blood samples are collected with needles of 19-23G , .Patients
with very small veins or collapsible veins may require a small
needle used with syringes . On the other hand , blood donors
providing a unit (450mL )of blood or plasma are usually drawn with
a 16 G needle . Collection of large single sample volume can be
facilitated with a butterfly set. This consists of a needle and a long
flexible tube attached to a syringe . The tube can be taped to the
patient ‘s arm to withdraw a large sample over a larger interval of
time than would occur with an evacuated system or syringe alone.
 The length of the needle is usually either 1inch →11/2 inches . The
choice of length depends on the characteristics of the phlebotomy
site . (depth of veins, scarred tissues ) and the phlebotomy’s
preference. All needles in routine use today are disposable and
sterile , so that blunt, barbed or contaminated needles should not
be a factor of error . Visual examination of the tip prior to
venipuncture is a good practice .
 When an evacuated system is used , tubes for collection should be
in the order : 1. Sterile blood culture.2.Tubes without additives
(serum ) .3.Na citrate or Heparinized tubes. 4.Tubes with other
additives (EDTA, Flouride)