1. General Approach in Investigation of Haemostasis
Lecture 1: Introduction

2. Preanalytical Variables including
Sample Collection.
Site Selection.
Storage Requirements.
Transportation of Specimen.

3. Haemostasis
Hemostasis is a complex interaction between vessels, platelets and coagulation proteins that, when working properly, stops bleeding while maintaining blood flow in the vessel.
Specific tests are available to evaluate platelet function, coagulation proteins, natural occurring inhibitors and fibrinolysis.

4. Sample Collection
Proper sample collection is of utmost importance for reliable test results to evaluate the bleeding patient, thrombosis or fibrinolysis (preanalytical phase)
All these tests are influenced by sample collection, sample processing and sample storage.
The laboratory will not evaluate samples that are hemolyzed, clotted, contain fibrin strands or improperly stored.
Reference Laboratory Services will immediately notify the client of any problems with the sample.
When blood is withdrawn from a vessel, changes begin to take place in the components of blood coagulation. Some occur almost immediately, such as platelet activation and the initiation of the clotting mechanism dependent on surface contact.

5. Sample Collection Anticoagulant of choice 3.8% or 3.2% Sodium Citrate
3.2 % Preferred as the standard measure due to stability and closeness to the plasma osmolality
Anticoagulant/blood ratio is critical (1:9)
Exact amount of blood must be drawn. No short draws are acceptable, this will falsely increase results due to presence of too much anticoagulant
CLSI guideline is +/- 10 % of fill line
Purpose of the anticoagulant is to bind or chelate calcium to prevent clotting of specimen
(CLSI ) Clinical and Laboratory Standards Institute.
* CLSI : Clinical and Laboratory Standards Institute

6. Sample Collection
Other anticoagulants, including oxalate, heparin, and EDTA, are unacceptable.
The labile factors (factors V and VIII) are unstable in oxalate, whereas heparin and EDTA directly inhibit the coagulation process and interfere with end-point determinations.
Additional benefits of trisodium citrate are that the calcium ion is neutralized more rapidly in citrate, and APTT tests are more sensitive to the presence of heparin.

7. Sample Collection : Samples with High hematocrits
According to the latest CLSI (formerly NCCLS) guideline on coagulation testing, it is important to adjust the sodium citrate volume when a patient’s hematocrit is greater than 55%.
Examples of patients who may have elevated hematocrit values are newborns or people with polycythemia vera.
NCCLS* recommends adjusting anticoagulant ratio for patients with hematocrits exceeding 55%
High hematocrits may cause falsely prolonged test results due to an over- anticoagulated sample
Formula correction achieves a 40% hematocrit
(NCCLS) National Committee for Clinical Laboratory Standards.
* National Committee for Clinical Laboratory Standards

8. X = (100–PCV)*vol./(595–PCV)
Where:
X= volume of sodium citrate
Vol =volume of whole blood drawn
PCV= patient’s hematocrit
Examples:
Patients Hct= 60%, V= 5 mL
X=(100-60)*5 / (595-60)
= 40*5 / 535 = 0.34 ml
Patient Hct = 25%, V=5 ml
X=(100-25)*5 / (595-25)
= 75*5 / 570 = 0.65 ml
HCT
Citrate (ml)
0.20
0.70
0.25
0.65
0.30
0.61
0.55
0.39
0.60
0.36
0.31
0.27

9. Site Selection Untraumatic venipuncture is required
Traumatic venipunctures release tissue factor and initiate coagulation
Fingersticks/Heelsticks are not allowed
Indwelling IV line draws are discouraged
Contain heparin & diluted blood
Falsely increased results
Order of Draw
Evacuated tube system
Blue top is 2nd
If 2nd tube drawn, 1st top must be anticoagulant free (i.e. red top)

10. Storage Requirements Prothrombin Time: PT
Uncentrifuged or centrifuged with plasma remaining on top of cells in unopened tube kept at 2-4 oC or oC must be tested within 24 hours of collection
Activated Partial Thrombin Time: APTT
Uncentrifuged or centrifuged with plasma remaining on top of cells in unopened tube kept at 2-4 oC or oC must be tested within 4 hours of collection
Other Assays
Fibrinogen, Thrombin Time, Factor Assays
Centrifuged with plasma remaining on top of cells in unopened tube kept at 2-4 oC or oC must be tested within 4 hours of collection

11. Storage Requirements TEST PLASMA STABILITY AT RT CENTRIFUGE TO PREPARE
PLATELET-FREE PLASMA
REFRIGERATION
(Or transport on ice)
FREEZE
PLATELET-
FREE
PLASMA PT
24 hours
Do not refrigerate
If >24 hour delay in testing
PTRX
PTT
4 hours
If >4 hour delay in testing
PTTRX
2 hours
Within one hour of collection
If >2 hour delay in testing TT
OTHER
ASSAYS

12. Storage Requirements Other general notes
Perform coagulation tests ASAP
Specimen may deteriorate rapidly (especially factors V and VIII)
If the testing is not completed within specified times, plasma should be removed from the cells and placed in a frost free freezer
- 20 oC for two weeks
-70 oC for six months

13. Transportation of Specimen
Send specimen on ice OR deliver to lab ASAP
Separate cells from plasma immediately via centrifugation

14. Platelet Poor Plasma Platelet –Poor plasma (PPP)
Platelet-Poor plasma is necessary for coagulation testing to prevent activation of platelets and release of PF4, a heparin inhibitor.
The plasma platelet count must be < 10,000 /mm3.
Specimen has been centrifuged for x g
Why is PPP essential?
Contains platelet factor 4 (heparin neutralizer)
Contains phospholipids (affects lupus anticoagulant and factor assay testing)
Contains proteases (affect testing for vWF)

15. Platelets Poor Plasma preparation:
To prepare platelet-Poor plasma
Centrifuge the blue top evacuated tubes (CLSI, formerly NCCLS recommendation is 1500 rpm for 15 minutes).
Using a plastic pipette, immediately remove the top 2/3 of the plasma to a plastic aliquot tube.
Centrifuge this plasma sample and remove the top ¾ of the plasma to a second plastic aliquot tube with a fresh plastic pipette.
Freeze the specimen within one hour of collection.

16. Platelets Rich Plasma (PRP)
Platelet-Rich plasma (PRP)
Used in platelet function studies
x /L
Specimen must be centrifuged for x g

17. Common Collection Problems
Error
Consequence
Comment
Short draw
<2.7 mL
PT/PTT falsely prolonged
Anticoagulant to blood ratio exceeds 1:9
Failure to mix specimen after collection
Blood clots form when anticoagulant & blood do not mix
Excess vigorous mixing
PT/PTT falsely shortened
Hemolysis and platelet activation cause start of cascade
Hemolysis
Reject specimen
Improper storage: wrong temperature or held too long
Must follow storage requirements
Chilling in refrigerator or placing on ice
PT falsely shortened
Chilling to 4 oC activates factor VII.

18. Common Collection Problems
Error
Consequence
Comment
Inadequate centrifugation
PTT loses sensitivity for lupus anticoagulants and heparin.
Factor assays inaccurate
Prolonged tourniquet application
Falsely elevates vWF, factor VIII
Tourniquet causes venous stasis,
Drawing coagulation tube after to other anticoagulant tubes
PT/PTT falsely affected
Contamination
Probing the vein
PT/PTT falsely shortened
Tissue thromboplastin is released activating coagulation
Heparin contamination from line draw
PTT falsely prolonged
Heparin keeps the blood from clotting
Lipemia
Test may not work
Photo-optical methods affected

19. Principles of Laboratory Analysis
The more detailed investigations of coagulation proteins also require caution in their interpretation depending on the type of assay performed. These can be divided into three principal categories, as described in the following sections.
Immunological
Assays Using Chromogenic Peptide Substrates (Amidolytic Assays)
Coagulation Assays
Other Assays

20. Immunological
Include immuno-diffusion, immuno-electrophoresis, radioimmunometric assays, latex agglutination tests, and tests using enzyme-linked immunosorbent assays (ELISA).
Fundamentally, all these tests rely on the recognition of the protein in question by polyclonal or monoclonal antibodies. Polyclonal antibodies lack specificity but provide relatively high sensitivity, whereas monoclonal antibodies are highly specific but produce relatively low levels of antigen binding.

22. latex agglutination kit: Latex microparticles are coated with antibodies specific for the antigen to be determined. When the latex suspension is mixed with plasma an antigen–antibody reaction takes place, leading to the agglutination of the latex microparticles.
Agglutination leads to an increase in turbidity of the reaction medium, and this increase in turbidity is measured photometrically as an increase in absorbance.
Usually the wavelength used for latex assays is 405 nm, although for some assays a wavelength of 540 or 800 nm is used. This type of assay is referred to as immuno- turbidimetric.

23. Notes:
Do not freeze latex particles because this will lead to irreversible clumping.
An occasional problem with latex agglutination assays is interference from rheumatoid factor or paraproteins. These may cause agglutination and overestimation of the protein under assay.

24. Chromogenic Assay
Chromogenic, or amidolytic, methodology is based on the use of a specific color-producing substance known as a chromophore.
the chromophore normally used in the coagulation laboratory is para-nitroaniline (pNA), which has an optical absorbance peak at 405 nm on a spectrophotometer.

25. Coagulation Assays
Coagulation assays are functional bioassays and rely on comparison with a control or standard preparation with a known level of activity.
In the one-stage system optimal amounts of all the clotting factors are present except the one to be determined, which should be as near to nil as possible.
The best one-stage system is provided by a substrate plasma obtained either from a patient with severe congenital deficiency or artificially depleted by immuno-adsorption.

26. Coagulation Assays
Coagulation techniques are also used in mixing tests to identify a missing factor in an emergency or to identify and estimate quantitatively an inhibitor or anticoagulant.
The advantage of this type of assay is that it most closely approximates the activity in vivo of the factor in question. However, they can be technically more difficult to perform than the other types described earlier.
Mixing studies are tests performed on blood plasma used to distinguish factor deficiencies from factor inhibitors, such as lupus anticoagulant, or specific factor inhibitors, such as antibodies directed against factor VIII. Mixing studies take advantage of the fact that factor levels that are 50 percent of normal should give a normal Prothrombin time (PT) or Partial thromboplastin time (PTT) result.
If the problem is a simple factor deficiency, mixing the patient plasma 1:1 with plasma that contains 100% of the normal factor level results in a level ≥50% in the mixture (say the patient has an activity of 0%; the average of 100% + 0% = 50%). The PT or PTT will be normal (the mixing study shows correction). However, if there is an inhibitor that inactivates the added clotting factor, the resulting factor level will be low and the clotting test will be prolonged (fails to correct). Therefore, correction with mixing indicates factor deficiency; failure to correct indicates an inhibitor.

27. Other Assays
Using snake venoms (The Taipan venom time employs a reagent isolated from the venom of the Taipan snake (Oxyuranus scutellatus) that directly activates prothrombin in the presence of phospholipid and calcium.)
Aassay of ristocetin cofactor (used to diagnose von Willebrand disease )
The clot solubility test for factor XIII.
DNA analysis is becoming more useful and more prevalent in coagulation. However, this requires entirely different equipment and techniques