Lab testing in Coagulation

Question 1

Coagulation testing temperature

Answer 1

always at 37 C

Question 2

Coag specimen

Answer 2

plasma w/ sodium citrate (3.2%) at 9:1 ratio

requires Ca2+ to be added to the testing bc sodium citrate will bind all available calcium

Question 3

Platelet-Poor plasma (PPP)

Answer 3

plasma containing less than 10x10^9/L platelets

Question 4

Platelet-Rich Plasma (PRP)

Answer 4

plasma containing ~200-300x10^9/L

Question 5

Testing of Primary Hemostasis

Answer 5

peripheral smear, platelet count, platelet aggregation, bleeding time & platelet function analyzer, platelet secretion studies, flow cytometry

Question 6

Specimen problems w/ platelet counts & estimates

Answer 6

clumping- due to capillary puncture
satellitism - caused by EDTA & leads to falsely low counts
giant platelets- counted as WBC; falsely low count
fragmented RBCs- ocunt as plt; falsely elevated count

Question 7

Platelet aggregation studies

Answer 7

addition of aggregating reagent to PRP - measure change in transmittance
2 waves: primary & secondary
* know charts on slide 21 in lab testing pdf

Question 8

Bleeding time

Answer 8

measure of platelet function
3 types: duke, ivy, template (!)
prolonged w/ aspirin etc

Question 9

Bleeding time: template

Answer 9

standardized back pressure & standardized depth
normal bleeding time 1-9 minutes
not very sensitive
should NOT be performed if plt count is less than 100x10^9/L

Question 10

Platelet function analyzer

Answer 10

replaces the BT- eliminates many of the variables
pumps whole blood (in citrate) through each of 2 apertures containing either : collagen/epi or collagen/ADP
& measures time necessary for plt to occlude the aperture

Question 11

Flow cytometry for primary hemostasis

Answer 11

useful for GPlb/IX deficiency (Bernard-Soulier) & GPIIB/IIIa deficiency (Glanzmann’s thrombasthenia)

Question 12

Testing of Extrinsic pathway

Answer 12

prothrombin time (PT)

Question 13

Prothrombin time (PT)

Answer 13

screen for inherited or acquired deficiencies in the extrinsic & common pathway
measures factors: I, II, V, VII & X
monitors oral anticoagulant therapy- coumadin /warfarin
range 10-13 seconds

Question 14

PT procedure

Answer 14

specimen & reagents & 37C

plasma specimen + thromboplastin reagent (contains Ca2+)

Question 15

PT & INR

Answer 15

INR is the international normalized ratio

used to correct for differences in coag instruments

Question 16

INR formula

Answer 16

INR = (PT patient/ PT normal) ^ISI
0 to >6
theraputic is 2-3

Question 17

PT sources of error

Answer 17

short draw - falsely shorten the PT
delay between collection & teting may lead to decreases in factor V
patient high hematocrit- can lead to prolonged PT

Question 18

Testing of Intrinsic pathway

Answer 18

APTT or PTT-performed by adding platelet phospholipid substitute & contact activator (APTT reagent) & Ca2+ to activate factor XII

Question 19

APTT

Answer 19

screen for intrinsic & common pathway
measures all factors except VII (extrinsic) & XIII
28-35 seconds
monitors heparin therapy

Question 20

sources of error for APTT

Answer 20

blood collection error (short draw)
hematocrit
sample processing etc

Question 21

Activated Clotting time (ACT)

Answer 21

used to monitor the effectiveness of high dose heparin therapy
not performed in the clinical lab - point of care test

Question 22

Thrombin Clotting time

Answer 22

thrombin time TT, TCT
measures clotting time of the last step in the coag cascade- fibrinogen (!) to fibrin by thrombin (test of common pathway)
used to detect dysfibrinogenemia

Question 23

TCT source of error

Answer 23

collection etc

can be falsely prolonged due to heparin

Question 24

Reptilase Time

Answer 24

clotting time similar to thrombin time except that a snake venom is used instead of thrombin
reptilase is a thrombin like enzyme
NOT PROLONGED BY HEPARIN

Question 25

Fibrinogen Assay

Answer 25

recommended test for estimating fibrinogen level high [thrombin] is inversely proportional to [fibrinogen] thrombin reagent is 25x more concentrated than in TCT, patient plasma needs to be diluted

Question 26

APTT normal & | PT abnormal

Answer 26

possible causes: 1. factor deficiency in extrinsic pathway probably VIII 2. specific factor inhibitor

Question 27

APTT abnormal & | PT normal

Answer 27

possible causes: 1. Factor deficiency in intrinsic pathway (XII, XI, kallikrein, IX, or VIII) 2. Specific factor inhibitor 3. lupus anticoagulant

Question 28

APTT abnormal PT abnormal TCT normal

Answer 28

possible causes: 1. factor deficiency in common pathway 2. vitamin K defect 3. liver disease 4. inhibitor present

Question 29

APTT abnormal PT abnormal TCT abnormal

Answer 29

possible causes: 1. factor deficiency (I) 2. severe liver disease 3. DIC 4. inhibitor

Question 30

Test to evaluate specific factor deficiency

Answer 30

when PT &/or APTT are prolonged 1. mixing studies-differentiate factor def. from inhibitor 2. specific factor assay

Question 31

Mixing study

Answer 31

performed to differentiate between factor deficiency & inhibitor this procedure will correct the prolonged PT or APTT if it is caused by a deficiency of one or more of the coag factors

Question 32

Mixing study precedure

Answer 32

patient's plasma mixed 1:1 w/ normal plasma if normal then factor deficiency is suspected if NOT normal then suspect an inhibitor rerun after heating for 2 hours if APTT is still normal = factor def. then perform specific factor assay!

Question 33

Mixing study results for Factor deficiency

Answer 33

immediate mixing study: corrected | after 2 hour incubation: corrected

Question 34

Mixing study results for Lupus-like anticoagulant

Answer 34

immediate mixing study: no correction | after 2 hour incubation: no correction

Question 35

Mixing study results for Specific inhibitor (factor VIII)

Answer 35

immediate mixing study: correction | after 2 hour incubation: no correction

Question 36

Factor Assay

Answer 36

performed to confirm a specific factor deficiency & to determine the actual activity of that factor w/in the plasma the degree of correction produced w/ the patient's plasma is compared to a reference curve most likely will be Factor VIII

Question 37

Fibrinolytic System

Answer 37

2 major tests: | Fibrin degradation products & D-dimer

Question 38

Fibrin Degradation Products (FDPs)

Answer 38

Plasmin cleaves fibrin & yields FDPs normally D & E fragments do not reach plasma concentrations of 2 um/mL assay test based on antigen-antibody reaction

Question 39

Increased FDP is seen in:

Answer 39

DIC, deep vein thrombosis, pulmonary embolism, liver disease, alcoholic cirrhosis, kidney disease, etc etc etc

Question 40

D-dimer Assay

Answer 40

``` more specific test for plasmin lysis of fibrin beginning to replace FDPs excellent marker for DIC (positive) 3 methodologies: semiquantitative assay quantitative assay latex agglutination ```

Question 41

Testing of Thrombophilia

Answer 41

antithrombin assays protein C assays protein S assays

Question 42

Mechanical clot detection

Answer 42

incorporates a change in electrical conductivity between 2 metal electrodes immersed in a solution when clot formed, fibrin strands act as conductor between probes causing constant electrical current

Question 43

Photo-optical detection of clot formation

Answer 43

measured by a change in optical density of a test sample | widely used today

Question 44

Chromogenic detection of clot formation

Answer 44

color intensity is measured spectrophotometrically & is directly proportional to the concentration of chromophore tag

Question 45

Immunologic detection methods of clot formation

Answer 45

antigen level is proportional to the amount of light absorbed