PROTHROMBIN TIME (PT)
PROTHROMBIN TIME (PT)
Plasma is reclassified in the presence of excess tissue factor, and clotting time is assessed.
Test tubes, citrated plasma, centrifuge, timer, water bath, tissue extract.
At 37°C, tissue extract (usually from rabbit brain or lung) is added to plasma prepared by centrifuging citrated blood. Simultaneously a timer is started and time taken for clot formation is noted.
Out of the three factors assessed (V, VII, X, II & I), three (X, VII & II) are vitamin - K dependent. Prolongation of PT may be associated with deficiency of one or more factors or presence of an inhibitor. Main clinical use is in controlling anti coagulant therapy.
Write briefly on:
a. In-v ivo anticoagulants
b. In-vitro anticoagulants
c. Physiological anticoagulants
d. What are the limitations of BT & CT determination by the above methods?
e. How are intrinsic & extrinsic pathways of coagulation assessed? Mention their mechanism of action.
f. What is clotting time?
BLOOD GROUPING & RH (Rh.) TYPING
To determine the blood group of a person -ABC system and Rh type.
The blood group is determined by observing the reaction between the red cells and a sample of serum containing a known agglutinin.
Porcelain tile with depressions, Anti A, Anti B, Anti D sera, citrated saline, normal saline, rectified spirit, watch glass, lancet.
Anti A serum is blue in colour
Anti B serum is yellow in colour
Anti D serum is colourless
Take 1 ml of citrated (1% Sodium citrate solution in 0.9% saline) saline in a clean and dry watch glass. Under sterile precautions, prick the fingertip, add 3 drops of blood to citrated saline. Mix well by gently rocking the watch glass. Thus a uniform red cell suspension is obtained. Take the clean dry porcelain tile and mark Anti A, Anti B, Anti D and ‘5’ against four depressions on the tile. Put one drop each of Anti A serum, Anti B serum, Anti D serum and normal saline in the corresponding depressions. Add one drop of red cell suspension to each of the four depressions, without the dropper touching the sera. Mix the red cell suspension and serum using separate rods. Wait for 8 to 10 minutes. At the end of 10 minutes, look for any agglutination. All positive and negative results should be confirmed with microscope.
If agglutination is present, red cells are seen clumped together (sprinkled chilli powder appearance). This is usually visible with the naked eye, In doubtful cases, the result may be confirmed by microscopic examination.
If there is agglutination in depressionA, the blood group isA, if there is agglutination in depression B, the blood group is B. If there is agglutination in bothAand B, the group isAB and if there no agglutination inAor B, the group iso.
If there is agglutination in depression D, the Rh type is positive and if there is no agglutination it is Rh negative. Normal saline is used as control to check any agglutination due to contamination or auto agglutination.
In the ABC system, individual are classified in to A, B, AB, and C groups depending on the presence or absence of agglutinogensAand B in the red cells.
Anti A, Anti B
In Rh system individuals are classified into Rh positive (93%) and Rh negative (7%) depending on the presence or absence of Rh antigen (D antigen).
Significance of blood grouping:
1. Blood transfusion
2. Medico-legal importance
3. Disputed paternity
4. Proneness to certain diseases
1. Separate droppers should be used for the different sera.
2. Agglutination should be observed before the mixture gets dried up.
1. What is Bombay blood group?
2. What are the complications of mismatched blood transfusion?
3. What are the tests done before transfusion and types?
Kumkum / safron - Crocus sativus
Crocuses belong to the family Iridaceae. The saffron crocus is classified as Crocus sativus, It is a shrub. Leaves are seen towards the base of the stem and are compactly arranged.Read More about safron.....