Testing of coagulation

Coagulation is  a  complex  process  by  which  blood  forms  clots.  It  is  an  important  part  of hemostasis  (the  cessation  of  blood  loss  from  a  damaged  vessel),  wherein  a  damaged  blood vessel  wall  is  covered  by  a  platelet  and  fibrin-containing  clot  to  stop  bleeding  and  begin repair  of  the  damaged  vessel.  Disorders  of  coagulation  can  lead  to  an  increased  risk  of bleeding (hemorrhage) or obstructive clotting (thrombosis).

1- Prothrombin Time Blood Test-PT

This test is done to evaluate the blood for its ability to clot. It is often done before surgery to evaluate how likely the patient is to have a bleeding or clotting problem during or after surgery. 

Normal PT Values: 10-12 seconds (this can vary slightly from lab to lab) 

Common causes of a prolonged PT include vitamin K deficiency, hormones drugs including hormone replacements and oral contraceptives, disseminated intravascular coagulation (a serious clotting problem that requires immediate intervention), liver disease, and the use of the anti-coagulant drug warfarin. Additionally, the PT result can be altered by a diet high in vitamin K, liver, green tea, dark green vegetables and soybeans. 

2- Partial Thromboplastin Time Blood Test-PTT

This test is performed primarily to determine if heparin (blood thinning) therapy is effective. It can also be used to detect the presence of a clotting disorder. It does not show the effects of drugs called ―low molecular weight heparin‖ or most commonly by the brand name Lovenox. 

Normal PTT Values: 30 to 45 seconds (this can value slightly from lab to lab)

Extended PTT times can be a result of anticoagulation therapy, liver problems, lupus and other diseases that result in poor clotting.

3- International Normalized Ratio Blood Test-INR

Normal INR Values: 0.8–1.2  INR.

The INR is used to make sure the results from a PT test is the same at one lab as it is at another lab. In the 1980’s the World Health Organization determined that patients may be at risk because the results of a PT test would vary from one lab to another, based upon the way the test was done. The normal range for one lab would be different than a normal value from another lab, creating problems for patients who were being treated in several locations. In order to standardize the results between labs, the INR was created. The INR result should be the same, regardless of the location where the tests are performed. 

4- Bleeding time

Bleeding time is a medical test done on someone to assess their platelet function

A-Ivy method

The  Ivy  method  is  the  traditional  format  for  this  test.  While  both  the  Ivy  and  the  Duke method  require  the  use  of  a  sphygmomanometer,  or  blood  pressure  cuff,  the  Ivy  method  is more invasive than the Duke method, utilizing an incision on the ventral side of the forearm, whereas  the  Duke  method  involves  puncture  with  a  lancet  or  special  needle.  In  the  Ivy method,  the  blood  pressure  cuff  is  placed  on  the  upper  arm  and  inflated  to  40  mmHg.  A lancet  or  scalpel  blade  is  used  to  make  a  shallow  incision  that  is  1  millimeter  deep  on  the underside of the forearm.

A standard-sized incision is made around 10 mm long and 1 mm deep. The time from when the  incision  is  made  until  all  bleeding  has  stopped  is  measured  and  is  called  the  bleeding time. Every 30 seconds, filter paper or a paper towel is used to draw off the blood.The test is finished  when  bleeding  has  stopped  completely.A  normal  value  is  less  than  9  and  a  half minutes. A prolonged bleeding time may be a result from decreased number of thrombocytes or impaired blood vessels. However, it should also be noted  that the depth of the puncture or incision may be the source of error.

Normal values fall between 2 – 9 minutes depending on the method used.

B-Duke Method

With the Duke  method, the patient is  pricked  with a  special  needle or lancet,  preferably on the earlobe or  fingertip, after having been swabbed with alcohol. The prick is about 3–4 mm deep. The patient then wipes the blood every 30 seconds with a filter paper. The test ceases when bleeding ceases. The usual time is about 1–3 minutes.

5- Clotting Time (CT (

The  time  required  for  a  sample  of  blood  to  coagulate  in  vitro  under  standard  conditions  is called "clotting time". 

Principle. The whole blood clotting time is a rough measure of all intrinsic clotting factors in the  absence  of  tissue  factors.  Variations  are  wide  and  the  test  sensitivity  is  limited.  Whole blood, when removed from the vascular system and exposed to a foreign surface, will form a solid clot. Within limits, the time required for the formation of the solid clot is a measure of the coagulation system

 Lee  and  White  method    5  ml  of  blood  is  collected  in  an  autoclaved  syringe  and  the  stop watch is  switched on as soon as blood  enters the syringe. One  ml of  blood is  delivered in 4 clean dry test tubes and these are kept in a water bath at 37° C. After 2 minutes, the tubes are examined every 15 seconds, by very gently tilting them. Clotting time is noted when the tube can be completely inverted without spilling the blood. Clot retraction and  clot  size are also observed after one hour and 24 hrs.

Significance - Prolonged when -

-  There is factor deficiency. 

-  Anti-coagulants like heparin has been added to the blood.

Ref Range: This range should be between 5 to 10 minutes. 

6- D-dimer

D-dimer  is  a  fibrin  degradation  product  (or  FDP),  a  small  protein  fragment  present  in  the blood  after  a  blood  clot  is  degraded  by  fibrinolysis.  It  is  so  named  because  it  contains  two crosslinked D fragments of the fibrinogen protein. D-dimer concentration may be determined by  a  blood  test  to  help  diagnose  thrombosis,it  has  become  an  important  test  performed  in patients  suspected  of  thrombotic  disorders.  While  a  negative  result  practically  rules  out thrombosis,  a  positive  result  can  indicate  thrombosis  but  does  not  rule  out  other  potential causes. Its main use, therefore, is to exclude thromboembolic disease where the probability is low. In addition, it is used in the diagnosis of the blood  disorder  disseminated intravascular coagulation.  D-dimer  testing  is  of  clinical  use  when  there  is  a  suspicion  of  deep  venous thrombosis  (DVT)  or  pulmonary  embolism  (PE).  In patients  suspected  of  disseminated intravascular coagulation (DIC), D-dimers may aid in the diagnosis Various  kits  have  a  93-95%  sensitivity  and  about  50%  specificity  in  the  diagnosis  of thrombotic disease. 

7- platelet count 

How is it used

Bleeding disorders or bone marrow diseases, such as leukemia, require the determination of the number  of  platelets  present and/or  their ability to  function  correctly.  A platelet count is often ordered as a part of a complete blood count, which may be done at an annual physical examination.  It  is  almost  always  ordered  when  a  patient  has  unexplained  bruises  or  takes what appears to be an unusually long time to stop bleeding from a small cut or wound. In an adult, a normal count is about 150,000 to 450,000 platelets per microliter of blood.