Taking a close look at coagulation tests, coagulation profile, PT, APTT
Have you ever thought how blood, which is a fluid, stays within the body without leaking out in case there is a wound? This is because of a complex mechanism called clotting occurring within the body. Just as there is a risk of bleeding out if the clotting mechanism is inadequate, clotting of blood more than what’s normal in a person is also disastrous. This condition gives rise to the ability to cause severe consequences like strokes and heart attacks. This balance is deranged in certain disease conditions and bleeding and clotting tests are performed in order to identify and asses these disease conditions.
Today, we will discuss about these tests which can measure the ability for blood to clot in your body. We contacted Dr K.A.C. Wickramaratne, Consultant Haematologist, Senior Lecturer in Pathology, Faculty of Medicine, University of Ruhuna, to discuss about these commonly requested blood tests.Following are excerpts of an interview done with Dr. Wickramaratne.
QWhat is clotting, coagulation and bleeding?
When blood flows out from blood vessels following cut injuries or when blood is collected into a plain tube, liquid blood becomes a gelatin like mass after a little while. Later it becomes hard. This process is called ‘clotting’ or coagulation, which is natural and essential to stop bleeding due to wounds. When liquid blood, which runs through the blood vessels, form similar masses within the blood vessels, we call it a thrombus. Whether it is a clot or a thrombus, the process and the factors used are same. The leading causes for deaths in the world include ‘clots’ in heart vessels or brain or ‘bleeding’ following injuries.
People can develop diseases with increased tendency to bleed. We call such diseases ‘bleeding disorders’. Bleeding disorders can be acquired due to many different illnesses or due to certain medications. For an example, liver disease can increase the risk of bleeding. Bleeding disorders can be inherited. Fortunately, such diseases are rare.
The most common form is when blood ‘clots’ form inside blood vessels causing heart attack and brain attack. When blood clotting is excessive we need treatment to make the blood thin or non clottable within vessels. Monitoring of such drug treatment is very important.
Q What is a clotting profile?
When a test request includes the term ‘profile’ it means that the report will contain results from a battery of investigations. How many tests are included in the profile depends on the availability of tests in the laboratory and the requirements of the clinicians. Therefore, the clotting profile available will vary from each laboratory.
The tests related to clotting include prothrombin time and international normalized ratio (PT/INR), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen, and fibrinogen degradation products etc. Therefore, a clotting profile would include these investigations and a Full Blood Count and some other different tests based on level of laboratory’s test menu.
QWhat is the sample needed for coagulation profile (for PT/APTT)?
Generally the blood sample required for any test in clotting profile or coagulation profile is the same. It should be venous blood collected from a neat venipuncture. The sample should be quickly transferred to a tube containing specific chemical.
The person who collects the blood sample should make sure that the blood is filled up to the mark indicated on the tube without exceeding or going below the line. Immediately, the blood filled tube should be mixed gently to make sure the chemical is thoroughly mixed with blood. Without the above mentioned precautions, the risk of the test giving a false result is high.
Q How should you prepare before your blood is collected for these tests?
No special precautions or preparations are needed for coagulation tests. However, if the test is done to monitor the response to Warfarin therapy (a drug given to make blood non clottable inside blood vessels) remember to give your blood sample in the morning. Otherwise all these tests can be done as random tests.
QHow should the samples be transported?
Samples collected for coagulation tests should be transported at room temperature within a short period of time to the laboratory. For APTT, it is recommended that the test should be done within six hours from collection.
QWhen do we need these tests?
As I mentioned previously, if bleeding or clotting is a problem (when a bleeding disorder or thrombophilia is suspected), these tests are requested. However, considering its critical nature, these tests are reserved for clinicians to decide on when to do.
Tests of coagulation are requested before surgeries or before performing invasive procedures as a precaution to assess bleeding risk (or risk of clot formation) by surgeons. Based on these results, surgeons can take actions to treat such conditions and prevent bleeding during surgery. If PT and APTT are normal, a surgeon can confidently perform the surgery as he knows there is no major bleeding risk (except for rare conditions).
Women with an excessive menstrual flow (menorrhagia), or any individual with easy bruising, bleeding patches or bleeding in to joints etc. may need these tests. In intensive care, a critically ill patient needs coagulation tests frequently.
When monitoring treatment for bleeding disorders or thrombophilic conditions, these tests are done to assess the response to treatment. For example, warfarin or heparin treatment is given to a patient. We need these tests to monitor the status of the patient. Heparin is a drug used in treating heart attacks (myocardial infarction) or clot formation in leg veins or anywhere else in the body. We need APTT to monitor heparin treatment. We also need PT/INR to monitor warfarin therapy which we might discuss in future articles.
QHow are these tests performed and reported?
PT, APTT and almost all the other tests in coagulation profile are automated in many laboratories. Still some laboratories use traditional manual methods. PT, APTT and TT are reported in seconds while others are reported as concentrations. The time taken to form a ‘clot’ in seconds during test process is the results of PT/APTT and TT tests.
Q Can coagulation test results be erroneous?
Yes, this happens frequently, mainly due to sample collection errors. Therefore, the sample quality is very important. The test process needs meticulous attention as well. There should be daily quality control and monitoring.
Q Can the laboratory perform any other test with the same sample?
These are special tests and therefore, except for the tests of coagulation, no other tests can be performed using the same sample. Even the same test needs repetition and it should be done within a short period of time. If not, storage at freezing temperatures is needed.
Summary-The coagulation profile is a battery of investigations giving clues on how healthy your blood clotting system is. It provides very important information for the clinician for proper diagnosis and care of a patient with bleeding or thrombosis. Quality of these test results depend on many factors and collection errors are the most important. A laboratory with ISO 15189 or CAP accreditation, a qualified team including Haematologists to supervise is worth remembering.
