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03.06 Coagulation Studies (PT, PTT, INR)

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  1. Coagulation studies
    1. Normal Value Range
    2. Pathophysiology
    3. Special considerations
    4. Abnormal values

Nursing Points


  1. Normal value range
    1. PT – 11-14 seconds
    2. INR – 0.8-1.2
    3. PTT – 25-35 seconds
  2. Pathophysiology
    1. Intrinsic pathway
      1. Coagulation signals come from in the cell or inside the body
      2. PTT – Partial Thromboplastin time
      3. Used for heparin therapy
    2. Extrinsic pathway
      1. Coagulation signals come from external damage
      2. PT – Prothrombin time
      3. INR – International Normalized Ratio
        1. Used to standardize the test due to different tissue factors added
      4. Used for coumadin therapy
  3. Special considerations
    1. Sent in a blue top tube (citrate)
    2. Utilize the entire vacuum to make sure tube is full
    3. If patient is on heparin therapy, time is crucial to the lab draws for therapeutic range
  4. Abnormal values
    1. PTT
      1. Increased values
        1. DIC
          1. Treatments include different types of blood transfusions and sometimes critical care
        2. Liver disease
        3. Vitamin K deficiency
        4. Von Willebrand disease
          1. Treatment includes medications such as desmopressin
        5. Excessive heparin therapy
    2. PT/INR
      1. Increased values
        1. DIC
        2. Liver disease
        3. Vitamin K deficiency
        4. Warfarin therapy
      2. Decreased values
        1. Elevated vitamin K
        2. Birth control


  1. Assess patients for excessive bleeding or risks of bleeding

Nursing Concepts

  1. Lab Values
  2. Clotting

Patient Education

  1. For patients who have bleeding disorders, instruct patients to be cautious of injury.
  2. If patient has thrombocytopenia, instruct patient to seek emergency treatment in the event of bleeding that does not stop.

Reference Links

Study Tools

Video Transcript

Video Transcript

All right in this lesson, we’re going to take a look at coagulation studies.

So in order to understand coagulation studies you have to understand what’s included in them. So we’re going to evaluate three specific things. First one is PT or Prothrombin time, PTT or partial thromboplastin time, and INR, which stands for international normalized ratio. Now the first two tests are to evaluate clotting capabilities, and this is done literally in time. The last test, INR, is actually not measured in time but is actually a ratio of the patient’s PT versus a normal PT plugged into some crazy formula. What you need to know is that it’s a standardized test because of the way they have to perform the test. So let’s get into the ins and outs of what all of these values are.

The first thing we’re going to talk about are the two different pathways for coagulation; the intrinsic pathway versus the extrinsic pathway. Coagulation pathways and cascades are extremely complex. Intrinsic pathways are coagulation signals sent because there’s injury occurring inside a cell or the body. So if there is some sort of injury inside the body, it’s going to trigger the intrinsic coagulation pathway. The way we actually test to look for intrinsic pathway coagulation, is with the PTT, which also tests for factors XII, XI, IX, VIII, X, V, II and I. Your patients that are on Heparin therapy are going to use this test to determine the efficiency of that Heparin.

Now the other one is the extrinsic pathway, and this is injury that occurs outside the seller body. So this is something like some sort of trauma. What we do then is measure apt and an INR for those patients. like we just talked about the INR test is a standardized test. The way it works is they actually will introduce a tissue factor into a blood sample and see how long it takes to form a fibrin clot. Then they do some crazy calculations and you get your INR. You’re going to see this test for your patients that are on some sort of Warfarin therapy.

At this point, I’m sure that you’re wondering hey why is there a different process and different tests for measuring these two different anticoagulants. Here’s the difference. Coumadin interferes with the specific factors, and those are measured specifically with the PT and INR. Heparin however, Enhances an enzyme that’s not even related to vitamin K, and that makes that test more specific to PTT. There’s a cheat sheet that’s going to be attached to this lesson that’s great for looking at these different types of Pathways and how the different drugs interact throughout them so I really recommend that you check them out.

But what do you need to know specifically? The things that you need to recognize for your patients are that your PTT is a test used to evaluate Heparin, and that the PT INR is used to evaluate Warfarin Therapies.

So what tubes do we send them in and what is the process look like?

You’re one to send all of your coagulation studies typically in a blue top tube, and this has citrate in it. An important thing about this is that there’s a specific amount of citrate solution in the tube, and it’s directly proportional to the amount of blood that you put in. So this means that you need to fill that tube all the way up. The other thing you would think about is timing with sending in some of these coagulation studies. If your patients on a specific Heparin drip, you’re probably going to have to redraw your PTT at specific intervals, so pay attention to what your lab orders are, what your provider’s orders, and what your facility policy is regarding these particular Labs because their time is sensitive.

hat is an abnormal lab value look like for coag studies?. Well they’re based on time. You’re going to see increase or prolonged clotting times in situations like DIC or disseminated intravascular coagulation. The way that we treat these patient is that they’re going to get blood transfusions of different types of clotting factors and platelets in other types of fluids, and the goal there is their clotting factors are going haywire, so reintroducing a lot of these can help to reset the system. Those patients are often going to get critical care, just because they’re so tenuous. You’re also going to see it and liver disease and vitamin K deficiency. Another time you’re going to see a prolonged PTT is in a condition called Von Willebrand disease, which is where the Von Willebrand factor is altered and it causes prolonged clotting times. One of the treatments for this is a hormone called desmopressin. Another time that you may actually see prolonged PTT times are when your patient is receiving excessive Heparin therapy, so this is why we monitor them so closely until they are stable.

What about PT and INR?

You will see prolonged PT times and and increased INR in patients with d i see, liver disease, vitamin K deficiency, and Warfarin therapy. It’s not uncommon to see slight increases in INR for those patients and Warfarin therapy, but ask your providers what their goal is for that.

Decrease PT times and decrease INR are not very common, but you will see them in patients that have excessive or elevated vitamin K levels, or you’ll see them in patients that are on birth control. This is why blood clots are very common for patients that are on birth control, because it increases the risk.

Our nursing concepts for this lesson really focused on lab values and clotting when we are dealing with coagulation studies.

So let’s recap.

PT INR is a measurement of Prothrombin time, and you’re going to use this to test Warfarin.

PTT is your partial thromboplastin time, and that’s going to be used to test for Heparin.

All of these tests are evaluated in time, with the exception of INR. The thing to remember here is that excessive time means that there is an increased risk for bleeding.

When you’re submitting your blood samples for your coax studies, remember you’re going to submit them in a blue top tube and follow facility policy.

Lastly the one thing that you want to recommend is that you need to talk to your patients about the type of medication that they’re taking because they are at risk for bleeding. If they don’t understand the risk, they could potentially put themselves In Harm’s Way, so do your due diligence and educate your patient.

That’s it for a lesson on coagulation studies. Make sure you check out all the resources attached to this lesson. Now, go out and be your best selves today. And, as always, happy nursing!!