Heparin Drips: Help Me Understand PT's, PTT's, and INR's

zambezi, BSN, RN · Mar 30, 2005

PTT: Partial thromboplastin time

aPTT: activated partial thromboplastin time

These test for the same functions but the aPTT is a more sensitive version of the PTT that is used to monitor heparin therapy.

The range of therapeutic values for this lab test can vary from place to place...we just switched reagents used for the test and as a result all of our "normal" values changed.

The PTT is a one stage clotting test, it screens for coagulation disorders. IT detects deficiencies of the thromboplastin system and can show defects in the extrinsic coagulation mechanism pathway.

The aPTT is used to detect deficiencies in the intrinsic coagulation system and monitors heparin therapy.

IF the aPTT and PT are both drawn, further clarification of coagulation defects is possible. ie: a normal PT with an abnormal aPTT means that the defects is within the first stage of the clotting cascade. IF you have a normal PTT with an abnormal PT suggests a possible factor VII deficiency. If they are both prolonged, it can mean that there is deficiency of factor I, II, V, or X. Typically it is up to the doc to sort through the whole clotting cascade...

As for heparin therapy: in the blood, heparin combines with a alpha-globulin (Heparin cofactor) to form a potent antithrombin. This is a direct anticoagulant. The IV heparin that we use produces an immediate anticoagulant effect. Therapeutic values are typically 2-2.5 times the normal values. Heparin doesn't dissolve current clots (it can partially lyse them) but it does help prevent new clots from forming or previous clots from growing. The heparin is titrated to bring the aPTT within the desired range so that the patient is correctly anticoagulated. Careful monitoring is required because if the patient is not anticoagulated enough they could incur more damage due to more clots forming or current clots enlarging. IF the aPTT is too high, the patient is at risk for spontaneous bleeding, which is why we not only monitor labs but the patient as well (look for pink urine/hematuria, bleeding gums, oozing from wounds, bruising). Letting the patient know what to look for is like a second set of eyes for you too so have them report any of these symptoms.

PT: Prothrombin time Normal: 11-13

INR: International normalized ratio: a comparative rating of PT ratios (represents the observed PT ratio adjusted by the international reference thromboplastin)

Prothrombin is a protein produced by the liver for the clotting of blood. Production is dependent on adequate Vit.K intake and absorption. During the clotting process, prothrombin is converted to thrombin.

The PT thes directly measures a potential defect in stage II of the clotting mechanism through analysis of the clotting ability of 5 plasma coagulation factors (prothrombin, fibrinogin, factors V, VII, X). The PT commonly is ordered to monitor coumadin therapy.

Coumadin is an indirect anticoagulant therapy (heparin is a direct anticoagulant therapy). Often heparin initiates anticoagulant therapy and coumadin is later added and then the heparin is weaned off. Coumadin acts via the liver to delay coagulation by interfering with the action of the vitamin k related factors which promote clotting. They delay vit. K formation and cause the PT to prolong. The anticoagulant dose is adjusted until therapeutic range is reached. Coumadin takes 48-72 hours to make a measurable change in PT (typically 3-4 days of therapy).

Cardiac patients on coumadin are usually maintained at 2-2.5 times the normal baseline values. If below, the treatment may be ineffective and the old clot may expand or new clots may form. IF PT too high, bleeding can occur--so monitoring is very important. Various medical conditions, diets, etoh use, etc can cause the PT to increase or decrease.

The use of INR is more sensitive than PT. The target INR is typically 2-3

All of these tests are coagulation studies. The medications we are giving the patient works by interfering with the clotting cascade (so the patient's blood will "be thinner"). Therapeutic values (anticoagulation) are important to prevent further expansion of the clot and to prevent new clots. Too much anticoagulation can cause the patient to bleed (alot!). If using heparin, it is a good idea to keep an eye on platelets as well and keep an out out for sings of heparin induced thrombocytopenia (HIT).

It is our job to understand what the values mean because we are monitoring the patient (esp. while on heparin). In the unit that I work in, if the aPTT is prolonged, we follow our standard protocol to change the heparin dose and remonitor the lab values in 6-8 hours if we have to adjust the heparin dose. If the patient is within the desired range, we monitor every am or as needed. IF the aPTT is high, we know to monitor for increased signs of bleeding, keeping an eye on the H/H to make sure that it hasn't dropped significantly from previous levels, etc. The doctors makes the changes for coumadin dosages based on the PT/INR values. Another point to mention is that if you (or the phleb) are drawing the labs and have heparin running do not draw above the site of any IV (particularly the one with heparin) or your labs will be very increased causing you to turn down or off the heparin when in fact the patient may not be well anticoagulated--try to draw your labs in an arm that does not have an IV running (or at least draw well below the site).

I got a lot of this information from great book by Frances Fischbach...the book is called a manual of laboratory and diagnostic tests. IT is really easy to read and has all kinds of interesting stuff in it...I would recommend either having the floor you work on get one or buying one yourself as it is a very helpful reference for all kinds of tests and studies.

Nrs_angie, BSN, RN · Apr 10, 2005

That helps alot.

But I have questions still about heparine drips and calculating them.

First... I don't get when they say 2-2.5 X the normal value...

Could someone tell me first... What are the normal values for each

PT
INR
PTT
aPTT

Then I have also heard of a Control Number. Where is that and how do I find it. They also say it is 1.5-2.5 X the control number or something like that.

I don't understand... are you supposed to multiply that number by 2.5 or what?

This is soooo confusing to me.

Then with calculating the drip rates and raising it or lowering it.

Can someone give me an example of how a drip rate is increased or lowered. Please be specific... I am really confused.

Thanks so much

UM Review RN, ASN, RN · Apr 10, 2005

nrs_angie said:
That helps a lot.
But I have questions still about Heparine drips and calculating them.

I don't know how much help I can be here, because we rely on a heparin drip protocol at our hospital, but I'll try. First, I've reorganized your questions to group them together by topic. I've included my website resources so you can investigate further.

(Brace yourself for a mega-post.)

First, you need to realize that coumadin is associated with the pt/inr measurement, and heparin is associated with aptt measurement.

Why do we use heparin? Because you can get it into a patient's system fast, and because it can get out of the patient's system fast.

Coumadin takes longer to act and is more difficult to control. Coumadin is the long-term anticoagulation therapy, and until the pt/inr are therapeutic, you'll see the patient on heparin.

Quote
This is soooo confusing to me.
First... I don't get when they say 2-2.5 x the normal value...
Then i have also heard of a control number. Where is that and how do i find it. They also say it is 1.5-2.5 x the control number or something like that.
I don't understand... Are you supposed to multiply that number by 2.5 or what?

The International Normalized Ratio (INR)

INR was created by the world health organization because pt results can vary depending on the thromboplastin reagent used. the inr is a conversion unit that takes into account the different sensitivities of thromboplastins. the inr is widely accepted as the standard unit for reporting pt results.

nrs_angie said:
Could someone tell me first... what are the normal values for each
PT
INR
PTT
APTT

https://en.wikipedia.org/wiki/Prothrombin_time#International_normalized_ratio

PT/INR: The reference range for prothrombin time is 7-10 seconds; the range for the inr is 0.8-1.2.

The PTT and APTT that you mention are the same test.

Heparin Therapy

The APTT is used to monitor standard or unfractionated heparin but not low molecular weight heparin (lmwh) therapy.

To sum:

because there are different pathways to form clots, there are different products and different tests to detect the effectiveness of anticoagulation products.

Basically, coumadin's test is the PT/INR. Heparin's is the APTT.

Some of your confusion might lie with the fact that we test for several different clotting factors when a patient is on heparin therapy. The reason is obvious: if the patient's aptt is therapeutic, that's good. But while they're on heparin therapy, if their platelets are too low, the patient will bleed out. That's bad. Even if the heparin is not the culprit.

nrs_angie said:
Then with calculating the drip rates and raising it or lowering it.
Can someone give me an example of how a drip rate is increased or lowered. please be specific... I am really confused.
Thanks so much.

At my hospital, we don't calculate. We follow a protocol sheet. Every 6 hours, we have a PTT drawn. I can't recall offhand, but I think that if the aptt is between 50-75, it's therapeutic. Higher, and we have to reduce the drip rate (with another nurse to witness the change and verify it) as well as hold the heparin for a certain period of time. If the APTT is too low, we might have to give a bolus, then increase the drip rate.

You're right. It is complicated, even with a protocol to follow. In addition, we have to have a daily PT/INR, CBC, and once the patient is therapeutic x2 APTTs, we draw only a daily APTT.

Also, with a patient on heparin, please make sure that the lab draws the sample from the other arm, not the one getting the heparin. It skews the results, I'm told.

I sure hope you could make sense of this, angie. If you have any more questions, feel free to ask. I might not know, but I can sure track down some interesting net resources to help you find out!

surviveslu · May 20, 2011

Would like to know what your hosp protocol requires in terms of hep drip documentation?

christina4nursing · Jun 26, 2011

Just wanted to thank you for your helpful post. I needed it badly. learned alot and have to talk with the lab at my hospital and find out the specific protocol too. Im a new grad and had some difficulty with heparin drips my last day on the floor. Reading through all this will really help me out next time i am on the floor and have a patient on the heparin drip. Thanks again.