Low INR

[heartburst]

I've had my St Jude's valve since April 1st and I'm feeling great. My INR has gone down to 1.5 a couple times. I think it will take sometime for my body to adjust. My warfarin dose is a single 2.5mg pill per day, on Wednesdays I take 2. The clinic slightly increases the dose if I dip to low by doubling a single days dose.
My question is: how dangerous is that if at all? Can clots form when INR is low and break free sometime later when INR is in range and do damage?

I tried to attach a graph, but I get a prompt saying I'm not authorized to upload content.

 

[dick0236]

I've had my St Jude's valve since April 1st and I'm feeling great. My INR has gone down to 1.5 a couple times. I think it will take sometime for my body to adjust..........
My question is: how dangerous is that if at all? Can clots form when INR is low and break free sometime later when INR is in range and do damage?

The newer valves seem to function well with a lower INR value than the old valves (like mine). Is your INR range 2-3 or 2.5-3.5? If it is 2-3, a 1.5 should cause no problem.....but don't let it stay there. If it is 2.5-3.5, I'd talk with your cardio about not letting it go to a 1.5 level. Clots can, an do, form when INR falls close to normal......been there, done that and they can, will, cause damage if they break loose.

FYI.....clotting time in seconds at various INR levels*:
INR.....clots in seconds

1.0..... 12 (normal non-coagulated INR)
1.5..... 17
2.0..... 21
2.5..... 26
3.0..... 30
3.5..... 34

*UTHSC Dept of Pathol

 

[pellicle]

Hi

I've had my St Jude's valve since April 1st and I'm feeling great. My INR has gone down to 1.5 a couple times. I think it will take sometime for my body to adjust.

your body does not adjust ... you do not build immunity or tolerance. So if anyone at a clinic has put that idea into your head they are wrong.

1.5 a couple of times is mismanagement plain and simple. Please contact me by PM if you wish and I'll do my best to steer you straight on this.

My warfarin dose is a single 2.5mg pill per day, on Wednesdays I take 2. The clinic slightly increases the dose if I dip to low by doubling a single days dose.

common but not the correct approach ...

My question is: how dangerous is that if at all? Can clots form when INR is low and break free sometime later when INR is in range and do damage?

Ok, the short answer is "its probably OK, but avoid it"

The logner answer is: I wouldn't advise it often but on very rare occasions the evidence (specifically around management of operations for those on warfarin) suggests that you should be OK

Basically it works like this: there are two ways clots can cause you difficulty:

1. they form and adhere to the valve surface,
2. they form in the blood and continue to grow before they are munched up by the body

so we with mech valves (just like Atrial Fibrilation patients) can form blood clots freely in the blood. In our case they are triggered by (among other things) the closing and opening jets of pressure caused by the valve. To see this, get a tap running gently, stick your thumb over it to block it. As you just about get it blocked it squirts out at high velocity (compared to its trickle). That's a Jet

So, when your INR is lower than 2 the possibility of this occuring increases. We know from the GELIA study that people with valves like you have who's INR was down to 1.7 reported no additional problems. These are early studies and its unwise to just leap in and do that yourself until we know how more general this applies to the population (likely that it does) and how it relates to you specifically (unknown without testing).

So that suggests that dips below 1.7 to (say) 1.5 would be unlikely to cause harm from strokes in the short term (meaning 1 or two days). None the less I'd avoid it.

On the point of growth on the valve surface that's another issue which I don't believe that the GELIA study addresses. Thrombus is like snow, it attracts more thrombus. So if its ensconced on your valve it may grow. Below are two images of obstructive valve thrombosis:

This is obviously from a person with obstruction

And then this is from an animal (if I recall correctly) which was used to demonstrate the accumulation of thrombus on the valve surface

you can see the surface of the valve is covered in a thin "paint" of thrombus, So to my understanding this accumulates with successive low INR events and is gradually washed off by blood flow when INR is higher (like over 2) in much the same manner as water flowing over rocks reduces the growths there..

So you do not want to be at a low INR for lengthy periods (low meaning under 2 lengthy meaning days) for then this can build up and break off and then will be big enough to form a clot in blood vessel and cause you harm..

 

[LondonAndy]

My INR has gone down to 1.5 a couple times....

It is worth bearing in mind that INRs are subject to some variation, whether a blood draw at a clinic or using a meter at home, so if my INR was that low I would be concerned and up my Warfarin dose.

I had a six-monthly visit to my anti-coagulation clinic earlier this week to check my CoaguChek XS is operating within tolerance. The clinic blood draw was 2.52, and 3 minutes later my machine said 2.8 (my therapeutic range is 2.5 to 3.5), so I continue to be almost 100% in range for the last year but could be only just. I am not worried, but think I will aim slightly higher than I have been, just in case the clinic result is more accurate.

 

[Agian]

I have a coaguchek at home I use. I've noticed on two occasions that the blood draw was slightly lower than what I got at home. I'm happiest between 2.5 and 3. I adjust my own dose. I left the hospital with an INR of 1.4. Couldn't get out of their fast enough.

 

[Protimenow]

Occasionally doubling the dose is NOT the way to raise INR. The logic was to calculate a total WEEKLY dose, and try to take the same dose every day. The kind of variation that your clinic was suggesting is irresponsible. Even if you are safe at 1.5, keeping your INR around 2.0 or even slightly higher wouldn't make much (if any) difference in your daily activities. Why take the risk?

If your clinic can't manage your INR intelligently, you may have to find another clinic, or self-manage.

As far as test results go -- a blood draw is not always the 'gold standard' for anticoagulation management. There could be variance, depending on how the blood is handled, and how the test is run. The ANSI standard provides for a 30% difference between testing methods - a 1.7 on a blood draw could, conceivably, mean an actual INR of just under 1.2--a value that you do NOT want.

FWIW - I've tested all the commonly available meters (including CoaguChek XS, Coag-Sense, InRatio, and ProTime). I've found that the CoaguChek XS is frequently reporting an INR a few decimal points above the lab values. If your CoaguChek XS gives you a reading of 2.1, the lab may come up with values as low as 1.5. Thus, a lab test is certainly a good idea, so that you can compare your CoaguChek XS to the lab values.

I've found that my Coag-Sense gives me an INR that is usually below my blood draw results. This gives me a better sense of security than I get with the CoaguChek XS. If my Coag-Sense gives me a 2.1, the blood draw may be more like 2.5 or 2.6, which is fine with me. (BTW - the prothrombin time for meter and lab often fall within tenths of a second, indicating that the difference in calculated INR is related to a value for the reagent that is being used.

But, back to the main question -- I, personally, would NOT be happy with an INR of 1.5 (even with a new valve), and I wouldn't be happy with occasionally doubling the dose, rather than making a small increase in daily dosing to accomplish the same result.