How often do/should we test?

[Protimenow]

This subject has been addressed on other threads, and at other times, but I think it's good to bring it here, where the actual issue can be discussed.

I have St. Jude valve.

I have an InRatio (and a ProTime) INR test machine. I test weekly, unless my INR is out of range (which occasionally happens). If I'm out of range, I make my adjustments and check more often than weekly.

At times, I take a 'weekly' dose that requires a larger dose on some days than on others. I've found that my INR differs, depending on the day I take my INR, based on the dosage I took a few days earlier. On these occasions, although I may be 'in range', my INR is NOT stable. (And, yes, it can vary at different times of the day, and can't be expected to be the same ALL the time).

I know that some doctors are satisfied with testing every two weeks (which only tells how the INR is, based on dosage and other factors a few days earlier, but not what happened during the two week lapse.) Others conclude that, if INRs are within range every two weeks for a few months, it's okay to start testing monthly (which, again, allows for a LOT of time to be out of range without having it detected).

At one time, I agreed with these great learned minds. Once I got my tester, I tested weekly (usually).

At one time, testing involved a blood draw. It was expensive and inconvenient, and these factors made it easier to argue against more frequent testing.

Today, with meters available at relatively low cost, and test strips running between $5 and $10, and many warfarin takers able to do testing at home, I don't see the value of increased risk of stroke or embolism when weighed against the avoided cost of an extra test or two (or three) each month.

So I test weekly. I've suggested that others should do the same -- even if they THINK their INRs are stable, and their diets, activities and dosages don't change enough to take their INRs out of range. Not all have agreed.

I expect to get slammed by some who don't agree.

However, I think it may be good to have a conversation about this, and get some other experiences or histories.

 

[chaconne]

Protime,

Thanks for starting this thread. Personally, I enjoy lively debate and heated arguments, as long as it doesn't result in personal attacks and name calling. Sometimes it's difficult to know the state of emotion or intent through typed words, but I hope we can have a civilized discussion, and that no one feels threatened or overly criticized.

In the other thread:

http://www.valvereplacement.org/forums/showthread.php?38962-Coagucheck-vs-InRatio/page4

I mentioned data analysis of periodic INR fluctuations. It sounds like your INR is changing more rapidly than I originally thought was possible. How much does your INR change over 1 day? The sampling rate you might need to catch all spikes/dips may be more frequent.

 

[Protimenow]

Chaconne -- amen to the points you made about civilized discussion.

I don't know that my INR changes much more than anyone else's, but it is possible to make it drop like a rock by taking supplements or eating green foods with large amounts of Vitamin K. These changes can happen in hours. It may also be possible to raise an INR - perhaps not quite as quickly - by taking certain things that increase the effectiveness of warfarin. (Pycnogenol and testosterone are among the materials that can make an INR jump). Oral antibiotics can also raise an INR.

In short, the idea of having a 'stable' INR is more theory than fact, even for people who believe their INR is stable -- and who don't carefully consider the possible effect of ANY change in diet or medication. (This is why I check my INR a few days after making changes, just in case there are unexpected effects. It's also why I check online for known interactions between warfarin and any new substance that I consider taking).

 

[chaconne]

I don't know that my INR changes much more than anyone else's, but it is possible to make it drop like a rock by taking supplements or eating green foods with large amounts of Vitamin K. These changes can happen in hours. It may also be possible to raise an INR - perhaps not quite as quickly - by taking certain things that increase the effectiveness of warfarin. (Pycnogenol and testosterone are among the materials that can make an INR jump). Oral antibiotics can also raise an INR.

Wow, I hadn't realized that Vitamin K could cause INR to drop so quickly. Warfarin changes it on a few days basis but Vitamin K things can change it in hours? If so, this blows away my theory that you only need to sample on Warfarin's time table and this is why K is a good antidote to high INR. K is definitely the higher frequency component.

On the stability side, I would still argue from a probability and sampling point of view, that as long as your dose and INR value are stable over several months, you can assume it's stable in shorter intervals. The exception to this being what pem said in the other thread about someone eating too much vitamin K foods right after each test.

 

[Protimenow]

I have argued the same thing in the past -- that, if your INR has been stable for each test for a few months, and your dosing and diet haven't changed, that you can go for longer periods without testing. I no longer believe that, and I'm extremely glad to have a meter, so I can test my INR and make minor adjustments if necessary, and a bit more drastic adjustments when I somehow drift out of range.

Although having consistent results from test to test is comforting, and gives you the impression that the consistency means you can go for long intervals without testing, this isn't always necessarily the case. I'd much rather test too much than save a few dollars by skipping some tests and wind up, between tests, with a problem.

Also -- in addition to Vitamin K rich foods, I mentioned other foods and materials that can amplify warfarin's effects. Not all of these are well documented, and interactions may be hard to find when searching various databases. It's easy to make minor changes (more salads than usual for a few days, or an antibiotic for a few days, or something seemingly insignificant) that actually CAN push an INR out of range. Without more frequent testing, a person may not even know the INR has moved out of range.

 

[chaconne]

That you can have stable long term measurements, but fluctuations in between, points to unusual activities that don't occur often enough to land on the days you test, but cause changes in the INR. In this case, the INR would go to a stable value most of the time. I think it also depends on how long the "stable" period is. If it's infinite (you've been sampling INR for decades with no fluctuations in INR or dose), then the points in between are much more likely the same. If it's stable only a few months, sampling each month, the infrequent "noise" events may not be reflected.

In other words, the longer the stable period, the more likely it is that there are no events that occurred between the points you measured (the past), HOWEVER, this does not mean that you will not get a different INR the next time you measure. your past results don't mean your future success (like the stock market!).

.....well, maybe you do, if you know how your body reacts and what things cause fluctuation, or if your body chemistry just causes you to be naturally stable. There do seem to be stable and unstable users out there. I will soon find out what type I am.

Pardon my rambling, I'm just trying to get a grip on what I will be in for.

 

[Protimenow]

I'm sure you'll be just fine. Although there are a few people who don't do well on warfarin, the majority DO. There is genetic testing that can help to determine your starting dose -- but they may not bother with this testing. It's probably expensive, and the predictions are usually based on ethnic background.

(The next few paragraphs may sound a bit too much like a statistical discussion -- you're all welcome to skip to the end)

It's nice to assume that having the same (or similar) results on each test, with consistent results for many years, suggests that your likelihood of being stable all the time is interesting -- but probably not accurate. Imagine, for example, that a person gets tested monthly, say, on the fifteenth of each month. Imagine, too, that this person's weekly dosing requires higher doses on some days than on others. If this person goes by a dosing schedule that is based on the day of the month, and this person takes a higher dose on the 12th, 19th, 26th, and 5th of the month than (s)he does on other days, the test on the 15th will probably show a primary effect of the dose on the 12th. If the test had been taken on the 18th of the month, it may be significantly different. However, to the person having the test - -and his clinician - it will look as if this person has a stable INR. (Yes - stable on that day, but fluctuating when doses are lower). If the test on the 15th is at the bottom of the range, this would strongly suggest that on 4 or 5 days EACH WEEK, the INR would be below range, and not detected. (I was thinking of a sine wave of INR values, related to dosing and perhaps other factors, and the testing done at an inflection point -- giving the appearance of stability where none exists -- but chose not to elaborate on that one).

In the past, I believed that past consistency for many years DID predict future stability. I maintained my dose, and assumed that my INR was always in range. In retrospect, I believe this was dangerous and I'm lucky not to have had a problem.

What I think often separates the 'stable' from the 'unstable' users is how frequently they test. Those who test more frequently probably detect more fluctuations than those who infrequently test. Research shows that those to do self-testing are more often in range than those who don't. This is likely related to the increased frequency of testing, and the ability to make minor adjustments when necessary. Making testing infrequent, with little to go on other than consistent dosing, can result in more time out of range, because there are fewer data points at which to adjust. So, although frequent testers may seem to be less 'stable,' they're probably more able to stay in range than those who test infrequently.

(Back to plain talk)

Back to your situation -- I don't think you'll have any trouble managing your INR. It may take a while to regulate while your body heals. If you can, get your own meter. You can call in results to your doctor or an anticoagulation clinic or, if you and your doctor are comfortable with it, you might even manage your own dosing. This should make life with warfarin fairly easy for you.

There's a lot of research being done to come up with a magic drug that will prevent clotting on mechanical valves. If and when that drug comes out, your concerns with managing anticoagulation with warfarin may disappear. (Paying for this miracle drug may be a problem that replaces management with warfarin).

 

[chaconne]

It's nice to assume that having the same (or similar) results on each test, with consistent results for many years, suggests that your likelihood of being stable all the time is interesting -- but probably not accurate. Imagine, for example, that a person gets tested monthly, say, on the fifteenth of each month. Imagine, too, that this person's weekly dosing requires higher doses on some days than on others. If this person goes by a dosing schedule that is based on the day of the month, and this person takes a higher dose on the 12th, 19th, 26th, and 5th of the month than (s)he does on other days, the test on the 15th will probably show a primary effect of the dose on the 12th. If the test had been taken on the 18th of the month, it may be significantly different. However, to the person having the test - -and his clinician - it will look as if this person has a stable INR. (Yes - stable on that day, but fluctuating when doses are lower). If the test on the 15th is at the bottom of the range, this would strongly suggest that on 4 or 5 days EACH WEEK, the INR would be below range, and not detected. (I was thinking of a sine wave of INR values, related to dosing and perhaps other factors, and the testing done at an inflection point -- giving the appearance of stability where none exists -- but chose not to elaborate on that one).

Yes, the varying dose, leading to a sinusoidal INR is an issue. Here the sampling frequency can be in sync with the dose variance and the fluctuations are masked. But aren't these usually small INR fluctuations, that could be made even smaller by cutting pills in half and taking the same exact amount every day? I guess that even taking the same pill size every day leads to a small sinusoidal fluctuation in INR.

 

[RobThatsMe]

In simple terminology.. I test every two weeks. I used to test weekly, but over time, I realized that I was stable enough to test every other week. That being said, there are a few other interesting events that I noticed. If I adjusted while testing weekly, I had more swings in my range. Now that I am testing every other week, I do not see the same swings in my range.

Now, if I have to take some medication that is temporary, or had to reduce my dose for a minor surgery reason, then, I go back to weekly testing until I feel confident that I have again reached a stable level.

Will I ever go to monthly testing? Not a chance. I feel safe, and can easily adjust on an every other week schedule, as long as diet, eating habits, etc are constant. BUT... would not risk once a month testing. I like peace of mind.

This drug reacts differently with each person. Some of us have real major swings. Their body may process the drug faster than others. Some are not as strict with their eating habits. If you home test, you get to know your body, and how it reacts to the drug much better than any of the so called experts at the coumadin clinics. That being said, some of us when we become elderly, may have to rely more on the clinics due to the issues that come with old age.

As always, the above is based on my own experience and opinions developed while using this drug for the past 11+ years.

Rob

 

[Protimenow]

Rob:

I test weekly. I don't adjust my dose unless I am out of range -- or at the top of the range. I think that only correcting when you're out of range (or almost out) will reduce time out of range -- I let my body do what it will do with a standard dose. I make VERY FEW adjustments, even though I test weekly. I expect my INR to remain consistent, week after week, unless I make some changes in diet, activity, or supplements.

Like you, I figured it was safe to go to testing every two weeks. (With strips STILL being somewhat expensive for me, I figured that I'd save $10 or so each month by switching to testing every two weeks). The last time I tried to push it out to two weeks, something told me to test at ten days. On day 10, my INR was 1.1. If I had waited until day 14, I may have gone another four days uncorrected. Although it may not happen again, I'm more comfortable paying a few more bucks each month so I can test weekly than I would be in assuming ongoing consistency and testing every two or more weeks.

(I've been using warfarin for 20 years, and at one time thought I could tell, from symptoms, when my INR was high or low. Now, I'd rather use a meter to confirm, and feel a lot more comfortable this way)

 

[bahlvarun]

Speaking of symptoms, have you folks watched these, whenever I am in the front seat of my car, I put my hand on the hand break of the car(not a good Idea I know), after a few minutes it becomes light red, showing my INR is in range. Once I was sitting at my relatives place and resting on my hand, after a while I saw my hand was not have the symptom mentioned above in this post. I got my INR checked at it was below the range.

May be this is my way of testing without a meter ;-), I do test on a weekly basis though and look for such signs in my body.

 

[njean]

Speaking of symptoms, have you folks watched these, whenever I am in the front seat of my car, I put my hand on the hand break of the car(not a good Idea I know), after a few minutes it becomes light red, showing my INR is in range. Once I was sitting at my relatives place and resting on my hand, after a while I saw my hand was not have the symptom mentioned above in this post. I got my INR checked at it was below the range.

May be this is my way of testing without a meter ;-), I do test on a weekly basis though and look for such signs in my body.

I'm glad to see someone else who has "signs" when their INR is out of range. I've been testing for 36 years and when my INR is out of kilter, I start feeling weird! I have mentioned these symptoms before, here, to my doctors, and have been dubbed an odd ball, or laughed at because most believe there is no way to know when your INR is out of range!

One time I remember telling a cardiologist that one of the stronger signs I had when my INR was on the "thin" side, was that I would start getting a burning sensation inside the lower portion of my abdomen. The burning was/is located where I had the incision for a hysterectomy performed many years ago. He just started laughing and said, "is impossible, is impossible". But I think I got the last laugh when I fired him!

Another sign for me is, awful aches on all my joints and pain in my lower back and sleeplessness. And mind you, all these symptoms happen like I said, when my INR is on the high side. I don't seem to have any when it's on the low range.

So that's why I'm so glad I have my home monitor and am able to test when I want to or feeling really weird!

 

[Protimenow]

Chaconne -- you'll find that Warfarin and Coumadin are available in a wide range of dosages - 1 mg, 2 mg. 2.5 mg, 4 mg, 5 mg, 7.5 mg, and 10 mg (and probably others) Using a combination of these pills, it's possible to get practically any dose you need, within .5 mg or so. (Right now, I take 6 mg - one 4 mg and one half of another 4 mg -- if I had 1 mg warfarin, it could be 1/2 of a 10 mg and a whole 1 mg). Although it CAN be done, I'm not sure anyone would want to take more than two warfarins each day in order to reach these values.

The dosing schedules are based on a weekly total -- and some values just can't be divided into sevenths and dosages made to match.

But you're right - in most cases the fluctuations will probably keep a person in range. However, if your INRs are consistently at the low end of the range for each monthly test, and this is four days after taking your HIGHEST dose, it's possible that other times during the week or month the INR is below range.

I just get concerned when I hear of people testing infrequently because they assume that in range tests every month ASSURE THEM that their INRs during the entire month are in range. It just isn't always the case, and can be a heavy price to pay if serious deviations in INR occur during the month.

 

[Protimenow]

Norma -- yes, I still believe (though not quite as strongly) that it's possible to tell when my INR is out of whack. From such subtle symptoms as bruising more easily than normal (or having bruises pop up that shouldn't have) to other more subtle things (not having had a hysterectomy, I don't have a scar I can refer to -- and being male doesn't help), I actually DO think that some of us can tell.

It's probably why I tested at ten days recently when I was committed to testing every two weeks. SOMETHING inside me told me to test -- and I had a 1.1.

I've been taking warfarin for 20 years -- after 16 years, I figured that I can tell when the INR is out of range (but not as far out as necessary for bloody noses or other hemorraging), and get by with infrequent testing.

It's great to have a meter and to be able to self-test -- rather than relying on these feelings to tell me when to adjust my dosage and just hoping that I'm right.

 

[njean]

Chaconne -- you'll find that Warfarin and Coumadin are available in a wide range of dosages - 1 mg, 2 mg. 2.5 mg, 4 mg, 5 mg, 7.5 mg, and 10 mg (and probably others) Using a combination of these pills, it's possible to get practically any dose you need, within .5 mg or so. (Right now, I take 6 mg - one 4 mg and one half of another 4 mg -- if I had 1 mg warfarin, it could be 1/2 of a 10 mg and a whole 1 mg). Although it CAN be done, I'm not sure anyone would want to take more than two warfarins each day in order to reach these values.

The dosing schedules are based on a weekly total -- and some values just can't be divided into sevenths and dosages made to match.

But you're right - in most cases the fluctuations will probably keep a person in range. However, if your INRs are consistently at the low end of the range for each monthly test, and this is four days after taking your HIGHEST dose, it's possible that other times during the week or month the INR is below range.

I just get concerned when I hear of people testing infrequently because they assume that in range tests every month ASSURE THEM that their INRs during the entire month are in range. It just isn't always the case, and can be a heavy price to pay if serious deviations in INR occur during the month.

I'll tell you a little secret:

Before I had this last OHS in 2006, and before I had my home monitor, my cardiologist only required me to test monthly!!! I tested MONTHLY for 30 years at the lab. And very seldom was I out of range and never suffered an 'event' of any sort.

I've also had a number of other surgeries, besides the 3 OHS, and had to test more frequently right after those surgeries but that stands to reason.

I think what prompted my new cardio's to more frequent INR testing, is the fact that I now have a St. Jude mechanical aortic valve swapped out in 2006 and a much older, 36-year old Cooley-Cutter mechanical valve in the mitral position. The cooley-cutter mitral valve, resembles the Bijorn-Shiley that some of us lucky oldies had implanted back in the 60's and 70's.

Now, I suffer from Stage II-III CHF, due to scar tissue that has overtaken the old mitral mechanical valve making it virtually impossible to replace because of the risks involved. It is this same scar tissue that caused me to have to have the old aortic mechanical swapped out for a new St. Jude 5 years ago.

So I guess I CAN refer to myself as an odd ball......a very lucky oddball! I continue to live with one pretty new aortic and one really old mitral!

And one more thing I want to add: The doctors would be perfectly happy if I kept my INR at the higher range between 3.5 - 4.0 due to the age, mis-matched valves, however, they seem to finally sympathize with symptoms I feel when at the higher range.

 

[Protimenow]

Norma: With your older valve, 3.5-4.0 is the appropriate range (according to ABCs of Anticoagulation - a small medical book written for physicians, in my e-library). I tested monthly - or even less frequently - in the past. It's not necessarily unsafe --- but I certainly would NOT recommend it - especially with the easy availability of meters and strips.

Like you, my tests used to be 'tap-a-vessel' affairs -- and although there was probably little pain associated, they were inconvenient and expensive -- and seemed to justify a delay between tests. Plus, when the meters were not yet available, there was no choice - and even though risky, testing every 2-4 weeks seemed appropriate.

Today, with meters available (and, for some people, even affordable), the old logic of delaying INR tests (partially because of cost, even though few admit it) maybe shouldn't apply. When you can confirm that your INR is stable and in range for about $20 or so a month; and can make adjustments if, during the month, you wind up out of range, why wouldn't a person test weekly? Sure - the extra $15 or so may seem an unnecessary expense most of the time, but it'll prove to be well worth it if you ever DO go out of range and otherwise wouldn't know it.

 

[chaconne]

I don't know that my INR changes much more than anyone else's, but it is possible to make it drop like a rock by taking supplements or eating green foods with large amounts of Vitamin K. These changes can happen in hours. It may also be possible to raise an INR - perhaps not quite as quickly - by taking certain things that increase the effectiveness of warfarin. (Pycnogenol and testosterone are among the materials that can make an INR jump). Oral antibiotics can also raise an INR.

Couldn't one argue that you should test daily or even hourly, since INR could drop out of range in hours?

 

[ElectLive]

That you can have stable long term measurements, but fluctuations in between, points to unusual activities that don't occur often enough to land on the days you test, but cause changes in the INR. In this case, the INR would go to a stable value most of the time. I think it also depends on how long the "stable" period is. If it's infinite (you've been sampling INR for decades with no fluctuations in INR or dose), then the points in between are much more likely the same. If it's stable only a few months, sampling each month, the infrequent "noise" events may not be reflected.

In other words, the longer the stable period, the more likely it is that there are no events that occurred between the points you measured (the past), HOWEVER, this does not mean that you will not get a different INR the next time you measure. your past results don't mean your future success (like the stock market!).

.....well, maybe you do, if you know how your body reacts and what things cause fluctuation, or if your body chemistry just causes you to be naturally stable. There do seem to be stable and unstable users out there. I will soon find out what type I am.

Here's a graphic that may be of interest for these discussions:

Each data point (dot) represents a patient in a clinical trial using Warfarin. There were 6,000 patients total. The bottom of the graph represents total days on warfarin divided by total number of INR measurements, so basically the average frequency of testing. The left side of the graph represents percentage of time in range, which in this trial was INR 2 to 3. The black reference lines indicate 30 days and 64% therapeutic.

Now, I think it's a pretty revealing graphic, but it does have limitations for this discussion. These are single point representations of likely fixed individual patient patterns, not multi point of patients testing out different patterns to see what works best. But I think it does point to the wide spectrum of patient manageability that will exist at any given testing frequency.

I actually come at this from another angle. Diabetics (like me) consider many of these same issues, but it's at the scale of the day, not the month. Trending is a big catchword. What often works best is "overtesting". The logic is that you don't know how often you need to test, until you test significantly more than that amount and get a firm handle on what data is meaningful and what is useless. This isn't really groundbreaking of course, in fact some of the posts above seem to already touch on this strategy, as well as the importance of ramping up for expected changes.

I tell you what...diabetics are blessed with monitoring technology. Glucose meters that fit on top of a vial of strips, "lab grade" A1c testers now on the aisles of drugstores, and 24/7 (in 5 minute chunks anyway) wearable glucose sensors. Those glucose sensors are an interesting case study. When they first came out, it was a "wow" concept. But medicine isn't about the wow, it's about what is reasonable for improving patient care. So insurance coverage dragged behind. Who needs these new glucose sensors, after all, diabetics have been doing just fine without them, right?

Well, it just takes some determined manufacturers who want to make a big profit, and some willing doctors (the easy part) to start testing out patients, and before you know it, there's a load of study evidence that proves that the "wow" actually has some meat to it, that patients are actually better off because of it. Next thing you know, insurance coverage is commonplace, and sales soar. Now INR is a completely different testing technology, of course, but relative to the last post ("daily or even hourly"), imagine if you had a small device in your pocket that beeped when your INR went out of range. Sounds pretty far fetched, huh? Well, I don't know, the same thing seemed pretty far fetched to diabetics only about a decade ago. Is it unnecessary a lot of the time? Absolutely. Is it worth it, then, for the limited times when it does matter? I think so and thankfully my insurance company agrees.

Ok, so that's my detour, let me get back to the question at hand, since I actually have a question of my own. Are home testing devices with a weekly test strip allotment fairly commonplace with insurance coverage currently? If not, do any of the device manufacturers seem to be pushing the issue?

 

[Protimenow]

A few things - Chaconne - hourly doesn't make much sense, except for someone who is at the borderline of being in or out of range -- and the fluctuations over an hour will probably be a few tenths of a point. That said, with certain foods or medications, a person's INR COULD change significantly in a 12 or 24 hour period. (There are a lot of posts, over the past few years, from people who've had a lot more greens than usual, and whose INRs have taken significant drops. There are also posts advising users with INRs above their range to eat more greens for a few days - or others who decided on their own to do this when their INRs were too high). I wouldn't argue strenuously against daily testing - especially if the person realized that their diet or activity changed - or they added some new medication to their daily pills.

In fact, when my INR dropped a few months ago, I DID test daily for a few days (knowing that the INR would not represent full dosing effect for a few days, but also knowing that there IS a partial effect of warfarin within 24 hours, and the major effect occurs a few days later).

EL -- that's an interesting graphic, and, if I'm reading it right, it shows a disturbing number of people who are out of range.

At this point, there's no technology for determining INR without actually drawing blood and mixing it with a reagent. It would certainly be good if there was a device that attaches to the fingertip, or perhaps an optical device that looks through the skin and monitors blood flow to somehow compute an INR, but that's probably far down the road. By the time such a meter is available, it certainly would be great if there's a medication that simply suppresses the formation of clots on mechanical valves or inside the heart's chambers.

Currently, I don't know of any insurance that covers weekly testing - although this is possibly the case with some anticoagulation clinics. I can't comment on how commonplace the reimbursement for weekly testing supplies actually is. I suspect that some actuarial somewhere may determine that the cost of testing weekly, using a meter and relatively inexpensive test strip is less than the cost for emergency room care of patients with dangerously high or low INRs, or, worse, for hemorrhaging or stroke. (Actually, depending on the patient's valve, age, and length of time after surgery, the concept of dangerously low can be corrected just by temporary dose increase and more frequent monitoring until the patient is back in range).

IF the amount of tests with meters SHOULD double or quadruple (moving from two or four times a month to weekly), perhaps the cost of the strips will drop because of economies of scale - although the manufacturers will probably try for the same price, because they can probably get it. There are two strong competitors in the meter/strip business, and a third that is probably not doing as well in the United States. However, there doesn't appear to be any downward price pressure resulting from competition -- and there may not be as long as the manufacturers have patents on their strips and devices, and no third parties can compete by offering less expensive strips.

There may not be enough incentive for additional manufacturers to develop their own meters, and thus creating more competition for the testing dollar. (I'm trying to equate this with the issue of the inexpensive -- almost throwaway - blood glucose meters currently available. There's just not the same level of competition, or the volume of strips required for INR testing when compared to the multiple times daily testing of blood glucose).

Your question: "Is it unnecessary a lot of the time? Absolutely. Is it worth it, then, for the limited times when it does matter?" is relevant to INR monitoring, too. I suspect that most people are in range most of the time. But being out of range can be somewhat unpredictable, and can be catastrophic. That's one of the main reasons why I believe that weekly testing should be a minimum -- and that for the times when a person adds or removes a medication, changes diet, changes activities, etc., it may even be sensible to test even more often.

Having access to affordable meters and inexpensive supplies could make this possible.

(There is probably also a population of people who have no doctors, take warfarin, and don't have the resources to afford regular testing. It's important that this probably small, but underserved group, can get regular testing)

 

[chaconne]

Very interesting graph Elect.

The surprising thing to me is that it doesn't appear, according the cluster on the plot, that there is a correlation between frequency of testing and being in range. I would have expected the group of points to slope up toward 100% when days between tests were lower and down toward 0% when days between tests were higher. In other words, shouldn't testing more often mean being in range a greater % of the time? I would certainly expect some correlation. What am I missing?