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INR test and Warfarin dosage


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I have been taking Warfarin since I got my aortic valve replaced with a biological one last August in Japan. Unfortunately the cardiac surgeon was quite young and didn't tell me that I have to adjust the dosage of Warfarin quite often. Therefore my blood was in coagulation for nearly 3 months and I developed a flutter (kind of atrial fibrillation) and a thrombosis in an atrium. Now I'm in Thailand and I'm checking my INR level every week trying to keep it in the range between 2 and 3. I can't trust that doctor in Japan anymore so I don't know who could tell me the right dosage of Warfarin. In the hospital (Vajira) of Bangkok where I checked the INR they wanted me to do EKG, ECG and x-rays if I wanted to speak with a cardiologist. I asked to the Mission hospital and they want about 1600 baht to do the INR test and be visited by a cardiologist. Any convenient suggestion?

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Suggest if in Bangkok you go to Chula hospital and into the heart clinic on the first floor at OPD. First visit will possibly involve a little effort....take a Thai speaker with you.
Once in, you can get a 2/3 month check up including relevant blood tests

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It is really trial and error and even for the same person a dose that works well for a while may cease to do so.

Dosage changes should not be made more often than once a week as it takes time for the INR to change. And changes should be small.

There are drugs that do a much better job than warfarin at maintaining a steady rate of anticoagulation. They are, however, much more expensive.

With biological valves it is often possible to stop anticoagulation after a period of time, unlike mechanical valves where it must be taken life long.

Chula valve clinic is a good suggestion if you can tolerate the waits and other inconveniences.

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Thank you guys! I've just been hospitalised in Italy for 12 days and I got any possible test and examination there. I just need the INR test and the right dosage every 7-10 days. I think alternative anticoagulants are quite expensive in Japan, where I live and where I'll go in march after Thailand. It doesn't make sense to me to spend every week something like 2000 baht here in Thailand for a test that costs 200 baht and for a doctor opinion that would take not more than 2 minutes. After my first INR test in Thailand I got some suggestions by normal doctors or by students employed as doctors and frankly I found these suggestions untrustworthy. My next INR test will be on Wednesday and I will try to do it in Chula heart clinic. The next ones will be in Ranong, down south, and I guess it will be a mess. I've just tried to write to the Japanese hospital where I've got the surgery and the first disastrous check ups asking for an expert cardiologist that could help me by email with the right dosage after I write him/her the result of the INR test. Normally I wouldn't need warfarin anymore after 3 months from the surgery, but the 3 months in coagulation brought fibrillation, thrombosis and the need of anticoagulant, may be for the rest of my life according to the Italian doctors.

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You can get test kits to check the INR yourself. Or you can get it done at a lab rather than a hospital. In Bangkok, Bria Labs or RSU health Center can do this on demand.


You have a starting dose already.  You know the target INR. 


You can adjust dosage accordingly,  just remember to go slow and incrementally. For example, don't go up or down by more than 0.5mg at a time (unless INR is really off the charts high e.g. 4 or above) and always recheck INR a week after any adjustment.


Some people have to use alternating dosages to get it right, for example 3.0 mg/3.5mg on alternate days so keep that in min as an option.


Also note that there are a number of medications that interact with warfarin and may either block or enhance its action, so if you require any other meds be sure to research any possible interaction.



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Thank you Sheryl, your suggestions are really good. If I cannot contact any doctor I will keep on doing that, because I already started to decide the dosage 3 days ago. INR was 2,15 but it decreased from 3,14 in 12 days, so for 7 days I am taking alternately 7,5 and 10mg (average 8,5) a day instead of 8mg. A good cardiologist told me that in my conditions, with a thromb to be dissolved, I must stay in the 2-3 range and it is probably more dangerous to go below 2 than above 3..


I will be in Bangkok only 4 more days and I will go to the nearby hospital for the INR test. I stay in Phra Nakhon district and apparently there are no laboratories nearby.


I'm going to stay in an island with very limited facilities , like only generators for electricity from 6pm to 10pm, so it would be probably difficult the storage and the use of a self testing INR kit. 


I will probably go for the test in hospital every 7-10 days to Ranong, the town in mainland which is 3 hours away. Are 10 days too many?

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On 12/22/2018 at 7:40 PM, Sheryl said:

If you have changed dosage 7 days is best but could stretch to 10 if necessary.

If you have not changed dosage can go to 14 days and eventually once a month (when INR fairly stable).

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Very nice things to know, thanks a lot Sheryl

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there are no special storage considerations for a coaguchek pt/inr meter.

meter is battery powered.

having your own meter is the only way to go.

orafarin/warfarin is very affordable here and is over the counter.

i test weekly.

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I go to a private hospital once a month in Khampaeng Phet for a FBS and PT/INR test and that cost me


Date Tests Total cost
    Nursing + Midwifery charge   Physician evaluation + management     Lab investigation + pathology    
  FBS   PT+INR   CBC+HbA1c      


22 June 2017 yes ฿100 yes ฿100     ฿400   ฿600
21 September 2017                  
21 December 2017 yes ฿100 yes ฿100     ฿400   ฿600
29 March 2018 yes ฿100 yes ฿100     ฿400   ฿600
28 June 2018 yes ฿100 yes ฿100     ฿400   ฿600
25 October 2018 yes ฿150 yes ฿400 yes ฿900     ฿1,450
21 November 2018 yes ฿150 yes ฿400     ฿400   ฿950
20 December 2018 yes ฿150 yes ฿400 no   ฿400   ฿950


I take 6.5 mg of Orfarin and 2 x 500 mg daily as prescribed by the hospital doctor.


FBS results

Date mg/dl mmo/l
10 September 2013 138 7.7
08 October 2013 140 7.8
19 November 2013 130 7.2
19 December 2013 180 10
17 January 2014 117 6.5
25 February 2014 127 6.5
25 March 2014 138 7.7
08 April 2014 124 6.9
06 May 2014 124 6.9
18 December 2014 133 7.38
19 March 2015 136 7.55
18 June 2015 137 7.6
24 September 2015 131 7.3
28 December 2015 128 7.1
24 March 2016 132 7.3
23 June 2016 139 7.7
22 September 2016 122 6.8
23 December 2016 137 7.6
23 March 2017 146 8.1
22 June 2017 100 5.6
21 September 2017 129 7.2
21 December 2017 149 8.3
29 March 2018 165 8.9
27 June 2018 164 8.8
27 September 2018 191 10.6
25 October 2018 173 9.6
21 November 2018 143 7.9
20 December 2018 129 7.2


PT + INR results


INR International normalised ratio   About blood clotting
Test results      
  PT time in seconds range 10 - 14 PT time in seconds range 10 - 14 divided by 2 because I use Orfarin INR range of 1.9 to 2.5
10 September 2013      
08 October 2013 22.00 11.00 1.80
19 November 2013 22.00 11.00 1.80
19 December 2013 20.00 10.00 1.76
17 January 2014 16.00 8.00 1.37
25 February 2014 23.00 11.50 2.02
25 March 2014 14.00 7.00 1.12
08 April 2014 32.00 16.00 3.15
06 May 2014 33.00 16.50 3.29
03 June 2014 24.00 12.00 2.30
03 July 2014 17.00 8.50 1.37
31 July 2014 27.00 13.50 2.44
28 August 2014 27.00 13.50 2.58
25 September 2014 26.00 13.00 2.44
18 December 2014 23.00 11.50 2.16
18 March 2015 29.00 14.50 2.86
18 June 2015 26.00 13.00 2.44
24th September 2015 20.00 10.00 1.76
28 December 2015 22.00 11.00 2.02
23 March 2017 23.00 11.50 2.16
22 June 2017 23.00 11.50 2.16
21 September 2017 21.00 10.50 1.89
21 December 2017 28.00 14.00 2.75
29 March 2018 28.00 14.00 2.75
27 June 2018 25.00 12.50 2.30
27 September 2018 19.00 9.50 1.63
25 October 2018 22.00 11.00 1.71
21 November 2018 26.00 13.00 2.08
20 December 2018 28.00 14.00 2.75
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More expensive long tem is Xarelto (Rivaroxaban) which is one pill a day and no worries about dosage ( or how many green vegetables you're eating amongst other complications with warfarin)... Short term though like you may need it'll save all the testing and dosage hassles so may not work out hugely more expensive while doing its job immediately with less hassle. (i use it after a dvt years ago, and working offshore it makes testing and dosage levels irrelevant).


Either way, you'd obviously need to see a good heart specialist anyway either here or in Japan to sort it all out... it's shocking and disturbing that any surgeon ( heart ot otherwise, and of any age...) should be dispensing warfarin without proper follow up and checks on your required dosage levels for any reason, let alon after heart surgery. Ridiculous.



ps as i think mentioned above you - if i had gone down the warfarin route, after initial dosage and in hospital checks, the doctor explained that test strips and a testing meter are available so you monitor at home and save the hassle of further hospital checks beyond perhaps 6 monthly for precscription refill etc anyway.

The heart specilaist i was recommended/use was Dr Pradap at Bangkok General - he's heading for retirement next year.

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  • 5 months later...

First of all I wanna thank all of you for your precious suggestions. A bit late, I update my situation. While I was in the island for long time, I kept going to the hospital in the mainland every second week. Depending on the result of the INR test , I adjusted the dosage of warfarin according to your suggestions and INR was always between 2 and 3. A month after I came back to Japan, I could do the transesophageal eco cardio and it was great, the blood clot had disappeared. Straight away they did the heart electro version and even the atrial flutter disappeared. Now I should be alright. I keep on taking warfarin for 3 months and the doctor probably will suspend it if I will have no problems at the next checkup. I'm quite happy, many thanks again to all of you guys. I wish you all the best.

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