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PT/INR instant results? Accurate?

Specializes in OB, M/S, HH, Medical Imaging RN.

I have a PT/INR meter which I would liken to a glucometer. A drop of blood and it calibrates the PT/INR. I wonder does anyone know how accurate it is? The first patient I tested with it had a PT of 66.6 and a INR of 6.9. I called the doctor of course. He had the patient hold his coumadin for 3 days. I went back and retested and got an INR of 3.5. The doctor then told him to start back on the coumadin but at half the dose he had been on. Three days later I tested him and his INR was 4.9. Some patients I draw blood on for the PT/INR and some I'm told to just check with the meter. I wondering how accurate it is? I'm thinking the next time I draw blood for a PT/INR I ought to also check it with the meter and then see if the results turn out to be the same. Just wondering if any of you have experience with the PT/INR meter? Thanks


Specializes in Rehab, Step-down,Tele,Hospice.

Good timing Dutchgirl, for the last two patients I drew a PT/INR on, I got exactly the same reading : 4.2 and 31.3 both times, I was wondering if the dang machine was working or not?

Also question: does anyone know how long the plastic strip things are good for once out of the fridge?

CardioTrans, BSN, RN


We used the machines as well. If they are set up correctly before they are used then they are usually very accurate. If I ever got a big difference in 2 different strips from the same pt during the same visit, I would call the MD, let them know that I was going to do a venipunture as well. Then compare the results. We had it happen on 2 occasions and the machine needed to be recalibrated.

We were told the packs are good for 8 hrs after being removed from the fridge and that they needed to be at room temp for at least 45 min before using.

DutchgirlRN, ASN, RN

Specializes in OB, M/S, HH, Medical Imaging RN.

Wow. Unbelieveable! No one ever told me that they needed to be refrigerated, and the office does not refrigerate them. Nor are they aware that they are to be used at room temperature. I had mine in my car which was cold and I was told it's accurate no matter the temperature. I will go back and read the manual and bring that to everyone's attention. Thanks so very much!

I am an engineer not a nurse but have some inr home testing experience. My wife has A-fib and a mitral valve prosthesis. She also has inr instability which adds to the testing dilemma. We used the INRatio meter (strips do not require refrigeration) for more than a year but the cardiologist became suspicious when numbers change faster than coumadin therapy would suggest.

We did comparison readings between venipuncture and the meter for several weeks. The meter varied from a point or two to more than a full number from the lab reading. The greatest errors were when above target (her range is 3.0-3.5). We tried strips from different lots and even a replacement meter to no avail. The cardiologist lost faith in the meter and we are again driving to the lab once a week and sometimes more due to the instability.

As a side note I have read about treating inr instability with a constant vitamin K regimin of 100mcg per day. The theory being that working the coumadin against a K threshold is better than against a possible K deficiency. The cardiologist is unwilling to step out of the box and try it. If it were me I would try it but my wife is dubious.

We long to go back to the convenience of home testing. This week we have been snowed in so are two days late with the lab visit. Also the weekly testing keeps her from visiting her mother as we can't get same day test results in her hometown. I would appreciate any experience or suggestions as to an accurate meter.

we use the INRATIO machine , i have done a fingerstick and venipuncture on the same patient just to compare results and they were accurate, now not all strips need to be refrigerated, so that depends on the machine,,,,also the INRATIO can not be used if the patient is on Lovenox.

In addition to using the Hemosense Meter for regular use in my home health practice, I am an area trainer for Alere Medical who is a supplier of Hemosense Meters as well as Coagucheck. Please refer to the temperature storage for the strips for each individual meter based on manufacturer. Manufacturer has recommendations for use of the strips once they are removed from the multi strip bottle or individual foil packages and exposed to air or light. Meters will not test with strips that are outdated or damaged due to built in quality controls. Also how one collects the drop of blood (through excessively squeezing the finger rather than a gentle milking of the finger) can have an affect on results as it has been suggested that squeezing changes the blood components used to run the test. You have about 15 seconds from the time you prick your finger until the meter beeps that you have sufficient quantity to test and the test is running. Your blood begins to clot after 15 seconds which will skew the test results. Sometimes I have seen this as much as 0.5 pts. or greater! I emphasize this teaching point with pt's. I teach. Cardiologists in my area are reluctant to use metered results because they are more comfortable with the results they get from lab using a venipuncture as they are not comfortable with variances that great. They don't want their patient's throwing clots. Perhaps they are concerned that IST's (independant self testers) aren't using the meters correctly. Always refer to the manufacturer's instructions. Hemosense and Coagucheck have wonderful instructional DVD's available should you need to refresh your skills. Best of Luck!

BTW, our HH agency protocal is for venipuncture for PT/INR results over 4.0 with Hemosense for quality control. They are usually right on the money.

Edited by RubyRN,CHPN

Our agency also has a protocol to draw a venapuncture for an INR above 4.5. We use the InRatio machine. I have use the Protime Analyzer and coagucheck in home care. I have seen an increase in insurance co's providing pt's with their own machines when they are on long term Coumadin. I can't remember the name of the machine, but it is a good one that is faster and uses less blood than my InRatio and can be used when pt is on Lovenox.

With further research I find that standing vs sitting can have an effect as can milking. She always has to squeeze to get the drop and has squeezed twice to get the drop and also placed a second drop when the first wasn't adequate.

My wife has always stood at the kitchen counter when testing with the INRatio meter. I am wondering if sitting could make a difference.

Also I read that the meters are progressively positive in readings above 4.0 and that the patient should be referred to a lab in those cases.

For readings below 2.0 she takes Lovenox shots so that may account for some of the problems, but not for the variations when within the target range. I realize our comparison over ten or so readings was not a study by any means as all of these variables were not logged.

I appreciate the responses made on this thread, they are helpful.

"With further research I find that standing vs sitting can have an effect as can milking. She always has to squeeze to get the drop and has squeezed twice to get the drop and also placed a second drop when the first wasn't adequate."

Lets start with the low tech approach. I would have her stop squeezing her finger to attempt to get her sample. Rather from a sitting postion have her dangle her and below chair level. Have her warm pack her hand with warm moist compress, dry her finger well, this will improve her circulation. Lance the side of the finger pad, not directly on the callused area of her finger. Make sure if she is using a lancet holder device that it is set on the highest level to ensure a deep stick. If she is using a single use disposable lancet device have her hold the tip of device fast against the skin to ensure when the device is released, the lancet goes in deep enough. She will need a drop of blood for most of the current meters approximately the size of a split pea. Use one finger stick per test, never retest from the same finger stick. Use one test strip per test, never retest over with the same test strip if you got an error message due to insufficient quantity. Please refer to your manufacuturer/DME supplier for the most updated information on your meter. Some of the posts on this thread are for 2005 and refer to possibly an outdated meter and old technology. If she is having ongoing difficulties with her testing technique, please refer to your DME supplier so that they can further evaluate the situation. I would also have her test 12 hours after her last coumadin dose and try to stick to that schedule and see if that makes a difference in her results as serum drug levels vary. Coumadin is a dangerous drug if not monitored appropriately. Not getting your sample on the test strip before 15 seconds may cause a false low.You say she takes Levonox (very expensive med) for readings below 2.0; perhaps improved tesing technique may save some on your drug bill. I am curious where she had her meter training done.....were these techniques shared with you during your meter training?

I know you appreciate the assistance. Hope this helps.

Edited by RubyRN,CHPN

Ruby, thanks for the info, we are going to ask the INR nurses if we can give the meter another chance testing as you recommend. My wife says she is only at a 3 on the Auto-Lancet so she will up it rather than squeezing.

Another thought, since she has INR instability testing twice a week seems a better and more economical approach than having to resort to Lovenox every six or eight weeks (average). I haven't been able to determine if Medicare and BCBS would actually cover routine twice weekly testing. They haven't balked at occasional multiple tests. It would be more economical for me even if I had to purchase extra strips as Lovenox co-pay is around $120 for a qty of ten syringes. If Alere would bill the extra readings we could just not call them in.

If it were me rather than my wife I would try the 100mcg daily vitamin K therapy, but am hesitant to urge her to do so. My approach would be to start the vitamin K while in one of the Lovenox regimens so there would be no risk, but that's as they say a whole 'nother story..

How long does Lovenox remain in the system negating the use of strips?

We are trying to get back into the game, today the meter gave us 2.9 and the lab 3.1. We are suggesting to the cardiologist that we test up to twice weekly, Alere thinks Medicare and BCBS will cover if prescribed by the doctor. For example the 2.9 is just below target so we would test again in a couple of days. Alternatively, if we are permitted to remain on the meter I can purchase strips for less than $5 each in a box of 48. If we can avoid bottoming out then no Lovenox expense, pain and blue belly spots. Sounds like a win/win situation.

It is my understanding that Levonox does not impact PT/INR results as it works on intrinsic factors (probably bettered answered by your dispensing pharmacist.) It is my understanding traditional medicare programs pay for 52 meter strips a year (one a week) with certificate of medical necessity provided by your MD. As a trainer, my goal is training a patient to best practice with their meter and encouraging complicance with their physcian perscribed medication and monitoring program. With proper training and compliance, I have seen many people be very successful at home with monitoring and have improved control with their INR readings. Like I have said, coumadin is a drug that if not used correctly and monitored appropriately, can be dangerous. Best of luck.

That's a very nice, easy to use system as well. Drop of blood goes to the side of the strip vs. the top of the strip. Has a few extra steps to it's use but steps to obtain the sample are pretty much the same. Manufacturer recommends washing your hands with warm soapy water prior to obtaining sample vs. using alcohol prep. Best of luck.


Specializes in Home Health, Med surg.

Our agency has tested our machines for accuracy multiple times. Seems when we get bad readings, it's generally user error. Blood drops for our machines are to be obtained via a hanging drop, and no milking is allowed. A gentle steady pressure on dangling finger is okay supposedly. I've gotten the best results by warming the fingers with a moist compress, swab w/alcohol, wipe w/2x2, then obtain hanging drop via pipette which is then applied to the strip.

Our agency uses the Protime 3. It is approved by the FDA and has literature to support its accuracy. I am one who does not always take things at face value and have compared venipuncture results with the Protime results and found them to be right on target.

This machine uses a slide called a curvette.....and the blood is gathered from a fingerstick with a tenderlet. The curvettes can remain stored in a cool, dry place for up to 6 months. They do not need to be refrigerated......although I do advise the staff to not leave the machine in their cars overnight with the winter temperatures.

This machine cannot be used for patients on Lovenox. It is primarily used for those patients who have poor venous access.....although many of the MDs are requesting the machine be used so they can get immediate results.

The agency absorbs the cost for the procedure....which is about $6.00 a draw......but have found it to be worthwhile. We get accurate results, our homebound patients are not incurring costs for a lab to draw the specimen and those that are difficult sticks are not traumatized.

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