Inaccurate Venous Draws - Tube volume?

[JimChicago]

One question I have is when getting INR testing via venous draws I had the experience once of having a remark on the blood test results to the effect that:

"Coagulation Results May Be Affected By Improper Blood/Anti-Coagulant volume."

Also on the internet I found this article about how the volume of blood in the different tubes can result in a wrong INR result -
From:
http://www.annals.org/cgi/content/full/134/6/465
>>>>
A HIGH INR
The re-peated
INR, measured by a different phlebotomist, is 2.1.
Other patients also had spuriously elevated INRs on the
previous day. Because of the long half-life of the clotting
factors, the INR would have taken several days to passively
drift down from 4.9 to 2.1 (100).
Thus, this rapid reduction, along with the other ele-vated
INRs, leads us to suspect a laboratory or processing
error. We speak with the experienced phlebotomist who
drew the first INR. She had noted that the new batch of
blue-top tubes seemed to be filling more than usual; in an
attempt not to ?overfill? these tubes, she had removed them
once they had filled to the usual level (2.7 mL).
On inspection, we see that the laboratory has changed
from the Becton-Dickinson partial-fill tubes, which have
sufficient vacuum to draw 2.7 mL of blood, to a full-draw
tube designed to draw 4.5 mL of blood. This change was
triggered by a recent study showing that the partial-draw
tubes can result in inaccurate coagulation monitoring
(101). The full-draw tubes have the same external dimen-sions
as the partial-draw tubes, but they have a greater
volume of the anticoagulant sodium citrate and a greater
negative pressure. Although they are accurate when properly
filled, in this case the full-draw tubes resulted in spuriously
elevated INR values because they were filled with less than
4.5 mL of blood.

>>>>>

I was wondering if anyone else heard of this? - if getting a venous draw should I try to alert the phlebotomist that the tube fill volume is important for the INR to be correct?

 

[Ross]

I've never heard of it, but it sure sounds reasonable to me. When I was having venous draws, my INR was all over the place. Now that I'm going to a finger stick clinic, my INR is pretty stable and all readings have been on the higher side. The other lab would be anywhere and everywhere, so this could be why.

 

[Marty]

Venous Draw Problems?

Venous Draw Problems?

Volume is a problem. Also I used to worry how long my sample would be in the back of the truck, how hot it would get ,etc. Did get some crazy readings. Dr. Ansell advised me to rely on the Coaguchek finger stick.However I just had a venous draw for the first time in over two years as part of a complete physical. I did my Coaguchek the same day.Venous draw central lab INR 3.7. Coaguchek 3.6. I try to keep my INR by Coaguchek close to 3.5 because I have a mitral
mechanical which I was told are more prone to clots than aortics. Just had my fifth anniversary and smooth sailing so far.

 

[Guest]

The tubes for the test in a lab have a known amount of citrate solution in them to further keep the blood from clotting. When the lab runs the test, the machine injects the exact amount of a neutralizing chemical into the tube with your blood. Then the test is run. There are possibilities for error such as the tube not having the correct amount of citrate, the machine not injecting the right quantity of neutralizer etc. I suppose that not having a sufficient amount of blood is a possibility too. However, this is not just being off by a drop or two - it would have to be grossly wrong. But just like everything else mistakes can be made.

On a ranking of things that can go wrong with keeping your INR in range, this would probably be far down the list.

You can even make mistakes with the fingerstick. I have failed to dry the alcohol off a persons finger several times and got readings that were ridiculously high.

New topic

I did something that I had never done before yesterday. A 39 year old woman who had blood clots form in the arteries of both hands when she gave birth to her twins came in. She nearly lost both hands from the lack of circulation. She has veins from her legs implanted from the elbows down. Her surgeon told her to never let anyone draw blood from the elobows down. So I stuck her toe and drew the blood up in a capillary tube to put it on the CoaguChek. You learn something new every day.

 

[Ross]

*Caution--Toe Sticker on board*

Al "Bundy" Lodwick

 

[Guest]

I was wearing my valvereplacement shirt at the grocery store today and someone stopped me and asked about it. Her father is headed for the big zipper. So I got to talk about this website and all the good it does.

Then my son called and said - Jake wants to know if you want to go to the game tomorrow. So I asked Jake who? He said Jake Plummer (The quarterback of the Denver Broncos). He said Jake has two extra tickets and he called and asked if I wanted to take my Dad to the Denver - Detroit game. Well, that didn't take long to answer. My son said that he had played golf with Jake several times this past summer but I didn't know it would lead to this!!

 

[Ross]

Sounds like your going to have a good time! Enjoy it to the fullest. Wish I knew Jake.

 

[Marty]

Al and Jake the Snake

Al and Jake the Snake

Al, I bet you enjoyed the game today as the Broncos beat the Lions 20-16 and Jake passed 16 straight completions in the first half. The guy is phenomenal.You are lucky to have a son who is a golf pro. Not only do they meet some interesting people, you can also hopefully get some free tips. I have been trying to find the secret of the golf swing now for almost 70 years. Still looking.

 

[carlapv]

Finger Sticks

Finger Sticks

I wish I could get the finger sticks but my insurance will not pay for them and they are $48.00 each and I go every three weeks. My arms look like I'm a junkie so I wear long sleeves all the time and that is a bit uncomfortable here in Georgia . I am saving my pennies so that after my VR if BC/BS still won't pay I can get it myself.

Carla

 

[Guest]

Our seats were with the player's families.

 

[Birky]

coumadin

coumadin

When I had a protime last week I talked to the Nurse at the Coumadin Clinic about the home testing. She said that they do not have any patients at this time that have one. They do their testing with finger sticks and not the way I have to do them here.My arms are getting pretty sore. I think down the road I will look into getting one. We have Blue Cross for our insurance and I guess this is one company that is considering paying for them. I understand that each strip is around $4.00. The INR at the hospital is $37.00 and $13.00 for the pathologist which is a total of $50.00. I am still on a 3 week schedule. I had surgery on the 18th of this month and was off the coumadin for 4 days and after a week, it was where it was supposed to be. He wants me between 2 and 3. It seems like if you are on coumadin anything minor becomes a major.

 

[Ross]

Finger sticks are 1,000,000,000 times better then getting a venous draw. I was to the point that I couldn't handle anymore needles. I'd love to have poked some of the jerks that I had poking me!

 

[JimL]

Marcia, Don't hesitate to call QAS for help in getting your own machine, 1-800-298-4515.

I called recently, and they (Lance and Patricia) were extremely helpful. It turns out that, due to billing procedures, it's totally free to me to go to the coumadin clinic, but I would have to pay for part of the machine. For now, I'll just go to the clinic for the finger stick, but things may change in the future, and QAS is there.

 

[Guest]

I second that about contacting QAS. They are now handling all four types of testers.

 

[JimChicago]

This article implies that it's very difficult to get an accurate INR number from a venous draw especially when the sample is collection one place and sent overnite for processing:
http://www.averalabnet.com/newsletters/Winter98.htm

Collection, Transport, and Processing of Blood Specimens for Coagulation Testing.
The current recommendations for collection, transport, and storage of specimens for blood coagulation testing are summarized by the National Committee for Clinical Laboratory Standards in the document, "Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and Performance of Coagulation Assays" (H21 -A2).

The blood specimen may be obtained by venipuncture or from an indwelling catheter using an evacuated tube system or a syringe. If an evacuated tube system is used, the coagulation specimen should be the second or third tube obtained. Collect the coagulation specimen prior to the use of evacuated tubes containing any other anti-coagulant. If the blood must be drawn through an indwelling catheter, possible heparin contamination must be considered. The line should be flushed and the first specimen (at least 5 ml) discarded or used for other laboratory tests. In the case of any unexpected abnormal test result, a new sample should be obtained from a different location.

If the patient has a very high or low hematocrit, the citrate concentration of the evacuated tube must be adjusted. In cases of polycythemia (hematocrit >55%) the premeasured amount of citrate will be excessive for the reduced plasma volume and must be decreased. The coagulation time is lengthened and will progressively increase as the hematocrit rises. If the patient has severe anemia (hematocrit <20%) the premeasured amount of citrate will be inadequate for the increased plasma volume and must be increased.

Specimens that are clotted, hemolyzed, collected in the wrong tube, or are incompletely filled (<90% of expected fill) are not suitable for testing and should be rejected. Specimens that are lipemic or icteric may be unsatisfactory for most current instruments which use an optical detector.

The specimen should be transported to the lab and processed promptly. To obtain a plasma sample, the capped specimen is centrifuged at 2500 x g for 15 minutes. Carefully remove the plasma from cells, avoiding the buffy coat. The allowable time interval between obtaining the specimen and testing will depend on the temperature maintained during transport and storage of the sample:

22-24 C = 2 hours
2-4 C= 4 hours
-20 C = 2 weeks
-70 C = 6 months (rapidly frozen).
Coagulation factors such as V and VIII are labile and activity will be reduced if the specimen is improperly stored. If a specimen is to be frozen, it is recommended that the plasma be centrifuged a second time to create platelet-poor plasma (platelet count < 10,000). Freezing will lyse any remaining platelets and could cause normalization of an abnormal coagulation test.
>>>>

 

[Marty]

Great Information

Great Information

Nice work Jim. Confirms why so many venous draws in satellite offices get goofy results.

 

[Guest]

Thanks that was interesting.

I don't think that it is actually hard to get an accurate sample. I think that most of the samples will fit into the category. However, this gives some of the possibilities if the results seem to be inaccurate.

There are probably more people will elevated hematocrits due to smoking than there are with a true polycythemia (excess of red blood cells.) I have probably seen 5 or 6 people with smoking as the cause and only one who had polycythemia vera.

If your hematocrit is lower than 20% you are probably getting the test because you have already gone to the doctor with no energy or shortness of breath. Very few people with HCT of 20% will be walking around unassisted!