K+ levels: fingerstick or venous. help,,,

allnurses Guide · Sep 7, 2008

Depends how hard you had to aspirate to get it. I wouldn't think it would be very reliable due to mechanical hemolysis of the RBCs.

eaetaylor · Sep 9, 2008

Actually asked an endocrinologist about venipuncture vs. fingerstick. He told me that the blood glucose levels would not be as accurate, especially if dealing with edema. I would believe that would apply for K+ levels, also. According to him, the venipuncture would almost always be more accurate.

ChristineN, BSN, RN · Sep 9, 2008

On my unit we do fingersticks all the time for lab draws if a pt has bad/no veins. We generally don't have a problem with the labs, as long as they don't clot (which if yours was clotted, I would have hoped the lab would have told you).

mcmars · Sep 9, 2008

We actually just had the opposite happen yesterday evening. Finger stick K was 2.8 and venous re-stick to confirm...K was 5.0...so???

anurseuk · Sep 10, 2008

We would only take our samples either from an arterial line or venepuncture or central venous catheters... the same sample on two different ABG machines can be different (not usually by that much), the cells in the blood can be damaged by aspirating to forcefully, poor transportation of the sample or the sample clotting or not being processed quickly enough. Also can be higher if drawing blood from a CVC that has not been properly aspirated:) hope that helps

MBCRNA · Sep 11, 2008

Fingerstick can definately be inaccurate from hemolysis or clot. I have had it happen many times. You'll have to obtain a venous sample or maybe run it on an I-stat via ABG result...

PICNICRN, BSN, RN · Sep 17, 2008

I can tell you that in babies- we do heel sticks for lytes quite often. The K does come back elevated if the specimen is hemolized- the lab will usually mention this in the comment section so that we can decide if we want to redraw the lab. And there is sometimes a small difference between the lab specimen and the iStat.

lifeLONGstudent · Sep 17, 2008

Unable to get a venous sample, the tech pulled the blood from a finger stick. Wouldnt that make the K higher d/t hemolosys? K was 5.9. 48hours before from venous blood it was 3.6...... I brought it up to a couple of other RNs but I was dismissed. I think Im right. Any ideas or thoughts?

Call the lab and ask them to LOOK at the sample and see if it was hemolyzed. You are right - they should have documented it, but things happen when you are running 100 samples an hour.

INTRAcellular potassium is much higher than EXTRAcellular (which is serum). For K+, I think it is something like 5x - 8x more concentrated intracellularly. If it was hemolyzed, ask them to put a comment in the result so everyone knows the scoup when they look at results 4 days from now. If the sample was hemolyzed, red cells broke during poor collection, then they spilled all their INTRAcellular juices (K+) and that is why the K was falsely high.

Clotting doesn't affect the labs sample for these tests - they don't run WHOLE BLOOD glucoses. They all run either from SERUM (red tube or red tube with gel) or run it from PLASMA (has anticoagulant - usually lithium heparin). So, FYI - you really don't have to SHAKE or INVERT these samples -- and doing so can actually cause more hemolysis. And there are very few tests that matter if they are clotted... mainly purple tubes [EDTA: CBCs, ESR, etc] and blue tubes (CITRATE: coag studies].

As far as it not being as accurate in someone with edema, that is also true. Someone with 3+ edema -- you can press on their hands and see the fluid shift... so imagine sqeezing a finger that is full of edema -- your sample will be contaminated with that same fluid, thus lowering your glucose and K+.

You can do capillary sticks from feet, if they are not diabetic -- if they are diabetic, any kind of feet sticks are not good practice..... AND... you can do them on earlobes! Takes a little more effort, but less likely to be contaminated with tissue juices.

"Tissue juices" -- that is why you are supposed to wipe away the first drop of blood when you do a fingerstick glucose (but a lot of people don't do that)....

Warming any target (fingers, toes, earlobes) with a really warm washcloth for 2 minutes will help vasodialate capillary beds and make it bleed better --- less risk of contamination or hemolysis... and less work for you.

lifeLONGstudent

-- 1st bachelors degree -- laboratory science

-- 2nd bachelor -- nursing.