hyperkalaemia and CKD

Re: hyperkalaemia and CKD

Laurence Webb — Tue, 21 Feb 2012 19:07:32 GMT

[quote user="Martin Atkinson"]Common error when filling the pots - temptation is to fill the EDTA tube before the heparin or plain tube[/quote]I still have to fight this urge after over 16 years in practice. I recall being taught to ALWAYS fill the EDTA first at University. I don't know if this was because it was the way it had always been taught, although I wonder if it is because students and the inexperienced are often slow at getting samples, so have more spoiled EDTA samples due to clotting than artefactual hyperkalaemia/hypocalcaemia.

It took a few years before the penny dropped that it really wasn't beneficial most of the time and frequently was counterproductive.

For samples that are being sent away it's better to get into the habit of always centrifuging and decanting the serum or centrifuging gel tubes. The latter aren't ideal for every test and won't protect plasma indefinitely from K leakage from rbc, but they remove 1 step from the handling process (decanting serum) so I find them handy. Having a specific tube that everyone knows must be centrifuged before sending away also makes for better compliance from nurses packaging samples. Heparin tubes may or may not need to be centrifuged, people think they only need to be centrifuged just before running a test or they may be centrifuged but not decanted before dispatch. All frustrating errors when results are of questionable accuracy.

Re: hyperkalaemia and CKD

Martin Atkinson — Tue, 21 Feb 2012 17:49:44 GMT

[quote user="Hannah Bose"]

I wasn't the one to do the blood sample so I can't guarantee there wasn't any edta contamination. I knew that edta contamination lowers the calcium but I didn't know it would affect potassium. The calcium was wnl (2.57 [2-3]).

[/quote]

Common error when filling the pots - temptation is to fill the EDTA tube before the heparin or plain tube to reduce risk of clotting but just touching the top of the tube with the syring tip is enough to cause a big potassium artefact, the clue is in the name - potassium EDTA! That said hyperkalaemia is not uncommon in end-stage CKD but your urea, crea and UP/C don't suggest that. I'd repeat the K first to rule out an artefact.

PS I posted the original reply before you posted the one about repeating. Firstly I'm amazed you don't send separated samples for biochem anyway its surprising you don't get more artefacts and secondly I assume your 'stupid bloody machine' is a Vetscan. I have the same and am happy to run a comprehensive profile just to get K and Na, for what the rota costs it isn't worth the expense of an electrolyte analyser or the hassle of sending it away.

Re: hyperkalaemia and CKD

HMC — Tue, 21 Feb 2012 16:54:58 GMT

[quote user="Kate Richardson"] If you are able to check a sample in house to reassess potassium levels, that is what I would do first[/quote]

I cannot do that sadly without doing a whole comprehensive profile. Stupid blood machine design! So we're sending off.

Re: hyperkalaemia and CKD

HMC — Tue, 21 Feb 2012 16:53:10 GMT

I have spoken to Novartis and the external laboratory and the plan is to resample but this time decanting off the serum prior to posting to keep the sample fresh and stop K+ leeking from the RBCs. If the hyperkalaemia is genuine then the next step in the plan is to talk to RCW re the K+ supplementation in the renal diet.

Re: hyperkalaemia and CKD

Lorna McHardy — Tue, 21 Feb 2012 15:28:34 GMT

I don't suppose it's partially blocked, or retaining urine, possibly with a nasty UTI?

Re: hyperkalaemia and CKD

Kate Richardson — Tue, 21 Feb 2012 13:14:37 GMT

Agree hypokalaemia much more common with renal disease. You will often get artefactual elevations in potassium due to sample ageing and haemolysis. I assume the bloods went away to an external lab? If you are able to check a sample in house to reassess potassium levels, that is what I would do first; if not then I would check with your lab as to the best sample to send (I think heparinised plasma is best if I recall, so you can spin the sample and remove the plasma in house and send this). If the cat is truly hyperkalaemic, then I would stop the fortekor and see if the hyperkalaemia resolves. I don't think stopping the fortekor for say 4 weeks, will be detrimental long term.

Re: hyperkalaemia and CKD

HMC — Tue, 21 Feb 2012 12:56:41 GMT

Yes, I had to double check with the owner that the cat wasn't getting potassium supplementation, which would have made more sense knowing that hypokalaemia is more likely in CKD.

I will repeat the k+ and do a blood pressure.

Re: hyperkalaemia and CKD

Laurence Webb — Tue, 21 Feb 2012 12:00:46 GMT

Hypokalaemia is more common with CKD. Can you recheck the K level? One explanation for an unexpected hyperkalaemia would be EDTA contamination of the sample. Is Ca low (if checked)?

As an aside, if the UPC is high whilst on an ACE-i checking for hypertension and ruling out UTIs would be sensible