Ron Hines DVM PhD
Your Pet’s Blood Potassium Level (K+) In Your Dog And Cat’s Blood
Dissolved potassium (K+, a positive ion or “cation”) is an important constituent in all the cells of your cat or dog’s body. Potassium is also one of your pet’s important blood electrolytes. Although much less potassium as an electrolyte is found free in your pet’s blood than it is in its cells, that small amount of free blood potassium is critical for proper nerve, brain and heart function.
The amount of potassium in your dog or cat’s body is controlled by your pet’s kidneys. When potassium is in the body in excess, the kidneys excrete it into the urine to eliminate it from the body. When body potassium stores are low, the kidneys conserve potassium. (read here)
So, kidney problems of any kind in your dog or cat often lead to abnormal amounts of potassium in their blood stream (both lower levels and higher levels).
Your dog and cat’s blood platelets (aka thrombocytes) also contain large amounts of potassium. So, health problems that cause abnormal blood clotting and platelet destruction will also elevate your cat and dog’s blood potassium level.
Blood potassium level must remain within very strict limits, if not, many metabolic systems will stop functioning correctly. When blood potassium is too low (hypokalemia), muscle weakness and impaired (decreased) kidney function can result.
A complicating diagnostic problem for your veterinarian is that both higher-than-normal potassium and lower-than-normal blood potassium can show similar symptoms in your pet.
Both abnormally low and abnormally high blood potassium levels interfere with normal heart beat (arrhythmia). When K+ levels are abnormally high, heart rates can become abnormally slow (bradycardia) and can even cease (cardiac arrest). The other possible signs of excessive blood potassium levels (hyperkalemia) are poorly described in dogs and cats. In humans, those signs include muscle weakness and fatigue, as well as cardiac arrhythmia due to AV block.
Reasons Why Your Pet’s Potassium Levels Might Be Low (Hypokalemia):
The most common reason for low blood potassium level in your cat or in your dog is failing kidneys (=chronic renal failure or CRF). These are the pets that drink larger than normal amounts of water and produce large amounts of dilute urine that carries away potassium. Kidney failure is one of the most common health problems we veterinarians see in older pets.
Blood potassium level can also drop when the kidney’s urine flow that has been obstructed by things, such as kidney or bladder stones – is suddenly relieved through surgery or manipulation. In those cases, the cat or dog’s kidneys temporarily produce excessive amounts of urine (diuresis) as its body cleanses itself of the wastes that accumulated in their blood stream during the period of obstructed urine flow.
Hypokalemia (low blood potassium) can also occur in dogs and in cats that experience chronic diarrhea, such as dog with dogs with IBD or cats with IBD /or vomiting. Persistent diarrhea and/or vomiting due to dietary indiscretions can have a similar potassium-lowering effect.
Low blood potassium occasionally occurs when fluid accumulates in your pet’s abdomen due to peritonitis, pancreatitis or the pooled fluids [ascites] that accumulate due to heart or liver failure.
The drugs used to decrease those fluids (e.g. furosemide/Lasix® diuretic) can lower your pet’s blood potassium levels as well (a “potassium wasting” effect) – probably because they encourage large amounts of potassium-containing urine to be produced.
Some cats are prone to muscle disease (myopathy) and a few special cat breeds to muscle inflammation (e.g. hypokalemia in Burmese cats (read here), and myopathies in Sphinx cats). Those problems are often accompanied by lower blood potassium levels.
A lack of a dietary source of sufficient potassium when your dog and cat will not eat could conceivably cause hypokalemia – but in reality it rarely does.
Blood potassium levels go down slightly as the body becomes less acidic (metabolic alkalosis, high blood pH). That can occur due to persistent vomiting or after periods of rapid respiration (panting).
Uncontrolled diabetes in dogs and in cats, insulin injection overdose, adrenaline release due to stress, bacterial endotoxemias and high doses of corticosteroid medications have all been associated with hypokalemia.
Pets given large amounts of IV fluids that contain no potassium (in emergency situations) or when the fluids contain large amounts of bicarbonate buffer to meet other urgent needs (such as acidosis), can cause your pet’s blood potassium level to drop.
Fatty/ lipemic blood specimens can give incorrectly low potassium reading on some blood analyzer machines (=pseudohypokalemia).
Dogs and cats with acute (sudden) onset of kidney failure that includes kidney swelling and shut down (oliguric renal failure) no longer have the ability to produce sufficient urine (anuric kidney disease) to remove excess potassium from their bodies. In those cases, hyperkalemia usually develops.
Antifreeze poisoning, aminoglycoside antibiotics like gentamycin and amikacin as well as trimethoprim-containing antibiotics, digoxin given for heart disease, ACE inhibitors like enalapril given for heart problems and even leptospirosis infection can all be responsible for higher than normal blood potassium levels. That effect on potassium blood levels is primarily due to the damage these medications and diseases can cause to your dog and cat’s kidneys. Your veterinarian is going to be alerted to those issues through changes in your pet’s BUN and Creatinine levels – not its elevated blood potassium reading.
The same situation occurs with urinary tract stones when your pet’s kidneys are prevented from flushing excess potassium out of its blood stream. Feline urological syndrome (FUS), and other problems that interfere with your dog or cat’s normal urine flow will have a similar effect. So will any tears in its bladder, or ureters which leak urine into the pet’s abdomen. Accidents involving cars are the most common cause of that.
Pets (usually dogs) whose adrenal glands no longer produce sufficient aldosterone hormone (as in Addison’s disease and perhaps whipworm infection = pseudoaddisons disease) often have higher than normal blood potassium levels.
Many chronic health problems can lead to a body that is too acidic (metabolic acidosis). All of them can raise your pet’s blood potassium levels. They include uncontrolled diabetes (=diabetic ketoacidosis in dogs, in cats), starvation, shock and all the things that cause low blood pH, low blood bicarbonate or C02 levels and a high anion gap.
Akitas, (and perhaps other Japanese dog breeds), have naturally higher levels of potassium in their red blood cells. That makes their blood potassium readings harder to interpret (pseudohyperkalemia). That may be associated with their naturally having a higher number of thrombocytes in their blood than other breeds.
Plasma potassium should be measured from a heparinized blood sample and results interpreted based on plasma (not serum) potassium reference intervals. Serum should be promptly removed from blood and the sample analyzed quickly if an anticoagulant is not used.
Because most of your dog or cat’s potassium resides in the cells of its body tissue, not in its blood, just about any crisis that causes sudden widespread tissue destruction can cause a sudden increase in its blood potassium level too. Those can be a traumatic accident, a serious infection, cancer or obstructions to normal circulation.
Blood Collection And Other Lab And Clinical Errors, False Readings
A high or low blood potassium level on your pet’s labwork report will occasionally be a false reading. The most common reason for that is contamination of the sample with EDTA anticoagulant when a blood serum or plasma sample is sent off for analysis. Purple top collection tubes contain EDTA to prevent the blood sample from clotting. If that tube is filled first (and it usually is), and if a bit of EDTA remains in the needle, syringe or catheter, the next sample meant to collect serum might not completely clot. As that second sample stands before analysis, the WBC and RBC cells in it will break down and liberate more potassium. The same thing will occur when other anticoagulants contaminate the sample. Separator tubes (with mottled or “tiger” top stoppers) centrifuged shortly after collection minimize that problem. Any sample that sits too long before being analyzed is likely to falsely report a high potassium (Pseudohyperkalemia). Be suspicious of that if your pet shows no apparent health issues. A tourniquet left on too long, a traumatic venipuncture (needle stick), inappropriate needle diameter, sucking too hard on the syringe, out of balance centrifuges and alcohol or tame iodine wipes not allowed to dry have all been reported to falsely raise blood potassium readings. Samples standing at room temperature too long at first decrease, and then increase potassium reading. Blood samples need to be kept at 15-25C until processed. That is why in human blood analysis labs, potassium reports tend to be higher in the summer than in the winter. People fearful of needle sticks are also prone to higher potassium readings. Perhaps that occurs in our fearful pets as well. And, as I mentioned before, if your cat or dog does not appear ill, or the potassium reading does not correlate with some health issue that brought you to your veterinarian, a moderate increase in its blood potassium level may not be significant (= not correlate with the clinical picture). The same goes for spurious (falsely low) blood calcium readings. Others call them artifacts. Your veterinarian will be suspicious that such an error occurred when your pet’s attitude and other lab values do not match the results of its potassium results.
For reasons unknown, a few breeds of dogs, primarily Japanese dog breeds, have more potassium in the red blood cells than other breeds. If even a small number of those dogs’ red blood cells are injured (fractured, hemolyzed) during blood collection, it will increase its blood potassium level report. Serum samples from dogs and cats should be straw colored, never pink.
Because changes in blood potassium levels have so many possible causes, follow-up tests are too numerous for me to list. But your veterinarian might begin with: CBC/ WBC and blood chemistry values, urinalysis, sodium:potassium ratio, ACTH stimulation test (if Addison’s disease is suspected), electrocardiogram (ECG)
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