Tests used to Diagnose Kidney Disease in Dogs
This section will go over the more common tests for kidney disease, as well as some of the more complex ones. I find that people are often told that their dogs have "renal failure", with no indication of whether it is chronic or acute, early stage or end stage, and without proper information about what should be done based on the diagnosis. In addition, too often no one looks to see if there might be a treatable cause for the kidney problem. This section will review a number of different tests to help you better understand what your dog's diagnosis may mean, and what additional tests you may want to have done. Also see IRIS Staging of CKD and Relevant Diagnostic Tests for Chronic Kidney Failure for more information.
Disclaimer: I am not a veterinarian, nor do I have any formal training in any medical field. The information presented here is not meant to replace your vet's advice or prescribed medications, but only to suggest additional options to explore, based on your dog's condition.
Note about measurements: I refer to the standard US measurement of Creatinine and BUN in mg/dL, but have also supplied the converted numbers in mmol/L (BUN, or Urea) and µmol/L (Creatinine) for those outside the US. To convert BUN (Urea) from mmol/L to mg/dL, divide by 0.357 (or multiply by 2.8). To convert Creatinine from µmol/L to mg/dL, divide by 88.4. See Unit Conversion for more info and a calculator that will do the conversion for you..
- Creatinine is the most specific test for kidney disease. When creatinine is elevated above the normal range (usually about 1.6 mg/dL, or 141 µmol/L), this generally means that there is a problem with the kidneys. It does not tell you whether the problem is acute or chronic, or what the cause is, or whether it can be cured, but it is a sign that your dog is having kidney problems and action needs to be taken.
- Early Renal Insufficiency: In general, creatinine values up to about 2.0 (177 µmol/L) are indicative of mild, or early stage, kidney disease (or early renal insufficiency, as my vet terms it). In cases like these, it may still help to make dietary modifications to reduce phosphorus if blood phosphorus level is above 4.5, but these reductions do not need to be as drastic as when the values are higher, and it is probably not necessary to do other treatments at this stage, such as sub-q fluids (unless your dog is drinking so much that she is having trouble staying hydrated, such as getting up during the night to drink). Adding calcium to each meal if you are feeding a home made diet (to act as a phosphorus binder) would be advisable, and possibly antacids, particularly if your dog is showing any signs of inappetence or gastric problems. I would also give fish oil supplements (body oil, NOT liver oil), at the rate of 1,000 mg (300 mg combined DHA and EPA) per 10 lbs of body weight, along with Vitamin E (50, 100 or 200 IU for small, medium and large dogs), and discontinue any Vitamin A and D supplements (including cod liver oil) added to commercial foods. Additional recommended supplements include a B-complex vitamin and CoQ10, which may be beneficial for dogs with kidney disease. See the Supplements section for more info.
- Moderate Kidney Disease: Values from 2.1 up to about 5.0 (177-442 µmol/L) are more significant, but it is still likely that your dog may not be showing any symptoms (other than increased drinking and urination) with these values. At this stage, a greater level of phosphorus reduction would be indicated, along with antacids, calcium (which acts as a phosphorus binder) if you are feeding a home made diet, and probably sub-q fluids, particularly if your dog is polydipsic (drinking a lot of water). The same supplement advice mentioned above, regarding giving fish oil, Vitamin E, Vitamin B-complex and CoQ10, and avoiding added Vitamins A and D supplements (beyond minimum daily requirements), would continue to apply.
- Severe Kidney Failure: Values above 5.0 (442 µmol/L) indicate more severe kidney failure, and are often accompanied by clinical signs such as vomiting and lack of appetite. At this stage, fluids can be very important, especially when your dog is vomiting, and your dog may even need to be hospitalized for IV fluids (I personally feel it is best to bring them home at night, if at all possible, even if they need to stay at the vet's during the day). Antacids (Pepcid, Zantac or Tagamet) or acid suppressors (such as Prilosec), should be given, along with Carafate (anti-ulcer medication) and Reglan (metoclopramide) for vomiting if needed, with your vet's approval. Protein in the diet may need to be reduced at this time to control symptoms, though if your dog does not want to eat, it's most important that you get some food into them, even if it isn't the best. Use the same supplements as recommended above (give fish oil, vitamin E, vitamin B-complex and CoQ10, do not give extra vitamins A or D). Note that when kidney function is seriously reduced, the amount of some medications, such as Pepcid, may also need to be reduced, due to the increased time it takes for the kidneys to clear them from the body. Be sure to discuss the dosage of any medications you are giving with your vet.
- BUN (Blood Urea Nitrogen, also sometimes just called Urea) is also commonly used to diagnose kidney problems, although it is not kidney specific, and values may be elevated for other reasons, particularly if you did not fast your dog for 12 hours before the test was done. If BUN is slightly above normal but creatinine is in the normal range, the odds are that the kidneys are fine, especially if the urinalysis is also OK (normal urine specific gravity and no significant amount of protein in the urine).
- Values in the high 20's, up to even the mid 30's (around 12.5 mmol/L) if the dog was not fasted, are not a concern if other values (creatinine, urine specific gravity, protein in the urine) are normal. Dehydration and stress can also contribute to elevated BUN.
- If BUN is above 80 mg/dL (28.6 mmol/L), this is a sign of uremia and is usually accompanied by clinical signs such as vomiting and inappetence. In this case, as when creatinine is above 4.5 mg/dL (398 µmol/L), it may be necessary to reduce protein in the diet to help control these symptoms. BUN is more reflective of diet, and less reflective of the stage of kidney disease, than creatinine, but it is still not necessary to feed a low protein diet when BUN is below 80 mg/dL (28.6 mmol/L), although you should definitely be feeding a lower phosphorus diet at that point.
- Phosphorus: Elevated phosphorus is dangerous and needs to be controlled. It is questionable how important dietary phosphorus is when blood levels remain below 4.5 mg/dl (1.45 mmol/l), but my feeling is that it may still help to reduce phosphorus in the diet to at least a low normal level. You should also be sure to use adequate calcium (which binds phosphorus), even when phosphorus levels are normal. When phosphorus levels are above 4.5, then it is important to reduce phosphorus in the diet, and to use phosphorus binders if needed, plus you may need to do other treatments as well. If you are home feeding, and your dog's phosphorus levels are <4.5, you can add calcium to help bind phosphorus. Add about 1/2 teaspoon of ground eggshell per pound of food (1/2 teaspoon ground eggshell yields about 2,500 mg of calcium carbonate, which has 1000 mg of elemental calcium). If you prefer, you can use Tums instead (be sure to use the product that contains only calcium), or another form of calcium (see phosphate binders for more information). If the phosphorus levels are over 4.5, you may need to use more calcium, or talk to your vet about using an aluminum based phosphorus binder instead. See the section on Phosphate Binders for more information. Elevated phosphorus levels (hyperphosphatemia) can be related to abnormal parathyroid hormone (PTH), which can be caused by kidney disease, so if it persists, you should do a PTH test so it can be treated if needed.
- Calcium: Elevated calcium is often a sign of abnormal parathyroid hormone (PTH). When your dog's calcium levels are elevated, it is important that you NOT give additional calcium as a phosphorus binder, but use one of the aluminum based binders instead (although if you are feeding a home made diet, you would still add some calcium to ensure that nutritional requirements are met). Calcitriol can be used to help control hyperparathyroidism, but only if phosphorus levels are normal. See the section on Calcitriol for more info. Another possible cause of elevated calcium is Addison's Disease. According to the Merck Veterinary Manual, "Mild hypercalcemia (less than or equal to 15 mg/dL) has been reported in up to 30% of dogs with hypoadrenocorticism (Addison's disease)." Keep in mind that your dog could have atypical Addison's Disease, where only cortisol is low, even if the sodium/potassium ratio is normal. Since elevated calcium levels are an unusual side effect of kidney disease in dogs, I would have your dog tested for Addison's if the calcium levels are high.
- Sodium/Potassium Ratio: If your dog's sodium:potassium ratio (sodium level divided by potassium level) is below normal (27 or below), this is an indication of Addison's Disease (hypoadrenocorticism), which can cause kidney failure. Addison's Disease can be fatal if not treated, but it is treatable. Addison's Disease is often misdiagnosed as kidney disease, so it may be worth testing for this disease, even if the sodium:potassium ratio is normal, especially in younger female dogs. See this article on Addison's Disease for more info.
- Total Protein and Albumin levels may be decreased if you are not feeding your dog enough protein, or if your dog has a protein losing disease. Albumin is needed to help absorb fluids, so it is important that it stays in the normal range. If your dog has significant protein in the urine, it's important to try to find the underlying cause and treat it, if possible. Protein-losing kidney disease can be linked to hypertension (high blood pressure), and to infection or inflammation elsewhere in the body. Decreasing protein in the diet can help to control inflammation in the kidneys that is contributing to protein loss, but too little protein in the diet can make the protein malnutrition worse, so it's a balancing act. Low albumin combined with high globulin can be a sign of tick disease, such as Ehrlichia. If other signs of tick disease are also seen, such as thrombocytopenia (low platelets), and if no other cause for the protein loss can be identified, you might try treating the dog presumptively with high doses of Doxycycline, even if tests are negative, since it's not always possible to rule out the possibility of tick disease with tests.
- Hematocrit (HCT), Platelets, RBC, WBC. Anemia can be caused by kidney disease, and is measured by Hematocrit (also called Packed Cell Volume, or PCV) and RBC (red blood cells). If your dog is anemic, you may need to treat with hormone (Erythropoietin/Epogen) injections, or even a blood transfusion. Elevated WBC (white blood cells) may indicate infection, such as with Leptospirosis. Low platelets may be a sign of Tick Disease. See the section on Additional Tests below for more information on testing for these diseases.
Azotemia (elevated BUN and Creatinine) combined with normal urine specific gravity (1.030 and above) may indicate prerenal problems, such as Addison's Disease, or postrenal problems, such as kidney or bladder stones. see Localization of azotemia: Test your skill for more information.
It is also important to do a urine culture and sensitivity when you have indication of kidney disease. A urine culture is the only way to rule out a urinary tract infection, this cannot be done by simple urinalysis and observation of whether there is bacteria in the urine or not. A culture and sensitivity will also help you determine the best antibiotic to use for treatment, if an infection is present. Bacterial infections can cause kidney disease (pyelonephritis), so it is important to rule this out when dealing with kidney problems. Dogs with kidney problems are also at greater risk of developing urinary tract infections. Although vets prefer to do a urine culture using a sterile urine sample (cystocentesis), I hive had good luck doing cultures on free caught samples.
Proteinuria: If more than a trace amount of protein is found in the urine, you should do a urine protein:creatinine (UPC) ratio to determine how significant it is. Significance to some extent is related to the stage of kidney disease: for dogs with normal kidney function (creatinine < 1.5), a UPC of 2.0 or less should be investigated for an underlying cause and closely monitored, while those with UPC > 2.0 should be treated. For dogs with creatinine levels above 1.4, UPC over 0.5 should be treated.
Certain types of kidney disease, particularly glomerulonephritis (GN), are associated with high amounts of protein in the urine (UPC > 3.0), and this may be the first sign of kidney problems in dogs affected with these diseases. See the Links section for more information on GN. Note that Antech offers a Urine Profile (see SA570 under Diagnostic Profiles) that includes a urinalysis, UPC ratio and numerous other values that can be helpful for only about $30 more than a UPC alone, so this might be something to ask your vet about if you are dealing with a dog that has or is suspected to have kidney problems. This article on Proteinuria is technical, but has a great deal of information about the meaning of protein in the urine, and what these additional tests may mean. There can be many causes of protein loss in the kidneys -- according to the article Protein Losing Nephropathy: An Overview, "Some of the more common infectious agents to keep in mind when diagnosing protein losing kidney diseases include: Brucellosis, Ehrlichiosis [Tick Disease], Leptospirosis, Borreliosis [Lyme Disease], Leishmaniasis [uncommon in the U.S.], chronic bacterial infections, and heartworm disease. Noninfectious causes include inflammatory bowel disease [IBD], systemic lupus erythematosus [SLE] and hyperadrenocorticism [Cushing's Disease], among others." See below for more information on testing for Leptospirosis and Tick Disease.
There is a new test that can find trace amounts of protein in the urine and serve as an early warning of kidney disease. This test is called the Heska ERD (Early Renal Disease Detection). See The E.R.D.-Screen™ Urine Test for information on this test specifically related to the Chinese Shar-Pei. There is additional information about the meaning of this test in the E.R.D. Healthscreen Urine Test Clinic Lab Book.
There is also a urine test called Electrophoresis that can provide diagnostic clues to the source of protein in the urine. See the following sites for a little more info:
Urinary and Serum Protein Alterations in Dogs with Natural Ehrlichia Canis Infection using Electrophoresis
Total Protein Electrophoresis
Grapes and raisins have also been linked to kidney failure in dogs if consumed in quantity. See this article on Acute Renal Failure for more specific information about this problem. While ARF is more dangerous in the short term, it is often curable, especially if caught early, and your dog may have a completely normal life afterwards (although ARF can also cause CRF, chronic renal failure). Here are some of the tests to consider:
- Leptospirosis is a bacterial infection that can cause kidney failure, especially in young dogs, and more often in male dogs, though females can also be affected. Most standard vaccinations include Lepto, but that does not mean your dog will not get this disease. The vaccinations do not last very long (vaccinations against bacterial diseases are not as long-term as vaccinations against viruses), the estimated duration is generally 3 to 9 months, and vaccinations will only cover 2 to 4 of at least 8 types of lepto that are known to affect dogs. While lepto has been considered rare, I am hearing more and more cases of it, and am beginning to think it may be much more common than is commonly believed, especially since dogs can have lepto without showing any symptoms. The treatment for Lepto is penicillin, so if you have a dog who suddenly shows symptoms of kidney disease (excess drinking and peeing) and has elevated creatinine and BUN, it makes sense to go ahead and start treatment while waiting for the results of the test to come back, which can take several days, especially if your dog is young. The test for lepto is a blood test for titers, and may not show positive results until the dog has been symptomatic for at least a week, so even a negative test, if done early, does not rule out this disease. Treatment with penicillin for two weeks is followed by treatment with doxycycline for four weeks, to eliminate the carrier state. In animals with only mild clinical signs, doxycycline can be used for both initial and elimination therapy. See the Links section for more information on this disease.
- Tick Disease: there are several kinds of tick disease that can cause kidney problems, including Lyme Disease, Ehrlichia, and Babesiosis. The treatment for most of these is high doses of Doxycycline, so again, it may make sense to try treatment while waiting for tests to come back if tick disease is suspected, especially if other symptoms are present, including thrombocytopenia (low blood platelets) or nonregenerative anemia. As with Lepto, the test is a blood test for titers, which may not show up immediately. See Tick Disease and Tick Disease FAQ for more information.
- Addison's Disease: as mentioned above, Addison's Disease (hypoadrenocorticism) is often mistaken for kidney disease, as it can affect the kidneys. Although a sodium:potassium ratio of 27 or below is indicative of Addison's Disease, a normal ratio does not rule it out. The test for Addison's is a blood test called an ACTH Stimulation Test, which involves taking some blood, then injecting the dog with a substance, waiting one hour, and taking blood again. The test is not dangerous or terribly expensive and may be worth doing, especially in younger, female dogs, who are the ones most likely to be affected by Addison's. Hypothyroidism is also often linked to adrenal dysfunction, especially Addison's Disease, so it may be especially important to test for Addison's if your hypothyroid dog seems to be showing signs of kidney failure. See this article on Addison's Disease for more information.
- Cushing's Disease (hyperadrenocorticism) is the opposite of Addison's Disease, and is more common in older dogs. Cushing's will generally show other symptoms as well as kidney disease, such as hair loss, pot belly and increased appetite, so it is probably not worth testing for unless you see these types of symptoms. See this article on Cushing's Disease for more information.
- Blood Pressure may be elevated in dogs with kidney disease, although this is less common than with people. Unfortunately, it is difficult to test blood pressure in dogs, so it may be difficult to determine whether your dog has this problem or not (and difficult to monitor treatment, if it is thought to be needed). Ace inhibitors can be helpful with high blood pressure, see the section on Medical Treatment for more info. Note that there is no evidence that lowering dietary sodium will help to lower blood pressure. See this article on High Blood Pressure and IRIS 2006 Treatment Recommendations for more info on this condition.
- Biopsy: vets often want to do a kidney biopsy to determine the cause of kidney disease, but I am opposed to this test. A biopsy will damage the kidney, and usually will not provide information that changes the prognosis or treatment (my guideline for when an invasive or expensive test might be warranted). I would question your vet strongly about how such a test might help your dog (and how likely they are to survive it) before proceeding with such an invasive and dangerous test.
- Iohexol Clearance Test: this is another test I do not recommend, as Iohexol can actually damage kidneys. This test estimates GFR (Glomerular Filtration Rate), but the UPC (urine protein:creatinine ratio) test can also do this (see above under Urine Test for more info). Personally, I would never think of using something that is potentially toxic to the kidneys to measure GFR, which is not very important -- it is simply a measure of kidney function, and if you have elevated creatinine and BUN, you already know that the kidneys are not functioning as well as they should and any action you take can be based on that, without knowing GFR, which would not change either treatment or prognosis.
- Renal Scintigraphy: this advanced (and probably expensive) test is one of the only ways of determining how much each kidney is affected. Since kidney disease will not show up until 75% of kidney function is lost, both kidneys would be affected and I don't know how useful this type of test might be. The one person I know who had it done had a very young dog that had a chronic kidney infection that took several months to diagnose, and she wanted to know how badly the kidneys had been affected.