Dr Susana Silva
DVM CertSAM DipECVIM-CA MRCVS
RCVS and European Specialist in Veterinary Internal Medicine
We often say “oh, under 8 years old pre-op bloods aren’t really necessary”. However, occasionally, we do pick up something unusual. In this blog, we’re going to look at just such a case.
This is Harvey, a 5 year old male neutered Labrador. One of your colleagues has detected marked gingivitis at a routine vaccination, and has booked him in for a dental, although only a scale and polish is anticipated. The admit nurse has persuaded his owners to run a pre-op profile, but his owners report no problems and a quick clinical exam detects no abnormalities. However, you decide to wait until the bloods come back before giving him his premed and going to theatre.
While the haematology is unremarkable, these are the biochemistry results:
|“Harvey” – Biochemistry|
|Patient Result||Reference Range||Units|
|* – abnormal result.|
What is your interpretation of the results and what would your plan be for the patient? Would you proceed with the dental at this point?
The slightly high globulins probably represent an inflammatory reaction to the gingivitis.
More concerning are the raised urea and creatinine. These results demonstrate azotaemia, which in an “apparently healthy” animal is more likely to be renal than pre-renal or post-renal in origin. Additionally, as the patient is reported to be well in himself, this most likely represents chronic kidney disease (CKD) rather than acute kidney injury (AKI).
At this point however, it would be unwise to proceed with the dental. It would be risky to drop Harvey’s blood pressure with anaesthesia and without knowing the underlying cause of the azotaemia, you cannot make an educated risk/benefit analysis.
There is no clinical or biochemical (normal haematocrit, low-normal albumin) evidence of dehydration. He is very bright, alert and eating well, and therefore there is no need to consider fluid therapy at the moment.
The diagnosis of likely CKD in an otherwise healthy animal is going to be a shock to the owners who don’t currently perceive the dog to be unwell. Your first step, therefore, should be to contact them, explain the finding and discuss the disease. You can then broach the subject of the potential investigations that are going to be needed and also how the results might affect treatment or prognosis. Diagnostics may well have to be phased in order to maximize compliance – remember, a client discovering a new disease in an apparently healthy pet often traverses the various stages of grief, starting with denial!
What further tests would you recommend to them?
A urine sample would be essential at this stage to assess the urine SG alongside the rest of the
urinalysis, which also has to include sediment evaluation.
You will also need to confirm the persistently elevated renal parameters before being completely sure of CKD (remember, transient azotaemia can sometimes occur due to non-renal causes).
Additionally, before formally staging the patient according to the IRIS (International Renal Interest Society), the renal parameters would need to be stable for around 3-4 weeks.
However, assessment of the UPC and blood pressure is definitely indicated at this stage.
Investigation of a possible cause of CKD is also an important step. What would you want to look for?
Harvey’s owners should be asked about potential exposure to toxins or nephrotoxic drugs, environment and vaccination history. In this case, the clinical records show that Harvey is appropriately vaccinated, and routinely receives flea treatment with moxidectin/imidacloprid (“Advocate”). He also lives in the countryside and has no known access to toxins.
Diagnostic tests to consider would include urine culture and sensitivity (even if the sediment is inactive!), trying to rule out hypoadrenocorticism (corticosteroid only deficiency is unusual but can occur, and does not present the inverted Na:K ratio that is usually seen in Addison’s) and testing for infectious diseases prevalent in the region (e.g. Leptospirosis).
As Harvey lives in the countryside and “Advocate” has no significant action against Ixodid ticks, Borreliosis (“Lyme’s Disease”) should also be considered, especially given the raised globulins.
If possible, abdominal imaging to assess the urinary tract (particularly looking for evidence of pyelonephritis or urolithiasis) should also be included in the plan. While pyelonephritis would be expected to cause an altered leukogram, recent research suggests that it is under diagnosed; however, it is less likely in a male dog.
Harvey’s owners consent to urinalysis with UPC and culture and also blood pressure measurement. A follow-up repeat measurement of renal parameters is scheduled for the following week.
|Results of Urinalysis , UPC and culture|
|Urine UPC||3.4 (ref< 0.5)|
|Sediment RBC < 5phpf WBC < 5phpf No crystals and no casts seen|
Systolic blood pressure with Doppler is 150mmHg.
What is your interpretation of the test results?
Harvey is proteinuric and in this case the proteinuria is likely renal in origin as there is no dysproteinemia, the urine sediment is inactive and the urine culture is negative. This is supported by the slightly low albumin in the original bloods, suggesting a protein losing nephropathy.
His blood pressure is 150mmHg, which according to the IRIS CKD staging system would be sub-staged as normotensive and therefore having minimal risk of target organ damage.
When the results of the urinalysis are received, the owner is contacted to discuss them. At this stage, it becomes a bit clearer that the dog might have started to drink a bit more over the last 6-12 months. However, be careful of taking that admission at face value – by now, the clients have probably been Googling “kidney disease in dogs” and there is a high risk of confirmation bias in their subsequent reports!
After explaining to the owner the importance of identifying a potential cause to try and stop, or at least slow, the disease’s progression, a follow-up renal parameter assessment is scheduled for a few days later.
Would it be worthwhile measuring SDMA?
Measurement of SDMA could potentially make us treat a patient with low body condition score as a higher IRIS CKD stage, but would be very unlikely to change our diagnosis. This patient has an adequate body condition score and as the owners are concerned about costs, SDMA was not measured.
At this stage, how would you like to manage the patient?
When the patient is seen for the repeat blood tests, a comprehensive discussion with the owner should be carried out. Points to discuss should include:
- further tests to perform and their impact on treatment
- management of CKD and the escalation of drugs that might be needed
- progression of disease and prognosis of CKD
Following this conversation, Harvey’s owner agrees to have more tests performed and therefore blood is collected for measurement of the renal parameters, basal cortisol, Leptospira and Borrelia serology. Urine is also collected for Leptospira PCR. At this stage, imaging is postponed due to costs.
As creatinine is still at similar levels, CKD can safely be diagnosed.
Regardless of the IRIS stage, all CKD patients that are proteinuric should be started on a renal diet. It might be wise the gradually introduce the diet – although as Harvey is a Labrador without frank clinical signs, diet acceptance is unlikely to be a significant problem! Additionally, treatment for proteinuria should be started with benazepril 0.5mg/kg SID.
Additional Test Results:
|Additional Test Results|
|Basal cortisol||100 nmol/l (ref: 125-250)|
|Leptospira serology||Negative for all serovars|
What is your interpretation of the results?
The basal cortisol being above 55 nmol/l makes hypoadrenocorticism extremely unlikely. An ACTH stimulation test is therefore not indicated at this point.
The Leptospira urine PCR and the Leptospira and Borrelia serology are negative making those diseases unlikely causes of the CKD.
What would your plan for reassessment and management be?
After 1 week of treatment, it would be important to re-evaluate the UPC, renal parameters and the blood pressure as a minimum. It might be worthwhile considering collecting the urine at home, as in-hospital collection might falsely elevate the UPC (never underestimate the stress response!).
Ideally we would want the UPC to return to normal (<0.5) or, as a minimum decrease by at least 50%. If this hasn’t happened we could consider increasing the ACE inhibitor to 0.5mg/kg BID and perhaps if this is not sufficient consider using telmisartan instead. A few days after each dose increase or change of drug, it would be wise to recheck renal parameters, electrolytes, blood pressure and UPC.
Depending on the progression of the disease routine check-ups are recommended at least every 3-4 months with assessment of complete haematology, biochemistry, urinalysis, UPC and urine culture.
Going forward, if the patient develops other problems, such as hypertension, this would need to be addressed specifically. The IRIS treatment recommendations for CKD should be followed.
Do you need to reschedule the dental?
This patient had initially presented for a dental scale and polish. Dental disease can be a contributing factor to protein-losing nephropathy and, as such yes, if possible the dental procedure should be rescheduled.
However, anaesthesia could potentially lead to worsening of the renal disease if hypotension occurred. Therefore, active blood pressure monitoring and intravenous fluid therapy should be used (keeping the mean arterial blood pressure above 70mmHg if possible, and definitely over 60mmHg), and as light a plane of anaesthesia as possible should be maintained.