Evaluation of the incidence of haematuria following the placement of subcutaneous ureteral bypass devices in 18 cats (2016–2022)

Abstract

Objectives

The aim of the present study was to evaluate the incidence of postoperative haematuria in cats treated with a subcutaneous ureteral bypass (SUB) device for the management of benign ureteral obstruction.

Methods

Medical records from a single referral institute were retrospectively searched for cats that underwent placement of a SUB device for the management of benign ureteral obstruction between June 2016 and June 2022. Signalment, history, diagnostic imaging findings, surgery duration, and pre- and postoperative clinicopathological data were recorded.

Results

In total, 18 cats presented with placement of de novo SUB devices: 14 unilateral SUBs and four bilateral SUBs. All 18 (100%) cats developed microscopic haematuria postoperatively. Median time to detection of microscopic haematuria was 1 month (range 1–11), with 16/18 (89%) detected on the first postoperative urinalysis. In total, 14 (78%) cats had persistent microscopic haematuria, two (11%) had recurrent microscopic haematuria and a further two (11%) cats had recurrent persistent microscopic haematuria. Severe haematuria (⩾50 red blood cells per high-power field) was identified in 13 (72%) cats; however, gross haematuria as a clinical sign was infrequently reported (n = 2/18, 11%). The median time to first detection of severe haematuria was 1 month (range: 1–31 months). Persistent severe haematuria was documented in seven cats, with a median duration of persistence of 17 months (range 5–31). Haematuria without a positive urine culture at any time point was present in 11/18 (61%) cats.

Conclusions and relevance

In this study population, postoperative persistent microscopic haematuria was a frequent finding in cats after SUB device placement. Further studies are necessary to understand if microscopic haematuria is a clinically relevant finding, and to further understand the aetiology of haematuria in such patients.

Introduction

Ureterolithiasis is the major cause of feline ureteral obstruction, most commonly calcium oxalate in composition. ¹ Less frequently reported causes include neoplasia, stricture, iatrogenic ureteral ligation/injury, solidified blood stones, mucus plugs and circumcaval ureters.^{2 –4}

Conservative management of feline ureteral obstruction historically has a low success rate, ⁵ and thus surgical management is frequently necessary. Techniques reported include ureterotomy, end-to-end neoureterocystostomy and ureteronephrectomy.^6,7 Ureterotomy is reported to have a mortality rate in the range of 18–21%,^5,6 and complications include uroabdomen and stricture formation.^4,6,7 Furthermore, the majority of cats affected by ureterolithiasis are chronic stone formers. Recurrent ureteral obstruction due to de novo urolith formation or passage of pre-existing nephroliths can occur in up to 40% of affected cats.^1,8 Thus, placement of double pigtail ureteral stents or a subcutaneous ureteral bypass (SUB) device has become more commonplace. Perioperative mortality rates with these procedures are reported to be in the range of 7.5–15.0%^{4,9 –11} and 6.0–20.8%,^7,12,13 respectively.

SUB devices consist of a nephrostomy catheter placed into the renal pelvis and a cystostomy catheter placed into the lumen of the bladder, which are connected via a subcutaneous port. The purpose of this device is to permanently bypass the ureteral obstruction, providing an alternative route to re-establish urine flow from the kidney into the bladder.

There are an increasing number of studies evaluating complications after the placement of a SUB device in cats. However, the literature regarding the characteristics of postoperative haematuria in this population is limited. A previous study reported postoperative microscopic haematuria in the absence of gross haematuria as a frequent finding in cats after SUB device placement for the management of benign ureteral obstructions. ¹⁴

Our hypothesis is that postoperative haematuria, independent of a positive urine culture, is a frequent finding in cats after SUB placement.

The aim of this retrospective study was to evaluate the incidence and characteristics of postoperative haematuria in cats with a SUB device placed for ureteral obstruction.

Materials and methods

Medical records from a single referral institute were retrospectively searched for cats that underwent placement of a SUB device for the management of ureteral obstruction between June 2016 and June 2022. Cats were identified by searching medical records for the following terms: ‘SUB’, ‘subcutaneous ureteral bypass’, ‘ureteral obstruction’, ‘ureterolithiasis’, ‘TFloLoc’ and ‘T-FloLoc’. Inclusion criteria included preoperative urinalysis in cats undergoing SUB placement and a minimum of three separate urinalysis samples obtained from the device via the subcutaneous port postoperatively. Cats were excluded if ureteral obstruction was secondary to trauma, neoplasia or ureteral ligation. A diagnosis of ureteral obstruction was made based on an assessment of urea, creatinine and the degree of renal pelvis and/or ureteral dilation on ultrasound. Haematological and biochemical parameters collected at the time of initial presentation and at discharge from the hospital included packed cell volume (PCV), creatinine, urea and potassium levels. Preoperative urinalysis, including urine culture, was performed either via cystocentesis or intraoperatively via pyelocentesis before SUB device placement and contrast administration. The surgeries were performed as outlined by the manufacturer (Norfolk Vet Products) under fluoroscopic guidance and using the SUB 2.0 in all cases. Information recorded included whether the ureteral obstruction was uni- or bilateral and the type of device placed (eg, use of a ‘Shunting PantsPort’). All surgeries were performed by a European College of Veterinary Surgeons (ECVS) boarded diplomate or an ECVS resident under their direct supervision. Procedural information recorded included anaesthesia and surgical time (mins) and perioperative antibiosis protocol.

Postoperative data were collected at one of the scheduled reassessment appointments (variable time points depending upon clinician and owner’s discretion) for ultrasound-guided flushing of the SUB device(s). Information obtained at each reassessment included the attending clinician’s clinical notes regarding clinical signs, biochemical parameters (urea and creatinine values), urinalysis (including urine specific gravity [USG], dipstick assessment and sediment analysis) and urine bacterial culture obtained in a sterile manner via the subcutaneous Huber port before saline flushing. Culture samples were considered positive if any growth in samples was found from the SUB ports. For cases involving bilateral SUBs, if urinalysis was performed on both sides, then the most abnormal results were included for that patient. Patency of the SUB device was confirmed via identification of visible jets/flow at both the nephrostomy and cystostomy catheters under ultrasound guidance during instillation of saline via the subcutaneous Huber port.

Microscopic haematuria and pyuria were assessed using a wet preparation sediment analysis as per the institution’s laboratory standard operating procedure. For wet preparation, each urine sample was centrifuged for 5 mins at 1500 g. The supernatant was decanted, leaving the precipitate and two or three drops of urine at the bottom of the tube. The tube was gently tapped a few times to re-suspend the button. A single drop of urine was placed onto a glass slide with a cover slip over it. To enumerate both red and white blood cells, the slide was assessed under 40× high-dry objective (high-power field [hpf]), and the average number of cells over 10 fields was calculated.

Microscopic haematuria was classified into mild, moderate or severe based on the number of red blood cells (RBC)/hpf as per reference values from the institute’s laboratory. Mild was defined as 3–20 RBC/hpf, moderate as 21–49 RBC/hpf and severe as greater than or equal to 50 RBC/hpf. Pyuria was defined as the presence of increased numbers of white blood cells within a urine sample (>3 white cells/hpf).

‘Recurrent’ haematuria was defined as the presence of microscopic haematuria in two samples, with at least one sample in between without microscopic haematuria. ‘Persistent’ haematuria was defined as two or more consecutive samples with microscopic haematuria. ‘Recurrent and persistent’ haematuria was defined as two or more consecutive samples with microscopic haematuria, in addition to the presence of microscopic haematuria in two samples, with at least one sample in between without microscopic haematuria. A positive bacterial culture on any postoperative urine sampling was also included in patients’ follow-up data.

Statistical methods

Given the small size of the study population, descriptive statistics were performed.

Results

In total, 35 cats had a SUB placed between June 2016 and June 2022; 17 cats were excluded because of insufficient follow-up data, as outlined in the inclusion criteria.

The median age within this study population was 7.3 years (range 2.3–12.5). All cats were domestic shorthairs. Of them, 12 cats were spayed females and six were castrated males. Median duration of clinical signs at first presentation was 7 days (range 1–168). Clinical signs reported included lethargy (n = 11), anorexia/hyporexia (n = 8), vomiting (n = 8), weight loss (n = 7), gross haematuria (n = 2), pollakiuria (n = 1), stranguria (n = 1) and polyuria/polydipsia (n = 1).

Aetiology of ureteral obstruction

Of the 18 cats, 17 cats had ultrasonographic evidence of ureterolithiasis as a cause for ureteric obstruction. Of the single cat without ultrasonographic evidence, the exact cause of obstruction could not be determined retrospectively; however, this cat did have ultrasonographic evidence of nephroliths within both kidneys. Urolith analysis was not available for any of the cats. Of the 18 cats included in this study, 14 had unilateral SUBs placed (left sided in eight cats and right sided in six cats) and four had bilateral SUB devices placed (two independent SUBs in three cats, and a two-to-one SUB using a ‘Shunting PantsPort’ in one cat). One cat had a single left-sided SUB placed and 48 h later had a second separate right-sided SUB placed.

Preoperative blood results (first presentation)

Median creatinine was 316 μmol/l (range 146–892, reference interval [RI] 53–140). Median urea was 17.8 μmol/l (range 9.2–88, RI 6.0–10.0]. Median potassium concentration was 4.3 mmol/l (range 2.9–5.3, RI 3.4–5.6). Median PCV was 30% (range 17–37, RI 25–45] and 5/18 (28%) cats were anaemic (haematocrit <29%).

Preoperative urine specific gravity results

Median USG at first presentation was 1.019 (range 1.009–1.039). In the presence of documented azotaemia, 12/15 (80%) cats had an inappropriate urine concentration (USG <1.035), while 3/15 (20%) cats had evidence of appropriate urine concentration (USG >1.035).

Preoperative or intraoperative urine culture results

Five cats had a positive urine bacterial culture collected pre- or intraoperatively. All five cats had a positive culture of Escherichia coli. All cats with a positive urine culture were treated with oral antibiotic therapy based upon antibiotic sensitivity results for a period of 4–6 weeks postoperatively at the attending clinician’s discretion. In all cases, repeat urine culture was obtained 5–7 days after discontinuation of antibiotics and all were negative for aerobic and anaerobic bacterial growth.

Preoperative haematuria results

A total of 11 cats had evidence of haematuria collected on preoperative urine samples obtained via cystocentesis. Of these cats, six (55%) had mild haematuria, one (9%) had moderate haematuria and four (36%) had severe haematuria. A positive urine bacterial culture was documented pre- or intraoperatively in three of these cats. Crystalluria was not documented in any of these samples.

Surgical factors

The median duration of surgery was 85 mins (range 45–120). Median duration of anaesthesia was 130 mins (range 90–180). In total, 16 cats received cefuroxime (20 mg/kg IV at the beginning of the procedure) while two cats were already receiving amoxicillin-clavulanate (20 mg/kg q8h) and so did not receive intraoperative antibiotics.

Postoperative urine culture results

Seven cats had a positive urine bacterial culture during follow-up. Of the cats, six (86%) were spayed females. Of the seven cats with a positive postoperative urine bacterial culture, three (43%) had a positive urine bacterial culture pre- or intraoperatively. Two of these three cats had the same bacterial species identified pre- and postoperatively (both E coli species). Of these three cats, one had a positive urine bacterial culture on the seventh urinalysis (E coli species) 6 months postoperatively, while the remaining two cats had a positive urine bacterial culture identified on the third urinalysis at 8 and 9 months postoperatively, respectively. Two cats had documented negative urine bacterial culture after antibiotic therapy (both E coli species). The other cat had an ongoing positive culture at the end of the study period.

In four cats, a persistent positive urine bacterial culture was documented. One cat developed a de novo postoperative positive urine bacterial culture for Staphylococcus species (after prior antibiotic therapy for a preoperative E coli positive urine bacterial culture). This patient subsequently developed a persistent positive urine bacterial culture for E coli 16 months postoperatively. This patient developed a draining sinus tract forming over the SUB port, culminating in the need for a left-sided ureteronephrectomy (41 months after the original surgery). One of these cats was lost to follow-up (persistent positive urine bacterial culture at the last reassessment at 33 months postoperatively) and one cat had recurrent positive urine bacterial culture (E coli), which was also lost to follow-up. The final cat had a positive urine bacterial culture for Enterococcus species documented on the first routine urinalysis postoperatively and developed a persistent positive urine bacterial culture of a multidrug-resistant Pseudomonas species 22 months postoperatively.

Overall, the bacterial species identified postoperatively were E coli species (n = 4), Klebisella oxytoca (n = 1), coagulase negative Staphylococcus species (n = 1), Staphylococcus chromogenes (n = 1), Enterococcus species (n = 1) and Pseudomonas species (n = 1).

Postoperative lower urinary tract clinical signs

In total, 11 (61%) cats had a lower urinary tract clinical sign reported on at least one occasion. Clinical signs reported included pollakiuria in five cats, stranguria in nine cats, gross haematuria in two cats and vocalisation during urination in one cat. One cat developed acute onset pollakiuria and failing to urinate 4 months postoperatively and was subsequently found, on further investigation, to have a partial urethral obstruction due to the presence of a calculi (stone analysis was not performed). Clinical signs, microscopic haematuria and urine bacterial culture results at the time of clinical signs are summarised in Table 1.

Table 1.

Descriptive table highlighting cats with lower urinary tract clinical signs, as well as the results, where possible, of presence of microscopic haematuria on wet sediment analysis and urine bacterial culture at the time of clinical signs

Symptomatic cat identifier	Clinical signs reported	Severity of microscopic haematuria at time of clinical signs	Urine bacterial culture result at time of clinical signs
1	Recurrent pollakiuria (three separate occasions)	Mild haematuria on one sample, no haematuria on two samples	All negative
2	Single episode of pollakiuria 4 months after SUB placement	Severe	Negative
3	Single episode of stranguria	Not assessed	Not assessed
4	Single episode of vocalisation	Mild	Negative
5	Single episode of stranguria	Not assessed	Negative
6	Single episode of stranguria	None	Negative
7	Recurrent stranguria and pollakiuria (three separate occasions)	Mild haematuria on one sample, no further samples provided for other episodes	Negative on two samples, no other samples provided for other episodes
8	Recurrent stranguria and gross haematuria (four separate occasions)	Mild haematuria on four samples	Positive on first sample, negative on the other three subsequent episodes
9	Single episode of stranguria	Severe	Positive
10	Pollakiuria at 1 month postoperatively, then recurrent pollakiuria and stranguria on two further occasions	Mild haematuria on first episode, severe haematuria on second and third episode	Negative on all three episodes
11	Recurrent stranguria	Severe on all occasions	All negative
12	Two episodes of stranguria, pollakiuria and a single episode of gross haematuria during first episode	Moderate on first episode, mild on second episode	Positive on both episodes

SUB = subcutaneous ureteral bypass

Postoperative haematuria results

In total, all 18 (100%) cats developed microscopic haematuria postoperatively. The median time to first postoperative urinalysis was 30 days (range 9–184). The median time to detection of microscopic haematuria was 1 month (range 1–11), with 16/18 (89%) detected on the first routine postoperative urinalysis. In total, 14 (78%) cats had persistent haematuria, two (11%) cats had recurrent haematuria and two (11%) cats had recurrent and persistent haematuria. Haematuria without a positive urine bacterial culture at any time point was present in 11/18 (61%) cats. Of these 11 cats, six (55%) had mild haematuria, one (9%) had moderate haematuria and four (36%) had severe haematuria.

Severe haematuria

A severe haematuria result, detected at any time point postoperatively, was identified in 13 (72%) cats. The median time to first detection of severe haematuria was 1 month (range 1–31). A single severe postoperative haematuria result was detected in five cats. This was associated with pyuria but not a positive urine bacterial culture in two cats, and with a positive urine bacterial culture in three cats.

Severe persistent haematuria

Seven cats had persistence of severe haematuria, which continued to the end of the study period or when lost to follow-up. The median duration of persistence was 17 months (range 5–31). The median number of samples with persistent severe haematuria was five (range 2–6).

Of these seven cats, six had a unilateral SUB placed and one had a bilateral system placed using a ‘Shunting PantsPort’. One cat had persistence of severe haematuria for 5 months (two consecutive samples) and then had a recurrence of severe haematuria at 19 months before being lost to follow-up. One cat also had recurrence of severe haematuria, after first detection at 1 month with concurrent pyuria but no positive urine bacterial culture or clinical signs, and on the third sample at 16 months (without pyuria, positive urine bacterial culture or clinical signs).

Of the seven cats with persistent haematuria for two consecutive samples or more, three had no pyuria detected on any sample. Of the seven cats with severe persistent haematuria, six had no positive bacterial urine culture identified at any time point in the postoperative follow-up period. Of these seven cats, three cats had microscopic haematuria (two mild, one moderate) detected on preoperative urinalysis. Ureteral calculi as the cause of ureteral obstruction were present in all seven cats. One cat with persistent severe haematuria had a persistent postoperative positive urine bacterial culture with Klebsiella species and pyuria in all samples (n = 6) over 31 months. Five owners within this subgroup reported clinical signs on at least one occasion postoperatively (intermittent pollakiuria or stranguria). One cat had no reported clinical signs at any follow-up appointment. The final cat demonstrated no clinical signs until acute onset lethargy at 17 months postoperatively with investigations revealing an unspecified blockage resulting in a non-patency of the SUB device requiring revision surgery 17 months after the original SUB placement.

Discussion

In this study population, all patients developed microscopic haematuria, of varying severity, within 1 month of surgery. To the authors’ knowledge, this is the first study to attempt to characterise postoperative haematuria in this population.

The frequency and characteristics (including severity and duration, association with clinical signs or development of postoperative complications) of haematuria developing postoperatively in feline patients undergoing SUB device placement for the management of benign ureteral obstructions are limited. The characteristics of haematuria after ureteral stent placement in cats for ureteral obstructions are also poorly characterised, but gross haematuria appears to be an uncommon finding after this procedure. ⁹

By comparison, in humans, the presence of gross haematuria after the placement of ureteral stents is considered an infrequent but well-known complication, with reported rates in the range of 8.7–25.0%.^{15 –17} In humans, microscopic and mild macroscopic haematuria associated with ureteral stents is typically regarded as self-limiting and considered to arise due to urothelial irritation.

However, care needs to be taken when comparing haematuria in the context of ureteral stents vs SUB device. This is particularly important in the context of human medicine whereby the use of ureteric stents is temporary compared with the permanent placement of a SUB device.

In cats, the nephrostomy portion of the SUB device traverses renal parenchyma to access the renal pelvis rather than being located solely in the lumen of the ureter and the renal pelvis as with ureteric stents. This limits an accurate comparison between the classical self-limiting haematuria infrequently observed with ureteric stents in humans and the persisting microscopic haematuria observed in our study population.

A previous retrospective study involving 61 cats undergoing SUB device placement for the management of benign ureteral obstructions reported a high prevalence of microscopic haematuria in 186/218 (85%) samples, ¹⁴ similar to the findings in our study. In addition, a recent study evaluating cats with SUB devices compared with those with idiopathic chronic kidney disease (CKD) also reported a high prevalence of microscopic haematuria in the SUB device subgroup. ¹⁸

Notably, in our study, gross haematuria was reported much less frequently (n = 2/18, 11%), which is similar to a previous retrospective study which reported gross haematuria as a clinical sign in 14/115 (12%) cats. ¹²

Although 13 cats had severe microscopic haematuria (on at least one or more occasions), only two of these cats presented with a history of gross haematuria as a clinical sign. This could suggest that severe microscopic haematuria may occur in the absence of appreciable clinical signs of gross haematuria. However, the observation of this clinical sign may be confounded if patients are urinating outdoors rather than using litter trays. Owing to the retrospective nature of this study, the number of patients using litter trays compared with those urinating outdoors could not be determined. As such, the absence of reported gross haematuria does not exclude its occurrence; therefore, this may be a contributory factor in the discrepancy between documented severe microscopic haematuria in the absence of a history of observed gross haematuria.

The clinical significance of recurrent or persistent microscopic, severe microscopic or macroscopic haematuria in this patient population is unknown.

Persistent or intermittent haematuria not associated with a urinary tract infection was reported in 11/60 (18%) cats in one retrospective study, for which none of these cats suffered from progressive anaemia or obstructive blood clots during the follow-up period after ureteral stent placement. ⁹ Conversely, in another study, cats with SUB devices, when compared with cats with idiopathic CKD, had significantly lower PCV in spite of having less advanced stages of CKD. Possible causes proposed by the authors of this study included influence of sedation at time of sampling, decreased erythropoietin production (considered less likely given most cats in the SUB group were International Renal Interest Society stage 1–2), secondary to systemic inflammation or prior surgery, or due to chronic urinary blood loss as evidenced by the high prevalence of haematuria in the study population. ¹⁸ In another retrospective study, gross haematuria was found to be significantly associated with the historical presence of dried solidified blood calculi resulting in ureteral obstruction. These authors proposed that such a finding was thought to be associated with the potential presence of idiopathic renal haematuria and thus could be considered in patients with haematuria, in the absence of a urinary tract infection, before and after ureteral patency intervention techniques. ¹² Although idiopathic renal haematuria may explain the presence of persistent haematuria in a small minority of cats after SUB device placement, it is unlikely to be the explanation in the majority of cases given the low prevalence of this diagnosis in our and previous studies with high prevalences of haematuria.^12,18

The persistent nature of microscopic haematuria evidenced in this population may reflect the permanent nature of the SUB device, resulting in continual urothelial irritation via the cystotomy catheter. Another contributory factor to consider is the possibility of bleeding at the time of sampling – for example, subcutaneous bleeding due to trauma from the Huber needle. The latter is particularly important to factor in when considering the patients in this study population with mild to moderate haematuria for which the number of RBC present may be reflective of sampling method rather than the presence of a true pathological process. In addition, bleeding of renal origin due to vascular damage or chronic irritation within the renal pelvis, or the aforementioned role of idiopathic renal haematuria, must also be considered as other possible sources.

The development of a ureteric arterial fistula (UAF) with SUB devices has not been previously reported; therefore, the role of UAF formation as another source of bleeding in this population group is unclear. In human medicine, UAF is a pathological communication between a ureter and an artery, usually the common iliac artery. The severity of bleeding with UAF can be variable from chronic intermittent microscopic haematuria to severe gross haematuria. In humans, the exact pathophysiology of UAF formation remains to be completely elucidated. Risk factors for the development of secondary UAF include chronic indwelling ureteral stents, pelvic surgical intervention, pelvic radiation therapy and vascular surgery. Proposed mechanisms of secondary UAF formation include fibrosis, ischaemic injury and friction between the ureter and artery. This can eventually lead to localised necrosis and the formation of a fistula.^{19 –21} In humans, a diagnosis of UAF is often achieved through the use of angiography and contrast-enhanced CT. It is unclear whether the placement of a SUB device, with subsequent inflammation and fibrosis of the surrounding retroperitoneal region and urinary system, could lead to UAF formation.

Unfortunately, because of the retrospective nature of this study, patients with severe persistent microscopic haematuria did not undergo further investigations to identify the source of the bleeding. As such, it is difficult to comment further on the most likely sources for the bleeding in these patients. Overall, it is likely that there were several different sources of bleeding given the variability in the severity of the microscopic haematuria.

It is of interest to note that the median time to first detection was 1 month for cats with severe haematuria. As seven cats demonstrated persistence of severe haematuria, the likelihood that surgical manipulation was the sole reason for the development of postoperative severe haematuria is low, as this would be expected to result in transient self-limiting postoperative haematuria. Conversely, we may have expected the severity of haematuria to progress over time because of ongoing worsening of chronic urothelial irritation and bleeding. However, the findings from our study contradict this hypothesis, given that the majority of patients developed severe haematuria within the first month after surgical intervention.

Finally, although some of the cats in the study population did have a positive urine bacterial culture at certain time points, the persistent severe haematuria identified in this population was predominantly sterile as only one of these seven cats had evidence of a persistent Klebsiella species positive urine bacterial culture. Of cats suffering lower urinary tract clinical signs, as evidenced in Table 1, patients had varying severity of microscopic haematuria, and 8/12 (67%) cats had no positive urine cultures at the time of clinical signs. In addition, 4/12 (33%) cats had at least one severe microscopic haematuria noted at the time of clinical signs, of which only one cat had a positive urine bacterial culture at a time of clinical signs and severe microscopic haematuria. Although our study population was too small to make meaningful conclusions from this finding, a previous study found that microscopic haematuria, including severity, was not a predictor for either positive urine cultures or the presence of lower urinary tract signs in cats with SUBs, supporting the hypothesis that haematuria in this patient population occurs most commonly because of a sterile process. ¹⁴

The main limitation of this study is the retrospective nature and small population size. As such, in patients suffering from severe persisting haematuria, no investigations were undertaken to try and determine the source for the bleeding via imaging and/or blood tests, such as assessment for additional systemic risk factors for bleeding tendencies (eg, appraisal of coagulation times was not undertaken in any patient). These limitations preclude further conclusions as to the most common sources for persistent haematuria to be established. A cut-off to define haematuria (⩾3 RBC/hpf) is lower than another study evaluating haematuria in this patient population. ¹⁴ As such, this lower cut-off value may be a contributory factor in the prevalence of cats with microscopic haematuria in this study. Therefore, it cannot be excluded that low numbers of RBC in our patients’ postoperative urinalysis may be a reflection of sampling techniques rather than truly reflective of a pathological process. Indeed, more investigations are necessary to evaluate if threshold levels for samples collected from SUB devices using Huber needles require different RBC level cut-offs compared with those traditionally used in voided, catheterised and cystocentesis samples, respectively. In addition, follow-up time periods and intervals as well as laboratory tests performed during each reassessment was the result of independent clinician discretion, precluding complete comparisons.

Another limitation is the lack of ongoing monitoring of physiological and clinicopathological parameters. Thus, we cannot determine the possible impact of ongoing severe persistent haematuria on the development of anaemia and/or contribution to physiological effects. Given the retrospective nature of the study, sampling time points as well as postoperative investigations undertaken – such as imaging modalities and blood and urine assessment – were subject to variations at the clinicians’ and owners’ discretion, leading to incomplete or missing data. As a result of the retrospective nature of this study, and complexity of defining urinary tract infections within SUB patients, the use of the term ‘urinary tract infection’ in cats presenting with a positive urine culture has been avoided. Although each urine sample collected directly from the SUB device followed the same institutional protocol under sterile conditions, factors that could contribute to positive urine cultures in this study population may include any potential contaminant or presence of subclinical bacteriuria. Information pertaining to whether an active sediment was evident, any or concurrent lower urinary tract signs were present or resolution of such signs after antibiotic administration was not always readily available. As such, we have not been able to define the clinical significance of positive urine cultures any further.

Future multicentre studies are warranted to evaluate the risk factors associated with mild, moderate and severe haematuria, as well as exploring possible underlying aetiologies, and to determine the true overall incidence of haematuria in these patients.

Our findings suggest that the incidence of postoperative haematuria in cats after the placement of a SUB device for the treatment of ureteral obstructions is considerable. However, it cannot be fully excluded that, given the small study population, there may be a subset group of cats that do not develop postoperative haematuria. The clinical significance of postoperative haematuria and its relation to urinary tract infection in cats is also unclear. Given device occlusion with blood clots is reported in 8.1% of cats, ¹² it is possible that persistent severe haematuria could be a predisposing factor for this complication. However, as this complication was not reported in our population group, it remains to be determined whether persistent severe haematuria is a risk factor for its development.

Conclusions

Postoperative microscopic haematuria is a frequent finding after SUB device placement for the treatment of ureteral obstruction in cats. In this study population, a large proportion of cats demonstrated persistence of severe haematuria (39%), with a median duration of 17 months, in the absence of gross haematuria. At present, it remains unclear whether this is a clinically significant finding or a risk factor for the development of future complications, – for example, future risks for device occlusion. This emphasises the importance of complete sediment analysis as routine practice during follow-up assessments. Future studies are required to assess for possible causes and risk factors for the development of postoperative haematuria, as well as to determine the clinical significance of long-term microscopic haematuria in such patients.