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Urology

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UROLOGY PATHOLOGY

  • STRUVITES
  • OXALATE UROLITHS

What is RSS (Relative Super Saturation) index?

RSS (Relative Super Saturation) index

RSS is calculated with a specific software, from the analysis of 13 minerals in the urine. It falls within 3 zones:

  • Zone of undersaturation: uroliths cannot form. Existing struvites crystals will dissolve. Str RSS<1
     
  • Zone of metastable saturation: pre-existing crystals can grow. But new uroliths won’t form.
    Str RSS<2.5 / Ox RSS<10-12
     
  • Zone of oversaturation: urolith formation is highly likely. Str RSS>2.5 / Ox RSS>10-12

PATHOLOGY KEY POINTS

  • Urolithiases: 3% dogs seen at veterinary hospitals/practices1,2
  • More than 80% of lower urinary tract uroliths are struvite or calcium oxalate3,4
  • Multifactorial origin (e.g. inappropriate diet, metabolic, hormonal, drinking behaviour, drugs)3,5
  • Often associated with urinary tract infection (cause or consequence)3,6,5
  • Struvite uroliths are most common in female dogs and calcium oxalate uroliths in male dog4,5
  • More frequent in toy- or small-sized breeds (e.g. Shih Tzu, Miniature Schnauzer, Bichon Frise, Lhassa Apso, Yorkshire Terrier)3,4,5

RSS (Relative Super Saturation) index

RSS is calculated with a specific software, from the analysis of 13 minerals in the urine. It falls within 3 zones:

  • Zone of undersaturation: uroliths cannot form. Existing struvites crystals will dissolve. Str RSS<1
  • Zone of metastable saturation: pre-existing crystals can grow. But new uroliths won’t form. Str RSS<2.5 / Ox RSS<10-12
  • Zone of oversaturation: urolith formation is highly likely. Str RSS>2.5 / Ox RSS>10-12

DIAGNOSIS, ASSESMENT AND PROGNOSIS

  • History and clinical signs1,7:
    • Urination: dysuria, stranguria, pollakyuria, inappropriate urination, hematuria
    • Systemic signs (particularly if obstruction): reduced appetite, vomiting, lethargy, weight loss, signs of abdominal pain
  • Radiography/ultrasonography of the urinary tract3,8
  • Urinalysis: crystalluria, urine specific gravity (increased), urine pH (neutral or acidic pH for calcium oxalate calculi and alkaline pH for struvite calculi)3, presence of bacteria and/or blood cells in urine5
  • Urine culture and sensitivity if infection (primary or secondary)3
  • Blood biochemical profile to assess possible underlying cause and associated disorders (e.g. azotemia, hyperkalemia, metabolic acidosis often associated with obstruction)3,5
  • Analysis of removed or voided uroliths to determine the type3

1. Tion MT et al. A review on urolithiasis in dogs and cats. Bulg J Vet Med 2015; 18 (1): 1-18.
2. Hill PB et al. Survey of the prevalence, diagnosis and treatment of dermatological conditions in small animals in general practice. Vet Rec 2006; 158(16): 533-9.
3. Bartges JW, Callens AJ. Urolithiasis. Vet Clin North Am Small Anim Pract 2015; 45(4): 747-68.
4. Houston DM, Moore AE. Canine and feline urolithiasis: examination of over 50000 urolith submissions to the Canadian veterinary urolith centre from 1998 to 2008. Can Vet J 2009; 50(12): 1263-8.
5. Okafor CC et al. Risk factors associated with struvite urolithiasis in dogs evaluated at general care veterinary hospitals in the United States. J Am Vet Med Assoc 2013; 243(12): 1737-45.
6. Smee N et al. UTIs in small animal patients: part 2: diagnosis, treatment, and complications. J Am Anim Hosp Assoc 2013; 49(2): 83-94.
7. Hardie EM, Kyles AE. Management of ureteral obstruction. Vet Clin North Am Small Anim Pract 2004; 34(4): 989-1010.
8. Hecht S. Diagnostic imaging of lower urinary tract disease. Vet Clin North Am Small Anim Pract 2015; 45(4): 639-63.