Tests for renal function and integrity Flashcards
What is the function of the kidneys?
- Excretion of waste products
- Control of body fluid balance
-maintenance of water, electrolyte + acid-base balance
-conservation of nutrients
-regulation of blood pressure - Production of hormones
-erythropoietin
-calcitriol (vit D)
-renin
What does the kidneys conserve?
- Water
- Glucose
- Amino acids / proteins
- Na+
- Cl-
- HCO3-
- Ca2+
- Mg2+
What does the kidneys excrete?
- Urea
- Creatinine
- PO4
- K+
- H+
- NH4+
- Lactate + ketones
- Bilirubin
What tests can be done for renal function?
- Blood tests = biochem, haematology, blood-gas analysis
- Urinalysis = USG, dipstick, sediment
What is physiology of urea?
- Synthesised in hepatocytes - eliminates excess NH4+ formed in tissues
- Freely passes Glomerular filtration barrier
- Half reabsorbed in PCT rest excreted
- Small proportion excreted in faeces
What causes increased urea?
- Decreased excretion - prerenal, renal, postrenal
- Increased production =
-increased haemorrhage (intestinal)
-increased proteolysis
-increased protein intake
What causes decreased urea?
- Decreased synthesis =
-liver insufficiency / PSS
-Decreased protein intake
-Urea cycle enzyme deficiencies - Increased excretion = any cause of polyuria
What is physiology of creatinine?
- Produced from creatine degradation in muscles
- Freely passes GF barrier
- not reabsorbed = more accurate to measure than urea
What causes increased creatinine?
- Decreased excretion = prerenal, renal, postrenal
- Increased production =
-high muscle mass
-increased protein intake
What causes decrease in creatininine?
- Decreased production = reduced muscle mass
What is azotaemia?
- Increase in nonprotein nitrogenous compounds in the blood
What causes prerenal azotaemia? CS? USG? Tx?
- Due to reduced renal blood flow
-hypovolaemia / decreased CO = decreased GFR = decreased clearance - CS = dehydration +/or hypovolaemia
- USG = >1.030 in dogs,
-USG >1.035 in cats - Tx = fluid therapy
What causes renal azotaemia? USG?
- Due to kidney disease (loss of 75% of nephron function)
- USG = <1.030 in dogs
-USG <1.035 in cats
-Usually isothenuria = 1.008-1.012
What causes post renal azotaemia? USG? Dx?
- Urinary tract obstruction
- Leakage of urine within body
- USG varies
- Dx = hyperkalaemia
-Creatinine conc higher in peritoneal fluid than blood
What test can be used for early detection of CKD?
Increased SDMA (symmetric dimethylarginine)
-With 40% reduction in GFR
-(compared to creatinine 75% loss of GFR)
What neoplasms can be associated with increased SDMA?
Lymphoma
What would happen to phosphorus + calcium with azotaemia?
- Hyperphosphataemia = decreased renal clearance of plasma P
- Calcium - may decrease, increase or stay normal =
-Decreased formation of VitD
-Increased Ca bound to nonprotein anions
=Measure free (ionised) Ca = normal/decreased
What would happen to potassium with azotaemia?
- Increased =
-decrease renal excretion
-redistribution between intracellular + extracellular compartments - Decreased =
-Increased urinary loss - PU
-Increased GI loss - vomiting/diarrhoea
-Decreased dietary intake - anorexia
What would happen to pH, amylase + lipase with azotaemic animals?
- Decreased pH = decreased renal excretion of H+
- Increased amylase + lipase =
-Decreased renal excretion + inactiviation
What is uraemia?
- Urine in blood
- Clinical syndrome = vomiting, anorexia, weight loss, diarrhoea, anaemia, muscle tremors, convulsions, coma, ulcerative stomatitis
What should be checked on physical exam of urine?
- Colour - normal = yellow/amber
-red/brown = RBCs, HGB, myoglobin - Clarity - clear / mildly turbid
-cloudy = cells, crystals, bacteria - Solute conc - USG, Freezing-point osmometry (gold standard)
What can cause hyposthenuria? (lower SG than plasma)
- Problem with production of / response to ADH
-need functioning nephrons
What can cause pre-renal proteinuria?
- Systemic inflammation
- Haemoglobinaemia
- Myoglobinaemia
- Bence-Jones proteinuria
What can cause post-renal proteinuria?
- Pyuria
- Haematuria
What should be done if renal proteinuria? When would you treat?
- UPCR (urine protein creatinine ratio)
- Treat = UPCR >0.5 in dogs
-UPCR >0.4 in cats - UPC >2 = glomerular disease
If glucosuria is not due to hyperglycaemia, what is the cause?
- Defective reabsorption by damaged / abnormal proximal tubules
- Fanconi syndrome, proximal tubular toxicosis, ischaemia
What can cause haem in urine?
- Haematuria = haemorrhage into urogenital tract
- Haemoglobinuria = intravascular haemolysis
- Myoglobinuria = myocyte damage / necrosis
What can cause erythrocytes in urine sediment? (haematuria - haemorrhage)
- Pathological haemorrhage = UTI, urolithiasis, neoplasia, coagulopathy
- Iatrogenic haemorrhage = during cystogentesis / catheterisation
- Oestrus
What can cause leukocytes in urine sediment (pyuria)?
- UTI = septic (bacteria, fungi), non-septic (urolithiasis, neoplasia)
- Genital tract inflammation = prostatitis, vaginitis
What can cause epithelial cells in urine sediment?
- Neoplasia
- Inflamed / hyperplastic mucosa
- Sometimes healthy animals
What are different casts in urine sediment?
- Hyaline casts → primarily with glomerular proteinuria
- Epithelial casts → active tubular degeneration or necrosis
- Granular casts → tubular degeneration, necrosis or inflammation
- Leukocyte casts → inflammation involving renal tubules
- Erythrocyte casts → glomerular or tubular haemorrhage
- Waxy casts → primarily with chronic renal disease
What are different crystal s in urine sediment?
- Struvite = healthy animals, UTI, urolithiasis
- Calcium phosphate = healthy, urolithiasis
- Calcium oxalate dihydrate = healthy, urolithiasis, hypercalciuria, hyperoxaluria
- Calcium oxalate monohydrate = hypercalciuria = ethylene glycol toxicity
- Cystine = cystinuria
- Amorphus = healthy animals
