lab Evaluation of the Renal System Flashcards
Approach to Assessing Kidney Function
- History and physical exam
- Anemia – yes or no?
> possible for chronic kidney disease (normocytic, normochronic, non-regenerative due to decreased erythropoietin) - Biochemical profile – urea, creatinine, phosphorus, K+, albumin
> indicators of reduced GFR
> high K with evidence of kidney injury = acute
> with chronic, electrolytes tend to balance out - Urinalysis – gross appearance, dipstick, and microscopic examination
- Bacterial culture and antimicrobial sensitivity
- Urine protein:Urine creatinine ratio
> creatinine lost at a steady state, so we can compare things to it
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- Renal function tests – fractional excretion studies – not terribly common
- Renal biopsy – not terribly common
Laboratory Tests – Diagnosis of Kidney Disease
- on serum
- Urea, creatinine & phosphorus
* Serum urea nitrogen, blood urea nitrogen (SUN, BUN) - Albumin
> high = dehydrated
> low while globulin normal = protein losing nephropathy
Laboratory Tests – Diagnosis of Kidney Disease
- on urine
- USG
- Urinalysis
- Urine protein: urine creatinine ratio
Azotemia
Increased nitrogenous waste in blood
- Urea, Creatinine, SDMA
Urea, Creatinine, SDMA - assess what?
Assess the glomerulus
- Urea, Creatinine, SDMA = GFR
> increase with decreased GFR
Proteinuria + decreased albumin (and normal globulins)
PLN
what happens to urea in the kidney? is it a good indicator of glomerular function?
40% filtered back in, 60% out
- not the best indicator of glomerular function but we still use it
> non-kidney conditions can affect levels too
Increased Urea – Prerenal reasons
- increased Protein in diet
- increased Endogenous protein catabolism
> GI bleeding, fever, infection, necrosis, hyperadrenocorticism (steroid hepatopathy)
Increased Urea – Prerenal – Ruminant specific reasons, what this means
- Ruminants – salivary & blood urea go to rumen
- Rumen microflora create amino acids from urea
> Increased urea can be caused by:
1. Rumen stasis
2. Decreased GFR - Urea not as useful an indicator of GFR in ruminants as in other species
Decreased Urea reasons
- Hepatic insufficiency (>80% loss)
- Portosystemic shunt (PSS)
- Decreased water resorption in tubules
* e.g., Osmotic diuresis
* Water resorption creates concentration gradient for urea resorption
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(4. Loss caudal GIT – horse)
(5. protein malnutrition)
creatinine - what happens to it as it enters the kidney?
- what is it?
creatinine > 100% goes into ultrafiltrate (as with everything else) and 1005 goes out into urine
- made from muscle creatine phosphate which is an energy storage molecule (produced by breakdown of muscle at steady state)
Increased Creatinine – Prerenal reasons
- increased Crt well-muscled individuals, particularly males
* Greyhounds, Belgian blue cattle
Decreased Creatinine reasons
- Young animals
- Muscle atrophy
> e.g., hyperthyroid cat, older animal, cachexia
SDMA - what happens to it in the kidney
- produced at steady state in the body, not influenced by muscle mass
- 100% comes out in urine
Symmetric Dimethylarginine – Interpretation
- what do we need?
- use?
- gold standard?
- Still need a full UA
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Early CKD – Increased SDMA, creatinine WNL - More sensitive than creatinine
- Muscle mass decreased? No problems!
- Feline CKD 17 mo before creatinine increased
- Canine CKD ~10 mo before creatinine increased
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Gold standard: use both creatinine and SDMA to stage stable CKD patients
Interpreting Azotemia and USG
- Azotemia + isosthenuria (USG 1.007 – 1.012)
* KIDNEY FAILURE
* Especially if dehydrated
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* Further assessment required
> What is hydration status? Might be appropriate?
> Interference w. concentrating capacity
>If it’s not repeatable, it’s not significant
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Postrenal Azotemia
- when do we see this?
Obstruction of urinary outflow distal to nephron
* FLUTD (feline lower urinary tract disease)
* Goat urolithiasis / foal bladder rupture
> Rupture & leakage of urine into the peritoneal cavity
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* USG not helpful in determining postrenal azotemia
> USG species-appropriate… initially
* Prolonged blockage > kidney injury > kidney failure
> e.g., hydronephrosis, shock, etc.
Proteinuria - types
- Prerenal (increased protein in blood)
- Renal (glomerular & tubular)
- Postrenal (hemorrhagic / inflammatory)
Prerenal Proteinuria
- what do we see?
- reasons
Protein normal or increased on the biochemical profile
* Physiologic – e.g., fever, exercise
* Hypertension – e.g., from endocrinopathies, heart disease > increased pressure forcing proteins out
* Multiple myeloma (Bence-Jones proteinuria)
* Hemoglobinuria
* Myoglobinuria
* Post-colostral proteinuria
Renal Proteinuria - types, reasons
- what do we see?
Glomerular proteinuria
* Hypoalbuminemia noted on biochem
* Some injury to filtration barrier
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Tubular proteinuria
* Early stages, albumin normal on biochem
* Usually associated w. acute / congenital kidney diseases
> e.g., Fanconi’s syndrome, admin of gentamycin
* Proximal tubules damaged / defective – filtered proteins not resorbed
* Loss of low MW proteins and amino acids
Postrenal Proteinuria
- causes
Postrenal proteinuria (hemorrhagic / inflammatory)
* Hemorrhage into genitourinary tract
> Renal or bladder calculi, impaired hemostasis, blood vessel damage from inflammation, trauma, neoplasia, etc.
* With inflammation will often see pyuria and sometimes “sub-optimal” USG
UPCR – Interpretation
(urine protein : creatinine ratio)
- normal levels
- purpose of measurement
- what do do with results?
Normal ratio:
- Dog or cat: <0.2
Borderline:
- Dog: 0.2-0.5
- Cat: 0.2-0.4
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* Estimate quantity of urinary protein excreted / d
* Proteinuric: demonstrate persistence by re-evaluating in 2 to 4 weeks
* Borderline: re-evaluate within 2 months
* Most <0.2
* Proteinuria between 0.2 – 2.0 is tubular or glomerular
* Proteinuria >2.0 is considered glomerular
> UPCR >2, no need to demonstrate persistence = severe proteinuria
Nephrotic Syndrome – Protein-losing nephropathy leading to abdominal transudation
- what do we see?
- Glomerular disease
- Hypoalbuminemia
- Hypercholesterolemia
- Edema / abdominal transudation
* Loss of plasma oncotic pressure - Hypercoagulable state
* Loss of antithrombin
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* In Short:
When there’s Protein in the Urine
LOOK AT CHOLESTEROL & REMEMBER ANTITHROMBIN
* Animal in hypercoagulable state!
USG for cat dog, cow, horse?
- what does USG tell us?
cat: 1.035
dog: 10.30
cow, horse: 1.025
> Interpret with hydration status
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- is assessing distal collecting duct, as this is where we bring water back into the body
> if we are losing water, we have more dilute urine, if we are keeping water in the body we have more concentrated urine
> ADH receptors allow insertion of aquaporins to bring water back in
