Proteinuric Disease Flashcards
Causes of proteinuria
Altered glomerular permeability
- immune complex deposition
- vascular inflammation
- altered RBF
(can be functional in fever or with exercise)
- Intraglomerular hypertension
Excessive filtered load of albumin in glomerular disease –> secondary interstitial tubulonephritis
Impaired tubular handling
- decreased absorption of LMW proteins that are filtered (lower severity than for glomerular disease)
DDx: Fanconi Syndrome, Renal ischemia, nephrotoxins
- Overload proteinuria (multiple myeloma, Hgb, colostrum)
- Urinary tract inflammation
False positives in high concentrated or alkaline urine
If the urine remains yellow (microscopic haematuria), then there is negligible chance that a UPC >0.5 will be solely due to the added blood.
Clinical significance of proteinuria
Proteinuria is associated with increased risk of mortality (3x in dogs) and complications (1.5x) even when renal function is good
Markedly proteinuric dogs and cats treated with ACEi show renoprotective effects (ie, effects that decrease or delay adverse outcomes), a reduction in the magnitude of proteinuria is also observed during treatment
Methods of measuring proteinuria
Dipstick - 80% sensitivity but POOR SPECIFCITY (high false positive). Correlate with USG and pH
Urine Sulfosalicylic acid - more accurate for proteins that may not be measured by DS (ie Bence Jones). Mix supernatant with SSA and assess turbidity. Does not add much information for cats if DS negative
UPCR - wide daily variation best to use pooled samples
Urine protein electrophoresis - to detect BJ bodies (interpret with serum PE)
sulfate polyacrylamide gel electrophoresis (SDS-PAGE)
pattern of protein banding can help determine if glomerular damage, tubular damage, or both are contributing to the proteinuria
(most often mixed in dogs).
Urinary IgM and IgG are significantly associated with immune complex mediated glomerulonephritis (ICGN) compared with other glomerular and tubular disease categories
Recommended test for detection of albuminuria in cats
urine albumin detection in the feline patient should always be performed with a higher quality assay such as the species-specific albuminuria ELISA
feline urine samples, both routine-screening tests (dipstick and SSA) performed poorly and appear to be of minimal diagnostic value
In 239 urine samples from 37 cats with CKD the sensitivity and specificity for a > trace reaction on the dipstick and for a > 5 mg/dl reaction on the SSA were 81%/68% and 63%/96%
How and why is microalbuminuria detected
quantitative immunoassays at reference laboratories
Testing indicated where screening for proteinuria produces equivocal or conflicting results
Young dogs and cats that have a familial risk for developing proteinuric renal disease and a more sensitive screening test is desired.
Screening dogs or cats with illness that have negative UPCR though illness is associated with proteinuria
Steps in proteinuria investigation (7) from ACVIM consensus
Assessment of proteinuria involves investigation of: localisation (site/mechanism of proteinuria); documentation of persistence; determination of magnitude
1) Exclude extraurinary post-renal dz (use cysto sample)
2) Exclude pre-renal disease (dysproteinemia, fever, exercise)
3) Identify urinary post-renal by identification of inflammation in urine
4) determine if interstitial renal (inflammation and signs of nephritis, renal pain, fever)
5) Identify if pathologic glomerular (UPC >2)
6) Functional renal - mild UPC increase and resolves with subsequent evaluatin
7) If persistent low grade then consider pathologic glomerular (low grade) or tubular disease
When is UPCR indicated
patient with 2+ results without pyuria, or 1+ results in urine with USG <1.012
Do not use this test if preglomerular or overload proteinuria is suspected or if there is interstitial proteinuria, or post-renal proteinuria from haemorrhage or inflammation (interstitial proteinuria).
Recommendations for evaluating change in UPCR trends
probably need to differ by as much as 40%, especially in the lower ranges of abnormality, to conclude with a high level of confidence that the prevailing magnitude of proteinuria actually has changed
Variation of UPCR observed in cats with values within the reference range suggests that serial UPCRs need to differ by as much as 90% (ie, nearly double) to conclude with a high level of confidence that a cat’s magnitude of proteinuria has increased
When to investigate proteinuria and when to intervene
Monitor if:
Nonazotemic and persistent microalbuminuria
Nonazotemic and UPCR >0.5 (+/- treatment for underlying condition if found
Diagnostic investigation if:
Nonazotemic with rising microalbuminuria
Nonazotemic with persistent renal proteinuria UPCR >1
Treat if:
After appropriate treatment of any underlying disease. Treatment indicated in dogs with azotemic CKD and UPC >0.5; cats with CKD and UPC >0.4; nonazotemic dogs/cats with UPC >2.0
Change in diet - reduced by high quality protein; omega-3 FA supplementation
ACE inhibitor
Typical findings of tubular vs glomerular proteinuria
UP:UC > 0.4 and <2 in azotemic dogs: Proteinuria is thought to be mostly tubular with less of a glomerular component.
UP:UC ≥2 in non-azotemic or azotemic dogs: This is considered compatible with glomerular proteinuria
Tier classification of proteinuria
Tier I - Persistent renal proteinuria without hypoalbuminemia or azotemia
A - Persistent subclinical renal proteinuria that is not accompanied by any discernible renal-related signs or sequelae
B - Persistent renal proteinuria with hypertension as the only discernible renal-related sign or sequelae, with or without evidence of target organ damage
Tier II - Renal proteinuria associated with hypoalbuminemia, with or without any of its associated complications or sequelae (mainly oedema and thromboembolic events), but not azotemia
A - Persistent renal proteinuria with hypoalbuminemia, but without hypertension or azotemia
B - Persistent renal proteinuria with hypoalbuminemia, plus hypertension (with or without evidence of target organ damage)
Tier III - Renal proteinuria associated with renal azotemia
A - Renal proteinuria with renal azotemia, but not hypertension or hypoalbuminemia
B - Renal proteinuria with renal azotemia and hypertension (with or without evidence of target organ damage), but without hypoalbuminemia
C - Renal proteinuria with renal azotemia and hypoalbuminemia (with or without any of its associated complications), which often (but not always) are accompanied by hypertension (with or without evidence of TOD)
Additional diagnostics in progressive proteinuria or UPC >3.5 +/- low albumin or azotaemia
Aim is to identify the underlying cause of disease as well as determine severity of sequelae.
CBC, Biochem, UA
2 UPCRs from at home samples - get an estimate of ongoing proteinuria
Urine culture
Blood pressure measurement - if increased look for extrarenal causes (adrenal, heart, drugs, fluid/salt overload)
If low Albumin: look for neoplasia, look for GI disease, assess liver function
Characterise progression of azotaemia if present
Ultrasound abdomen - look for renal/adrenal changes and presence of ascites
Thoracic rads - look for infiltration and effusion
Infectious disease testing: Borrelia (lyme), Leishmaniasis, HWD; Ehrlichia, Leptospirosis (IDEXX snap 4dx)as appropriate depending on geographical location
Examine oral cavity and skin for infections.
Immune mediated disease testing
When to investigate for immune mediated disease in proteinuria
1) also exhibits concurrent extrarenal clinical signs or laboratory test findings that might be explained by an immune-mediated disease (PUO; joint swelling; anaemia; thrombocytopenia; dermatological changes)
Test for auto-antibodies such as ANA; Coomb’s test; RF.
possibility that the glomerular disease actually is part of a multisystemic immune-mediated disorder (eg, systemic lupus erythematosus) becomes highly relevant, both diagnostically and therapeutically
2) patient with renal proteinuria but does not exhibit any other signs or test abnormalities that might be explained by an immune-mediated disease
no evidence available that indicates that the results of any test for the presence of autoantibodies (eg, ANA, Coombs’) that reliably differentiates those that have an immune-complex glomerulonephritis from those that do not (in dogs with proteinuria)
Considerations for renal biopsy
- provides a definitive diagnosis but is not required if an underlying cause of proteinuria is detected and treatable
-Dogs with suspected glomerular disease benefit the most from a renal biopsy before the disease has progressed to an advanced stage. Secondary fibrosis and interstitial tubulonephritis mask original glomerular disease
- Cortical tissue only and preserve samples in different fixatives
Tests run on renal biopsies
Transmission electron microscopy
–> Detects electron dense deposits and their locations in the glomerulus
–> if no EDD, focus on evaluatin of the glomerular filtration barrier
Immunostaining
–> looks for immune complex desposits (IgG, IgM, IgA, C3)
Light Microscopy
–> overall structure but unlikely to determine cause of glomerular disease
Disturbance of any of the components of the glomerular filtration barrier – loss of the endothelial glycocalyx, abnormalities/ remodelling of the GBM, electron dense deposits along the GBM, podocyte foot process fusion or podocyte loss – can result in proteinuria.
Pathogenesis and histo of membranoproliferative GN
Type 1 Usually associated with a primary infectious disease process - immune complex accumulation on the subendothelial side of the glomerular basement membrane
→ complement activation
→ mesangium cell expansion, inflow of leukocytes
→ Thickened capillary walls, mesangial hypercellularity
IFM can demonstrate immune complex deposition and determine type of Ig present (but some cases have complement deposits only)
TEM can also identify the immune deposits
Type 2 - same as above but dense deposits not immune deposits, unknown origin
→ not associated with infectious disease
Histo and pathogenesis of membranous glomerulopathy
most common glomerular disease in cats,
SubEPIthelial antibodies (unique to MN) - urinary side of GBM
→ less inflammation as Ab are away from circulation thus rarely has evidence of inflammatory response in glomerulus
Primary disease is possibly a true autoimmune disease targeting antigens of podocyte
Histo: GBM is uniformly thickened, IFM determines site of Ig → beaded appearance along the GBM with silver stains
→ Progressive thickening of GBM determines the chronicity/severity of lesion
→ IC induced podocyte injury (through complement activation)
Without IFM and TEM would not be able to see the location of Ig complexes and thus would only see glomerulosclerosis
Pathogenesis and histo of Proliferative glomerulonephritis
Most commonly occurs after resolution of infection (in humans) or with persistent infections (but these are more likely to cause MPGN or MN). Usually associated with secondary disease
which have caused endocapillary or mesangial proliferation
Mesangial PGN: mesangial cell hyperplasia (>4 cells per mesangial area), ↑ mesangial matrix
Endocapillary PGN: endocapillary cell proliferation +/- increased mesangial cellularity.
+ Increased matrix,, and increased mononuclear cells and deposits of immune complexes
IFM - identifies the GBM Ig deposits and mesangium proliferation
TEM - further localises the immune complexes
Proteinuric kidney diseases with ICGN
MPGN
MN
PGN
IgA Nephropathy
Pathogenesis and histo of IgA Nephropathy
seen in dogs with hepatic or enteric diseases
Enteric disease - excessive IgA formation
Hepatic Disease - reduced IgA clearance
IFM - predominance of IgA positivity (polymeric) trapped in mesangium.
Concurrent IgG and IgM or C3 are common but less intense
Pathogenesis and histo of renal amyloidosis
Deposition of fibrils formed by polymerisation of proteins with beta-pleated sheet formation
Amyloid deposits formed by the polymerization of the acute phase reactant SAA. Persistent elevations of SAA needed for reactive amyloidosis
There are multiple polymorphs of SAA and possibly some are more amyloidogenic. There may also be inherited deficiencies in ability to degrade SAA
Histo: amyloid stains with congo red, expands the mesangium and GBM. Acellular material
TEM not needed to confirm diagnosis
Breeds: Shar Pei, Collies
Abyssinian, Siamese
Pathogenesis and histo of hereditary nephritis
diverse group of inherited glomerular diseases that are the result of a defect in basement membrane collagen type IV
→ Defective collagen → premature deterioration of GBM
English Springer spaniel (auto recessive), Samoyeds, and Cocker Spaniels, Dalmatians and Bull terrier
Histo: renal cortical hypoplasia or membranoproliferative or sclerosing GN
TEM: required for diagnosis → multilaminar splitting and fragmentation of GBM
Pathogenesis and Histo for minimal change disease
Rare disease, primary lesion loss of anionic charge selectivity in GBM → collapse of podocyte foot processes and loss predominantly of albumin
TEM - demonstrates marked podocyte foot process effacement
MOA of RAAS inhibition in renal proteinuria and diffrences in ACEi and ARB
reducing haemodynamic forces that favour filtration of protein
ACEi: decrease efferent > afferent arteriolar resistance (as AngII has more effect on efferent). May also have multiple other effects by reducing the AngII mediated remodelling and fibrosis of the renal tissues
ARBs: Specific inhibition of AT1 receptor thus more specific inhibition of the undesirable AngII effects (compared to ACEi) and less likely for escape pathways to result in undermining of drug effects (although note that aldosterone breakthrough is detected in some dogs on RAAS inhibitors, it is not associated with proteinuria outcome
Recent evidence for ACEi or ARB in treatment
JVIM 2020: prospective, randomised, double‐masked clinical trial comparing TEL to Enaalapril for treatment of renal proteinuria. At progressively higher dosages of each drug, telmisartan antiproteinuric effects were superior to those of enalapril
JVIM 2021: retrospective study of ARB, dual Tx or ARB+MM for renal proteinuria. 3 dogs that previously received telmisartan failed to show improvement when benazepril was added as combination treatmen
JVIM 2021: UPC of group ACEi + TEL was significantly lower (P = .01) in comparison to TEL alone by 3.8 (95% CI: 0.8‐6.8) and ACEi alone
→ NB dual RAAS blockade may be associated with higher risk of azotaemia progression or AKI compared to either drug alone.
When use of immunosuppression is justified in PLN
Underlying disease may be found in up to 63% of cases (basically 50:50 chance that they need suppression). Ideally the decision to commence immunosuppressive therapy is based on thorough evaluation and renal biopsies. Due to lack of trials there is insufficient evidence to prove a benefit of treatment.
The rationale underlying the recommendation to initiate immunosuppressive therapy is based on the prediction that suppression of humoral or cell mediated immunity and the associated glomerular inflammatory response will favourably influence the progression, severity, and clinical outcome of the disease
→ Clear evidence of electron dense deposits (subendothelial, subepithelial, mesangial or intramembranous) on TEM; or positive staining for Ig, light chains or C3 on IFM
→ DDx non-specific immune entrapment such as amyloid deposits
Other managements in PLN
Antithrombotics - JVECCCs recommend use in curative domain, use anti-coag due to VTE being documented +/- anti-platlet
DIET - less is known about primary proteinuric disease than CKD, but reduced dietary protein did help to reduce magnitude of proteinuria.
Addition of Omega 3s can help to lower glomerular pressure and be renoprotective → there is evidence of benefit in humans with IgA nephropathy
ANTIHYPERTENSIVES - as per ACVIM review , assess after ACE/ARB use and then add CCB if still indicated
VITAMIN D - recent study demonstrated reduced levels of metabolites and VDBP in dogs with renal proteinuria. Likely multifactorial including increased loss and reduced conversion to calcitriol. Currently no evidence for a role in supplementation in treatment of this disease
Potential adverse effects that may necessitate stopping RAAS inhibitors
Hyperkalaemia
Worsening azotaemia
Hypotension
Non-specific histo changes seen in PLN affecting tubules and why do they occur
chronic proteinuria causes tubular damage → tubulointerstitial fibrosis, tubular degeneration and atrophy
Protein in tubules is reabsorbed by the proximal tubules, but the resorbed proteins are cytotoxic and increase tubular cell workload.
Initial compensatory hypertrophy, but eventually the cell fails to meet increased demand and dies
Glomerular injury → ↓ perfusion of tubulointerstitium → additional injury
What is nephrotic syndrome
simultaneous presence of —proteinuria (due to glomerular disease causing damage to filtration membrane and loss of selectivity),
Hypoalbuminemia (most common LMW protein lost, but larger proteins including Ig can be lost also and ATIII),
Extravascular fluid accumulation (oedema due to reduced oncotic pressure and RAAS activation from reduced GFR increasing Na/water retention +/- endothelial dysfunction and altered vascular permeability), and hyperlipidemia (liver stimulated to make additional protein which includes cholesterol to maintain oncotic pressure)
3 different hypothesis for cause of oedema in nephrotic syndrome
Underfill - fluid loss due to reduced oncotic pressure > what can be reabsorbed by lymphatics –> reduced ECV and activation of RAAS –> Na and H2O retention
(hypernatraemia is common but not imporived by RAAS inhibition)
Overfill and Tubulointerstitial inflammation - excessive Na retention is primary defect (protein stimulating Na reabsorption in tubules or AngII production by leukocytes)
Vascular hyperpermeability - altered vascular permeability
Which glomerulopathies are more likely to cause nephrotic syndrome
MN
Amyloidosis
MPGN
Based on study where not all dogs had IFM/TEM performed
Treatment of nephrotic syndrome
Primarily aimed at addressing proteinuria:
- RAAS inhibition, antihypertensives
—> essential to slow the progressive nephron damage
AND increased oncotic pressure to minimise oedema
- control hypertension: ACEi, Na restriction
- antithrombotics
- interventions to remove cavitary effusions only indicated if causing impact on QoL
Delay diuretics until after trying RAAS inhibition unless fluid is life threatening (may cause hypovolaemia and exacerbate kidney injury)
-IVFT generally not needed as patients are HYPERvolemic
If hypovolemic need very judiciously and gradually increased with monitoring of BP, K, sCr, Wt)
Monitoring therapeutic efficacy in proteinuria
ACVIM 2013 consensus
Impact of treatment on (1) proteinuria (as measured by UPC)
–> At low UPC values (near 0.5), a minimum change of 80% is required to demonstrate a significant difference,
–> At high UPC values (near 12), a minimum change of 35% is necessary
(2) renal function (as measured by serum creatinine concentration),
(3) serum albumin concentration.
Aim to get serum albumin to >20g/L; complete response is >25g/L
