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Signature ✍️
Laboratory
- Linear, progressive ↑ in SCr not qualifying as AKI (>3-7 days)
- Metabolic acidosis, azotemia, hyperphosphatemia, hypocalcemia
- Hyperparathyroidism (secondary)
- Anemia (↓ EPO)
- Isosthenuria (specific gravity fixed ~1.010)
Imaging
- Small, echogenic kidneys bilaterally (fibrotic collapse)
✋ Exception: CKD ⊕ kidney enlargement can be seen in infiltrative diseases (amyloidosis, polycystic kidney disease), emphysematous pyelonephritis, early diabetic kidney disease (hyperfiltration), & HIV nephropathy
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DDx 🏳️🌈
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- Diabetes (GBM thickening, mesangial expansion, nodular glomerulosclerosis)
- “Hypertension” (at least 50% found to have CM-TMA)
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- Extrinsic (Supply vs. Drainage) 🚫
- ↓ Supply 🔴
- Renal artery stenosis (↑ risk if unilateral kidney)
- Atheroembolic disease (subacute hypoperfusion)
- ↓ Drainage 🟡
- Bilateral retroperitoneal fibrosis
- Chronic UVJ vs. bladder outlet obstruction
⛳ Clue: discordant, severely atrophic kidney relative to contralateral kidney
- Intrinsic (Anatomic Approach) 🟤
- Vascular 🔴
- Primary TMA DDx
- Glomerular 🧶
- Base Rate
- Nephrotic: FSGS = most common
- Nephritic: IgA nephropathy = most common
- Estoria = Genetic
- Type 4 collagen, nephrin, podocin
- Tubulointerstitial 🟤
- Base Rate
- Inpatient: recurrent AKI → ATN (e.g. recurrent ICU admission)
- Outpatient: NSAID excess, lithium toxicity
- Toxic Cell Lysis
- TLS: urate nephropathy
- Chronic hemolysis: tubular hemosiderosis
- Crystalline
- Nephrocalcinosis DDx
- Paraprotein
- Light chain proximal tubulopathy
- Crystal-storing histiocytosis
- Heavy Metals
- Lead, cadmium, copper
- Autoimmune
- IgG4-RD
- Sjogren’s
- Genetic
- AD tubulointerstitial kidney disease (UMOD, MUC1)
- Infection
- Granulomatous (e.g. Whipple’s)
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Principles❗️
Diabetes ⊕ CKD: Recognizing Esoteria 🐎
- Kidney biopsy should be pursued if:
- Active urinary sediment
- Systemic inflammation
- Albuminuria w/o retinopathy (type 1)
- Brisk ↑ albuminuria & ↓ eGFR
Diagnostic Armamentarium 🧰
- Linear trend of creatinine (i.e. confirm CKD rather than AKI → solve correct problem)
- Over-the-counter Rx reconciliation (NSAIDs) ⊕ Prescribed Rx (Lithium)
- Skin exam (e.g. nodularity of crystals, palpable purpura of vasculitis)
- Past medical history (e.g. fat malabsorption, gastric bypass, systemic signature), Family history (i.e. dialysis, deafness, gout, recurrent stones)
- Urinalysis (screen for glomerular disease) → 24 hour urine albumin & protein (⊕ gap = tubulointerstitial disease)
- Urine microscopy (crystal evaluation) & 24 hour Urine oxalate (oxalosis)
- Renal ultrasound/Doppler (confirm no post-renal disease, renovascular stenosis)
- BMP, VBG (assess for RTAs), CBC & hemolysis screen (hemosiderosis, TLS)
- Paraprotein screen (SPEP, SIFE, SFLC, UPEP)
- ANA, SSA/SSB, ANCA, anti-GBM, C3/C4 (autoimmune screen)
- Renal biopsy ⊕ genetic testing (”end of the road”)
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