Table 3.
| Diagnostic Test | Findings | Pathologic Condition (s) |
|---|---|---|
| Urinalysis with microscopy | Hyaline cast | Prerenal azotemia |
| Muddy brown cast | ATN | |
| Dysmorphic RBC & RBC casts | GN | |
| WBC casts | AIN | |
| Crystals | Crystal induced nephropathy, drugs, nephrolithiasis | |
| Monomorphic RBCs, WBCs | UTI, Nephrolithiasis, Genitourinary tumors etc | |
| Protein | GN, Monoclonal gammopathy | |
| CBC with peripheral smear | Anemia, Schistocytes, low platelets | TMA |
| Serum osmolality | Osmolar gap & severe metabolic acidosis | Toxin |
| Creatinine kinase | >5000 IU/L | Rhabdomyolysis |
| Serologic tests | HIV antibody | HIV associated nephropathy, HIV induced immunocomplex kidney disease |
| Hepatitis serology | Membranous GN, MPGN | |
| ANA, dsDNA | Lupus nephritis | |
| C- ANCA, P- ANCA | ANCA vasculitis | |
| Rheumatoid factor, Cryoglobulins | Cryoglobulinemia, MPGN | |
| Anti—GBM antibody | Good pasture syndrome | |
| ASO | Infection related GN | |
| Low Complement levels | Lupus, Infection related GN, atheroemboli, MPGN, shunt nephritis | |
| Fractional excretion of sodium (FeNa) * | <1% | Prerenal azotemia |
| Fractional Excretion of urea (Fe Urea) | <35% | Prerenal azotemia |
| POCUS (Volume Assessment) | IVC diameter ↓ (>50% w/inspiration) | Hypovolemia |
| Renal USG | Hydronephrosis, Hydroureter | Nephrolithiasis, Retroperitoneal fibrosis, BPH, Phimosis, Ureteral obstruction |
| Renal vein thrombosis | Hypercoagulable state | |
| Renal biopsy | Variable | GN, ATN, AIN, crystal induced nephropathy |
| Newer biomarkers | ↑ NGAL, KIM 1, (TIMP-2)∙(IGFBP7) ** |
"Damage biomarkers" increased much before rise in creatinine |
ATN: Acute tubular necrosis, GN- Glomerulonephritis, AIN: Acute interstitial nephritis, UTI: Urinary tract infection, ANA: Antinuclear antibody, ANCA: Antinuclear cytoplasmic antibody, GBM: Glomerular basement membrane, MPGN: Membranoproliferative glomerulonephritis, ASO: Anti Streptolysin, POCUS: Point of care ultrasound, IVC: Inferior vena cava, NGAL: neutrophil gelatinase–associated lipocalin, KIM-1: Kidney injury molecule -1, TIMP 2- Tissue inhibitor of metalloproteinases-2, IGFBP7: Insulin like growth factor-binding protein 7. Notes: UA dipstick ++ for blood but no RBCs - Suspect rhabdomyolysis. If urine protein creatinine ratio quite elevated but urine dipstick with low grade proteinuria - Suspect multiple myeloma. BUN out of proportion to Cr - Suspect GI bleeding, high dose steroids, high protein feeding. Urine eosinophils have low sensitivity (30.8%) and specificity (68.2%) for AIN1 so not diagnostic of AIN. * FeNa is affected in CKD, diuretics, contrast administration, acute GN and Rhabdomyolysis so is not quite reliable in cause of AKI diagnosis. ** FDA approved in 2014.