Table 9.1-3. Urine microscopy features in the evaluation of acute kidney injury

Features

Comments

Cells

1) >3 RBCs/HPF: Quantity and morphology assessment required; dysmorphic RBCs are associated with GN

2) WBCs: Associated with infection or inflammation:

a) PMNs associated with infection

b) Eosinophilia associated with AIN, cholesterol emboli, or schistosomiasis

3) Epithelial cells:

a) Squamous cells are usually contaminants

b) Transitional cells usually due to bladder irrigation or catherization, rarely due to malignancy

c) Renal tubular cells seen in ATN

Casts

1) Hyaline cast: Nonspecific, seen in strenuous exercise and dehydration

2) Granular cast (muddy-brown cast): Seen in ATN

3) Waxy cast: Seen in CKD

4) Fatty cast: Seen in nephrotic syndrome, mercury and ethylene glycol poisoning

5) RBC cast: Seen in GN

6) WBC cast: Seen in AIN, pyelonephritis, and GN

Crystals

1) Acidic urine: Uric acid or calcium oxalate

2) Alkaline urine: Triple phosphate or calcium phosphate

AIN, acute interstitial nephritis; ATN, acute tubular necrosis; GN, glomerulonephritis; HPF, high-power field; RBC, red blood cell; PMN, polymorphonuclear neutrophil; WBC, white blood cell.