Chapter 19: Nephrology

HEMATURIA

Microscopic hematuria: >5 RBCs per high-power field in a urine sample

Epidemiology

• Microscopic hematuria: 3–4% incidence on single urine sample; falls to 1% or less for two or more positive samples

Differential Diagnosis

Red Urine with a Negative Dipstick for Blood

• Medications: Chloroquine, deferoxamine, metronidazole, nitrofurantoin, pyridium, rifampin, salicylates, doxorubicin

• Dyes: Fruits/vegetables (beets, blackberries, food coloring)

• Metabolites: Melanin, methemoglobin, porphyrin, urates, tyrosinosis

• Bacteria: Serratia urinary-tract infection (UTI) (some strains produce a red/burgundy pigment)

Positive Urine Dipstick for Blood, but Absence of Red Blood Cells (RBCs)

• Hemoglobin: Suggests a hemolytic process

• Myoglobin: Associated with rhabdomyolysis from trauma, infection, prolonged seizures, or severe electrolyte abnormalities

Repeatedly Positive Urine Dipstick for Blood and Presence of RBCs (Hematuria)

• Urinary tract: Cystitis/urethritis, hypercalciuria, urolithiasis, trauma, coagulopathy, sports hematuria (may be traumatic or nontraumatic, the latter due either to increased filtration pressure or to increased glomerular permeability as a result of hypoxic damage to the nephron as blood is redistributed to contracting skeletal muscles)

• Kidney, nonglomerular: Acute tubular necrosis (ATN), interstitial nephritis, pyelonephritis, sickle cell disease or trait, cysts, tumors (e.g., Wilms), trauma, vascular anomalies (e.g., renal vein thrombosis)

• Kidney, glomerular: Glomerulonephritis (GN) (see “Glomerulonephritis” section)

Pathophysiology

• Lesions in the glomerulus, renal interstitium, vasculature, or urinary tract result in bleeding or leakage of RBCs into the urinary tract.

Clinical Manifestations

• Glomerular hematuria typically presents with brown or cola-colored urine with RBC casts, dysmorphic RBCs, and proteinuria.

• Urinary tract or vascular causes present with gross hematuria, occasionally with blood clots, eumorphic RBCs (normal appearing), and absent or minimal proteinuria.

• Hypertension, edema, and/or acute kidney injury (AKI) suggest acute GN.

• Abdominal mass suggests tumor, hydronephrosis, polycystic kidney disease, or obstruction.

• Certain rashes are associated with Henoch–Schönlein purpura (HSP) or systemic lupus erythematosus (SLE).

• Fever and dysuria suggest a UTI.

Diagnostics

The diagnostic pathway depends on whether there is gross or microscopic hematuria as well as other abnormal findings. Begin with a urinalysis with microscopy as well as a thorough history and physical exam.

• Microscopic hematuria: In the absence of RBC casts, proteinuria, hypertension, AKI, or other concerning clinical signs, repeat urinalysis weekly for 2 weeks (without exercise)

• Gross hematuria with proteinuria, dysmorphic RBCs, RBC casts, hypertension, or AKI indicates glomerular origin: Send serum electrolytes, blood urea nitrogen (BUN), creatinine, CBC with differential, and serum complement (C3, C4) (see Table 19-1). If postinfectious GN is suspected, send anti–streptolysin O (ASO) and/or anti-DNase B titers. Consider further evaluation such as antineutrophil antibody and antineutrophil cytoplasmic antibody based on clinical presentation

• Gross hematuria without proteinuria or RBC casts: Suggests an extraglomerular origin. Send for urine culture if ...