Chapter 6-02: Diagnostics in Nephrology

Leukocytes

Detects presence of pyuria

• Infection

• Bladder tumor

• SLE

• Medication effect

• Elevated urine glucose, protein, ketones, specific gravity

• Certain oxidizing antibiotics (e.g., cephalexin, nitrofurantoin)

• Contamination

Nitrite

Detects evidence of bacteriuria

• Bacterial infection

• Elevated specific gravity, pH <6.0, vitamin C

• Contamination

Urobilinogen

Detects hepatic damage or obstruction; aids in differentiation between obstructive and hemolytic jaundice

• Low: May suggest biliary obstruction (due to less than typical amounts of conjugated bilirubin reaching the intestine for conversion to urobilinogen)

• High: Hemolysis, hepatobiliary disease

• Elevated nitrite levels

• Phenazopyridine

Protein

Detects glomerular disease or damage. Urine dipstick is sensitive for albumin, but has very low sensitivity for non-albumin proteinuria (e.g., tubular protein, immunoglobulins)

• Primary or secondary renal damage

• Urine that is acidic or dilute

• Dipstick best detects albumin so may miss non-albumin protein (e.g., abnormal antibodies produced by plasma cells in multiple myeloma)

• Urine that is alkaline or concentrated

• Phenazopyridine

pH

Assesses renal function for excretion of acids and ability to maintain acid–base balance

• Acid-base disturbances

• Renal tubular acidosis (RTA)

Blood

Detects presence of free hemoglobin, myoglobin, or RBCs

• Hgb: Extensive/rapid intravascular hemolysis

• Myoglobin: Skeletal muscle trauma (e.g., rhabdomyolysis, seizure)

• RBC: See “hematuria below” or “Trauma, infection, stone, malignancy or GN”

• Elevated specific gravity

• Captopril

• Vitamin C

• Menstrual bleeding

• If assessing for blood, myoglobin can cause a false positive

Specific gravity

Assesses renal ability to concentrate/dilute urine

• Low: Diabetes insipidus, renal disease, increased fluid intake, diuresis

• High: Hypovolemia, low effective circulating volume (heart failure, cirrhosis, nephrotic syndrome), SIADH, contrast dye

• Alkaline urine

• IV contrast

Ketone

Assesses for evidence of stressors (which cause incomplete fat metabolism)

• Fever

• Starvation

• Diabetic ketoacidosis

• Delay in urine examination

• Elevated specific gravity

• Some medications (e.g., mesna, levodopa, phenolphthalein)

Bilirubin

Detects hepatic damage or obstruction; aids in differentiation between obstructive and hemolytic jaundice

• Hepatobiliary disease

• Hyperthyroidism

• Septicemia

• Chlorpromazine

• Selenium

• Phenazopyridine

Glucose

Detects evidence of hyperglycemia (and therefore, often, diabetes)

• Hyperglycemia (usually due to diabetes)

• Proximal tubule dysfunction (Fanconi syndrome)

• SGLT2 inhibitors

Of note, glucosuria in the setting of normal serum glucose may indicate Fanconi syndrome.

• Elevated specific gravity

• Uric acid

• Vitamin C

• Ketones

• Levodopa