Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (237 page)

   A urine culture should be performed to detect infecting microorganisms.

   Urine microscopy should be performed to detect the presence and level of red cells, white cells, urinary casts, and crystals.

   Calculi should be collected by urination through a stone screen, for chemical analysis.

   Hematuria: Gross or microscopic, occurs in 80% of symptomatic patients and is the single most definitive predictor of a calculus in patients with unilateral flank pain. However, hematuria is not detected in 10–30% of patients with documented nephrolithiasis.

   Renal function tests: Useful for interpretation of hypercalcemia.

   Crystalluria: Diagnostically useful for cystine crystals (in familial cystinuria) or struvite crystals.

   Cyanide-nitroprusside test: Positive (false positive may occur with sulfurcontaining drugs). Calcium oxalate, phosphate, and uric acid should arouse suspicion about possible causes, but they may occur in normal urine.

   Neutrophilia: Suggestive of infection, for example, in the finding of struvite crystals.

Suggested Readings

Coe FL, Parks JH, Asplin JR. The pathogenesis and treatment of kidney stones.
N Engl J Med.
1992;327:1141–1152.

Elton TJ, Roth CS, Berquist TH, et al. A clinical prediction rule for the diagnosis of ureteral calculi in emergency departments.
J Gen Intern Med.
1993;8:57–62.

Teichman JM, Long RD, Hulbert JC. Long-term renal fate and prognosis after staghorn calculus management.
J Urol.
1995;153:1403–1407.

HEMATURIA

   Definition

   The term
hematuria
refers to the microscopic detection in urine of >2 RBCs per high-power field. It should not to be confused with hemoglobinuria, a term reserved for the presence of free hemoglobin in urine.

   Hematuria may be macroscopic (grossly visible as red or brown urine) or microscopic (detectable only by microscopy). It can be classified as glomerular or nonglomerular in origin. Centrifugation allows one to differentiate hematuria (RBCs in sediment) from hemoglobinuria (normal sediment, heme-pigmented supernatant), which can be tested for heme with a urine dipstick.

   Who Should Be Suspected?