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Urinalysis: A Comprehensive Review
JEFF A. SIMERVILLE, M.D., WILLIAM C. MAXTED, M.D., and JOHN J. PAHIRA, M.D. Georgetown University School of Medicine, Washington, D.C.

A complete urinalysis includes physical, chemical, and microscopic examinations. Midstream clean collection is acceptable in most situations, but the specimen should be examined within two hours of collection. Cloudy urine often is a result of precipitated phosphate crystals in alkaline urine, but pyuria also can be the cause. A strong odor may be the result of a concentrated specimen rather than a urinary tract infection. Dipstick urinalysis is convenient, but false-positive and false-negative results can occur. Specific gravity provides a reliable assessment of the patient's hydration status. Microhematuria has a range of causes, from benign to life threatening. Glomerular, renal, and urologic causes of microhematuria often can be differentiated by other elements of the urinalysis. Although transient proteinuria typically is a benign condition, persistent proteinuria requires further work-up. Uncomplicated urinary tract infections diagnosed by positive leukocyte esterase and nitrite tests can be treated without culture. (Am Fam Physician 2005;71:1153-62. Copyright© 2005 American Academy of Family Physicians.)

Urinalysis is invaluable in the diagnosis of urologic conditions such as calculi, urinary tract infection (UTI), and malignancy. It also can alert the physician to the presence of systemic disease affecting the kidneys. Although urinalysis is not recommended as a routine screening tool except in women who may be pregnant, physicians should know how to interpret urinalysis results correctly. This article reviews the correct method for performing urinalysis and the differential diagnosis for several abnormal results.

Strength of Recommendations
Key clinical recommendation	Label	References
Patients with dipstick results of 3+ or greater may have significant proteinuria; further work-up is indicated.	B	5
Patients with microscopic hematuria (i.e., at least three red blood cells per high-power field in two of three specimens) should be evaluated to exclude renal and urinary tract disease.	C	19, 20
Exercise-induced hematuria is a relatively common, self-limited, and benign condition. Because results of repeat urinalysis after 48 to 72 hours should be negative in patients with this condition, extended testing is not warranted.	C	30
A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, opinion, or case series. See page 1046 for more information.

Specimen Collection
A midstream clean-catch technique usually is adequate in men and women. Although prior cleansing of the external genitalia often is recommended in women, it has no proven benefit. In fact, a recent study1 found that contamination rates were similar in specimens obtained with and without prior cleansing (32 versus 29 percent). Urine must be refrigerated if it cannot be examined promptly; delays of more than two hours between collection and examination often cause unreliable results.2

Physical Properties: Color and Odor

Foods, medications, metabolic products, and infection can cause abnormal urine colors (Table 1).3 Cloudy urine often is a result of precipitated phosphate crystals in alkaline urine, but pyuria also can be the cause.

TABLE 1 Common Causes of Abnormal Urine Coloration
Color	Pathologic causes	Food and drug causes
Cloudy	Phosphaturia, pyuria, chyluria, lipiduria, hyperoxaluria	Diet high in purine-rich foods (hyperuricosuria)
Brown	Bile pigments, myoglobin	Fava beans Levodopa (Larodopa), metronidazole (Flagyl), nitrofurantoin (Furadantin), some antimalarial agents
Brownish-black	Bile pigments, melanin, methemoglobin	Cascara, levodopa, methyldopa (Aldomet), senna
Green or blue	Pseudomonal UTI, biliverdin	Amitriptyline (Elavil), indigo carmine, IV cimetidine (Tagamet), IV promethazine (Phenergan), methylene blue, triamterene (Dyrenium)
Orange	Bile pigments	Phenothiazines, phenazopyridine (Pyridium)
Red	Hematuria, hemoglobinuria, myoglobinuria, porphyria	Beets, blackberries, rhubarb Phenolphthalein, rifampin (Rifadin)
Yellow	Concentrated urine	Carrots Cascara
UTI = urinary tract infection; IV = intravenous. Adapted with permission from Hanno PM, Wein AJ, Malkowicz SB. Clinical manual of urology. 3d ed. New York: McGraw-Hill, 2001:75.

The normal odor of urine is described as urinoid; this odor can be strong in concentrated specimens but does not imply infection. Diabetic ketoacidosis can cause urine to have a fruity or sweet odor, and alkaline fermentation can cause an ammoniacal odor after prolonged bladder retention. Persons with UTIs often have urine with a pungent odor. Other causes of abnormal odors include gastrointestinal-bladder fistulas (associated with a fecal smell), cystine decomposition (associated with a sulfuric smell), and medications and diet (e.g., asparagus).

Dipstick Urinalysis

False-positive and false-negative results are not unusual in dipstick urinalysis (Table 2). The accuracy of this test in detecting microscopic hematuria, significant proteinuria, and UTI is summarized in Table 3.4-13

TABLE 2 Causes of False-Positive and False-Negative Urinalysis Results
Dipstick test	False positive	False negative
Bilirubin	Phenazopyridine (Pyridium)	Chlorpromazine (Thorazine), selenium
Blood	Dehydration, exercise, hemoglobinuria, menstrual blood, myoglobinuria	Captopril (Capoten), elevated specific gravity, pH < 5.1, proteinuria, vitamin C
Glucose	Ketones, levodopa (Larodopa)	Elevated specific gravity, uric acid, vitamin C
Ketones	Acidic urine, elevated specific gravity, mesna (Mesnex), phenolphthalein, some drug metabolites (e.g., levodopa)	Delay in examination of urine
Leukocyte esterase	Contamination	Elevated specific gravity, glycosuria, ketonuria, proteinuria, some oxidizing drugs (cephalexin [Keflex], nitrofurantoin [Furadantin], tetracycline, gentamicin), vitamin C
Nitrites	Contamination, exposure of dipstick to air, phenazopyridine	Elevated specific gravity, elevated urobilinogen levels, nitrate reductase-negative bacteria, pH < 6.0, vitamin C
Protein	Alkaline or concentrated urine, phenazopyridine, quaternary ammonia compounds	Acidic or dilute urine, primary protein is not albumin
Specific gravity*	Dextran solutions, IV radiopaque dyes, proteinuria	Alkaline urine
Urobilinogen	Elevated nitrite levels, phenazopyridine	-
IV = intravenous. *-False-positive results are caused by false elevation; false-negative results are caused by false depression.

TABLE 3 Accuracy of Urinalysis for Disease Detection
Condition	Test	Results	Sensitivity (%)	Specificity (%)	PPV	NPV
Microscopic hematuria4	Dipstick	>= 1+ blood	91 to 100	65 to 99	NA	NA
Significant proteinuria5	Dipstick	>= 3+ protein	96	87	NA	NA
Culture-confirmed UTI6-13	Dipstick	Abnormal leukocyte esterase	72 to 97	41 to 86	43 to 56	82 to 91
		Abnormal nitrites	19 to 48	92 to 100	50 to 83	70 to 88
		Abnormal leukocyte esterase or nitrites	46 to 100	42 to 98	52 to 68	78 to 98
		>= 3+ protein	63 to 83	50 to 53	53	82
		>= 1+ blood	68 to 92	42 to 46	51	88
		Any of the above abnormalities	94 to 100	14 to 26	44	100
	Microscopy	> 5 WBCs per HPF	90 to 96	47 to 50	56 to 59	83 to 95
		> 5 RBCs per HPF	18 to 44	88 to 89	27	82
		Bacteria (any amount)	46 to 58	89 to 94	54 to 88	77 to 86
PPV = positive predictive value; NPV = negative predictive value; NA = not applicable; UTI = urinary tract infection; WBCs = white blood cells; HPF = high-powered field; RBCs = red blood cells. Information from references 4 through 13.

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