Urine Dipstick Testing: InFocus Everything You Need to Know

1 24 EMN June 2007By James R. Roberts, MDAuthor Credentials andFinancial Disclosure:James , MD, is the Chairmanof the Department of Emergency Medi-cine and the Director of the Division ofToxicology at Mercy Health Systems,and a Professor of Emergency Medicineand Toxicology at the Drexel UniversityCollege of Medicine, both in Philadel-phia. Dr. Roberts has disclosed that hehas no significant relationships with orfinancial interests in any commercialcompanies that pertain to this educa-tional Objectives:After reading thisarticle, the physician should be able to:1. Identify the limitations of Urine dip-stick Describe the value of Urine Discuss the use of Urine Dipstick testing as it pertains to Date:June 2007 Emergency physicians routinelyorder urinalysis (UA) many timeseach shift. It s usually a straight-forward issue, and most physiciansthink they are well versed in the inter-pretation of the results: You give it aglance, and make a decision.

2 The dip-stick analysis, the microscopic exam,and other information gleaned from aUA make their way into decision-makingfor a variety of diagnostic, therapeutic,and disposition issues. Like most thingslearned in detail many years ago, theinterpretation of the UA should be revis-ited on a regular basis. I find myself thinking I know every-thing about a certain test only to findthat the guidelines have changed, tech-nology has advanced, and previouslyheld dogma is now relegated to the sta-tus of misconception. With that in mind,I ll review the ins and outs of the urinal-ysis in emergency medicine. When oneconsiders the complexity of the UA, it isobvious that this is not a simple test. Theintricacies and subtleties are actuallyquite amazing. This month s columnfocuses on Dipstick testing , and nextmonth s will review Urine : A ComprehensiveReviewSimerville J, et alAm Fam Physician 2005;71(6):153 The authors of this nifty review dis-cuss the value of the standard UA for thediagnosis of many urinary tract condi-tions, including malignancy and meta-bolic issues.

3 The review discusses thecorrect method for performing a urinaly-sis and highlights the importance anddiagnostic value of a number of abnor-mal results found on the Dipstick andwith microscopy. Information gained forthe UA is termed invaluable by theseurologists from Georgetown University. Specimen Collection: For mostmen and women and in most ED situa-tions, a midstream clean-catch tech-nique is usually adequate. According tothese authors (but many woulddisagree), the time-honoredritual of cleaning the externalgenitalia in women has little orno proven benefit, although itis commonly emphasized. Insome reviews, contaminationrates are similar in specimensobtained with or without priorcleaning. (Arch Intern Med2000;160:2537.) Urine shouldbe refrigerated if it cannot beexamined for more than twohours because delayed analy-sis can produce Properties: Avariety of foods, medications,metabolic products, and infec-tions can cause abnormalurine colors and odors.

4 Nor-mal Urine is clear and light yel-low in color. Concentratedurine produces a darker color,a common finding in the morn-ing after overnight waterrestriction. Cloudy Urine canbe normal, usually caused byprecipitated phosphate crys-tals in alkaline Urine . Significant pyuriaalso can cause clouded Urine . Urine clarity is a good but not infalli-ble guide to the presence or absence ofUTI. (Pediatrics2000;106[5]:E60.)Although many believe that odoriferousurine is a sign of infection, it can simplyrepresent a concentrated specimen orreflect diet. Urine that has prolongedbladder retention time can develop anammonia-like odor. A fecal smell in theurine suggests a GI-bladder fistula. Cer-tain foods such as asparagus or beetsand a variety of medications can changethe odor or color of Urine . Myoglobincolors the Urine brown, carrots can pro-duce a deep yellow color, and pseudo-monas infections, propofol, and ami-triptyline may give a blue/green hue tothe Analysis: The accuracy ofdetecting microscopic hematuria, signifi-cant proteinuria, or urinary tract infec-tion is a subject of much interest andpracticality to emergency physicians.

5 Theurine Dipstick has false-positive and false-negative results, and a list is presented inthe table. It also should be noted that thecommonly used Urine Dipstick has a finitelifespan, should be kept in a closed con-tainer, and should not be constantlyexposed to air. testing with outdated andimproperly stored materials can lead toerroneous results. As an overview, dip-stick testing is quite helpful, serving as ascreening test for some conditions and adefinitive test for others. In complicatedcases or serious disease, Dipstick testingmust be correlated with microscopy andclinical Specific Gravity: Urine spe-cific gravity (USG) generally correlateswith the Urine osmolality. The most use-ful information derived from the USG isinsight into the patient s hydration statusand the concentrating ability of latter function is disrupted in a vari-ety of diseases. The normal USG ranges from USG less than is suggestiveUrine Dipstick testing : Everything You Need to know InFocusThe eyeball is no longer adequate or proper JCAHO or lab procedure to read andrecord results of the Dipstick .

6 A machine is used to read the Dipstick and print outthe results. Quality assurance is very problematic unless this routine is 1 in a SeriesAccuracy of Urinalysis for Disease DetectionConditionTestResultsSensitivity (%)Specificity (%)Microscopic Dipstick >1+ blood91-10065-99hematuriaSignificant1 Dipstick >3+ protein9687proteinuriaCulture-DipstickAb normal 72-9741-86confirmed UTIleukocyte esteraseAbnormal19-4892-100nitritesMicro scopy >5 WBC/HPF90-9647-50>5 RBC/HPF18-4488-89 Bacteria (any46-5889-94amount)1. Defined as 3 plus or greater on : Adapted from Am Fam Physician2005;71 relative hydration, and values greaterthan indicate relative conditions that increase theUSG without regard to hydration includ-ed glycosuria and Syndrome of Inappro-priate Antidiuretic Hormone Secretion(SIADH). In such cases, osmolality is themore important parameter to decreased USG, also known as diluteurine, is associated with diuretic use,diabetes insipidus, adrenal insufficiency,aldosteronism, or a plethora of condi-tions causing impaired renal function.

7 It should be noted that the purpose ofthe kidney is to concentrate Urine whenneeded. Many renal diseases alter thisconcentrating function and result in afixed specific gravity about , thespecific gravity of the glomerular fil-trate. This is known as isosthenuria, acondition seen, for example, in patientswith renal dysfunction due to sickle celldisease. Urinary pH: In general the Urine pHreflects the serum pH, but the primaryand normal function of the kidney is toacidify the Urine . Normal serum pH , but the normal urinary pH rangesfrom to 8. Because of normal meta-bolic activity, the generally acceptednormal pH of Urine is about to Inrenal tubular acidosis (RTA), the kidneycannot acidify the Urine , so the Urine canbe alkaline while the patient s serumdemonstrates a metabolic acidosis. The Urine pH can be related to Urine can be the result of ingestionof fruits (hence the use of cranberryjuice) that acidify the Urine .

8 Diets high incitrate and in citrus fruits, legumes, andvegetables can cause alkaline eaters tend to have more acidicurine, and vegetarians tend to have alka-line Urine . In the presence of a docu-mented UTI, alkaline Urine may suggestinfection with a urea-splitting organism(such as proteus). In alkaline Urine ,triple phosphate crystals (magnesiumammonium phosphate crystals) canform a staghorn calculus. Uric acidstones form in an acidic :The strict definition ofhematuria by the American UrologicalAssociation is the presence of 3 or morered cells per high-powered field in twoof three Urine samples. The Urine dip-stick is used to test for the peroxidaseactivity of erythrocytes, not for the actu-al presence of the physical RBC. Ofcourse, myoglobin and hemoglobin pro-duce a positive Dipstick for hematuriabecause these substances also will cat-alyze this reaction; these are the end-products of hemolyzed RBCs or musclebreakdown.

9 High doses of vitamin C willinhibit this process, and can invalidatethe Dipstick for this test. This also holdstrue for stool guaiac testing ; vitamin Ccan produce a false-negative occultblood in stool. It has always been stan-dard that a positive Dipstick for blood inthe absence of RBCs by microscopy isindicative myoglobinuria or hemoglobin-uria, not true authors present a table listing 45causes of hematuria. Although somerare ones, such as Fabry s disease, willlikely escape the detection and knowl-edge of the emergency physician, it isimportant to know that hematuria canbe associated with malignant hyperten-sion, numerous urinary tract cancers,infections, nephrolithiasis, nephritis(lupus) and vasculitis, tuberculosis, anda variety of drugs, including the obvious,heparin and warfarin. RBC casts are classic for acuteglomerulonephritis. Hematuria also canbe associated with TTP, renal veinthrombosis, sickle cell trait, or merelyrunning a marathon.

10 Contrary to popularbelief, significant hematuria will not ele-vate the protein concentration to therequired cut-off deemed positive, 3 plusor more on the Dipstick . The authorsnote that up to 20 percent of patientswith a gross hematuria have a urinarytract malignancy, so this conditionrequires a full work-up. Hematuria, inthe absence of proteinuria or RBC casts,suggests a pure urologic cause(stones/malignancy) for hematuria. Proteinuria:Healthy kidneys limitthe protein permeability of the glomeru-lar capillaries, but diseased kidneysallow more protein to be filtered so pro-teinuria is a hallmark of a variety ofrenal diseases. Blood proteins are nor-mally filtered and then reabsorbed bythe proximal tubule cells. Urinary pro-teins include primarily albumin, butsome serum globulins are detected. TheJune 2007 EMN25 Continued on next pageInFocusUrine Dipstick testing : Causes of False-Positive and False-Negative ResultsDipstick test False-positive testFalse-negative testBilirubin Phenazopyridine (Pyridium) Chlorpromazine (Thorazine), seleniumBlood1 Dehydration, exercise, hemo-globinuria,Captopril (Capoten), elevated specific gravity,menstrual blood, myoglobinuria, semen pH < , proteinuria, vitamin C,in Urine , highly alkaline Urine , oxidizing Dipstick exposed to airagents use to clean perineum GlucoseKetones, levodopa (Larodopa),Elevated specific gravity, uricdipstick exposed to airacid, vitamin CKetonesAcidic Urine , elevated specificDelay in examination of urinegravity, some drug metabolites,( , levodopa)Leukocyte3 Contamination,2 Elevated specific gravity, glycosuria, ketonuria,Esterasenephrolithiasisprotein uria, cephalexin (Keflex), nitrofurantoin(Furadantin)