genitourinary disorders
Bacterial Urinary Tract Infections
Diagnosis of Bacterial UTIs
Urinalysis Sometimes urine culture Diagnosis by culture is not always necessary. If done, diagnosis by culture requires demonstration of significant bacteriuria in properly collected urine. If a Overview of Sexually Transmitted Infections (STI) is suspected, a urethral swab for STI testing is obtained prior to voiding. Urine collection is then by clean-catch or catheterization. To obtain aclean-catch, midstream specimen, the urethral opening is washed with a mild, nonfoaming disinfectant and air dried. Contact of the urinary stream with the mucosa should be minimized by spreading the labia in women and by pulling back the foreskin in uncircumcised men. The first 5 mL of urine is not captured; the next 5 to 10 mL is collected in a sterile container. is preferable in older women (who typically have difficulty obtaining a clean-catch specimen) and in women with vaginal bleeding or discharge. Many clinicians also use catheterization to obtain a specimen if evaluation includes a pelvic examination. Diagnosis in patients with indwelling catheters is discussed elsewhere (see Diagnosis ). Testing, particularly culturing, should be done within 2 hours of specimen collection; if not, the sample should be refrigerated. 10 WBCs/mcL. The presence of bacteria in the absence of pyuria, especially when several strains are found, is usually due to contamination during sampling. Microscopic hematuria occurs in up to 50% of patients, but gross hematuria is uncommon. WBC casts, which may require special stains to differentiate from renal tubular casts, indicate only an inflammatory reaction; they can be present in Acute pyelonephritis , Pyuria in the absence of bacteriuria and of urinary tract infection (UTI) is possible, for example, if patients have Urinary Calculi , a uroepithelial tumor, Dipstick testsalso are commonly used. A positive nitrite test on a freshly voided specimen (bacterial replication in the container renders results unreliable if the specimen is not tested rapidly) is highly specific for UTI, but the test is not very sensitive. The leukocyte esterase test is very specific for the presence of>10 WBCs/mcL and is fairly sensitive. In adult women with uncomplicated UTI with typical symptoms, most clinicians consider positive microscopic and dipstick tests sufficient; in these cases, given the likely pathogens, cultures are unlikely to change treatment but add significant expense. Culturesare recommended in patients whose characteristics and symptoms suggest complicated UTI or an indication for treatment of bacteriuria. Common examples include the following: Pregnant women Postmenopausal women Men Prepubertal children Patients with urinary tract abnormalities or recent instrumentation Patients with immunosuppression or significant comorbidities Patients whose symptoms suggest Symptoms and Signs or Patients with recurrent UTIs (≥3/year) Samples containing large numbers of epithelial cells are contaminated and unlikely to be helpful. An uncontaminated specimen must be obtained for culture. Culture of a morning specimen is most likely to detect UTI. Samples left at room temperature for>2 hours can give falsely high colony counts due to continuing bacterial proliferation. Criteria for culture positivity include isolation of a single bacterial species from a midstream, clean-catch, or catheterized urine specimen. Forasymptomatic bacteriuria, criteria for culture positivity based on the guidelines of the Infectious Diseases Society of America (seeGuidelines for the Diagnosis and Treatment of Asymptomatic Bacteriuria in Adults, 2019) are Two consecutive clean-catch, voided specimens (for men, one specimen) from which the same bacterial strain is isolated in colony counts of>105/mL Among women or men, in a catheter-obtained specimen, a single bacterial species is isolated in colony counts of>102/mL Forsymptomatic patients, culture criteria are Uncomplicated cystitis in women:>103/mL Uncomplicated cystitis in women:>102/mL (This quantification may be considered to improve sensitivity to E. coli.) Acute, uncomplicated pyelonephritis in women: > 104/mL Complicated UTI:>105/mL in women; or>104/mL in men or from a catheter-derived specimen in women Acute urethral syndrome:>102/mL of a single bacterial species Any positive culture result, regardless of colony count, in a sample obtained via suprapubic bladder puncture should be considered a true positive. in mixed flora may be a true pathogen ( Diagnosis reference ). Occasionally, UTI is present despite lower colony counts, possibly because of prior antibiotic therapy, very dilute urine (specific gravity<1.003), or obstruction to the flow of grossly infected urine. Repeating the culture improves the diagnostic accuracy of a positive result, ie, may differentiate between a contaminant and a true positive result. Newer molecular urine testing may sometimes reveal unusual pathogens in patients with refractory or recurrent UTI. Clinical differentiation between upper and lower UTI is impossible in many patients, and testing is not usually advisable. When the patient has high fever, costovertebral angle tenderness, and gross pyuria with casts, pyelonephritis is highly likely. The best noninvasive technique for differentiating bladder from kidney infection appears to be the response to a short course of antibiotic therapy. If the urine has not cleared after 3 days of treatment, pyelonephritis should be sought. Symptoms similar to those of Cystitis and Men with symptoms of cystitis that do not respond to usual antimicrobial therapy may have Prostatitis . Seriously ill patients require evaluation for Sepsis and Septic Shock , typically with complete blood count (CBC), electrolytes, lactate, blood Patients who have dysuria/pyuria but no bacteriuria should have testing for a sexually transmitted infection (STI), typically using nucleic acid-based testing of swabs from the urethra and cervix (see Diagnosis ). Most adults do not require assessment for structural abnormalities unless the following occur: The patient has≥2 episodes of pyelonephritis. Infections are complicated. Nephrolithiasis is suspected. There is painless gross hematuria or new renal insufficiency. Fever persists for≥72 hours. Urinary tract imaging choices include ultrasonography, CT, and intravenous urography (IVU). Occasionally, voiding cystourethrography, retrograde urethrography, or cystoscopy is warranted. Urologic investigation is not routinely needed in women with symptomatic cystitis or asymptomatic recurrent cystitis, because findings do not influence therapy. Children with UTI often require imaging. 1.Hooton TM, Roberts PL, Cox ME, et al: Voided midstream urine culture and acute cystitis in premenopausal women.N Engl J Med369(20):1883-1891, 2013. doi: 10.1056/NEJMoa1302186 