Interpretation of Urine Cultures

As previously mentioned, UTIs may be completely asymptomatic, produce mild symptoms, or cause life-threatening infections. Of importance, the criteria most useful for microbiologic assessment of urine specimens is dependent not only on the type of urine submitted (e.g., voided, straight catheterization) but the clinical history of the patient (e.g., age, sex, symptoms, antibiotic therapy).

One major problem in interpreting urine cultures arises because urine cultures collected by the voided technique may be contaminated with normal flora, in cluding Enterobacteriaceae. Determining what colony count represents true infection from contamination is of utmost importance and is related to the patient's clinical presentation. A number of studies have proposed the use of different cutoffs in colony counts based on clinical presentation; an example of one such set of guidelines is given in Table 57-2.

Ideally, the clinician caring for the patient should provide the laboratory with enough clinical information to allow specimens from different patient populations to be identified.2,11 These specimens could then be selectively processed using the guidelines in Table 57-2. However, because microbiology laboratories frequently receive little or no clinical information about patients, questions have been raised as to whether these cutoffs are practical and realistic for routine laboratory use. Further complicating urine culture interpretation is the increasing difficulty in distinguishing between infection and contamination as the criterion for a positive culture is lowered from 105 CFU/mL to 102 CFU/mL. Because of these issues, many laboratories establish their own interpretative criteria for urine cultures based on the type of urine submitted (e.g., clean-catch midstream, catheterized, and surgically obtained specimens such as suprapubic aspirates). Variations in interpretative guidelines occur from one laboratory to another but some generalities can be made; these are listed in Table 57-3. Some examples of urine culture results are shown in Figure 57-5 to illustrate some of these interpretations. (For delineation of complete urine protocols, refer to sources listed in the Additional Reading at the end of this chapter.)

Table 57-3 General Interpretative Guidelines for Urine Cultures

Result

Specific Specimen Type/Associated Clinical Condition, if Known

Workup

pathogen orfbr each of two potential pathogens

CCMS urine/pyelonephritis, acute cystitis, asymptomatic bacteriuria, orcatheterized urines

Complete*

a103CRVmL of a single potential pathogen

CCMS urine/symptomatic males orcatheterized urines or acute urethral syndrome

Complete

aThree organism types with no predominating organism

CCMS urine orcatheterized urines

None. Because of possible contamination, ask for another specimen

Eithertwo orthree organism types with predominant growth of one organism type and <104 CFU/mL of the other organism type(s)

CCMS urine

Complete workup for the predominating1 organising); description of the other organising)

fc102 CFU/mL of any number of organism types (set up with a 0.001- and 0.01-mL calibrated loop)

Suprapubic aspirates, any other surgically obtained urines (including ileal conduits, cystoscopy specimens)

Complete

A complete worttup Includes identification of the organism and appropriate susceptibility testing.

•Predominant growth =10* to 0s CFU/mL.

CPU, Colony-forming unit; CCMS, clean-catch midstream urine.

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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Responses

  • robel
    What are the consequences of not using a CCMS specimen for cultures?
    1 year ago

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