Urine colony counts.

Q Could you give me the "pros and cons" of doing a total colony count on a urine culture vs. doing individual colony counts on pathogens in a urine culture. We are in the process of standardizing several labs in our system, and this is an issue for which we cannot find much information to reference.

A Urine colony counts should always be done per isolate and not as a total colony count of all organisms. For example, if a clean-catch urine culture grew greater than 100,000 cfu/mL of E coli and 5,000 cfu/mL of a coagulase-negative staphylococci (CNS), you would want to report as in Example A, not as in Example B.

Example A) APPROPRIATE

>100,000 cfu/ml E coli

5,000 cfu/mL CNS (or insignificant growth)

Example B) NOT APPROPRIATE

>100,000 cfu/mL E coli and CNS

Example A appropriately confers the culture results, where Example B could lead a clinician to treat for both E coli and the coagulase-negative Staphylococcus, when only treatment of the E coli would be appropriate as the 5,000 cfu/mL of the CNS most likely represents contamination.

Table 1 below lists general guidelines for urine culture interpretation and work up for one or more potential pathogens from urine cultures. Often, we do not receive patient history with our urine specimens for culture. In this case, Table 2 gives general guidelines that might be used.

--Susan E. Sharp, PhD, D(ABMM)

Director of Microbiology, Kaiser Permanente Pathology

Regional Laboratory; Associate Professor, Oregon Health and Science University

Portland, OR

Resources

1. Forbes BA, Sahm DF, Weissfeld AS, eds. Bailey and Scott's Diagnostic Microbiology. 10th ed. St. Louis, MO: Mosby; 1998.

2. Mandell GL, Bennett JE, Dolin R, eds. Principles and Practices of Infectious Diseases. 5th ed. New York, NY: Churchill Livingston; 2000.

Edited by Daniel M. Baer, MD

MLO's "Tips from the Clinical Experts" provides practical, up-to-date solutions to readers' technical and clinical issues from a panel of experts in various fields. Readers may send questions to Dan Baer by e-mail at [e-mail].

Table 1

                            Specimen type and/or
Result                      patient history              Work-up

>[10.sup.4] cfu/mL of a     CC/MS, IDC from patients     Work up the one
  single PP or for each     with pyelonephritis,         or both PP with
  of 2 PP                   acute cystitis, or           ID/AST
                            asymptomatic bacteruria,
                            OR SC
>[10.sup.3] cfu/mL of a     CC/MS, IDC from symptomatic  Work up PP with
  single pp                 male patients, OR SC, OR     ID/AST
                            acute urethral syndrome
>3 PP                       CC/MS, IDC, SC               No work up
1 PP at >[10.sup.5] cfu/mL  CC/MS, IDC                   Work up the one
  with 1 to 2 PP at                                      PP at
  <[10.sup.4] cfu/mL                                     >[10.sup.5]
                                                         cfu/ml with ID/
                                                         AST
1 PP at >[10.sup.4] cfu/mL  SC                           Work up the one
  with 1 to 2 PP at                                      PP at
  <[10.sup.3] cfu/mL                                     >[10.sup.4]
                                                         cfu/ml with ID/
                                                         AST
>[10.sup.2] cfu/mL of any   SB                           Work up all PP
  PP                                                     with ID/AST

Table 2

Specimen type and result                   Work-up

CC/MS: [greater than or equal to]          Work up the one or both PP
  [10.sup.4] cfu/mL of a single PP or for  with ID/AST
  each of 2 PP
SC: [greater than or equal to]             Work up the one or both PP
  [10.sup.3] cfu/mL of a single PP or for  with ID/AST
  each of 2 PP
CC/MS, SC: [greater than or equal to]3 PP  No work up
CC/MS: 1 PP at [greater than or equal to]  Work up the one PP at
  [10.sup.5] cfu/mL with 1 to 2 PP at      [greater than or equal to]
  <[10.sup.4] cfu/mL                       [10.sup.5] cfu/mL with ID/AST
SC: 1 PP at [greater than or equal to]     Work up the one PP at
  [10.sup.4] cfu/ml with 1 to 2 PP at      [greater than or equal to]
  <[10.sup.3] cfu/mL                       [10.sup.4] cfu/mL with ID/AST
SB: [greater than or equal to][10.sup.2]   Work up PP (up to three) with
  cfu/mL of up to 3 PP                     ID/AST

Key to tables:

CC/MS = clean catch and/or midstream
IDC = indwelling catheter
SC = straight catheter
ID/AST = identification and antimicrobial susceptibility testing (if
appropriate)
PP = potential pathogen
SB = suprapubic urine aspirates or other surgical obtained urine
specimens