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Reporting mixed urine culture.

Q Our OB/GYN POL recently switched to a hospital reference lab. When we send a CCMS CCMS Computing Center Management System
CCMS Committee on the Challenges of Modern Society (NATO)
CCMS Child Care Management Services
CCMS Cincinnati College of Mortuary Science
CCMS Cerebrocostomandibular Syndrome
 urine for culture, this lab performs a Gram stain gram stain

Staining technique for the initial identification of bacteria, devised in 1884 by the Danish physician Hans Christian Gram (1853–1938). The stain reveals basic differences in the biochemical and structural properties of a living cell.
 if the dipstick dipstick /dip·stick/ (dip´stik) a strip of cellulose chemically impregnated to render it sensitive to protein, glucose, or other substances in the urine.  is positive for leukocytes and/or nitrites. Our previous reference lab did not do this. Is this a new standard of care? Also, when reporting culture results, the hospital lab will report a colony count and specific definition of each colony type, (e.g., <10,000 coliform coliform /col·i·form/ (kol´i-form) pertaining to fermentative gram-negative enteric bacilli, sometimes restricted to those fermenting lactose, e.g., Escherichia, Klebsiella, or Enterobacter. , <10,000 alpha strep, <10,000 second coliform type, <10,000 Lactobacillus lactobacillus

Any of the rod-shaped, gram-positive (see gram stain) bacteria that make up the genus Lactobacillus. They are widely distributed in animal feeds, manure, and milk and milk products.
). Our previous reference lab would report out as "mixed genitourinary genitourinary /gen·i·to·uri·nary/ (jen?i-to-u´ri-nar-e) pertaining to the genital and urinary organs.

adj. Abbr.
 flora," which we would consider as probable contamination. Any thoughts on this?


A Urine culture is the most common test performed by most microbiology laboratories, and most urine cultures are negative. For this reason, screening methods are available that attempt to rapidly separate specimens containing significant counts of bacteria from negative specimens. In general, screening methods perform well with specimens containing at least 100,000 CFU/mL of bacteria but perform poorly when colony counts are lower.

Screening urine specimens by staining with the Gram stain is rapid and economical with regard to reagents, but is labor-intense and requires a trained technologist. Commercially available dipstick tests that detect leukocyte esterase (LE) and nitrite nitrite

Any salt or ester of nitrous acid (HNO2). The salts are inorganic compounds with ionic bonds, containing the nitrite ion (NO2) and any cation.
 are rapid, inexpensive and simple to perform, but their sensitivity is low in some patient populations. (1) If a dipstick is positive for LE and/or nitrites, this is an indication that the specimen may contain a clinically significant amount of white cells and/or bacteria. Conversely, a urine sample that is negative for LE and nitrites would not likely contain a significant amount of white cells or bacteria.

Performing a Gram stain only on urine samples that are positive for LE or nitrites increases the chance that the specimen will show positive results. This approach can likely provide initial information to the physician on what the causative organism might be, while limiting the labor-intensive Gram stain procedure to those specimens likely to show clinically relevant information. There are several ways to report urine culture results. In many patients, a CCMS urine specimen, which contains less than 10,000 CFU/mL, whether mixed or pure, can be considered nonsignificant non·sig·nif·i·cant  
1. Not significant.

2. Having, producing, or being a value obtained from a statistical test that lies within the limits for being of random occurrence.
, however, there are exceptions to this, and the reader is referred to the reference indicated above for further information. (1) Generally, reporting of less than "10,000 CFU/mL of mixed genitourinary flora" can be interpreted to indicate contamination, again with some exceptions. (1) Reporting a mixture of three or more colony types at less than 10,000 CFU/mL would indicate a similar finding.


1. Thomson RB, Miller JM. Specimen collection, transport, and processing: bacteriology bacteriology

Study of bacteria. Modern understanding of bacterial forms dates from Ferdinand Cohn's classifications. Other researchers, such as Louis Pasteur, established the connection between bacteria and fermentation and disease.
. In: Murray PR, Baron EJ, Jorgensen JH, Pfaller MA, Yolken RH, eds. Manual of Clinical Microbiology, 8th ed. ASM (1) (Association for Systems Management) An international membership organization based in Cleveland, Ohio. Founded in 1947 and disbanded in 1996, it sponsored conferences in all phases of administrative systems and management.  Press, Washington DC. 2003:320-322.

--Susan E. Sharp, PhD, DABMM

Director of Microbiology

Kaiser Permanente

Associate Professor

Pathology Regional Laboratory

Oregon Health Science University

Portland, OR

Edited by Daniel M. Baer, MD

MLO's Tips from the Clinical Experts department 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 fax, (503) 636-7932; or e-mail,
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Title Annotation:Experts Focus on Lab Concerns
Author:Sharp, Susan E.
Publication:Medical Laboratory Observer
Geographic Code:1U9OR
Date:Feb 1, 2004
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