Answering your questions

Feb. 1, 2004

Edited by Daniel M. Baer, MD

Reporting mixed urine cultureQ Our OB/GYN POL recently switched to a hospital reference lab. When we send a CCMS urine for culture, this lab performs a gram stain if the dipstick 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, <10,000 alpha strep, <10,000 second coliform type, <10,000 Lactobacillus). Our previous reference lab would report out as mixed genitourinary 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 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, 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. 

Susan E. Sharp, PhD, DABMM 
Director of Microbiology 
Kaiser Permanente 
Associate Professor
Pathology Regional Laboratory 
Oregon Health Science University 
Portland, OR 


  1. Thomson RB, Miller JM. Specimen collection, transport, and processing: bacteriology. In: Murray PR, Baron EJ, Jorgensen JH, Pfaller MA, Yolken RH, eds.
    Manual of Clinical Microbiology, 8th ed. ASM Press, Washington DC. 2003:320-322.

Plastic discard tubes

If you have a PT only to draw, and are using plastic tubes, what do you use as a discard tube since the red-stopper tube cannot be used? With glass tubes, we draw the red-stopper tube as the discard tube, then the citrate tube. A As of 1998, the NCCLS stopped recommending a discard tube when drawing only blue-stoppered tube for PT or PTT.1 If special factor assays are requested, a discard tube is still recommended. For facilities with plastic tubes, it is not prudent to use a tube with a clot activator, such as a plastic red-, yellow-, or speckled-top tube, as a discard tube. Carryover of the clot activator into the citrate tube can quantitatively affect results. Use a glass tube with no additive (red-top) or another citrate tube as a primer.

If you are drawing only a citrate tube directly through a winged infusion (butterfly) set, prime the tubing of the set so that the vacuum of the citrate tube is not partially exhausted with the air in the line, which can result in an underfilled tube. PTTs are very sensitive to short sampling, which is why tubes for coagulation testing should be filled to at least 90% of their stated volume. 

When drawing only a sodium citrate tube through a butterfly set with a tube holder adapter attached, use a glass tube with no additive (red-top) or another blue-top tube as a primer. Apply just long enough so that the tubing of the butterfly set is primed with blood. The tube to be sent to the testing facility can be completely filled.

Dennis Ernst, MT(ASCP)
The Center for Phlebotomy Education Inc.
Ramsey, IN 


  1. National Committee for Clinical Laboratory Standards. Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture. Approved Standard, H3-A4. 1998. 

Erroneous reports

I have read that when submitting a corrected report,
the original (erroneous) report is to be left on the chart, because if
the physician treated based on erroneous data, evidence of that data was
needed to support his treatment. Our lab protocol states that the
erroneous data will be removed from the patients chart. Are there
references to support this position?
A Erroneous reports must not be removed from a medical record. Lawyers love to find deletions because they are evidence of chart tampering. If this is a paper (noncomputer) report, leave it in the chart marked as erroneous, see corrected report. The person marking the report should sign and date the change. If the report is computer-generated, be sure that the computer tags it as corrected. In either case, it is important to show both the original report (erroneous) and the corrected report (corrected).

In the Laboratory General Checklist,1 used for CAP accreditation inspections, question GEN.43715, a Phase II item, asks, When a revised report is issued, is it clearly defined as such, and is the original information and changed information reported together?

The commentary explains that when a revised report is issued, the lab must have a mechanism to ensure that the new result and previous incorrect result are reported together. As clinical decisions or actions may have been based on the previous report, it is important to replicate previous data, interpretations, and reference intervals, together with the revised information. Previous and revised information must be identified as such, and ideally, these would be juxtaposed for easy comparison. The precise format is at the discretion of the lab. Unless specifically endorsed by the medical staff/clients, it is not acceptable to simply indicate that a result has been revised, expecting the reader to look up previous results in the lab chart. For extensive interpretive or textual data (e.g., surgical pathology reports), repeating the entire original and corrected pathology reports may be cumbersome, rendering the revised report format difficult to interpret. In such cases, a comment in the corrected report explaining the previous information and the reason for the correction may be more appropriate than repeating the entire original report.

Daniel M. Baer, MD
Professor Emeritus
Department of Pathology
Oregon Health and Science University 
Portland, OR


  1. College of American Pathologists, Laboratory Accreditation Program, Laboratory General Checklist. July;2003.
Daniel M. Baer is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLOs editorial advisory board. February 2004: Vol. 36, No. 2