Answering your questions

Feb. 1, 2003
Edited by Daniel M. Baer, M.D.

Wet mount bacteria reporting, venipunctures on children,
Miller disk use and arterial blood for tests

Wet mount bacteria reporting

Q: We need information about
reporting wet mounts. Should we report bacteria? Although bacteria are normally present in the vaginal area, some of us think that it would be diagnostically important. If we do report it, do we indicate as few, moderate, etc., or 1+, 2+, etc.? We all need to report the same elements. Also, should clue cells be reported in urine? By reporting clue cells in the urinalysis, would this help the health practitioner rule out a urinary tract condition vs. a vaginal condition?

A: Reporting the presence of bacteria
in a wet mount is not diagnostically helpful or standard procedure. As you stated, bacteria will normally be present on a wet mount. The more important question to answer is, What kind of bacteria is present? A gram stain provides a superior answer since this will differentiate between normal and abnormal vaginal flora. Additionally, the wet preparation should be examined for trichomonas, yeast/hyphae and clue cells (vaginal epithelial cells covered with gram variable rods).

Normal vaginal specimens show predominantly Lactobacillus. The most common organism found in vaginal infections is Gardnerella vaginalis. Infection with this organism is also termed bacterial vaginosis. Additionally, Mobiluncus and Bacteroides spp. are usually present and increased in bacterial
vaginosis.

Reporting clue cells in the urine provides one piece of information to the clinician, but is not a definitive clinical finding to diagnose a urinary tract infection or a vaginal condition. For a clinician assessing a patient with symptoms of abnormal vaginal discharge, the diagnosis of bacterial vaginosis can be made fairly easily by the presence of clue cells. On a wet mount, they have a granular appearance, and the borders are obscured. A gram-stained smear will show an altered vaginal flora, one filled with pleomorphic gram-negative to gram-variable rods and lacking in the normally present gram-positive lactobacilli. A positive whiff test (mixing vaginal secretions with a 10 percent KOH solution and noting a fishy smell) and a pH > 4.5 on the vaginal secretion lead to a fairly definitive diagnosis of bacterial vaginosis. Culture is usually not indicated.1,2

Bacteria in the urine are not necessarily indicative of a urinary tract infection. We know that specimens can easily be contaminated and show clinically insignificant elements. Some laboratories only report bacteria when observed in fresh specimens in conjunction with white blood cells. However, since the laboratorian does not have a complete clinical history, it is prudent to report the findings and let the provider determine the diagnostic significance. Bacteria in the urine are significant when culture results show the presence of >105 CFU/mL. Counts between 103 and 105 may indicate an incipient urinary tract infection. Collecting another clean-voided midstream urine specimen is recommended.3

Small numbers of epithelial cells and bacteria may be found in urine, but generally are of little significance. Contamination or prolonged storage before examination contributes to an increase in bacteria; however, the presence of any bacteria should be reported in a urine sample.4

How do you report these elements? Your procedure must clearly spell out your reporting format and standards. In our laboratory, we report bacteria and cellular findings as few, moderate and many, per high power field, and quantify these ranges. The presence of clue cells could be reported in the comment field.

You may want to consider soliciting input from medical staff who frequently order microscopic urinalysis, consulting with your pathologist and checking the NCCLS guideline on urinalysis reporting.5 Your ultimate goal is to provide consistent, relevant diagnostic reporting that allows the providers to make the appropriate diagnosis and prescribe effective therapy.

Juanita Petersen, MT(ASCP), MBA
Manager, Core Laboratory
Oregon Health and Science University
Portland, OR

References

  1. Wilson J, Braunwald E, et al. Harrisons Principles of Internal Medicine. 12th Edition. McGraw- Hill, Inc.; 1991.
  2. Delost M. Introduction to Diagnostic Microbiology. Mosby, Inc.; 1997; 487-488.
  3. Modern Urine Chemistry. Tarrytown, NY: Miles Inc.; 1991;63.
  4. Tips of Urinalysis.
    MLO. 2000; 16-17.
  5. NCCLS. Routine Urinalysis and Collection, Transportation, and Preservation of Urine
    Specimens
    . Approved Guideline GP 16-A2. Wayne, PA: NCCLS; 2001.

Venipunctures on children

Q: We have a doctor in our emergency department who insists on venous draws on all children for CBCs. Do you know of any benefit to venous draws vs. good capillary draws? The techs feel as though we are ruining the childrens veins and traumatizing them. Any recommendations?

A: Although capillary specimens
differ from venous specimens in glucose, potassium, total protein and calcium levels, venous blood for CBCs should correlate highly with blood from good capillary draws.1 The operative word here, though, is good. When improperly performed, CBC results from skin punctures can vary significantly. Results can be altered by tissue fluid, hemolysis and platelet clumping if the puncture is traumatic or if excessive squeezing is required. Therefore, it is not unreasonable for one to consider blood obtained by venipuncture to be the gold standard. It is clear that your ED physician questions the integrity of the specimens collected by skin puncture and has concerns that not all skin punctures are good skin punctures. Perhaps a discussion on the skills of your phlebotomists would reassure him/her. At the same time, a skills assessment of your phlebotomists may be necessary for your own reassurance.

It may be important to point out that, from the childs point of view, a capillary puncture can be the least traumatic means of obtaining a blood specimen. If the child is fearful of needles, so much so that he/she is moved to crying and screaming, it is important to know that crying can adversely affect WBC levels.1 It could be argued, therefore, that venipunctures on apprehensive children may yield compromised results, as well, and that in such patients, good skin punctures may yield more accurate results than venipunctures performed on frantic children.

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

www.phlebotomy.com

Reference

  1. National Committee for Clinical Laboratory Standards. Procedures for the Collection of Diagnostic Blood Specimens by Skin Puncture. Approved Standard, H4-A4, Villanova, PA, 1999.

Miller disk use

Q: Recently, we have begun using
the Miller ocular for performing reticulocyte counts, but havent been given an exact procedure to follow. When performing counts, do we include the RBCs and reticulocytes that touch the lines of the counting area? Our ocular consists of a small square directly in the middle of a larger square.

A: This has been a topic of interest
to MLO readers for several years and indicates a commendable interest in accurate and precise reticulocyte counts.1 Accurate reticulocyte counts are necessary for the calibration and control of automated reticulocyte counters.

A systematic bias can be introduced when using Miller oculars (also called disks) if they are used incorrectly. The difference is due to the application of the so-called edge rule. This rule states that red cells touching two sides of the small red cell counting square are not to be included in the cell count. A bias of the order of 30 percent is introduced if touching cells are not excluded, as is evident in the CAP survey results.2 A detailed description of the Miller disk-counting method can be found in the NCCLS/ICSH approved guideline, which was published several years ago.3

The accuracy of reticulocyte counts (both totals, as well as subgroups) is becoming increasingly important. In the clinical evaluation of therapies, look for the increasing use of the measurement of the immature reticulocyte fraction (IRF) which is an important indicator of left shift reticulocytes. Immature reticulocytes are an early indicator of bone marrow engraftment, as well as evidence of the response to erythropoietin therapy.4

John A. Koepke, M.D.
Professor Emeritus of Pathology
Duke University Medical Center
Durham, NC

References

  1. Koepke, JA. Reticulocyte counting with the Miller disc. Tip 9_1, in, Tips on Hematology . Medical Economics, Montvale, NJ. 1996.
  2. Koepke, JA. Update on reticulocyte counting.
    Lab Med. 1999; 30: 339-343
  3. Methods for Reticulocyte Counting (Flow Cytometry and Supravital Dyes) NCCLS Approved Guideline H44_A NCCLS, Wayne, PA; 1997.
  4. Davis, BH. Immature reticulocyte fraction (IRF): By any name, a useful clinical parameter of erythropoietic activity.
    Lab Hematol. 1996; 2: 2-8

Arterial blood for tests

Q: When we collect arterial blood
for a blood gas exam, we have blood left over that we dont want to waste. Can we use a heparinized arterial blood sample for CBC or chemistry tests and use the same reference ranges as that of a venous sample?

A: Heparin is a sufficient anticoagulant for red blood cell analysis, but may cause clumping of platelets or leukocytes. Therefore, a heparinized arterial blood sample cannot be used for CBC.1 However, it may be used for some chemistry tests, depending on the specific specimen requirement of each instrument, and you can use the same reference ranges as that of a venous sample.

Ching-Nan Ou, Ph.D.
Director of Clinical Chemistry
Texas Childrens Hospital
Professor of Pathology
Baylor College of Medicine
Houston, TX

Reference

  1. McClatchey K.D., ed.: Clinical Laboratory Medicine. 2nd ed. Philadelphia: Lippincott Williams & Wilkens; 2002: 804.
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 2003: Vol. 35, No. 2

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