Answering your questions

June 20, 2013

Editor’s note: Anthony Kurec, MS, H(ASCP)DLM, answers a question from an MLO reader. Anthony is Clinical Associate Professor, Emeritus, at SUNY Upstate Medical University in Syracuse, NY.


I have wondered for a long time what the proper way to evaluate a urine microscopic bacterial count is when the patient has many “clue” cells but there are no free bacteria in the background. It is obvious that if clue cells are seen they are covered with tiny rods, but it seems to have always been procedure in our lab not to give them recognition in the microscopic results other than to name them as clue cells. Granted, they do not actually represent a UTI, but what should we do other than report their presence? Is it wrong and misleading to give these bacteria a value from 1+ to 4+? They will, of course, grow on culture, but what is the right thing to do in this case?


Changes in vaginal flora, such as a decreasing normal presence of lactobacilli (large gram-positive rods) and an increased presence of other bacteria, particularly Gardnerella vaginalis (gram-negative to gram-variable pleomorphic rods), is associated with bacterial vaginosis (BV), the most common cause of vaginitis in women of reproductive age.1,2 Detection of BV is important as it has been associated with increased risk of sexually transmitted diseases, including HIV. In addition, women with BV may have an increased risk of preterm births, pelvic inflammatory disease (PID), endocervicitis, and post-operative infections.

Significant overgrowth of G. vaginalis or other anaerobic bacteria will increase the production of proteolytic enzymes which break down vaginal peptides, creating a more alkaline environment. Due to the upward shift of pH, these amines create an exfoliation of vaginal squamous epithelial cells that becomes part of the odiferous discharge, one of the four symptoms observed in BV (see below). In the more alkaline environment, the G. vaginalis bacteria effectively adhere to these exfoliated epithelial cells, thus producing clue cells.3-5

Confirming a diagnosis of BV is based on the presence of at least three of four characteristics as established by Amsel: 1) grayish-white discharge; 2) positive “whiff” test (a drop of 10% KOH + a sample of vaginal fluid generates a strong fish-like odor); 3) pH is greater than 4.5; and 4) presence of clue cells.2,6 Presence of clue cells found in a wet mount preparation of vaginal secretions is a strong indication for BV.1  Clue cells have also been observed in urine samples, semen, urethral discharges, and endourethreal swabbings.2 Gram-stained smears, Papanicolaou smears, and wet preparations stained with 0.1% methylene blue have been used in identifying clue cells.2  Studies have shown that 20% or more clue cells found during routine Papanicolaou smear review is a strong predictor of BV.3

Because the alkaline environment causes epithelial cells to develop a strong affinity for bacteria, the limited presence of “free” background bacteria may be in part due to this adherence process. The bacteria adhere so well to the epithelial cells that cellular detail of clue cells is often obscured by the bacterial matting on the cell surface, with unclear cellular edges and even indistinct nuclui.3 Accounting for the presence of bacteria in addition to clue cells (because by definition, clue cells are not clue cells if bacteria are not present), as with any urine or other fluid samples, could be reported, as it does not detract from the overall completeness of the urine examination. However, before clinicians render a diagnosis of BV, they would also consider the other symptoms as noted above. Check with your medical director to confirm whether or not reporting bacteria in addition to clue cells is useful information to clinicians. Your director may consider this redundant.


  1. Thomason JL, Gelbart SM, Anderson RJ, et al. Statistical evaluation of diagnostic criteria for bacterial vaginosis. Am J Obstet Gynecol. 1990;162(1):155-160.
  2. Catlin BW. Gardnerella vaginalis: characteristics, clinical considerations, and controversies. Clin Microbiol. 1992;Rev 5(3):213-237.
  3. Sobel JD. Bacterial vaginosis. Ann Rev Med. 2000;51:349-356.
  4. Discacciati MG, Simoes JA, Amaral RG, et al. Presence of 20% or more clue cells: an accurate criterion for the diagnosis of bacterial vaginosis in Papanicolaou cervical smears. Diagn Cytopathol .  2006;34(4):272-276.
  5. Marrazzo JM, Holmes KK. Sexually transmitted infections: an overview and clinical approach. In:  Longo DL, Fauci AS, Kasper DL, et al, eds. Harrison’s Principles of Internal Medicine. 18th ed. New York, NY: McGraw-Hill; 2012.
  6. Amsel R, Totten PA, Spiegel CA, et al. Nonspecific vaginitis: diagnostic criteria and microbial and epidemiologic associations. The Am J Med. 1983;74(1):14-22.

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