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Answering your questions on citrate anticoagulant for hematology, and clue cells.

Citrate anticoagulant for hematology

Q Can trisodium citrate be used as an anticoagulant for hemoglobin, hematocrit, and cell counts? If so, sample collection for our laboratory would be considerably less complex because we could do the routine complete blood count (CBC) and coagulation tests on the same sample of blood.

A Any procedures that simplify blood collection without sacrificing quality are welcome. But with current collection systems, a number of potential and actual problems would become apparent. They are not insurmountable, but let's review them.

If sodium citrate tubes were used (as presently supplied), hematology calibration methods would have to be modified due to the standard blood dilution of 1 part of anticoagulant to 9 parts blood. Appropriate modifications would be required to avoid systematic errors. A more subtle consideration is the osmolality of sodium citrate solutions. The more commonly used 3.8% (0.129 mmol/L) citrate is somewhat hyperosmolar for red cells, resulting in shrinkage of red cells and artifactual lowering of the hematocrit. The preferred 3.2% (0.109 mmol/L) citrate solution is isoosmolar and hence should not affect the hematocrit determination.

Efforts to standardize blood collection have been directed toward optimal specimen preservation. The now-preferred ethylenediamine tetraacetic acid (EDTA) anticoagulant (1.5 mg of EDTA/mL of blood) results in minimal problems in the usual CBC components, including the reticulocyte count. There is good preservation of morphology of both erythrocytes and leukocytes.

Rarely, the laboratory must try to obtain an accurate platelet count on a patient who exhibits an EDTA-dependent antibody. In such cases, a specimen collected in citrate can avoid this problem. But keep in mind the artifacts noted above (including dilution).

In one preliminary comparative study of citrate versus EDTA anticoagulants, these investigators showed acceptable comparisons between these 2 anticoagulants and urged more comprehensive studies.

John A. Koepke, PhD

Professor Emeritus of Pathology

Duke University Medical Center

Durham, NC


(1.) Perrotta G, Roberta L, Glazier, Schumacher HR. Use of sodium citrate anticoagulant for routine hematology analysis on the Cell-Dyn 4000: An opportunity to enhance efficiency in the clinical laboratory. Lab Hematol. 1998;4:l56-162.

Clue cells

Q Are clue cells significant when observed in a clean catch urine specimen?

A Clue cells are squamous epithelial cells (SEC) of the vagina that are coated with small rods such that the cell borders are obliterated. [1] The presence of clue cells in vaginal secretions is one of 4 characteristics that are used for the diagnosis of bacterial vaginosis (BV). The clue cells can be visualized in wet mounts or stained smears.

The SECs found during the routine microscopic examination of urine are usually derived from the terminal third of the urethra or the epithelium of the vagina. Therefore, the presence of clue cells (found only in the vagina) or numerous SECs in a dean-catch urine specimen from a woman usually indicates vaginal contamination of the specimen. This occurs frequently with poorly collected specimens. The presence of true clue cells in a urine specimen contaminated by vaginal secretions suggests that the woman may have BV. However, the laboratory diagnosis of BV must be confirmed on a vaginal specimen.

David L. Sewell, PhD, ABMM

Director of Microbiology

Veterans Affairs Medical Center

Portland, DR


(1.) Spiegel, CA. Bacterial vaginosis: Changes in laboratory practice. Clin Microbial Newsl. 1999;21:33-37.

Daniel M. Baer is professor emeritus of laboratory medicine at Oregon Health Sciences University in Portland, OR, and a member of MLO's editorial advisory board.
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Author:Baer, Daniel M.
Publication:Medical Laboratory Observer
Article Type:Abstract
Geographic Code:1USA
Date:Mar 1, 2000
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