Q & A

September 2005

Richard A. Savage, MD, Editor

Q.  Is it appropriate to stain for Helicobacter pylori in the duodenum?

A.  Helicobacter pylori has been shown to infect the duodenum in patients with gastric H. pylori infection. It occurs in the duodenum only in the presence of gastric (at least foveolar) metaplasia. H. pylori stains are not routinely needed in duodenal biopsies. However, if the duodenum shows gastric metaplasia and the patient's stomach cannot be evaluated, it may be reasonable to use a specific stain for H. pylori.

Lawrence J. Burgart, MD
Department of Pathology
Mayo Clinic
Rochester, Minn.
Chair, CAP Surgical Pathology Committee

Q.  What is the significance of two distinct RBC populations aside from the obvious transfusion? We recently had a CBC RBC histogram with two distinct population peaks and the patient had not been transfused in the last year.

A.  Two distinct peaks in the mean corpuscular volume plot indicates that an admixture of cells of two different sizes is present in the patient's blood. The question does not provide details of the MCV characterizing each peak or the red cell morphology on the blood smear, so the following are general comments.

Where there is an admixture of a lower MCV RBC population and a higher MCV red cell population, you commonly see a normal MCV (average cell size is normal) and a high red cell distribution width (width of the distribution is increased because of the two populations). Normal MCV and high RDW are characteristics of patients following transfusion; patients with early iron (developing microcytic population) or folate/vitamin B₁₂ (developing macrocytic population) deficiency; patients with homozygous hemoglobinopathies (admixture of many RBC forms); patients with myelofibrosis (morphologic variability from admixed extramedullary hematopoiesis); and patients with some forms of sideroblastic anemia. (X-linked sideroblastic anemia shows a classic example of a dimorphic blood smear.) Patients with large numbers of reticulocytes (those recovering from hemorrhage or those with iron deficiency who are starting treatment) may also demonstrate an admixture of different cell sizes. Spurious large cell populations may also be seen when there is red cell agglutination, which is interpreted by the instrument as a large red cell population. Evaluating RBC morphology on the smear is the key to interpreting cases where this admixture of cell sizes is present.

Bibiliography

Bessman JD, Gilmer PR, Gardner FH. Improved classification of anemias by MCV and RDW. Am J Clin Pathol. 1983;80:322-326.
Cornbleet J. Spurious results from automated hematology cell counters. Lab Med. 1983;14:509-514.

Robert Novak, MD
Department of Pathology
Children’s Hospital Medical Center of Akron (Ohio)
Chair, CAP Hematology/Clinical Microscopy Resource Committee

Q.  Is an easy-to-perform and reliable methodology available for performing the Jones methenamine silver stain for renal biopsy interpretation?

A.  The standard methods for the Jones methenamine silver, or JMS, stain, published in histotechnology textbooks and in the special September 1996 issue of The Journal of Histotechnology devoted to silver stains, are all potentially reliable and employ the basic steps common to argentaffin techniques: oxidation, silver impregnation, toning, and counterstain.

It is not easy, however, to reproduce the JMS stain by any method. The key to consistency is having a very experienced histotechnologist, who thoroughly understands renal microanatomy, microscopically control the silver impregnation and toning steps. The pathologist and histotechnologists should frequently review cases at the microscope and jointly agree on the desired stain intensity. A small number of technologists should perform this stain to improve consistency and maintain competency.

If achieving the desired intensity and distribution of staining is difficult, it may be helpful for the technologist to stain three to five serial sections, extending or shortening the time in silver by one to two minutes between each of these slides to refine the technique.

The following technical factors must also be addressed to achieve consistent staining:

• All glassware and forceps used in the procedure must be chemically cleaned.
• All solutions must be freshly prepared.
• Controls and patient tissues must be cut at identical thickness, typically two to three microns.

Finally, using automated stainers may improve reproducibility for those laboratories that perform this stain infrequently, lack technical expertise, or consistently encounter less than optimal staining. However, because the target pathology and tissue processing may vary, the standard protocols used by these instruments may not produce the desired intensity and distribution of staining in every case.

Sue E. Lewis, BS, HTL(ASCP)
University of Iowa Hospitals and Clinics
Iowa City
Member, CAP Histotechnology Committee