Q & A

March 2002

Q.  Should the bilirubin tablet test be used on all urine submitted for urinalysis since it’s tenfold more sensitive than the bilirubin dipstick test? Is this cost-effective or clinically significant? Is it necessary to confirm all positive dipstick bilirubin results with a tablet test?

A.  Dipsticks are used to screen urine for a number of potentially clinically significant substances. Dipsticks are used because they have advantages over individual tablet tests: These easy-to-use groups of tests provide complementary information (for example, glucose and ketones in a diabetic), are performed simultaneously, and the cost per individual screening test is low. There is general agreement that a chemical urinalysis should include screening tests for blood, protein, glucose, and white blood cells, and that other tests should be included in the battery as clinically appropriate. It is not considered essential to test routinely for a substance just because that test is available or that the most sensitive test available be used when performing a chemical urinalysis. (For example, the standard protein dipstick test is less sensitive than the microalbumin dipstick test yet it is far more commonly used.)

On most strips where bilirubin dipstick testing is found, the strip contains urobilinogen as a complementary test, and this combination provides considerable additional utility that would not result from tablet testing for bilirubin alone. The finding of bilirubin and urobilinogen in the urine suggests hemolytic or primary hepatic disease, whereas the finding of bilirubin alone suggests biliary tree or upper intestinal obstruction. Most laboratory professionals would endorse the use of a tablet test to confirm the bilirubin dipstick test when the bilirubin alone is positive, as false positives occur with some frequency (for example, they are associated with some nonsteroidal antiinflammatory agents) and a good tablet test exists. When bilirubin and urobilinogen are positive, the concern over the presence of a substance (other than a grossly visible dye) that causes a false-positive result in both tests is lower, and some would advocate that recourse to serum tests (for example, a liver panel) is a reasonable approach to further evaluating this constellation of abnormal screening tests.

Always remember that the types of screening tests offered and the approaches to further evaluations of positive screening tests should fit the clinical context as defined by the laboratory medical director in consultation with the participating medical staff.

Robert Novak, MD
Department of Pathology
Children’s Hospital
Medical Center of Akron
Akron, Ohio

Member, CAP Hematology/Clinical
Microscopy Resource Committee

Q.  Besides its role in diagnosing mesotheliomas, does the typing of mucins by histochemistry (neutral versus acidic, sulfo- versus sialo-) have practical applications in neoplastic surgical pathology?

A.  The current role of mucin histochemistry in the differential diagnosis of neoplasms is limited, as this function has been assumed in large part by diagnostic immunohistochemistry. Potential applications of mucin histochemistry include but are not limited to:

• Differentiating stromal and epithelial mucins. Stromal mucin is positive with the colloidal iron (CI) and Alcian blue (AB) stains and is removed by hyaluronidase digestion. Stromal mucin is typically negative with the periodic acid-Schiff stain following diastase digestion (PAS-D) and minimally mucicarmine positive. In contrast, epithelial mucins are PAS-D and/or mucicarmine positive and, when positive with the CI and AB stains, are hyaluronidase resistant. This application is still used, albeit less frequently today, when attempting to distinguish carcinoma from epithelial mesothelioma. This technique can be applied also as an adjunct to keratin immunohistochemistry in distinguishing carcinoma, particularly sarcomatoid forms, and synovial sarcoma from other sarcomas with epithelioid features; the latter exhibit only stromal mucin.
• Identifying glandular differentiation in adenocarcinoma. Documenting of intracytoplasmic mucin is a rapid and cost-effective method for establishing a diagnosis of adenocarcinoma. It is important to remember, however, that epithelial neoplasms do not reproducibly produce acid or neutral mucins. Therefore, identifying epithelial mucin requires using two stains, singly or in combination, typically PAS-D (neutral) and Alcian blue or mucicarmine (acid).
• Differentiating extraskeletal myxoid chondrosarcoma and chordoma (Alcian blue and colloidal iron positive, hyaluronidase resistant) from other myxoid neoplasms, particularly myxoid liposarcoma (AB/CI positive, hyaluronidase sensitive).
• Differentiating chromophobe renal cell carcinoma from conventional renal cell carcinoma and oncocytoma. This more recent, technically difficult application requires use of the Hale’s technique with careful attention to pH. Chromophobe renal cell carcinoma will show a diffuse strong reaction with a characteristic reticular pattern; the other neoplasms are characteristically negative or focally positive with a granular or droplet-like pattern.
• Identifying high-risk gastric intestinal metaplasia (IM). Incomplete intestinal metaplasia (types II and III) can be further subtyped using the high iron diamine-Alcian blue (HID-AB) stain to identify subsets of acid mucins. The HID-AB stains sialomucins blue and sulfomucins brown-black. Using this stain, type III IM, in which the columnar epithelial cells contain sulfomucins, can be differentiated from type II IM, in which the columnar cells contain only blue-stained sialomucins. Some, but not all, studies have shown that type III is the form of IM seen most frequently in association with adenocarcinoma; therefore, identifying this form may warrant close followup, additional biopsies, or both. Recently, the presence of sulfomucins has been associated with progression to adenocarcinoma in Barrett’s esophagus.

Bibliography
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Shah KA, Deacon AJ, Dunscombe P, et al. Intestinal metaplasia subtyping: evaluation of Gomori’s aldehyde fuchsin for routine diagnostic use. Histopathology. 1997;31: 277-283.

Sheehan DC, Hrapchak BB. Theory and Practice of Histotechnology. 2nd ed. St. Louis, Mo.: C.V. Mosby; 1980.

Skinnider BF, Jones EC. Renal oncocytoma and chromophobe renal cell carcinoma. A comparison of colloidal iron staining and electron microscopy. Am J Clin Pathol. 1999;111:796-803.

Tickoo SK, Amin MB, Zarbo RJ. Colloidal iron staining in renal epithelial neoplasms, including chromophobe renal cell carcinoma. Emphasis on technique and patterns of staining. Am J Surg Pathol. 1998; 22:419-424.

Torrado J, Ruiz B, Garay J, et al. Blood-group phenotypes, sulfomucins, and Helicobacter pylori in Barrett’s esophagus. Am J Surg Pathol. 1997;21:1023-1029.

Weiss SW, Goldblum JR. Enzinger and Weiss’s Soft Tissue Tumors. 4th ed. St. Louis, Mo.: C.V. Mosby; 2001.

Richard W. Brown, MD
Medical Director
Core Histology Laboratory
Memorial Hermann Healthcare System
Houston

Member, CAP Surgical
Pathology Committee