Laboratory Bulletin...

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Audra Wheeler
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1 Laboratory Bulletin... Updates and Information from Rex Healthcare and Rex Outreach September 1997 Issue Number 24 Homocysteine and vascular risk Introduction: This past June, the New England Journal of Medicine published an article correlating homocysteine levels and coronary artery disease. Plasma total homocysteine levels are a strong predictor of mortality in patients with angiographically confirmed coronary artery disease. A Harvard pathologist, Kilmer McCully, M.D., was the first to suggest that homocysteine might contribute to coronary artery disease in an article published in the American Journal of Pathology in Since 1992, there has been an increasing number of articles confirming that elevated serum homocysteine levels increase the risk of development of atherosclerosis. Some believe that homocysteine is as powerful a predictor of vascular disease as cholesterol. Biochemistry: Homocysteine is an amino acid in the blood that is derived from methionine. Dietary meat, eggs and milk serve as the major source for methionine. Homocysteine is converted back to methionine with the aid of Vitamin B12 and folic acid. Vitamin B6 (pyridoxine) aids in the conversion of homocysteine to cysteine. Both methionine and cysteine are used in the building of proteins (see diagram below). The breakdown of homocysteine requires adequate amounts of vitamin B12, B6 and folic acid. A deficiency of either of the three vitamins elevates plasma homocysteine levels. In individuals who are not vitamin deficient, only folic acid is capable of lowering plasma homocysteine. Pathogenesis: Based on the homocysteine theory of atherosclerosis, the underlying cause of the disease

2 is the imbalance between the methionine of dietary protein and the dietary intake of vitamins B6, B12 and folic acid that are necessary to prevent homocysteine accumulation in the cells and tissues of the body. Elevated homocysteine levels cause the liver to convert methionine to an active form of homocysteine, homocysteine thiolactone. Homocysteine thiolactone combines with LDL cholesterol and is released into the blood. This combined aggregate is taken up by the macrophage in the artery wall. Foam cells release homocysteine thiolactone causing damage to the lining of arteries and promoting smooth muscle proliferation. Over a period of time a plaque containing cholesterol is formed in the lining of the vessel. This theory is supported by children with inherited homocystinuria who have markedly elevated plasma levels and develop premature severe atherosclerosis before the age of 30. Hereditary homocystinuria: Children with homozygous hyperhomocysteinemia may have levels >200 μmol/l. Moderately high doses of vitamin B6 will lower homocysteine levels in about one-half of the affected children. In the heterozygous or hidden state of the disease, blood levels of homocysteine may be normal. However, after receiving an oral loading dose of methionine, the precursor of homocysteine, the blood levels of homocysteine become more elevated after two to six hours than what is observed in normal individuals without this hidden genetic defect. Blood Levels: Levels of homocysteine currently considered normal are between 5 and 15 μmol/l. Men with levels between 15 and 16 μmol/l are more likely to have vascular problems than men with levels of 10 to 12 μmol/l. A meta-analysis in the Journal of American Medical Association concluded that each increase of 5 μmol/l of homocysteine elevates heart disease risk by as much as a cholesterol increase of 20 mg/dl. In the Hordand homocysteine study, elevated plasma levels were associated with male gender, increasing age, smoking, hypertension, elevated cholesterol and lack of exercise. Testing for Homocysteine: Homocysteine is difficult to measure and requires gas chromatography/mass spectroscopy, or high-performance liquid chromatography. The methods are labor intensive and are only done in certain reference laboratories. Considering the growing interest in homocysteine, one would suspect that companies are working on less complex assays. Most physicians will not test for homocysteine until it is more conclusively linked to atherosclerosis. It is not clear if fasting levels are satisfactory to judge risk or is it necessary to test after a methionine load? Furthermore, most managed care organizations would not pay for testing because of lack of medical necessity. Treatment considerations: To date there are no treatment studies showing that folic acid supplements reduce the risk of atherosclerosis. However, vitamin B6, B12 and folate deficiencies can cause harmful elevations of homocysteine and this in turn raises the risk of atherosclerosis. Therefore, why not add oral folate, B12 and B6 to everyone s diet? It would be as easy as taking a multivitamin pill once a day. As a matter of principle, it is preferable to know who is deficient and who is not before instituting therapy. Furthermore, researchers have studied varying amounts of folic acid to lower homocysteine levels, but it is still unknown what an optimal dose might be to lower homocysteine levels. A Tuft s University study has shown that one-third of adults over the age of 65 are deficient in vitamins B6, B12 or folic acid. In this group of individuals, it may be reasonable to recommend vitamin B supplements equivalent to the RDA recommended dietary allowance. Stephen V. Chiavetta, M.D. Discontinuanc e of enzymatic Effective September 29, 1997, the laboratory will discontinue the enzymatic acid phosphatase assay. The establishment of Prostate Specific Antigen (PSA) as the analyte of choice for diagnosis and monitoring of prostate cancer has displaced the older enzymatic assay for prostatic acid phosphatase. In addition because of improved sample stability, the

3 prostatic acid phosphatase Cigarettes, Lipids, & Death new immunological assay for prostatic acid phosphatase has replaced the older enzymatic method. All requests for prostatic acid phosphatase will be sent to the reference laboratory for analysis by the immunologic method. Robert B. Brainard, Ph.D. Elaine Patterson, MT(ASCP) A recent, collaborative autopsy study from the Maryland Office of the Chief Medical Examiner and the Cardiovascular Division of the Armed Forces Institute of Pathology examines the relationship between a variety of risk factors and coronary artery plaque morphology in 113 men dying suddenly from coronary artery disease. 1 Complete autopsies were performed to exclude other causes of death. Following postmortem coronary arteriography, the arteries were step-sectioned in 3 mm. intervals. All segments showing >50% stenosis were examined microscopically. Postmortem blood was analyzed for total cholesterol, HDL cholesterol, glycosylated hemoglobin and thiocyanate. A history of smoking was presumed for serum thiocyanate levels >90 μmol/l. Diabetes mellitus was diagnosed if glycosylated hemoglobin was elevated. Pre-existent hypertension was evaluated by clinical history and microscopic evaluation of renal blood vessels. In 54 of the 113 cases (48%), there was severe atherosclerotic stenosis, but no thrombosis ( stable plaque ). In the remaining 59 cases (52%), there was acute thrombosis associated with a preexistent atherosclerotic plaque. There were 2 types of plaque present: vulnerable plaque (thin fibrous cap overlying lipid rich, macrophage rich core) and fibrous plaque (composed of smooth muscle and proteoglycans rather than lipid). Of the 59 cases of acute thrombosis, the majority (76%) resulted from the rupture of a vulnerable plaque. The remaining 24% were caused by erosion of a fibrous plaque. When the morphologic findings were compared to the risk factors, some interesting associations emerged. Cigarette smoking was more prevalent in the acute thrombosis group (75%) than the stable plaque group (41%, P <0.001). The ratio of total cholesterol to HDL cholesterol was significantly higher in the acute thrombosis/ruptured plaque group (8.5 ± 4.0) than either the stable plaque group (5.5 ± 2.4, P <0.001) or acute thrombosis/eroded plaque group (5.0 ± 1.8, P <0.001). Hypertension, age, African- American race, and glycosylated hemoglobin values were not significantly associated with either acute thrombosis, plaque rupture, or numbers of vulnerable plaques. The authors caution that their study is limited by autopsy bias and male bias. The results may not be applicable to patients surviving acute coronary events or women. They conclude that their findings support the thesis that hypercholesterolemia predisposes patients to rupture of vulnerable (lipid rich) atherosclerotic plaques and that such patients may benefit from lipid lowering management. Cigarette smoking increases the odds of acute thrombosis in men with coronary atherosclerosis. John D. Benson, M.D. 1. Burke AP, et al. Coronary Risk Factors and Plaque Morphology in Men with Coronary Disease Who Died Suddenly. N Eng J Med 336: , Synovial fluid crystal examination Examination of synovial fluid for pathologic crystals is a service provided by the Rex Hospital pathologists. The crystal examination is generally available as a Routine priority. Recognizing that there are occasions when such examination is critical for urgent patient management (e.g. when the differential diagnosis includes septic arthritis requiring surgical intervention), the pathologists at Rex will perform this examination on a STAT basis when clinically indicated in the judgment of the attending physician. To avoid confusion and expedite service, the attending physician is requested to contact the Rex pathologist on call personally to discuss the need for a STAT crystal examination. The pathologist can alert the laboratory staff to be on the lookout for the specimen and arrange an appropriate means of communicating the result directly to the physician.

4 John D. Benson, M.D. CSF and urine bacterial antigen tests not cost effective Over the past few years, bacterial antigen tests have been used to supplement standard procedures for the diagnosis of bacterial meningitis. Published data have now shown that these tests add little to what can be learned from a combination of CSF chemistry tests, cell counts, and Gram s stains for the diagnosis of bacterial meningitis. 1 In addition, false positive tests have been reported in the literature and these incorrect results may lengthen hospital stay, prolong antibiotic therapy, and lead to clinical complications. 1 In a paper published in June of 1995, Dr. Reller and associates from Duke reported on a 10 month review of bacterial antigen tests on CSF performed at Duke and a private specialty pediatric hospital. They reported that All latex true-positive cerebrospinal fluid samples showed the causative microorganism by Gram stain. Detailed chart review of the 57 positive samples showed that the latex result was false-positive in 31 (54%), true positive in 22 (38%), and indeterminate in 4 (7%). Therapy was not altered on the basis of any of the true-positive LA results. The 31 false-positive results led to additional cost, prolonged hospitalization, and some clinical complications. They conclude that their retrospective study does not support the current use of latex rapid bacterial antigen detection tests. 2 On March 24, 1997, the FDA issued a Safety Alert concerning the risk of tests for direct detection of Group B Streptococcal antigen. They state, antigen tests are an adjunct to diagnosis and multiple studies have shown that antigen tests are NOT an appropriate substitute for properly performed bacterial culture in the diagnosis of GBS colonization or infection. Data collected at Rex Hospital Laboratory for the period September 1996 through February 1997, show that of 95 bacterial antigen tests performed on CSF, none were positive. In one case, the bacterial antigen test was negative while the Gram stain showed many Gram positive diplococci and the culture grew Streptococcus pneumonia. Infrequently, these tests have been helpful in the interpretation of difficult Gram stains but this is not considered essential. Based on this review of the literature and the Rex data, Rex Laboratory will no longer offer bacterial antigen tests on CSF or urine when the current reagent supply is exhausted (2-3 weeks). In special cases where the CSF cell count is abnormal and the Gram stain is negative, if warranted, bacterial antigen tests may be ordered as reference tests and will be sent to Wake Medical Center for STAT testing. Wake charges $55.50 for this test and offers the test 7 days a week, 24 hours a day. If there are any questions or comments, please contact the Clinical Microbiologist, Dr. Kleeman, or any pathologist. Karl T. Kleeman, Ph.D. 1. Clinically Relevant, Cost-Effective Clinical Microbiology, Michael L Wilson, MD, American Journal of Clinical Pathology, February, Rapid Bacterial Antigen Detection Is Not Clinically Useful, Barth Reller et al, Journal of Clinical Microbiology, June, For further information, call the Laboratory ( ). Telephone extensions are: Pathologists Direct Line (3201), Dr. Brainard (3056), Dr. Kleeman (3063), Sharon Logue (Lab Director 3055), Robin Ivosic (Core Lab Manager 3053), Linda Lompa (Blood Services Manager

5 ), Kimberly Skelding (Customer Services Manager 3318), Rex Outreach ( ), Karen Sanderson (Lab Compliance Specialist 3396).

Laboratory Bulletin...

Laboratory Bulletin... Updates and Information from Rex Healthcare and Rex Outreach February 1997 Issue Number 17 Urinary Microalbumin (an ideal test for real managed care) Microalbuminuria is the term