Q and A
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August 2006 Richard A. Savage Q: Our laboratory has recently taken responsibility for point-of-care testing. Can you tell me what the requirements are for verifying the analytical measurement range for glucose meters as well as Hemocue and ABG instruments? Are we required to run linearity standards every six months? This is time consuming and expensive. Is there an alternative? A. The analytical measurement range, or AMR (formerly known as reportable range), is the range of analyte values that a method can directly measure on the specimen without dilution, concentration, or other pretreatment not part of the usual assay process. Each laboratory establishes the AMR that provides acceptable results for the intended clinical use. Periodic linearity studies are not required once the initial instrument validation of the AMR is completed. If the instrument is not an FDA-cleared/approved single-use device, calibration verification/AMR validation is required at least every six months. This involves running a material of known concentration at the low, mid, and high concentrations of the established analytical measurement range. Materials may include, but are not limited to, calibrator material, linearity material, previously tested patient specimens, or previously run proficiency testing material. If the analyzer is a single-use device that is FDA cleared/approved and either waived or of moderate complexity, you must follow the manufacturer’s instructions for calibration, calibration verification, and related procedures, with documentation of results (CAP point-of-care testing checklist question POC.07850). Susan O. Schultz, MT(ASCP) Q: Are there guidelines for reporting the presence of sperm in routine urinalysis specimens? Is it reported for males only? Should it be reported for pediatric patients? Are there medicolegal ramifications? A. The basic answers to these questions are yes, no, yes, and yes. This topic was addressed in this column in 2001 (CAP TODAY; April 2001:94). As Robert Novak, MD, then chair of the CAP Hematology and Clinical Microscopy Resource Committee, stated, studies have found sperm in 13 percent of specimens from adolescent males. Sperm are also seen in normal women’s urine following intercourse, although this is more difficult to quantitate. Spermaturia should be noted in all patients—male and female—younger than age 10, and the lab should contact the patients’ physicians and discuss the findings with them. In certain cases, such as institutionalized patients in nursing homes, spermaturia should be reported to the patient’s physician and possibly to local law enforcement, depending on local custom and law. Prospective discussions with local prosecuting attorneys may be necessary to establish custom and procedure. Richard A. Savage, MD Q: A patient who was taking Coumadin had a marked elevation of her international normalized ratio to 8.0. She had been consuming large quantities of soy and soy-based products. Can soy prolong the prothrombin time? How can soy affect the coagulation mechanism, and does it affect platelet aggregation? A. Humans have consumed soy isoflavones as part of soy-based diets without evidence of adverse effects. Although diets rich in soy appear safe and potentially beneficial, the long-term safety of high quantities of soy isoflavones is not yet known. We do not know with certainty how and to what extent soy isoflavones interact with clot formation or whether the action of isoflavones is similar to that of estrogen. The principal isoflavones in soybeans and other soy foods are genistein and daidzein. One cup of soymilk contains approximately 30 milligrams of isoflavones, and four to five percent of the isoflavones are in the form of aglycones. Isoflavones of soymilk are absorbed in the proximal small bowel. In the lower small bowel, bacterial deconjugating enzymes from microbial flora hydrolyze the isoflavones to produce genistein and daidzein. The biliary ducts and renal system then excrete them. The bioavailability of genistein varies in different products. Even with the relatively low bioavailability of isoflavones, genistein can be absorbed in sufficient quantities to exert its biological effects. In a small number of cases, a sub-therapeutic international normalized ratio, or INR, has been reported in patients on warfarin who consume soymilk.1 Although a direct effect of soymilk on warfarin could not be proven, reports of such cases suggest that soy isoflavones may interact with warfarin. Soy protein interacting with warfarin may be more common than the literature suggests. Although soybeans have high amounts of vitamin K, soy protein in the form of soymilk contains only trace amounts of vitamin K and would not be expected to be associated with vitamin K-altered warfarin metabolism. However, a soy protein-mediated variation in vitamin K production by gut bacteria or altered vitamin K metabolism from ingesting soymilk cannot be ruled out. Genistein was shown to inhibit platelet aggregation in vitro. Clinical studies have also shown that soy protein isolate can increase isoflavinoids to levels that are insufficient to significantly inhibit platelet aggregation ex vivo.2,3 Further studies are necessary to determine the effect of soy isoflavones on platelet aggregation. References:
Jayashree Krishnan, MD |
