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Bioelectrical Impedance Analysis (BIA) May Predict AIDS




 

AIDS TREATMENT NEWS Issue #225, June 16, 1995

An inexpensive, non-invasive electrical measurement predicted three-year survival better than CD4 (T-helper cell) count or any of several other measurements tested, in a recently reported prospective study of 75 patients.(1) In 1990, when the study began, the 75 patients had an average CD4 (T-helper) count of 176.2, and no AIDS-defining infections; a number of other baseline measurements were also recorded. During the 1000 days of followup, 29 of the 75 died of AIDS-related causes. Statistical analysis was used to see which of the baseline measurements were most predictive of survival three years later.

Bioelectrical impedance is measured by a simple machine which can be used in a physician's office; the machine usually costs several thousand dollars, and the cost of bioelectrical impedance is generally reimbursed by insurance. The measurement consists of two numbers: electrical resistance, and capacitive reactance; from these numbers, a third number, the phase angle, can be calculated mathematically.

From these three numbers, plus the patient's height, weight, sex, and age, it is also possible to estimate body cell mass, fat-free mass, and other body parameters. These estimates, however, may be less accurate than the resistance, reactance, and phase angle, because their computation also requires certain constants, which have been derived from historical experience with other patients and therefore may not be entirely correct for the particular patients being measured. (The phase angle does not suffer from this inaccuracy, because it is computed entirely from the reactance and resistance of the patient who is being measured, without the use of any historical data derived from other patients.) The current study found that the phase angle was the best single predictor of who would survive for three years. Also, body cell mass, serum cholesterol, CD4 cell count, and serum albumin were predictive to a lesser degree, while age, weight, serum protein, and serum triglycerides were not statistically significant in predicting survival in this study. [Viral load was not measured in this research, so it could not be compared with BIA as a measure of survival.] Statistical analysis suggested that the volunteers with a median phase angle (which was 5.46 degrees in this study) had a somewhat greater than 50% survival during the 1000 days. Those at the 25th percentile (phase angle 4.87) [meaning that 25% of the patients in this study had a lower phase angle, 75% had a higher value] only had about a 15% survival. For those at the 75th percentile (phase angle 5.96), survival was better than 80%. [Caution: These numbers depend on particular characteristics of patients in this study, and also on certain statistical assumptions made by the authors; they cannot automatically be applied to other patients.

Survival would almost certainly be better today, since treatments have improved in the five years since these patients were measured. And there are different kinds of BIA machines; the one used in this study was a single-frequency quadripolar model. Also, the measurements can vary depending on factors such as how much water is in the body, and whether one has certain opportunistic infections. The numbers above are included to help give a general picture of the test; but these specific figures cannot be applied literally in other contexts. Each patient needs to be evaluated individually -- and trends in repeated testing are usually more informative than single measurements.] The authors speculate that the phase angle may be a measurement of the electrical integrity of cell membranes. BIA has also been used as a measure of lean body mass, which is lost in wasting syndrome; in this study, however, patients started at an earlier stage of illness, without clinical indications of wasting. Other researchers have suggested that BIA may be a way of diagnosing wasting early, before it shows in weight loss or other symptoms.

Comment This study only shows the value of BIA for prognosis -- predicting how well individual patients are likely to do. It does not show whether or not IMPROVING the phase angle, as a result of nutritional or other treatment, means that the patient is likely to live longer.

BIA, however, is accepted as a means for measuring nutritional status and body cell mass, and has been validated for this purpose in AIDS patients.(2,3) Until more definitive information is available, it may be reasonable to accept improvement in BIA measurements as an indicator of improved health, as an indicator (although not proof) that a treatment regimen may have been working.

Because of the small amount of electricity used in BIA, the only safety concern we have heard is for patients with implanted defibrillators.

The ease and low cost of BIA suggest that this potential surrogate marker of HIV disease progression should be more widely studied and be more widely available.

For More Information In December 1994, the U.S. National Institutes of Health held a major conference on bioelectrical impedance analysis. The proceedings of that meeting have been published.(4) Major chapters of the proceedings are: What does bioelectrical impedance analysis (BIA) measure? How should BIA be performed, and how can measurements be standardized? How safe and valid is the BIA technology in the estimation of levels of adiposity? What are appropriate clinical uses of BIA technology, and what are the limitations? How safe and valid is the use of BIA technology to estimate body cell mass and total body water status? For additional information about BIA, contact Cade Fields- Gardner, at The Cutting Edge, 708/516-2455.

References 1. Ott M, Fischer H, Polat H, and others. Bioelectrical impedance analysis as a predictor of survival in patients with human immunodeficiency virus infection. JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES AND HUMAN RETROVIROLOGY May 1, 1995; volume 9, number 1, pages 20-15.

2. Sluys TEMS, van der Ende ME, Swart GR, van den Berg JWO, Wilson JHP. Body composition in patients with acquired immunodeficiency syndrome: a validation study of bioelectric impedance analysis. JOURNAL OF PARENTERAL AND ENTERAL NUTRITION 1993; volume 17, number 5, pages 404-406.

3. Jacobs, DO. Bioelectrical impedance analysis: A way to assess changes in body cell mass in patients with acquired immunodeficiency syndrome? JOURNAL OF PARENTERAL AND ENTERAL NUTRITION 1993; volume 17, number 5, pages 401-402.

4. NIH Technology Assessment Conference on Bioelectrical Impedance Analysis in Body Composition Measurement, December 12-14, Bethesda, Maryland. Sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases, and the NIH Office of Medical Applications of Research.



 


Copyright © 1995 -AIDS Treatment News, Publisher. All rights reserved to AIDS Treatment News (ATN), Email AIDS Treatment News .

Information in this article was accurate in June 16, 1995. The state of the art may have changed since the publication date. This material is designed to support, not replace, the relationship that exists between you and your doctor. Always discuss treatment options with a doctor who specializes in treating HIV.