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.
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
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.
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