Qi Q, Monier-Faugere MC, Gent Z, Malluche HH
Predictive value of serum parathyroid hormone levels for
bone turnover in patients on chronic maintenance hemodialysis
Am J Kidney Dis
(Oct) 26:622-631 1995
This article described the correlation of PTH values with a relatively
unfamiliar (to nephrologists) measure of bone turnover, activation
frequency. This measurement requires assessment of both bone
formation and bone resorption for its calculation. Seventy-nine
patients were studied. Half were biopsied for study purposes only,
whereas half were biopsied for a variety of clinical concerns, some of
which were not clearly specified. Twenty percent had two biopsies.
The results suggested that a single serum PTH level discriminated
poorly between high, normal and low bone turnover states, whether
activation frequency or the more familiar bone formation rate was
used. High bone turnover could be seen with PTH levels of 80 to
1800 pg/ml, normal bone turnover between levels of 15 and 440, and low
bone turnover between 0 and 600. PTH levels above 450 pg/ml were
almost always associated with high bone turnover, although how many of
the data points represent duplicate biopsy results is unknown. PTH
values between 80 and 450 pg/ml could be any condition, while values
below 80 were nearly equally divided between normal and low turnover
states. The authors conclude that PTH levels between 65 and 450 pg/ml
do not discriminate between the various bone lesions and that such
patients should have a bone biopsy to distinguish their bone disease.
Comment: With regard to adynamic bone disease, what has been
recommended by previous investigators is a goal PTH of 1.5 to 5.0 times
the upper limits of normal (100 to 300 pg/ml).
Some studies have shown good (but not perfect) discrimination of low
from normal bone turnover at a PTH of 100 and normal from high
turnover at a PTH of 300. The
conclusions by Qi et al, purporting to show that
PTH values between 65 and 450 are of no value whatsoever in predicting bone
turnover (formation) rates are not entirely convincing, as this study suffers
from a number of methodologic
difficulties. One has to do with use of activation frequency as a
measure of bone turnover. This measure includes both bone formation
and resorption. The latter can not be accurately quantitated (in
contrast to bone formation) so it is at best an estimate. Activation
frequency has been used mostly in osteoporosis studies; this paper is
the first large scale use in renal osteodystrophy. Activation
frequency has not been validated in any longitudinal, reproducible way
in renal patients and many people question its use in osteoporosis as
well. Interestingly, the bone formation rate and activation frequency
data look essentially identical, raising some questions about the
additional value of the newer methodology.
While 79 patients were studied, the actual size of the patient
population they were recruited from is not given. The population was
not well characterized, with half being presumably asymptomatic and
half being evaluated for problems which are not clearly specified.
The fact that 20% had two biopsies with both biopsies included in the
report is likely to increase the amount of data, but does not provide
a real diversity of bone lesions. The patients were also on a
variety of treatments with respect to calcitriol, aluminum, calcium,
etc. In a study from the southern US an important bit of demographic
data, race, was not included. Since normal blacks appear to have a
lower bone formation than whites, and bone formation is an important
result of this study, it is surprising not to see it here. Only one
PTH level was determined. Most clinicians would not base an important
clinical decision on a single laboratory value; at least 3 PTH
determinations per patient would have been preferable.
(Sherrard)
To go back use the BACK button on your browser.
Otherwise click on the desired link to this article below:
CRF by problem area :
Bone disease/aluminum