Pollock et al.
Total body nitrogen as a prognostic marker in maintenance
dialysis patients
J Am Soc Nephrol
(Jul) 6:82-88 1995
Pollock et al compare nutritional parameters in 154 dialysis patients [82
PD and 74 HD] in a single centre, predominantly cross-sectional, study of
prevalent patients. As well as standard nutritional indices, they measure
total body nitrogen [TBN] using prompt neutron activation analysis, a
technique they have studied before. They also calculate nitrogen index
[NI] which is a ratio of actual:predicted TBN.
They show that, compared to their HD patients, their PD patients have
been less time on dialysis, are larger, have greater percentage body fat
and lean body mass, have higher NI, have similar protein and caloric
intake, but have lower serum albumin. They show NI to be a good predictor of
survival with a value
less than
80% associated with a more than fourfold increase in one year mortality.
In HD, but not in PD, NI correlates with serum albumin and caloric intake
but not protein intake. Surprisingly, in two year follow-up studies of 36 HD
and 26 PD patients
still on the same modality, there was no change in NI on HD but a
significant improvement on PD.
Comment: Notable points in this study are high PD usage [>50%] and a
low
proportion of diabetics [8%]. Problems with the study are the somewhat
confusing methodology, the difficulty distinguishing between those
differences that preceded modality selection and those that resulted from
it, and the usual problems with case mix in any modality comparison
study. Compared with the recent Cianciaruso paper
[AJKD 1995; 26:475] which
emphasized subjective global nutritional assessment, the Pollock study is
more favourable to PD. This may reflect the different case mix or perhaps
the different techniques used.
(Blake)
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