Rubidium deficiency in dialysis patients

Background. Since dialysis has brought long-term survival to uremic patient s, we can now speculate on more subtle problems derived from imbalance or s ub-optimal regulation of some elements such as trace metals. We focused on the rubidium (Rb) status in dialysis patients (HD), as concerns about its p ossible deficiency have been raised. Methods. Rb in uremic patients was eva luated by: A) serum concentration (graphite furnace atomic absorption spect roscopy) from blood samples of 70 patients on chronic hemodialysis (HD) in comparison with 75 controls; B) tissue concentration (neutron activation an alysis) from autopsy or biopsy samples (20) of HD patients in comparison wi th 21 controls; C) in vivo intradialytic mass balance during standard bicar bonate dialysis in 8 HD patients. Results. A) Serum Rb concentrations in HD patients significantly were lower than in normal controls (304 +/- 81 mug/ L versus 350 +/- 74 mug/L p <0.001, log-transformed 5.68 +/- 0.28 versus 5. 84 +/- 0.20, p <0.001). Univariate logistic regression analysis found a sig nificantly higher risk of serum Rb < 250-300 and 350 mug/L in uremic patien ts than in controls (Odd ratios or 12.6, 95% CI 2.77 - 57.04; 4.0, 95% CI 1 .92 - 8.4; 2.08, 95% CI 1.02 - 4.25, respectively). B) Rb was significantly lower in tissues of HD patients, including brain (2250 +/- 1520 ng/g versu s 5490 +/- 1250 ng/g, p=0.0002) than normal controls. C) Rb was transferred from the patients' blood to the dialysis bath during a standard bicarbonat e dialysis session, giving mean intradialytic Rb removal of 4.0 +/-1.1 mg/s ession. Conclusions. These results confirm that Rb deficiency may arise in uremic p atients, and indicate that diffusive dialysis treatments allow Rb removal w hich, however, with a standard bicarbonate schedule does not seem to be any greater than that expected with normal urine output (20 mg/week). Further studies are needed to clarify the roles of many factors in this Rb deficien cy, including the effects of uremia by itself, pre-dialysis factors (diet, impaired renal function and drugs), dialysis procedures (frequency, hours, diffusive/convective components) or other biochemical/clinical parameters ( hemoglobin, body mass index, age). The finding of a Rb deficiency in uremia is important as it has a role in neurobehavioural functions, mainly as an antidepressant. As Rb deficiency may be implicated in central nervous syste m alterations which strongly influence the quality of life, we believe that monitoring serum Rb in uremic patients and clarifying the causal mechanism s of deficiency will facilitate future therapeutic approaches.