Evaluation of the PD adequest program in Japanese patients on peritoneal dialysis.

To perform adequate peritoneal dialysis, it is necessary to individualize the dialysis regimen. PD Adequest is a software program based on the three-pore model that can be used to predict solute clearance and ultrafiltration volume during peritoneal dialysis. We evaluated the ability of this program to predict the solute clearance and ultrafiltration volume in Japanese patients on peritoneal dialysis. The weekly creatinine clearance and weekly urea Kt/V were determined in 45 patients. The PD Adequest was used to simulate their current dialysis regimens and the predicted values of these parameters were calculated. Strong positive correlations were obtained between the actual and predicted weekly creatinine clearance (r = 0.993) and weekly urea Kt/V (r = 0.991). In conclusion, this program is potentially useful for designing peritoneal dialysis regimens in Japanese patients, even though they have a smaller body mass than Canadians and Americans for whom it was designed.     

Retrospective evaluation of renal kt/V(urea) at the initiation of long-term peritoneal dialysis at the University of Missouri: relationships to longitudinal nutritional status on peritoneal dialysis

The purpose of this study was to examine the impact of low levels of residual renal function (RRF) on nutritional status in end-stage renal disease patients starting peritoneal dialysis (PD) at baseline and after a year on dialysis. We conducted a single center retrospective analysis of 116 patients who started long-term PD in a university teaching hospital from 1989 to 1998 and were followed for 1 year. Patients were divided into four equal groups according to their initial renal Kt/V(urea) (L/week) levels at the start of PD and followed for 1 year. There were no interventions. The relationship between dialysis adequacy (renal and total Kt/V(urea)) and nutritional status was studied at baseline and at 1 year. Baseline data for patients who survived were compared with the baseline data of those who died and with their own 1 year data. At baseline, the mean serum albumin (3.31 g/dl, p < 0.0001) and lean body mass (47.20% body weight, p < 0.04) of group 1 were significantly lower than in groups 2, 3, and 4. Levels of normalized protein equivalent of nitrogen appearance (nPNA) were significantly lower in group 1 than in groups 3 and 4 (p < 0.005). Although group 1 patients showed trends toward improvement in nutritional parameters, they never caught up with the other groups. At the end of 1 year, the lower total Kt/V(urea) in group 1, with the lowest RRF, was associated with the lowest mean values for nutritional status and the highest death rate. Comparison of baseline and 1 year data of survivors showed that nutritional status improved or remained stable in groups 3 and 4, who exceeded the minimum recommended adequacy targets as per Dialysis Outcome Quality Initiative criteria (mean 12 month total Kt/V(urea) 2.18 and 2.58, respectively). Comparison of baseline data of survivors and those who died showed that patients who died had lower mean values for serum albumin, nPNA, lean body mass, and body weight across all groups. Low RRF at the start of dialysis is associated with poor nutritional status. Also, patients who start dialysis with low RRF and poor nutritional status do not have significantly improved nutritional status even after 1 year on dialysis.     

Comparative survival analysis of urea kinetic based indices

BACKGROUND: Although urea kinetic modeling indices for measuring dialysis dose are recommended by world expert groups, it is not quite clear whether some of these are superior in predicting the outcome over others. This prospective, single-center study was carried out with the aim to compare predictive value of different indices and methods of measuring dialysis dose. METHODS: The analysis included 93 anuric patients having been on hemodialysis for at least 2 years who were followed-up for 75-months. The dialysis dose was measured by Kt/V (formal UKM, 3 and 2 urea samples), Kt/V (Daugirdas), Kt/V (Lowrie), eKt/V (Daugirdas), URR and TAC urea. RESULTS: Correlations between dialysis indices and survival time were significant for all indices (p<0.01) except for TAC. All indices, except for TAC urea, were significant predictors of mortality (multivariate Cox regression analysis; p<0.01) and differences of significant levels among these colinear parameters were small. CONCLUSION: All examined indices except for TAC urea were highly predictive of patient mortality. Daugirdas and Lowrie simplified Kt/V indices are as predictive of all-cause mortality as more complex formal UKM methods in long-term patients on a 3x4h/week schedule.     

Hemoglobin normalization results in lower dialysis dose, despite high dialysate flow. Single needle offers inadequate dialysis

Anemia correction by erythropoietin favorably affects dialysis outcome but may also reduce dialysis efficiency increasing morbidity and mortality. Single needle dialysis (SN) and high dialysate flow (DF) are dialysis variations. We studied the effect of hemoglobin (Hb) normalization on dialysis adequacy under high DF. We also compared double needle (DN) and SN dialysis efficiency. Seventeen stable anuric patients (13 M, 4 F), aged 62 (40-90), on hemodialysis for 48 months (8-204), were studied in two, 6 months apart, periods of low (A) and high Hb (B), during a midweek 4 h dialysis with DN and SN. DF was 500 in A and 800 ml/min in B. Rebound urea samples, 20 min post dialysis, were used for computer calculated double pool urea kinetics. Hb levels were 128 +/- 8 g/L (B) vs. 119 +/- 14 g/L (A), P < 0.03. Despite the use of higher DF less dialysis was delivered in B vs. A, under DN or SN (DN: URR 64.8 +/- 5.8 vs. 69.7 +/- 5.2%, Kt/Vequil. 1.09 +/- 0.19 vs. 1.26 +/- 0.21, nPCR 1.37 +/- 0.29 vs. 1.60 +/- 0.36g/kg/day, changes <0.001, SN: URR 49.7 +/- 7.5% vs. 52.6 +/- 8.8%, Kt/Vequil. 0.74 +/- 0.16 vs. 0.82 +/- 0.23, nPCR 1.05 +/- 0.33 vs. 1.20 +/- 0.31, changes NS). SN was found significantly (P < 0.001) less efficient than DN in A and B. Serum creatinine drop was significantly (P < 0.001) less in both periods with SN vs. DN. Hb (SN in B) correlated inversely to Kt/V (r = -0.5705, P < 0.02) and URR (r = -0.6432, P = 0.005). Hb correction to normality is associated with a decrease in dialysis efficiency. The use of high dialysate flow does not compensate for this loss. SN delivers inadequate dialysis independently of dialysate flow or hemoglobin concentration.     

Inadequacy of dialysis, chronic inflammation and malnutrition in Nigerian patients on chronic hemodialysis

PURPOSE: To identify the extent of underdialysis, chronic inflammation and malnutrition and their interrelationships in Nigerian hemodialysis patients. METHODS: In a prospective study including 10 adult patients, (6 men, 4 women) on hemodialysis in North Central Nigeria, malnutrition was assessed by body mass index (BMI), serum albumin and prealbumin, and bioimpedance (BIA) pre-and post dialysis, inflammation was evaluated by C-reactive protein (CRP) and adequacy of dialysis was judged by frequency of the hemodialysis sessions and Kt/V urea. RESULTS: Post-dialysis BMI was 21.3 (19.9, 24.3) kg/m2 (< 20 kg/m2 in 4 patients), serum albumin 31.5 (24.0, 32.0) g/L (< 30.0 g/L in 5), serum pre-albumin 25.2 (15.3, 31.1) mg/dL (< 18.0 mg/dL in 4), serum CRP 4.8 (1.2, 11.5) mg/dL (> 1.0 mg/dL in 8), phase angle 4.2 (3.7, 5.1) degrees (< 3 degrees in 3) and body fat deficit was diagnosed by BIA in 4 patients. Weekly frequency of dialysis was 3 times in 2 patients, twice in 1 and 1.2 in one patient receiving dialysis only twice weekly). By combined frequency of dialysis and Kt/V urea values, no patient received an adequate dose of dialysis and, indeed, all patients had overt symptoms of uremia. Low body weight, low serological and BIA nutrition indices, and high CRP levels occurred in the same patients. Patients on dialysis for > 1 year had worse nutrition indices than those on dialysis for < 1 year. CONCLUSIONS: Underdialysis was universal, while poor nutrition and chronic malnutrition were found in the majority of the small number of patients studied. These three adverse conditions, which were interlinked, may be common in Nigerian hemodialysis patients, because their underlying socioeconomic causes are widespread.     

Validation of a two-pool model for the kinetics of beta2-microglobulin

Secondary amyloidosis due to beta-2-microglobulin (beta2-m) is a serious long-term complication in patients on regular dialysis therapy. Beta2-m can be considered a middle-molecule marker used to facilitate the assessment of dialysis efficacy. For this purpose, a validated model that calculates characteristic efficacy parameters, such as Kt/V, TAC and generation rate, is needed. There is general agreement that beta2-m-kinetics should be described by a two-pool model, but little has been published to validate such an approach. We measured the beta2-m concentration profiles of eight stable patients during hemodialysis (HD) at the start of treatment, after 30 minutes, after 60 minutes, and every hour until the end. Thereafter they were measured at 10-minute intervals for an hour. The dialyser clearances were determined from the plasma concentrations in front of and behind the dialyser twice during each session - after 1 hour, and 4 hours from the start of treatment. The kinetic parameters of a two-pool model (e.g. the compartment volumes V1 and V2, the mass transfer coefficient K12 and the generation rate G) were determined from the optimal fit of the measured concentration profile. The table below summarises the results by giving the mean and standard deviation for each parameter: [table: see text]. Inter-individual differences in V1/V2 and K12 were high, ranging from 2.5 to 10.0 for V/V2 and from 26 to 140 for K12. Error analysis suggested that these wide ranges were due to the method and that in reality the probable range of V is 25-36% of TBW, of V1/V2 3.5-5.3, and of K12 30-80 ml/min. With standard values for these three parameters (V = 30% of TBW, V/V2 = 4.4 and K12 = 55 ml/m), equal for all patients, and their respective ranges, Kt/W can be calculated with a standard deviation of 13%. Kt/W > 1.2 secures the maximum possible beta2-m removal with three HD treatments a week. CONCLUSIONS: The parameters of a two-pool model of beta2-m kinetics can be derived from concentration profiles obtained under routine dialysis conditions, but accuracy is not completely satisfactory. Similar to the dialysis dose for urea (Kt/Vurea) the dialysis dose for beta2-m (Kt/Vbeta2-m) can be calculated from the pre- and post-dialysis concentrations of beta2-m, body weight, ultrafiltration and dialysis time. Kt/Vbeta2-m > 1.2 secures the maximum possible removal of beta2-m in HD with three sessions per week.     

New empiric expressions to calculate single pool Kt/V and equilibriated Kt/V

Most formulae used for Kt/V computations are cumbersome and require variables that are not always available. Even the simplest models involve urea distribution volume or patient postdialysis weight. Calculating urea reduction ratio (URR) is easier and does not require additional variables, but it fails to account for residual renal function or for the removal of urea when urea levels do not change, e.g., during ultrafiltration. The goal of this study was to derive new expressions to calculate Kt/V based on URR using bivariate and multivariate linear and nonlinear models, with the URR adjusted for ultrafiltration volume and time on dialysis. Models were derived from a database of 598 dialysis records with a mean spKt/V of 1.6 (range 0.74-2.8). Models were validated on the same dataset that they were derived from and a separate dataset consisting of 17,190 dialysis records. The validation was made by comparing the empirically derived models with the Gotch and Daugirdas formulae. Among our empirically derived expressions, the closest approximation of the "gold standard," Kt/V, is the multivariate linear model of URR adjusted for ultrafiltration volume. When information about ultrafiltration is not available, the bivariate exponential formula can be successfully used to estimate Kt/V.     

Two spent dialysate samples are sufficient for hemodialysis efficacy assessment

INTRODUCTION: The measure of dialysis efficacy is expressed as Kt/V value (calculated from predialysis and postdialysis blood urea concentration). The aim of this study was to assess the possibility of direct calculation of Kt/V value from two spent dialysate samples by using the regular blood-based Kt/V calculation formula with dialysate samples used as surrogates for blood samples, and to detect the most appropriate couple of dialysate samples for Kt/V estimation. PATIENTS AND METHODS: Fifty-two single hemodialysis treatments in 34 anuric patients on chronic bicarbonate low-flux hemodialysis were observed. Kt/V values according to Daugirdas formula from two blood samples and from two dialysate samples were calculated. RESULTS: Kt/V values calculated according to Daugirdas 2 nd generation formula from blood samples (Kt/V sp Daugirdas) were in significant correlation with all Kt/V values obtained from two spent dialysate samples. The highest correlation coefficient (r = 0.74, p < 0.001) and the least standard error of mean of the differences were found between Kt/V sp Daugirdas and value obtained with substitution of urea concentration from dialysate samples taken 60 minutes after dialysis start and at the end of the dialysis into Daugirdas 2 nd generation formula (Kt/V D C D(60) -C D(e) ), which can be expressed as a equation of linear regression y = 0.47 + 0.86x. The highest correlation coefficient (r =0.74, p < 0.001) was found between Kt/V sp Daugirdas values equilibrated according to Daugirdas rate formula, and Kt/V D C D(60) -C D(e) value, which can also be expressed as an equation of linear regression y = 0.43 + 0.73x. CONCLUSION: The results of this study clearly show the sufficiency of only two spent dialysate samples for direct estimation of the Kt/V values, with no blood sample required.     

Diacap alpha-polysulfone HI PS: a new dialysis membrane with optimum beta2-microglobulin elimination

BACKGROUND: Plasma concentration of beta2-microglobulin (beta2-m) in the case of renal insufficiency is about 20 to 30 times higher than normal. Beta2-m is associated with secondary amyloidosis, a late complication of regular dialysis therapy. To prevent the complications of secondary amyloidosis beta2-m should therefore be eliminated as efficiently as possible during dialysis treatment. This can be accomplished with dialysis membranes which guarantee sufficient clearance for this molecule. It is a matter of discussion whether removal of beta2-m by dialysis may be able to prevent secondary amyloidosis. METHODS: The dialyzers Diacap HI PS 15 (B. Braun Melsungen) and F70 S (Fresenius Medical Care) were compared in five anuric dialysis patients. Arterial blood was taken at the start and at the end of dialysis. Dialysate samples were taken after 30 and 210 minutes and filtrate samples after 60 and 240 minutes from the start of dialysis. Beta2-m and total protein concentration were measured in plasma, filtrate and dialysate. SDS-PAGE of proteins in the filtrate was carried out and kinetics of beta2-m (Kt/V(beta2-m)) were calculated using the Stiller/Mann model. RESULTS: In both dialyzers beta2-m is detectable at any time in the dialysate leaving the dialyzer. In the filtrate beta2-m concentration is about 10 times higher than in the dialysate. Protein pattern in filtrate of both dialyzers is similar and corresponds to that of the glomerulum filtrate. Beta2-m reduction ratio is slightly lower than urea reduction ratio. Using both dialyzers Kt/V(beta2-m) was 0.80, removing about 60% of the generated beta2-m. CONCLUSIONS: In both dialyzers there is considerable removal of beta2-m. Examination of beta2-m kinetics showed an optimum of Kt/V(beta2) of 0.80 which can not be surpassed. Only 60% of generated beta2-m can be removed by three times per week hemodialysis therapy using high-flux dialyzers.     

Antibody response following Hepatitis B vaccination in peritoneal dialysis patients: does normalized urea clearance matter?

OBJECTIVES:

Data on the factors that contribute to the antibody response to hepatitis B virus vaccination in peritoneal dialysis patients are scarce. The current study was conducted on a group of peritoneal dialysis patients to learn how the response to hepatitis B virus vaccination varies according to the patient''s clearance of urea normalized to total body water (Kt/V).

METHODS:

A convenience sample of 33 peritoneal dialysis patients (13 women and 20 men, with a mean age of 49±12 years) was administered double doses (20 µg IM in each deltoid muscle) of recombinant hepatitis B vaccine at 0, 1, 2, and 6 months. Response to immunization was measured at one to three months after the final dose of vaccine. The subjects were divided into groups according to the level of antibodies to hepatitis B surface antigen (anti-HBs), including non-responders (<10 IU/L), weak responders (10-100 IU/L), and good responders (>100 IU/L).

RESULTS:

Among non-responders, weak responders, and good responders, significant differences were found in age (54±12 vs. 56±9 vs. 45±12 years, respectively; p = 0.049) and recombinant human erythropoietin use (20 vs. 29 vs. 76%, respectively; p = 0.016). No significant differences in weekly total Kt/V (p = 0.704), weekly peritoneal Kt/V (p = 0.064) and residual glomerular filtration rate (p = 0.355) were found across the three groups.

CONCLUSIONS:

Delivered clearance measured by weekly peritoneal Kt/V and total clearance measured by weekly total Kt/V did not predict the response to hepatitis B virus vaccination in patients on peritoneal dialysis.     

Lower residual renal function is a risk factor for depression and impaired health-related quality of life in Korean peritoneal dialysis patients

We retrospectively evaluated demographic and biochemical parameters associated with depression and health-related quality of life (HRQOL) in maintenance peritoneal dialysis (PD) patients. This study included 105 patients maintaining PD at Seoul National University Hospital. Data were collected from electronic medical record. Korean Beck's Depression Inventory and Korean version of Kidney Disease Quality of Life short form, version 1.3 were used to evaluate depression and HRQOL, respectively. Moderate to severe depression was found in 24.8% of patients. Patients with lower normalized protein equivalent of nitrogen appearance (nPNA) (< 1.2 g/kg/day), lower weekly renal Kt/V(urea) (< 0.2), and lower serum albumin level (≤ 4.0 g/dL) were associated with depression (P < 0.05). Among them, lower weekly renal Kt/V(urea) was the only independent risk factor associated with depression (OR = 3.1, P = 0.007). Depressed patients showed significantly lower scores in every dimension of HRQOL (P < 0.001). Lower weekly renal Kt/V(urea) (β = 0.24, P = 0.005) and lower nPNA (β = 0.15, P = 0.03) were the independent risk factors associated with lower kidney dialysis component summary, whereas lower plasma hemoglobin level was the consistent risk factor for lower physical component summary (β = 0.22, P = 0.03) and mental component summary (β = 0.22, P = 0.01). Depression is a prevalent psychological problem in PD population. Residual renal function is the most important factor associated with depression and impaired HRQOL in PD patients.     

Left ventricular hypertrophy in patient on dialysis

Left ventricular hypertrophy (LVH) is a significant factor for higher mortality caused by cardiovascular diseases, which are the main cause of death (45%) in hemodialysis patients. In this study we analyzed the link between hypertension nad anemia, which are the main risk factors for the occurrence of LVH. The study included 40 patients (20 M and 20 F, age 20-80 years) who were treated with chronic dialysis. Using the method of transthoracic echocardiography, in M-mode, 38 patients underwent measurement of the thickness of intraventricular septum and posterior wall of the left ventricle at the end of diastole. LVH was expressed through the left ventricle mass index (LVMI) > 131 g/m2 for male and > 100 g/m2 for female. The efficiency of dialysis was calculated with the standard formula (Kt/V1,2). The patients on erythropoietin therapy received medium maintenance dose of 4000 units per week. Blood pressure and hemoglobin data were included in the calculations. A statistically higher rate of hypertension was found in males (M 17/20, F 10/20, p = 0.04), and of myocardial hypertrophy in females (M 7/20, F 17/20, p = 0.004). Overall patient data analysis showed LMVI to be statistically significantly higher (p = 0.0004) in hypertensive patients, and so were the values of systolic and diastolic pressure (p = 0.0006) in spite of applied medication. Hemoglobin was significantly higher (p = 0.04) in LVH patients. A significant positive correlation was found between LVMI and arterial pressure (p = 0.006), and negative between LVMI and hemoglobin concentration (p = 0.03). There was no statistically significant correlation between LVMI and age, interdialytic fluid intake and Kt/V. These results indicate that among patients on chronic dialysis treatment, LVH is more frequent in those with hypertension. The higher hemoglobin concentration found in patients with LVH was probably due to the relatively small number of patients. It is necessary to reduce the effect of risk factors for LVH by using better therapeutic options, thus to decrease the mortality in dialysis patients.     

Predictors of erythropoietin responsiveness in chronic hemodialysis patients

The impact of dialysis intensity on erythropoietin (EPO) requirements is unclear. Previous work suggests that increased dialysis is associated with increased erythropoietin responsiveness (ERSP), but average dialysis intensity has increased since those publications. We hypothesized that ERSP would be independent of delivered Kt/V(urea) at current intensities of hemodialysis. We prospectively studied 135 stable chronic hemodialysis patients who receive iron and subcutaneous EPO dosed according to current guidelines. We collected biochemical, hematologic, and single pool urea kinetics data. ERSP was expressed as units per kilogram per week of EPO administered. Simple and multiple linear regression were used to identify characteristics predictive of ERSP. The mean age of the patients was 62 +/- 17 years (range, 17-90 years); 68 of 135 (50.3%) were women, and 120 of 135 (88.9%) were Caucasian. Mean delivered Kt/V(urea) was 1.60 +/- 0.49, with 102 of 135 (75.6%) of patients with a delivered Kt/V(urea) > 1.3. Univariate linear regression showed seven significant independent predictors of erythropoietin requirements. Low serum albumin (p < 0.001), low serum calcium (p = 0.002), high serum phosphate (p = 0.004), and high serum iPTH (p = 0.007) were all associated with lower levels of ERSP. Lower ERSP was also correlated with lower hemoglobin and lower serum iron and transferrin saturation. Delivered dialysis (Kt/ V(urea)) was not a significant predictor of ERSP (p = 0.61). Multivariate regression confirmed low serum albumin (p < 0.01), high serum phosphate (p = 0.001), high immunoreactive parathyroid hormone (p = 0.025), and low transferrin saturation (p < 0.0005) as predictors of low ERSP, and also found high serum ferritin to be correlated with low ERSP (p = 0.016). We found no relationship between erythropoietin responsiveness and intensity of hemodialysis in this population of patients with a mean delivered Kt/V(urea) of 1.6. This may indicate a threshold effect beyond which more dialysis will not improve ERSP. However, markers of an underlying inflammatory state and of secondary hyperparathyroidism were associated with decreased response to erythropoietin.     

Bimodal dialysis: theoretical and computational investigations of adequacy indices for combined use of peritoneal dialysis and hemodialysis

A theoretically correct method for evaluating the adequacy of bimodal dialysis (BMD), a combination of peritoneal dialysis (PD) and hemodialysis (HD) in the same patient, is lacking. We therefore performed computer simulations using a variable-volume, two-compartment urea kinetic model for 1-week treatments with 1) HD with three sessions, HD3, 2) continuous ambulatory PD, CAPD, 3) 6 days of CAPD and 1 day with HD session, and 4) 5 days of CAPD and 2 days with HD. Four dialysis adequacy indices (KT/V, stdKT/V, fractional solute removal, FSR, and equivalent clearance, EKR) were analyzed using four different reference methods for normalization of urea amount and concentration: 1) peak value, 2) peak average value, 3) time average value, and 4) treatment time average value. The analyses show that a proposed simplified rule of adding one third of weekly FSR for HD3 for each dialysis session and one seventh of weekly FSR for CAPD for each PD day for prediction of weekly FSR for BMD provides a fair prediction, although some corrections may be necessary, depending on the chosen reference method. In particular, KT/V may be added using this rule. We conclude that theoretically correct adequacy indices for BMD may be defined and calculated by using numerical simulations.     

The post: pre-dialysis plasma urea nitrogen ratio to estimate K.t/V and NPCR: mathematical modeling

The mathematical basis of the relationship between K.t/V and the ratio of the postdialysis (Ct) to predialysis (Co) plasma urea nitrogen levels (Ct/Co = R) is the urea kinetic model. The R vs. K.t/V relationship is modulated by the patient's normalized protein catabolic rate (NPCR), the dialysis session length, and the predialysis plasma urea nitrogen level, due to urea generated during the dialysis session; the latter increases Ct and hence raises R. The relationship between R and K.t/V is also affected by the amount of ultrafiltrate removed during the dialysis session, because convective urea removal, which is a part of K, does not result in a lowering of the (Ct). In stable adult maintenance dialysis patients receiving 3 treatments/week, with an NPCR of less than or equal to 1.1 g/kg/day and zero residual renal function, the target K.t/V is 1.05 and the target R will be about 0.41. In patients who require different K.t/V values, corresponding values of R can be computed. Based on an empiric examination of the urea kinetic equations, several formulas are proposed for estimating K.t/V from R and vice versa, which depend only on the dialysis session length t, the amount of ultrafiltrate UF, and the postdialysis weight W or V; e.g., K.t/V = - ln (R - 0.008.t-UF/W). After K.t/V has been estimated from R, t, UF and W, one can then estimate the NPCR in the residual renal urea clearance (Kru) has also been measured. From the estimated K.t/V, the Kru, and an estimated V, the total urea clearance over time corrected for V ("KT") is computed.(ABSTRACT TRUNCATED AT 250 WORDS)     

On-line monitoring of solutes in dialysate using absorption of ultraviolet radiation: technique description

PURPOSE: The aim of this work was to describe a new optical method for monitoring solutes in a spent dialysate using absorption of UV radiation. METHOD: The method utilises UV-absorbance determined in the spent dialysate using a spectrophotometrical set-up. Measurements were performed both on collected dialysate samples and on-line. During on-line monitoring, a spectrophotometer was connected to the fluid outlet of the dialysis machine, with all spent dialysate passing through a specially-designed cuvette for optical single-wavelength measurements. The concentrations of several substances of various molecular sizes, electrical charge, transport mechanism, etc. were determined in the dialysate and in the blood using standard laboratory techniques. The correlation coefficient between UV-absorbance of the spent dialysate and concentration of the substances in the spent dialysate and in the blood was calculated from data based on the collected samples. RESULTS: The obtained on-line UV-absorbance curve demonstrates the possibility to follow a single hemodialysis session continuously and to monitor deviations in the dialysator performance using UV-absorbance. The experimental results indicate a very good correlation between UV-absorbance and several small waste solutes removed such as urea, creatinine and uric acid in the spent dialysate and in the blood for every individual treatment at a fixed wavelength of 285 nm. Moreover, a good correlation between the UV-absorbance and substances like potassium, phosphate and beta2-microglobulin was obtained. The lowest correlation was achieved for sodium, calcium, glucose, vitamin B12 and albumin. CONCLUSIONS: A technique for on-line monitoring of solutes in the spent dialysate utilising the UV-absorbance was developed. On-line monitoring during a single hemodialysis session exploiting UV-absorbance represents a possibility to follow a single hemodialysis session continuously and monitor deviations in dialysis efficiency (e.g. changes in blood flow and clearance). The UV-absorbance correlates well to the concentration of several solutes known to accumulate in dialysis patients indicating that the technique can be used to estimate the removal of retained substances.