Predialysis Urea Research Articles

Prospective Evaluation of an In-Center Daily Hemodialysis Program

Short duration daily hemodialysis (DHD) emerges as a well-tolerated alternative to standard hemodialysis (SHD). In this prospective study 5 patients in SHD were recruited to participate in an in-center DHD program. The SHD consisted of 3 sessions of 4 h each per week. Nonproportional mixture machines without an ultrafiltration control device and low flow dialyzers were used. For DHD, dialysis equipment and procedures were kept the same. Dialysis sessions, however, began at 6 p.m. (from Monday to Saturday) and lasted 2 h. Data from the last 6 months on SHD of the same patients were compared with the ones from each semester on DHD. Bone biopsy was performed at start and at the end of the 2-year study period. Hypotensive episodes, hypertensive crisis, cramps and headaches became 7–10 times less frequent in daily dialysis. A significant fractional increase (∼12%) was seen in mean values for hematocrit. Predialysis urea levels as well as predialysis creatinine levels declined significantly. Also lower during the daily dialysis period were the mean values for both phosphorus and Ca×P product. Significant increases were found in serum bicarbonate, albumin and in dry weight. The frequency of mean blood pressure ≧110 mm Hg on arrival for dialysis was significantly lower in every semester on daily hemodialysis. A significant twofold improvement in quality of life scoring was observed. Finally, daily hemodialysis also seemed to be beneficial to low turnover bone disease and bone aluminum deposition. These beneficial effects occurred despite of an increase in the frequency of missing days. Results from the present study which prospectively addressed the role of in-center short daily hemodialysis in the management of ESRD are encouraging.

Computers in clinical practice: Screening renal patients for abnormal biochemistry and malnutrition

Objective: Develop and compare a computer program (CP) and a screening tool (ST) to determine the best method of identifying patients undergoing hemodialysis (HD) who are at risk of malnutrition. Investigate the benefits of using the CP to screen biochemical test results of patients undergoing HD, continuous ambulatory peritoneal dialysis (CAPD), nephrology patients, and transplant recipients for abnormal levels, such as hyperkalemia. Design: The CP was designed by using the program Proton (Clinical Computing Clinical Information Systems, Middlesex, England). Proton can automatically download biochemical results from pathology, making it possible to generate a list of patients with results outside a desired biochemical range in accordance with national renal standards for adult patients. Biochemical measures of nutritional status were used to define malnutrition as 2 or more results outside of these parameters: 10% weight loss; Kt/V < 1.1; predialysis urea, <20 mmol/L; phosphate, <0.75 mmol/L; and potassium, <3.3 mmol/L. One hundred eighty-four HD patients were incidentally screened for their risk of malnutrition by using both the CP and the ST. Setting: Richard Bright Renal Unit, Bristol, England, and 4 satellite HD units in Southwest England. Patients: Three thousand five renal outpatients, including 468 patients with diabetes, had blood test results screened by the CP for abnormal levels. This included 235 HD patients (unit A, n = 32; unit B, n = 58; unit C, n = 70; Unit D, n = 24; home HD unit, n = 51), 88 CAPD patients, 416 transplant recipients, and 2,266 nephrology patients. Main Outcome Measure: The CP and the ST were compared with standardized dietetic assessments (SDAs) for validity. In the clinic setting, the length of time taken to review biochemical test results was measured before and after implementation of the CP. Results: The CP identified 36% of HD patients at risk of malnutrition, compared with 20% by the ST and 42% by SDA. However, only 57% of the STs were completed. The CP found 42% of transplant recipients and 92% of nephrology patients have glycosylatid hemoglobin levels >7, and 16% of HD patients have fluid weight gains >3 kg on 4 or more occasions in a month. Conclusion: Using the present parameters, the CP is not sensitive enough to correctly identify all HD patients at risk of malnutrition. Screening for serum cholesterol, prealbumin, protein equivalent of total nitrogen appearance, and C-reactive protein levels should be incorporated into the CP to compare it with a simple, inexpensive, and reproducible screening tool, such as subjective global assessment, to identify malnutrition in patients undergoing dialysis. The CP improves time management and rationalization of dietetic activity by screening abnormal biochemistry levels. Renal dietitians are urged to investigate the practicalities and the benefits of computers in clinical practice because early identification of malnutrition in patients allows dietitians to work in a more proactive manner. © 2002 by the National Kidney Foundation, Inc.

Nutritional screening tools for CAPD patients: are computers the way forward?

The aim of this study was to develop a computer programme (CP) to identify CAPD patients at risk of malnutrition as well as screen monthly biochemical results of transplant (tx), haemodialysis (HD), CAPD and nephrology (Ne) patients for abnormal levels such as hyperkalaemia. The CP was designed using the programme Proton. Proton can automatically download biochemical results from pathology making it possible to generate a list of patients with results outside a desired biochemical range in accordance with national renal standards for adult patients. Biochemical measures of nutritional status were used to define malnutrition as 2 or more results outside of these parameters (see Table 1): 10% weight loss, Kt/V < 1.9, normalised protein catabolic rate (nPCR) < 1.2: predialysis urea < 15 mmol/L, phosphate (PO4) < 0.75 mmol/L, potassium (K), < 3.3 mmol/L. The CP was compared with standardised dietetic assessments (SDA) for validity. An SDA includes a review of medical, social history, biochemistry (blood and urine), dialysis prescriptions, treatment plans, medications, weight changes, BMI, dietary intake compared to therapeutic guidelines with documented aims. The therapeutic guidelines used to complete dietary assessment include: protein 1.2-1.5 g/kg Ideal Body Weight (IBW), energy: aim for BMI of 20-25 kg/m2, sodium: 100-120 mmol/L, K: 1 mmol/kg IBW, fluid: urine output + medical advice, PO4: 175-200 mg of PO4/10 g of protein. 3005 patients from Richard Bright Renal Unit in Bristol, England, including 4 Satellite HD units, had blood results screened for abnormal levels using CP (see Table 1). In the clinic setting, the length of time taken to review biochemical results was measured before and after implementation. The CP identified 88% of CAPD patients at risk of malnutrition compared with 67% by SDA. The time taken to look up biochemical results of patients attending the outpatient clinics was reduced by approximately 30 minutes leaving only the diet history computer screen to review for each patient. The CP should be compared with subjective global assessment (SGA) for validity in the identification of malnutrition. Serum cholesterol, prealbumin, protein equivalent of total nitrogen appearance (nPNA), C reactive protein (CRP) and bicarbonate should be incorporated into the CP in order to improve its specificity. Using the present parameters, the CP over diagnosed the number of CAPD patients at risk of malnutrition. However, the CP improves time management and rationalisation of dietetic activity by screening abnormal biochemistry.

Predialysis urea concentration is sufficient to characterize hemodialysis adequacy.

Mathematical description of urea kinetics for a week showed that, under steady state conditions (i.e., total removal equals total synthesis), any predialysis urea concentration is expressed as a linear function of specific urea generation (G/V) and of dialysis schedule timing and sessional Kt/V (product of clearance, K, and session time, t, divided by the urea distribution volume, V). It also predicts that TACurea is proportional to the predialysis concentrations. The ratio between the two depends linearly on delivered weekly dialysis dose ([wDD] = T(G/V)/TACurea, with T the number of hours in 1 week). These hypotheses have been tested by retrospectively analyzing urea kinetc modelling data that include all predialysis and post dialysis concentrations of 163 patient-weeks. All patients were anuric, and dialysis frequency was thrice weekly. Accuracy is assessed with regression analysis between database numbers and computed values. The theoretical ratio between midweek concentration and TACurea (1.43) is close to the computed ratio (1.46, r2 = 0.909). TACurea (slope = 1.002, r2 = 0.997), specific generation rate G/V as a precursor to PCRn (slope = 1.007, r2 = 0.985), and wDD (slope = 1.002, r2 = 0.909) are all accurately computed from predialysis concentrations. To aid in the determination of the ratio for the different predialysis, concentrations using wDD a nomogram is included.

Is Post-Dialysis Urea Rebound Significant with Long Slow Hemodialysis?

Background: According to previous studies, postdialysis urea rebound (PDUR) is achieved within 30–90 min, leading to an overestimation of Kt/V of between 15 and 40% in 3- to 5-hour dialysis. The purpose of the study was to assess the impact of PDUR on the urea reduction ratio (URR), Kt/V and normal protein catabolic rate (nPCR) with long 8-hour slow hemodialysis. Methods: This study was performed in 18 patients (13 males/5 females), 62.5 ± 11.7 years of age, hemodialyzed for 3–265 months. Initial nephropathies were: 3 diabetes; 2 polycystic kidney disease; 3 interstitial nephritis; 2 nephrosclerosis; 3 chronic glomerulonephritis, and 5 undetermined. Residual renal function was negligible. The dialysis sessions were performed using 1- to 1.8-m² cellulosic dialyzers during 8 h, 3 times a week. Blood flow was 220 ml/min, dialysate flow 500 ml/min, acetate or bicarbonate buffer was used. Serial measurements of the urea concentration were obtained before dialysis, immediately after dialysis (low flow at t = 0), and at 5, 10, 20, 30, 40, 60, 90 and 120 min, and before the next session. The low-flow method was used to evaluate the access recirculation, second-generation Daugirdas formulas for Kt/V, and Watson formulas for total body water volume estimation. The difference between the expected urea generation (UG) and urea measured after dialysis (global PDUR) defines net PDUR (n-PDUR). Results: The n-PDUR usually became stable after 58 ± 25 (30–90) min. Its mean value was 17 ± 10% of the 30-second low-flow postdialysis urea (3.9 ± 2 mmol/l). This small postdialysis urea value and the importance of UG in comparison with shorter dialysis justify the use of n-PDUR. Ignoring n-PDUR would lead to a significant 4% overestimation (p < 0.001) of the URR (79 ± 7 vs. 76 ± 8%), 12% of Kt/V (1.9 ± 0.4 to 1.7 ± 0.38) and 4% of the nPCR (1.1 ± 0.3 to 1.05 ± 0.3). n-PDUR correlated negatively with postdialysis urea (r = 0.45 p = 0.05), positively with URR (r = 0.31 p = 0.01) and Kt/V (r = 0.3 p = 0.03) but not with K, and negatively with the urea distribution volume (r = 0.33 p = 0.05). Mean total recirculation, ultrafiltration rate, predialysis urea levels and urea clearance did not correlate with n-PDUR. Conclusion: We found a significant PDUR in long-slow hemodialysis after a mean of 1 h after dialysis. This PDUR has a less important impact upon dialysis delivery estimation than short 3- to 5-hour hemodialysis, especially for the lower Kt/V or URR ranges. This is explained by the low-flux, high-efficiency, and long-term dialysis. Its inter-individual variability incites us to calculate PDUR on an individual basis.

Carbamylated hemoglobin and carbamylated plasma protein in hemodialyzed patients

The carbamylation reaction in vivo involves the nonenzymatic, covalent attachment of isocyanic acid, the spontaneous dissociation product of urea, to proteins. Carbamylated proteins have been proposed as markers of uremia and indicators of uremic control. However, the utility of measuring carbamylated proteins has not been investigated adequately. Therefore, this study was done to determine the relationship between the carbamylation of long-lived protein (hemoglobin) with that of short-lived proteins (plasma proteins) in hemodialyzed patients. Significantly higher carbamylated hemoglobin (CHb; 157 +/- 40 microg valine hydantoin/g Hb) and carbamylated protein (CTP; 0.117 +/- 0.011 absorbance/mg protein) concentrations were found in hemodialyzed patients (N = 13) as compared to normal individuals (N = 9, 53 +/- 20 microg valine hydantoin/g Hb and 0.08 +/- 0.01 absorbance/mg protein, respectively). A high correlation was found between CHb and CTP concentrations (r = 0.87, P < 0.0001), demonstrating a strong relationship between these two different half-lived proteins. A six-month longitudinal study of seven hemodialyzed patients showed that the between subject correlations were significant for CHb versus CTP as well as CHb versus pre-dialysis urea. Correlations were not significant for CTP versus pre-dialysis urea or Kt/V, nor CHb versus Kt/V. Carbamylated hemoglobin fluctuated the most over this time period (30.1% +/- 20.2%), pre-dialysis urea and CTP varied less (18.3% +/- 13.4% and 14.9% +/- 7.5%, respectively), and Kt/V varied the least (6.3% +/- 3.3%). Within subject correlations were not significant between any two tests. It is unclear whether the lack of correlations found is real or a function of the small sample size. However, these data do show that CHb and CTP are positively associated and reflect the degree of urea exposure in the blood, but their usefulness for patients on maintenance hemodialysis is not clear.

Evaluation of high-flux hemodiafiltration efficiency using an on-line urea monitor

On-line urea monitoring of the effluent dialysate offers a real-time assessment of dialysis efficiency and metabolic/nutritional characteristics of hemodialysis patients. Quantitative parameters were evaluated by dialysate urea kinetic modeling (DUKM) with an on-line urea sensor in 23 patients treated by high-flux hemodiafiltration (HDF) (215 sessions of 210 to 240 minutes with a mean blood flow rate of 367 +/- 44 mL/min). Overall, the mean effective Kt/V was 1.52 +/- 0.29, the urea mass removed (22.8 +/- 5.5 g/session or 814 +/- 198 mmol/session), the solute removal index (SRI) 73% +/- 6.1%, and the mean normalized protein catabolic rate (nPCR), 1.15 +/- 0.31 g/kg/day. Blood urea kinetic modeling (BUKM), based on pre- and postsession urea concentrations, using equations from Daugirdas and Garred to calculate equilibrated Kt/V and nPCR, respectively, were in good agreement with DUKM, the differences observed appearing not clinically relevant. The variability of evaluated parameters was verified over consecutive sessions for a mean period of 3 weeks in the entire group. Mean variation in Kt/V was 8%; in urea mass removal, 18%; and in nPCR, 18%. When assessed over 1 week in a subgroup of 13 patients, Kt/V and PCR remained relatively stable, and urea mass removal per- and postsession declined from 23.5 +/- 8.0 g (840 +/- 285 mmol) to 18.7 +/- 6.3 g (667 +/- 225 mmol) from the first to the third session of the week, most likely as a consequence of interdialytic intervals. Predialysis urea concentrations followed the same trend. In the current study, DUKM with on-line urea sensor has confirmed that HDF is a highly efficient renal replacement modality; the variability observed in quantitative parameters supports a need for frequent adequacy monitoring. On-line urea monitoring of effluent dialysate is a simple device that provides the opportunity to tailor treatment to patient needs. (Am J Kidney Dis 1998 Jan;31(1):74-80)

Simple Equations for Protein Catabolic Rate Determination From Pre Dialysis and Post Dialysis Blood Urea Nitrogen

Several simple equations exist for Kt/V determination from pre dialysis (Cpre) and post dialysis (Cpost) blood urea. However, comparable equations have not been available for calculation of protein catabolic rate (PCR), an essential parameter for assessing patient status. Three simple formulas for PCR determination were developed from the urea mass balance equation for an anuric patient in protein steady state receiving thrice weekly dialysis. The simplest formula, PCR = 0.0076 [Kt/V] [Cpre + Cpost] + 0.17 relates PCR (in g protein/kg/day) to Kt/V and pre and post dialysis blood urea nitrogen measurements (in mg urea nitrogen/dl) for the midweek session. When tested for 540 simulated patients spanning a range of Kt/V (0.6-1.6); PCR (0.6-1.6 g/kg/day); dialysis duration t (2-4 hrs) and interdialytic weight gain expressed as a percentage of dry body weight gained daily (0-4%), this equation yielded a maximum error of less than +/- 5%, within the accuracy generally required for clinical needs. A more accurate formula, [formula: see text] where Clm is the logarithmic mean of Cpre and Cpost, gave maximum errors in PCR estimation for the same 540 simulated patients of less than +/- 0.6%. Both formulas require a precise value of Kt/V. The equation below incorporates a very accurate simple Kt/V equation recently published by the authors, allowing PCR to be expressed in terms of Cpre, the ratio of Cpost to Cpre (R), the ratio of session ultrafiltration volume (delta BW) to urea distribution volume (V), and dialysis time (t, in min). [formula: see text] This equation was accurate to within a maximum error of +/- 1% for the simulated patient group. These equations allow simple and accurate patient PCR determination, and should be used in conjunction with a simple formula for accurate Kt/V determination to guide end-stage renal failure patient therapy.

On-Line Dialysate Urea Monitor: Comparison with Urea Kinetics

The outputs of a new on-line dialysate urea monitor (UM) were compared to a urea kinetic model (UKM) and to dialysis direct quantification (DDQ) in 13 patients. As for urea extraction and predialysis urea level, a good degree of correspondence was found between UM and laboratory data. Kt/VUM (1.21) is intermediate between Kt/VUKM (1.28) and Kt/VUKM using the post-rebound urea value (1.14) or Kt/VDDQ (1.14). Passing and Bablok regression analysis indicated no systematic error between Kt/VUM and Kt/VDDQ. The percentage differences in nPCR by UM, UKM and DDQ were not significant, but the standard deviations were wide. The UM approach is very simple and practical, avoiding blood sampling, laboratory analysis and data handling. It is reliable enough for clinical practice. Compared with traditional urea kinetics, Kt/V computation by a mathematical elaboration of the dialysate urea profile drawn from several points theoretically invites fewer errors due to the analytical procedure.

Effect of dialysate temperature on central hemodynamics and urea kinetics

Use of cool dialysate is associated with increased intradialytic blood pressure, but the hemodynamic mechanism is unknown. Whether changes in dialysate temperature affect muscle blood flow, which may the alter the degree of urea compartmentalization, also is unknown. We measured hemodynamics and blood and dialysate-side urea kinetic indices in nine hemodialysis patients during two cool (35.0 degrees C) versus two warm (37.5 degrees C) dialysate treatments. The % change in mean arterial pressure was different when using the cool (+6.5 +/- 9.7 mm Hg) versus the warm (-13.4 +/- 3.6) dialysate (P < 0.01), despite comparable amounts of fluid removal. Percent changes in cardiac output were similar with the two dialysates, and thus the blood pressure effect was due primarily to changes in total peripheral resistance (% delta TPR, cool +26 +/- 13.6, warm +8.6 +/- 14.5; P < 0.02). During cool dialysate use tympanic membrane temperature changed by -0.51 +/- 0.23 degree C, whereas body temperature increased by 0.52 +/- 0.14 degree C during use of warm dialysate. Measured urea recovery normalized to the predialysis urea nitrogen concentration was similar with the two treatments: cool 31.3 +/- 0.039 liter-1; warm 29.7 +/- 0.021; P = NS. In a second study, post-dialysis urea rebound values from 15 seconds to 30 minutes, expressed as the percent of the post-dialysis SUN, were similar after the two treatments: cool 11.79 +/- 1.4; warm 12.21 +/- 2.27, P = NS.(ABSTRACT TRUNCATED AT 250 WORDS)

Simplified equations for monitoring Kt/V, PCRn, eKt/V, and ePCRn.

Although computer solution of the differential equations used in urea kinetic modeling has its advantages, simplified formulas that are actually approximate algebraic solutions to the same equations in the clinically useful range are also useful. The Kt/V can be resolved from the predialysis to postdialysis urea nitrogen ratio (R), the weight loss (UF), session length in hours (t), and anthropometric or modeled volume (V) using the equation: KtV = In (R - 0.008 x t) + (4 - 3.5 x R) x 0.55 UF/V. The equilibrated Kt/V (eKTV) can be estimated from the single-pool arterial Kt/V (spaKTV) or the single-pool venous Kt/V (spmvKTV) using a rate equation based on the regional blood flow model of urea kinetics: eKTV = spaKTV - (0.60)(spaKTV)/t + 0.03 = spmvKTV - (0.46) (spmvKTV)/t + 0.02. The normalized protein catabolic rate (PCRn) can be determined from either the single-pool or equilibrated Kt/V based on the predialysis urea nitrogen level (C0) and the Kt/V (KTV) using the generalized equation: PCRn = C0/(a + bKTV + c/ + KTV) + 0.168, where the constants a, b, and c vary depending on the dialysis schedule and the time of the week that the predialysis blood specimen has been drawn. Such equations can be used either for retrospective surveys, or for quality assurance purposes, as well as for bedside guidance in an individual patient. The actual modeled urea distribution volume can also be easily computed if some effort is made to estimate the dialyzer urea clearance.

Simple Kt/V Formulas Based on Urea Mass Balance Theory

The ratio Kt/V (K is patient clearance, t dialysis time, V urea space) has become the standard measure of dialysis adequacy. In this article simple Kt/V equations are developed theoretically from the urea mass balance equation. Two approximations lead to the most precise equation: [formula: see text] where R is the post to pre dialysis urea ratio, BW/V is the amount of fluid removed during dialysis (delta BW) expressed as a fraction of urea distribution space (V) at dry body weight (BW), and t is dialysis length in hours. A second equation arises with V approximated as 58% of BW. One further approximation leads to a simpler but slightly less precise Kt/V formula: [formula: see text] These and earlier published equations were tested with two sets of data: 1) 49 sessions involving 17 patients on maintenance dialysis and 2) 540 computer simulations spanning all likely values of Kt/V (0.6-1.6), protein catabolic rate (0.6-1.6), interdialytic weight gain (0-4% of BW per day) and dialysis session length (2-4 hr). The most precise formula (upper equation above) had a maximum error of 0.031 and 0.035 Kt/V units for the clinical and simulated data, respectively, whereas the lower equation was slightly less accurate with maximum Kt/V errors of 0.079 and 0.081, respectively. The proposed Kt/V equations are considerably more accurate than previously published formulas.

Patient Related Factors Leading to Slow Urea Transfer in the Body During Dialysis

We studied the trans compartmental speed of urea transfer by comparing concentration changes of blood urea nitrogen to mass changes of urea during 80 dialyses in six patients. The speed of urea transfer was studied as a dependent factor of 15 patient characteristics: age; gender; fluid overload; and pre and post values of and change in pulse and temperature, calcitonin gene related peptide, and mean arterial blood pressure. Concentration changes in blood urea nitrogen were measured as pre and post dialysis urea concentration, the total urea in the body was measured by pre dialysis urea and tritium total body water determinations, and the actual mass of urea removed by collecting all dialysate. As a mean, concentration of blood urea nitrogen fell 54% but the mass urea removed was only 40% for a mean ratio of 1.41. Nine factors were associated with the speed of urea transfer. Patients with fast transfer had more normal fluid balance, a normal pulse rate, body temperature, calcitonin gene related peptide values, and blood pressure both before and after dialysis. The patients with a slower transfer of urea had a lower blood pressure before and after dialysis and a more labile pulse rate and body temperature. Patients with unpredictable urea transfer were the most edematous and had the most labile blood pressure. It is important to know which patients have slow urea transfer. Such patients should not be treated by fast dialysis, and those with the slowest rates may do particularly well on continuous ambulatory peritoneal dialysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Sorbent membrane dialysis in uremia.

The inclusion of activated charcoal within hemodialysis membranes offers potentially improved plasma clearance of creatinine and middle molecules. However, the carbon becomes saturated with continued use and beyond 1 h removal of solutes is by dialysis alone. Two independently conducted crossover studies, to assess the efficacy of sorbent membrane dialysis (SMD) in the treatment of uremia, found predialysis urea levels increased by approximately 15%, creatinine by 10-15%, and inorganic phosphate levels by 10-18% on SMD compared to conventional hemodialysis. One study also observed "middle molecule' (peak "b') levels elevated. No differences were observable in the clinical status of patients. The results suggest that the charcoal content of the SMD device is too small to effect any advantages over conventional dialysis.

Serum beta2-microglobulin in hemodialyzed patients.

beta2-Microglobulin (beta2-M) concentrations were measured by radioimmunoassay in 63 patients treated with maintenance hemodialysis. Serum levels ranged from 12.5 to 92 microgram/ml and were found stable upon sequential measurements over a 6-month period. Excretion of beta2-M was achieved through urinary loss (up to 150 mg/day) and to a lesser extent by ultrafiltration across acrylopolynitrile but not cellophane dialysis membranes. Proximal tubular cells being the major site of beta2-M catabolism, stable levels in anephric patients indicated a defective production of beta2-M in uremic patients. Serum beta2-M levels were not correlated with predialysis urea, creatinine, hematocrit or middle molecule material. In vitro experiments do not support a possible toxicity of purified beta2-M but do not rule out the contribution of other low molecular weight proteins to uremic toxicity.

Production of urea nitrogen and creatinine in chronic azotemia and effect of hemodialysis.

Summary1. The daily rate of urea nitrogen and creatinine production was determined in 7 patients with chronic stable azotemia and 3 normal subjects, maintained on a reduced protein intake. In addition, the effect of hemodialysis on urea nitrogen and creatinine production was observed in all the azo-temic patients. 2. In 7 cases predialysis urea nitrogen production was similar to that found in normal subjects and averaged 55% of the nitrogen intake. In 2 cases urea nitrogen production was elevated, being equal to or exceeding the dietary nitrogen. The rate of creatinine production in the azotemic patients was slightly lower than that found in normal subjects. 3. Postdialysis urea nitrogen production increased significantly in 5 cases whose predialysis PUN ranged from 42 to 73 mg%, and decreased in 4 cases with predialysis PUN of 87 to 192 mg%. Creatinine production decreased in all but one case.