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Aims: To evaluate the quality of bedside estimation of glomerular filtration rate (GFR) in hospitalized elderly patients. Methods: We evaluated common estimators of GFR in 29 women and 32 men aged 60 and older hospitalized in a geriatric ward: creatinine clearance (CCR), the Cockcroft-Gault formula (CG), the modification of diet in renal disease formula (MDRD), Baracskay formula (BAR), and a newly developed formula derived recently by us (GCM). Inulin clearance (CINU) was used to assess GFR. Exclusion criteria were mental illness and urinary incontinence. Results: According to Bland and Altman accuracy and precision of all estimators were low and there was an underestimation of actual GFR: CCR 38.9 ml/min; CG 39.7 ml/min; MDRD 19.8 ml/min; BAR 34.0 ml/min, and GCM: 24.7 ml/min. The accuracy and precision of all methods were even lower in patients with a GFR of >90 ml/min and in patients with diabetes. In receiver-operating characteristics (ROC analysis) all formulas were superior to serum creatinine and overall MDRD disclosed the best results in detecting both a GFR of <90 ml/min and <60 ml/min. Conclusions: In general, estimation errors are large in an acute care setting. However, formula estimation is clearly superior to serum creatinine and CCR. MDRD gave the best results but may be replaced by the more simple CG and GCM formulas, whereas BAR was inferior.

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A secondary concentric cylinders cell was used to measure the thermal conductivity of binary mixtures of argon-nitrogen, argon-helium, and argon-neon approximately 20, 40, 60, and 80 vol. % a t 75°C. and pressures to 2,800 atm. Measurements were made also on the pure gases argon and nitrogen.The transport properties of dense gas mixtures are important in engineering design and in the theoretical interpretation of molecular interactions. Although limited data have been reported by Junk and Comings (1), Keyes ( 2 ) , and Gilmore and Comings ( 3 ) , chemical processes involving mixtures make it important to understand the transport behavior of mixtures at high pressures.A secondary cell of the type used by Kramer and Comings ( 4 ) and Gilmore and Comings ( 3 ) was used to measuie the thermal conductivity of binary mixtures of argon-helium, argon-nitrogen, and argon-neon at 75 O C. and to 2,800 atm. The conductivity values of carbon dioxide measured by Sengers ( 5 ) were used for cell calibration. Measurements were also made on the pure gases argon and nitrogen. EXPERIMENTAL PROCEDURESThe thermal conductivity cell (Figure 1) is similar to the Gilmore-Comings cell ( 3 ) and consists of two horizontal concentric cylinders totally immersed in the sample fluid. The Gilmore-Comings cell was modified by increasing the number of thermocouple junctions from three to five, which provided a thermopile consisting of five equally spaced thermocouple junctions in each cylinder. The cell was contained in a high pressure bomb with an I.D. of 2.5 in. The O.D. of the receiver was increased to 2.4 in. for a closer fit with the pressure bomb container in order to decrease the time in which the temperature reached equilibrium with the surroundings.Auxiliary equipment used for generating pressure and making the experimental measurements is described by Gilmore ( 3 ) . A Thermodyne temperature controller ( Hallikainen Instruments), installed in the oil bath, maintained a uniform temperature to the degree that variations with time could not be detected within the pressure bomb.The cell was calibrated by the procedure used by Gilmore ( 3 ) with carbon dioxide as the calibrating gas. Measurements were made on twelve binary mixtures of approximately 20, 40, 60, and 80 vol. % argon-nitrogen, argon-helium, and argonneon. Minimum purities of these gases were specified by the manufacturer (the Matheson Company) Experimental data (6, 7), smoothed and interpolated, are presented in Table 1." A regression analysis routine was used to fit polynomials in pressures over the range of measured data. The variance of the estimateis presented with the data ( Table 2 ) . DISCUSSION OF RESULTSResults for nitrogen were compared with those measured by Johannin and Vodar ( 8 ) up to 1,000 atm., their maximum. The values agree to within 2%Results for argon, compared to those of Sengers (Q), show a variation of up to 1.2%. Bezause Sengers' argon data were measured in the same cell he used to obtain the carbon dioxide data which the authors in turn used to cali...

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