Glomerular filtration rate calculation

Harmoinen A, Lehtimaki T, Korpela M, Turjanmaa V, Saha H. Diagnostic accuracies of plasma creatinine, cystatin C, and glomerular filtration rate calculated by the Cockcroft-Gault and Levey (MDRD) formulas. Clin Chem 2003 49 1223-5. 

The glomerular filtration rate (GFR) in normal males is estimated to be 125mL/min, and the results of the example calculation suggest that the drug is cleared by GFR. If the RCR had been less than 125 mL/min, tubular reabsorption of the drug would have been suspected. If it had been greater than 125 mL/min, tubular secretion would have been involved in the drug elimination. 

Blood samples were centrifuged at 1000 x g for 20 min at 0-4°. Ionized calcium levels were immediately determined in serum and urine samples using a calcium ion-selective electrode (Ionetics, Inc., Costa Mesa, CA) urine volumes were recorded. The remaining serum and urine were aliquoted for various analyses and stored at -40°. Serum insulin was analysed by radioimmunoassay (Amersham Corp., Arlington Heights, IL). Serum levels of total calcium, phosphorus and creatinine as well as urine creatinine were determined by colorimetric procedures using an automated analyzer (Centrifichem, Baker Instruments Corp., Pleasantville, NY). Glomerular filtration rates (GFR) were calculated from serum and urine creatinine data GFR = urine creatinine/serum creatinine. 

Jenkins et al. developed a capillary electrophoresis system for the measurement of iohexol as a marker of the glomerular filtration rate (GFR) with a run time of 5.25 min and a coefficient of variation (CV) of 4.3% at 80 mg L" [121]. The GFR, calculated from the plasma clearance, had a reproducibility of 5.47 %. A similar approach (liquid chromatography-mass spectrometry with positive electrospray ionization after enrichment by solid phase extraction) was applied by Putschew et al. for the determination of iodinated contrast agents in treatment plant effluents and surface waters [118]. 

After the equilibration period, clearance periods of 20 min are used. Urine samples are collected and perfusate is obtained at midpoint of the clearance period for the evaluation of overall kidney function. For determination of glomerular filtration rate (GFR) and fluid transport, 3H-labelled polyethylene glycol is added to a modified Krebs-Henseleit bicarbonate buffer. Electrolytes are determined in urine by standard flame photometry. Fractional excretions of water, electrolytes and test compounds are calculated. 

As an alternative to the standard clearance techniques which involve the collection of urine over a known period of time plus maintaining a constant plasma level of an appropriate marker, the glomerular filtration rate can be calculated from the rate of disappearance from the plasma of any tracer, where ... 

Indapamide did not significantly affect the function of patients with renal impairment and did not accumulate in the blood. In addition, the calculated half-life for indapamide in hypertensive hemodialysis patients is found to be very similar to the half-life observed in hypertensive patients with normal and compromised renal function (30). No adverse effect of indapamide on renal function is evident in normal volunteers, hypertensive patients or geriatric hypertensive patients after monitoring glomerular filtration rate or effective renal plasma flow (24). 

Creatinine has no useful function and is eliminated by renal glomerular filtration and to a small extent by renal tubular secretion. Creatinine clearance approximately parallels the glomerular filtration rate (GFR) and is used as a kidney function test. It is calculated as follows ... 

The ability of tubules to reabsorb or secrete a substance is variable. The maximum amount of a substance that the tubules can either reabsorb or secrete in 1 minute is called the Tm for that substance. ( T refers to the tubule and m stands for maximal). This parameter can be calculated by infusing the substance of interest intravenously until the capacity of the tubules to reabsorb or secrete that substance is exceeded. The reabsorptive capacity of the tubules (Tm) can be calculated by knowing the concentration of the substance of interest in both urine and plasma (Ps and U5, respectively), the rate of urine flow per minute (V), and the glomerular filtration rate (GFR). The formula for calculation of reabsorptive Tm for a substance is... 

For example, at low and high rates of urine flow, the minimal and maximal values of the may vary from 30% to 60% of the glomerular filtration rate. This occurs because various tubular segments are permeable to urea and allow passive reabsorption to occur under conditions of antidiuresis. The fractional excretion of urea (FE ,pa) is calculated as [(urine urea/ plasma urea)/(urine creatinine/plasma creatinine) x... 

Other studies have reported on examples for both intra- and inter-individual variations for canine thyroid function (Jensen and Hpier 1996), glomerular filtration rate (Kampa et al. 2002), and urine osmolality (van Vonderen, Kooistra, and Rijnberk 1997). Some data have been published for biological variations and critical difference calculations for dogs (e.g., fructosamine [Jensen and Aaes 1992] and acute phase proteins [Martinez-Subiela et al. 2003]) and for rabbits [Jensen, Wedp, and Bantz 1992]. 

Goates JJ, Morton KA, Whooten WW, Greenberg HE, Datz EL, Handy JE, Scuderi AJ, Haakenstad AO, and RE Lynch (1990). Comparison of methods for calculating glomerular filtration rate technetium-99m-DTPA scintigraphic analysis, protein-free and whole-plasma clearance of technetium-99m-DTPA and iodine-125-iothalamate clearance. Journal of Nuclear Medicine 31 424-429. 

Katayama R, Yamaguchi N, Yamashita T, Watanabe S, Satoh H, Yamagishi N, Finnhama K (2010) Calculation of glomerular filtration rate in conscious rats by the use of a bolus injection of iodixanol and a single blood sample. J Pharmacol Toxicol Methods 61 59-64 Kaul S, Diamond GA (2010) Diabetes breaking news Rosiglitazmie and cardiovascular risk. Nat... 

First-pass Gd-enhanced acquisitions allow, in the same time, to measure glomerular filtration rate. Several models have been proposed and GFR maps can also be calculated but validation with reference methods is still required (Fig. 3.42). 

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