Urine creatinine determination

Nitrogen compounds commonly determined are creatinine, urea, and uric acid. Creatinine is an end product of the energy process occurring within the muscles, and is thus related to muscle mass. Creatinine in urine is commonly used as an indicator and correction factor of dilution in urine. Creatinine in serum is an indicator of the filtration capacity of the kidney. Urea is the end product of the nitrogen luea cycle, starting with carbon dioxide and ammonia, and is the bulk compoimd of urine. The production of uric acid is associated with the disease gout. In some cases, it appears that the excess of uric acid is a consequence of impaired renal excretion of this substance. 

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. 

The inherent limitations of the Jaffe method for determination of creatinine have been discussed in section Assessment of Renal Injury by Serum Chemistry . Factors which result in reduced excretion of creatinine without acute tubular injury (e.g., chronic renal disease in aged animals with pronounced loss of nephron mass, prerenal reduction of GFR) will also result in reduced urine creatinine and falsely elevated enzyme activity when normalized to creatinine (Price 1982, Plummer et al. 1986, Casadevall et al. 1995). 

Serum was either used for measuring FSH immediately or frozen until hormone determination. FSH and creatinine in urine were determined immediately. Additional urine samples were obtained to determine assay characteristics. In order to determine storage conditions, urine samples were stored at room temperature, at 4°C, at -20°C without any addition, and at — 20°C with addition of glycerol. After 1 and 4 weeks, FSH and creatinine were determined again. 

Campins, P. Tortajada, L.A. Meseger, S. Blasco, F. Sevillano, A. Molins, C. Creatinine determination in urine simples by batchwise kinetic procedure and for injection analysis using the Jaffe reaction Chemometric study. Talanta 2001, 55, 1079-1089. 

Creatinine, an endogenous end product of muscle metabolism, is often measured in plasma and urine to determine creatinine clearance. Since, creatinine is freely filtered at the glomerulus and is not reabsorbed or secreted by the proximal tubule of most species, creatinine clearance provides a good measure of the GFR. Another endogenous compound, urea, is also cleared mainly by renal filtration and excretion. Increases in the blood or serum concentration of urea are indicative of decreased GFR. However, increases in BUN concentration occur only after substantial renal damage has been established. Thus, BUN concentration is not a sensitive indicator of nephrotoxicity and changes usually occur later than changes in other parameters (e.g., enzymuria). 

B. Other useful laboratory studies include electrolytes, glucose, BUN, creatinine, calcium, ammonia, liver transaminases, bilirubin, prothrombin time (PT), amylase, serum osmolality and osmolar gap (see p 32 serum levels > 1500 mg/L may increase the osmolar gap by 10 mOsm/L or more), arterial blood gases or oximetry, and EGG monitoring. Valproic acid may cause a falsepositive urine ketone determination. 

Blood samples were taken Monday, Wednesday and Friday in the morning before breakfast. Urine samples were collected during 2k hours daily. To check for errors in the urine collection endogenous creatinine in blood and urine were determined. Uric acid was measured by our modification [ ZtJLLNER, I963 ] of the uricase method. 

CDU should be reported as ng Cd/g CRTU, whiie B2MU should be reported as ng B2M/g CRTU. To derive the ratio of cadmium or B2M to creatinine, CRTU shouid be reported in units of g crtn/l of urine. Depending on the analytical method, it may be necessary to convert results of creatinine determinations accordingly. 

Pataki [121] has detected creatinine in urine on cellulose-D-layers. This procedure enables the creatinine to be separated from other JafF6-chromogens which interfere in the colour reactions on which many methods of determination are based. Quantitative evaluation of the creatinine spots, obtained using picric acid/sodium hydroxide, is possible since there is a linear relation between the square root of the spot surface area and the logarithm of the amount of substance applied (see p. 136) [122]. The rehabihty of the creatinine determination has been tested by parallel determinations of various amounts of creatinine in standard solutions and in urine. Tests on recovery gave a value of 95.7 3.4% of the creatinine added. Up to 20 (xg creatinine or ca. 20 [xl urine can be used in one determination larger amounts can lead to overloading of the layer. 

The GU levels of five healthy human urines were determined by this method. GU concentration being estimated to be 0.038 - 0.132 jig/mg creatinine with an average of 0.092 as shown in the figure 3. The result on the distributions of urea and serum GU level of normal rats and streptozotocin induced hyperglycemia rats is shown in Figure 4. The concentrations of GU in urine of streptozotocin-induced rats were significantly higher than that of normal rats. 

Representative Method Although each chemical kinetic method has its own unique considerations, the determination of creatinine in urine based on the kinetics of its reaction with picrate provides an instructive example of a typical procedure. 

Description of Method. Creatine is an organic acid found in muscle tissue that supplies energy for muscle contractions. One of its metabolic products is creatinine, which is excreted in urine. Because the concentration of creatinine in urine and serum is an important indication of renal function, rapid methods for its analysis are clinically important. In this method the rate of reaction between creatinine and picrate in an alkaline medium is used to determine the concentration of creatinine in urine. Under the conditions of the analysis, the reaction is first-order in picrate, creatinine, and hydroxide. 

This experiment includes instructions for preparing a picrate ion-selective electrode. The application of the electrode in determining the concentration of creatinine in urine (which is further described in Method 13.1) also is outlined. 

Although determination of creatinine clearance rate is a standard clinical procedure, it is difficult to carry out mainly because accurate collection of total urine output over a 24-hour period is required. It can never be certain that this requirement has been met. Since creatinine is produced continuously in muscle and is cleared by the kidney, renal failure is characterized by elevated serum creatinine levels. The degree of elevation is directly related to the degree of renal failure—if it is assumed that the production of creatinine in the muscle mass is constant and that renal function is stable. When these assumptions are valid, there is a direct relationship between serum creatinine level and kanamycin half-life, as shown in Fig. 9. The equation of the line in Fig. 9 is... 

The urine samples were analyzed using a modified version of a published method.8 The method involved fortification of the urine samples with an internal standard 3,4,5-trichloro-2-pyridinyl, which is a structural isomer of the 3,5,6-TCP metabolite of chlorpyrifos hydrolysis of labile acid conjugates to 3,5,6-TCP solvent extraction derivitization to the f-butyl-dimethylsilyl ester of 3,5,6-TCP and subsequent negative-ion chemical ionization gas chromatography/mass spectrometry (GC/MS) analysis. Creatinine was determined in urine using a modification of a method of Fabiny and Erting-shausen.9... 

To monitor the absorbed chlorpyrifos doses in human volunteers, urine was collected before and following a 4-hr activity period on the treated grass surface(re-entry). The urine was analyzed for 3,5,6-trichloropyridinol (3,5,6-TCP), the urinary metabolite of chlorpyrifos, and creatinine, which was determined to verify completeness of urine collection by each volunteer. 

Although the measurement of GFR with inulin is quite accurate, it is inconvenient because it requires the continuous infusion of this exogenous substance for several hours. More often, in clinical situations, the plasma clearance of creatinine is used to estimate GFR. Creatinine, an end-product of muscle metabolism, is released into the blood at a fairly constant rate. Consequently, only a single blood sample and a 24-h urine collection are needed. Measurement of the plasma clearance of creatinine provides only an estimate of GFR in fact, this measurement slightly overestimates it. A small amount of creatinine is secreted into the urine (about 10% on average). In other words, the concentration of creatinine in the urine is the result of the amount filtered (as determined by GFR) plus the amount secreted. 

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