Urine creatinine

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. 

Direct measurement of creatinine clearance (CrCl) requires collection of urine over an extended time interval (usually 24 hours) with measurement of urine volume, urine creatinine concentration, and serum creatinine concentration (Table 22-1). Because kidney function can fluctuate significantly during ARF, this method may underestimate or overestimate kidney function depending on whether ARF is worsening or resolving. 

Ucr = urine creatinine concentration, mg/dL V = volume of urine, mL Scr = serum creatinine concentration, mg/dL T = time of urine collection, minute (Note time equals 1440 minutes for a 24-hour collection)... 

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. 

Apply the same reasoning to this as to the level (concentration) of any other substance in the blood -be it a drug or an endogenous chemical. An unchanging plasma creatinine means, if volume of distribution is unchanged, that input equals loss from the plasma into the urine. Creatinine comes from creatine released continuously from our muscles. In old age muscle mass is less, and the input of creatine... 

Many commercial laboratories run renal profile tests that include proteinuria, urine creatinine, and serum urea nitrogen, as well as other clinical parameters pertinent to the development of renal dysfunction. Although these services tend to be expensive, they offer a fast and reliable way to measure a range of parameters. 

While low serum cholesterol levels have been observed in malnourished patients, largely as a result of decreased synthesis of lipoproteins in the liver, hypocholesterolemia occurs later in the course of malnutrition and is therefore not useful as a screening test. PEM usually results in low serum urea nitrogen (BUN), urinary urea, and total nitrogen. Estimation of 24-h urine creatinine excretion is also a valuable biochemical index of muscle mass (when there is no impairment in renal function). The urinary CHI is correlated to lean body mass and anthropometric measurements. In edematous patients, for whom the extracellular fluids contribute to body weight and spuriously high body mass index values, the decreased CHI values are especially useful in diagnosing malnutrition. 

The urine creatinine concentration should be used to normalize the quantity of any analyte of interest, as this will correct for incomplete urine collection or urine dilution that may have resulted from drinking water spillage within the metabolism cages (Haas et al. 1997). The quantity of creatinine in a spot urine sample serves as an accurate index of the 24 hour urine output in most species. 

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). 

Renal failure In about 50% of patients with acute hver failure, renal insufficiency develops. This can be expressed in three forms (7.) prerenal kidney failure due to hypovolaemia, (2.) acute tubular necrosis, mainly secondary as a result of circulatory hypotension with cylindruria, a higher concentration of sodimn in the urine (50—70 mmol/1) and a reduced urine creatinine/ser m creatinine quotient (<20) or urine urea/serrrm urea quotient (<3), or (3.) hepatorenal syndrome. (41) (s. tab. 17.3)... 

It should be noted that for urinary excretion studies the preferred design is to collect 24 h urine. In some special designs it can be argued that the use of spot urine samples and correction for urinary creatinine concentration may be a valid measure. A prerequisite for the spot urine - creatinine correction design is a solid argumentation that creatinine excretion is unchanged by the experimental condition or that it is not different between groups. A theoretical example is comparison of lean men versus fat females. Their cell number is comparable but muscle mass very different. Creatinine excretion is mainly... 

The quantity of urine creatinine is generally constant for an individual and approximately proportional to muscle mass. 

Urine creatinine is used to adjust the values of urinary biological indicators for example, creatinine measurements are necessary for correction of vanilmandelic and homovanillic acids, which indicate neuroblastoma and pheochromocytoma, when excreted in urine in abnormally increased concentrations. Ratios of vanilmandelic and homovanillic acids to creatinine have been utilized as a diagnostic index of these diseases. 

E275 Mauck, J.C., Mauck, L., Novros, J., Norton, G.E. and Toffaletti, J. (1986). Development of a single slide Kodak Ektachem thin-film assay for serum and urine creatinine. Clin. Chem. 32, 1197-1198, Abstr. 735. 

Note The reagent carrier as described is not intended for urine-creatinine assay. In spite of this, however, several studies conducted with this sample material have been published. 

Sugita O, Uchiyama K, Yamada T, Sato T, Okada M, Takeuchi K. Reference values of serum and urine creatinine, and of creatinine clearance, by a new enzymatic method. Ann CHn Biochem 1992 29 ... 

AH samples must be protected from light urinary porphyrin concentrations can decrease by up to 50% if kept in the light for 24 hours. Urinary porphyrins and PBG are best analyzed in fresh, random (10 to 20 mL) samples collected without preservative. Very dilute urine (creatinine less than 4 mmol/L) is unsuitable for analysis. 

Reference intervals are given in Table 32-3. Scanning the spectrum of the product is essential if interferences are to be identified. Imipenem, for example, often gives a peak at 580 nm with Ehrlich s reagent. The coefficient of variation at the cutoff of 9jjniol/L is approximately 10%, but becomes considerably less precise at lower concentrations. For this reason, very dilute urines (creatinine <1.5 pmol/L) are unsuitable. 

More recently, this method has been adapted for the measurement of NTx in serum. The use of serum eluninates the need to measure urine creatinine to correct for urine concentration and significantly reduces the within-subject day-to-day variation in NTx measurements. 

Einbrodt et al. (1976) exposed students to 0.26-0.92 ppm formaldehyde vapors for 3 hours, with urine samples collected immediately after exposure and 21 hours after exposure. Urine formaldehyde and urine formic acid (formate) concentrations were found to be higher immediately after exposure compared to 21 hours later however, no baseline sample was obtained prior to exposure. If historic formaldehyde and formic acid baseline levels were assumed, then a closer examination of these data indicates that more formaldehyde (and metabolite) was excreted in the urine than could have possibly been absorbed by inhalation, indicating another route of exposure (perhaps dermal), or co-exposure to another chemical that also has formate as a metabolite (e.g., methanol), or higher personal exposures than were actually measured. There was also no indication that the urine formate levels were adjusted to compensate for urine specific gravity using urine creatinine levels, which may have markedly influenced the test results. 

Normalization of Cannabinoid Urine Concentrations to Urine Creatinine Concentrations... 

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