Assessment of Renal Injury by Urinalysis

Urinalysis provides a unique opportunity to selectively and non-invasively sample a single target organ by examination of its endproduct. The levels of proteins and small molecules normally filtered, excluded from filtration, secreted or reabsorbed by the tubules can be used as indicators of the functional status of certain nephron segments, while injury can be assessed by examination of cellular enzymes which are preferentially leaked into the urine (Loeb 1998), or proteins which are either upregulated or leaked in circumstances of cellular injury and subsequently appear in the urine. 

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. 

Glucosuria in the face of normal plasma glucose may indicate a functional deficit in the proximal tubule that may precede the appearance of actual tubular necrosis or injury (Stonard et al. 1987 Finco 1997 Loeb and Quimby 1999 Newman and Price 1999 Aleo et al. 2002). Glucosuria is normal in gerbils. 

Excretion of markedly elevated levels of protein is indicative of glomerular disease, whereas low-level proteinuria indicates tubular damage or very early/lowgrade glomerular injury (Peterson et al. 1969 Finco 1997). Further determination of the severity and 

The presence of greater than 1-2 erythrocytes or neutrophils per high-power field confirms a positive result of dipstick analysis for blood or leukocyte esterase. Increased number of hyaline casts (small numbers are normal in most species), or the presence of granules (cells or cellular debris) within casts may be indicative of tubular injury. The presence of renal tubular epithelial cells in urine sediment strongly indicates tubular injury (Stonard 1990 Hofmann et al. 1994 Finco 1997 Finn and Porter 1998 Newman and Price 1999). 

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Twenty-four hour urine collection is preferred for best accuracy, although point-in-time samples can be used. Urine samples are collected from the species in question by appropriate methods (see section Assessment of Renal Injury by Urinalysis ). Total protein and creatinine are determined by appropriate methods (see under Assessment of Renal Injury by Serum Chemistry and Assessment of Renal Injury by Urinalysis ) and a urine proteimcreatinine ratio is calculated. 

Urine samples are collected and maintained as described in section Assessment of Renal Injury by Urinalysis . There are some special considerations in sample collection and handling that are critical to accurate assessment of urine enzyme activity (Vander-linde, 1981 Price, 1982 Plummer etal. 1986 Mueller et al. 1986, 1989, Loeb et al. 1997, Clemo 1998, Jung and Grutzmann 1988, Loeb 1998) ... 

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