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Practical use of urinary fractional excretion

September 1994
Journal of Equine Veterinary Science 14(9):464-468

DOI:10.1016/S0737-0806(06)81968-4

Authors:

Anima Vet

In summary, the FE of electrolytes and minerals is a practical, inexpensive and useful diagnostic tool that may enable recognition of renal and metabofic problems before they progress to an extreme, severely debilitating degree. Published normal values vary widely, but several studies have demonstrated the clinical relevance of FE measurement in renal tubular disease, metabolic diseases (such as NSH and low total body K), exercise-induced rhabdomyolysis, and in the determination of Ca and P balance in horses and ponies. The method is also valid in neonatal foals.

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Acidification is required for calcium and magnesium concentration measurements in equine urine

Article

Full-text available

Jan 2024
BMC Vet Res

Background Acidification of equine urine to promote dissociation of ion complexes is a common practice for urine ion concentration measurements. The objective of this study was to evaluate the effect of acidification and storage after acidification on calcium (Ca), magnesium (Mg) and phosphate (P) concentrations and on fractional excretion (FE) of these electrolytes. Thirty-two fresh equine urine samples were analysed between December 2016 and July 2020. Complete urinalysis (stick and sediment) was performed on all samples. Ca, Mg, P and creatinine concentrations were measured in supernatant of centrifuged native urine, urine directly centrifuged after acidification and urine centrifuged 1 hour after acidification. Urine was acidified with hydrochloric acid to reach a pH of 1–2. Ca, Mg, P and creatinine concentrations were also measured in blood plasma, and fractional excretion of each electrolyte was calculated. Equality of medians was tested with Friedman tests and Bland-Altman bias plots were used to show the agreement between conditions. Results Acidification had a statistically significant effect on Ca and Mg concentrations, FECa and FEMg. Bland-Altman plot revealed a strong positive proportional bias between Ca concentration in native and acidified urine with a mean bias of 17.6 mmol/l. For Mg concentration, the difference between native and acidified urine was small with a mean bias of 1.8 mmol/l. The increase in FECa was clinically relevant. Storage of acidified urine had no effect on any of the measured ion concentrations. All P concentrations in native urine samples were below the detection limit of the assay and statistical analysis and calculation of FEP was not possible. Conclusions Urine acidification is essential for accurate measurement of Ca and Mg concentrations and therefore FE calculations in equine urine. Storage time of 1 hour after acidification does not significantly change Ca and Mg concentrations.

Blood and urinary variables in horses supplemented with electrolytes

Article

Full-text available

Jan 2014

This study was designed to evaluate changes on variables in blood, urine and water balance in horses in response to a single dose of electrolyte supplementation. The essay was conducted on a randomised 3×3 Latin Square design repeated over time, with three animals and three treatments: Treatment 1: control group (without supplementation); Treatment 2: supplementation with a medium dose of electrolytes composed of: 0.25 g of NaCl + 0.125 g of KCl + 0.05 g of CaCl + 0.025 g of MgCl per kg of BW; Treatment 3: supplementation with a high dose of electrolytes composed of: 0.625 g of NaCl + 0.3125 g of KCl + 0.125 g of CaCl + 0.0625 g of MgCl per kg of BW, equivalent to 2.5 times the medium dose of supplementation. The electrolytes were supplied through a nasogastric tube 4 h after the morning meal. The diet provided had a forage:concentrate ratio of 70:30, composed of coastcross hay and commercial concentrate, with an estimated consumption of 2% of body weigth (BW). Horses received 116 mg/kg of BW of commercial mineral salt mixed in the concentrate. Samples of blood, urine and digesta were collected over a 12 h period after supplementation for analysis of sodium, potassium, chloride, calcium and magnesium concentration. Water intake and urine output were also measured. Electrolytic supplementation enhanced (P<0.05) the water intake, water retention and urine output. Blood variables were not altered by electrolyte supplementation (P≯0.05). The supplementation also influenced the sodium and chloride excretion in urine (P<0.05). Urine physicochemical characteristics and the concentration of electrolytes excreted with time were significantly altered as a function of the electrolytes supplementation.

Renal profile and urinary fractional excretion of calcium, phosphorus, and magnesium of lambs fed with different contents of phosphorus

Article

Full-text available

Oct 2021

Obstructive urolithiasis is common in confined sheep, and a predominant factor predisposing animals to this condition is nutritional management. The objective of this study was to evaluate the effect of different concentrations of phosphorus (P) on urinalysis, serum urea and creatinine, and serum and urine concentrations of calcium (Ca), P, and magnesium (Mg), as well as to establish the fractional excretion (FE) of these elements in confined lambs. Thirty male Santa Inês x Ile de France sheep at four months of age were divided into two groups according to the diet: Group 1 (G1, n = 15), with 0.43% P in their feed; and Group 2 (G2, n = 15) with 0.65% P. The diets consisting of 10% Coast-cross hay and 90% of a concentrate of soybean meal, wheat, and crushed corn were provided for 90 consecutive days, with water ad libitum. The time points (M) of blood and urine collection were determined as M0, immediately before the beginning of the diet, and at 15-day intervals: M1, M2, M3, M4, M5, and M6. Phosphorous-rich diets favored the appearance of triple phosphate crystals in both groups, causing calculogenesis in more than one third of the animals (11/30), emphasizing the relevance of conducting laboratory tests to aid in urolithiasis diagnosis. In addition, FE revealed an increased renal excretion of excess minerals in the diet, and therefore a greater predisposition for stone formation in relation to nutritional management.

Low performance of vitamin C compared to ammonium chloride as an urinary acidifier in feedlot lambs

Article

Full-text available

Jan 2020

Obstructive urolithiasis is highly prevalent disease in feedlot sheep. Urinary acidification is effective for disease prevention. Forty-five healthy 3-4 month-old male Santa Inês crossbred feedlot lambs were distributed into three groups of 15 animals each. Ammonium chloride (GA) at 400 mg/kg/day/animal, vitamin C (GC) at 4 mg/kg/day/animal, and a combination of the two (GAC) were administered orally for 21 d. Blood and urine samples were taken 7 d before beginning treatment (M0), immediately before (M1), and weekly for 21 d (M2, M3, and M4) for renal function tests, levels of Ca, P, and Mg in serum and urine, urinalysis, and fractional excretion (FE) analysis in these minerals. In groups GA and GAC, pH decreased in M2 and remained acidic throughout the experiment. A significant decrease in serum P and a urinary increase in Ca and Mg occurred in GA. The FE of Ca increased during treatments, but there was no interference with Mg. The FE of P was significantly lower in GA. Ammonium chloride was an effective urinary acidifier in sheep, but vitamin C administered orally did not provide stable results. Thus, based on our results, vitamin C supplementation may not effective for urinary acidification to prevent obstructive urolithiasis.

Urolithiasis: A comparative study in Guzerá cattle from properties with and without the problem

Article

Full-text available

Mar 2011
PESQUISA VET BRASIL

Many factors can contribute to the formation of urinary calculi, amongst these, the nutritional imbalances and the hardness of the water consumed by ruminants. The objective of this study was to identify the characteristics of properties which predispose to urolithiasis, through the evaluation in rural properties of the water, diet, and serum and urinary determinations of calcium, phosphorus, magnesium, chlorides, sodium, potassium, calculation of the fractional electrolyte excretion (FE), and creatinine, total protein serum levels, albumin and globulins. Samples of blood and urine of bovines, Guzerá, reared semi intensively, distributed for two groups, the first one, called urolithiasis group (Gu), composed by animals with history, clinical signals and ultrasonography confirmation of urolithiasis; the second one: controlled group (Gc), without history, nor signs of the illness. The bovines of the urolithiasis group consumed water with total hardness in the concentration of 166.0mg CaCO3/L. The diet of the animals of the Gu presented greater phosphorus concentration and inadequate Ca:P relation. The levels of serum and urinary phosphorus of the animals of the Gu were higher of the Gc, as well as the serum magnesium concentration (p<0,05). The creatinine concentrations didn't have an increase in the urolithiasis group, but occurred hypoproteinemia for hypoglobulinemia in the Gu (p<0,05). The FEs of calcium, phosphorus and sodium had not differed between the groups (p>0,05), but had significant reduction in the FEs of magnesium, chlorides and potassium of the urolithiasis group (p<0.05). The union of these factors contributed for urolithiasis occurrence, being the total hardness of the water and the high phosphorus diet concentration the major factors in genesis of the calculations in bovines.

Disorders of the Urinary System

Chapter

Jan 2018

Diagnostic value of renal function tests in horses

Article

Jul 2012
PRAKT TIERARZT

Renal diseases are common in horses with underlying severe systemic disease such as colic, sepsis, diarrhea and myopathy. Besides endoscopy of the urinary tract and ultrasound of the kidneys different laboratory parameters can help in gaining additional information on renal function. In such cases it is crucial to diagnose the disease and to provide a prognosis for the affected horse. Routinely blood urea and creatinine values are measured in horses with suspected renal disease. As urea production is proportional to dietary protein content creatinine is more suitable to diagnose renal disease. Creatinine and urea increase if the majority of nephrons (75 %) become nonfunctional. There are different creatinine- and urearatios helping to define the cause of renal impairment (prerenal/renal; acute/chronic). Determination of urine specific gravity gives additional information on function and concentrating ability of the kidneys. Glomerular filtration rate is the volume of plasma filtered per unit of time and is representative of glomerular function, whereas fractional electrolyte clearance gives information on the tubules where electrolytes are secreted or reabsorbed. Determination of serum electrolyte values is only significant in combination with fractional electrolyte clearance. Furthermore identification of gamma-glutamyltransferase in urine serves as an indicator for degeneration of tubular cells. This article shows that via determination of selected parameters numerous information on localisation and degree of renal function impairment can be obtained.

Disorders of the Urinary System

Chapter

Dec 2004

Maintenance fluid therapy in horses

Article

Jan 2015

K. Gary Magdesian

Maintenance fluid therapy is the provision of fluid and electrolytes necessary to maintain homeostasis of body water and electrolyte content on a daily basis. Maintenance fluids are generally considered to be hypotonic, unless free water needs are met through drinking; maintenance fluids often contain a higher concentration of potassium than do replacement fluids intended for the extracellular fluid (ECF) as potassium is the primary intracellular cation. Potassium may become deficient in horses off feed and receiving IV fluids without potassium supplementation. In addition to electrolytes, maintenance fluids may also contain dextrose; these dextrose-containing maintenance fluids may be isotonic in vitro, but effectively hypotonic as soon as dextrose is metabolized in vivo. A component of monitoring the adequacy of maintenance fluid therapy is evaluation for clinical signs of dehydration. Adverse effects of maintenance fluid therapy include fluid overload, catheter-related problems, and electrolyte disturbances.

Kidney Function and Damage

Chapter

Dec 2008

This chapter elaborates the biochemistry of kidney functions and diseases. Clinical biochemistry in nephrology is mainly used to diagnose and monitor renal dysfunction or damage. This is of special importance in human medicine, because of the frequent observation of renal failure in elderly people, and in canine and feline medicine, especially for the early detection of chronic renal failure. Kidney diseases are uncommon in equids and cattle. The latter show better resistance to a loss of kidney function than monogastric animals because of the filtration function of the rumen epithelium. The mammalian kidney consists of tens of thousands to millions of nephrons that function as parallel units. The larger the species, the greater the number of nephrons per kidney. This chapter begins with discussing the general structure of the kidneys. The chapter then describes the glomerulus and filtration process in kidney. Direct and indirect tests of glomerular function are explained. The chapter also discusses some tests of kidney damage. The chapter concludes with a discussion on biochemical changes that occur during some kidney diseases.

Clinical and biochemistry findings, and parathyroid hormone concentrations in three horses with secondary hyperparathyroidism

Article

Full-text available

Oct 1992

Three cases of horses with nutritional secondary hyperparathyroidism (NSH) are described. The horses showed typical thickening of the maxillae and mandibular bones with or without lameness. Laboratory findings included elevated concentrations of parathyroid hormone (carboxy-terminal and mid-molecule fractions), alkaline phosphatase and an increase in the fractional excretion rate of serum inorganic phosphorus.

Renal Clearance and Fractional Excretion of Electrolytes Over a 24-Hour Period in Horses

Article

Full-text available

Dec 1984

Four consecutive 6-hour urine collections were obtained from 10 healthy adult horses given free access to a complete pelleted ration and water. Samples of blood were collected from the jugular vein at the start of the test period and then every 6 hours for 4 consecutive samples. Mean renal clearance of creatinine (CCr) varied significantly during the four, 6-hour collections, ranging from 1.474 in period II to 2.702 ml/min/kg of body weight during period III (P less than 0.05). The CCr in period III was significantly different from the 24-hour mean value of 1.877 ml/min/kg (P less than 0.05). The mean 6-hour clearances of potassium (CK), chloride (CCl), and calcium (CCa) also varied significantly during the 4 collections (P less than 0.05). The 24-hour mean CK and CCl were different from the mean during period III (P less than 0.05). There was significant correlation between mean 24-hour CCr and CK (P less than 0.01); CCr and CCl (P less than 0.05); CNa and CK (P less than 0.01); CNa and CCl (P less than 0.01); and CK and CCl (P less than 0.001). The 95% confidence interval for 6-hour mean values of fractional excretion of Na (FENa) was 0.032% to 0.522%; FEK was 23.345% to 48.074%; FECl was 0.588% to 1.861%; and FECa was -0.158% to 6.723%. Although FENa, FECl, and FECa were highly variable within and between individual horses, mean values for periods I to IV did not differ significantly over time or from 24-hour mean values. The FEK varied less throughout the 24-hour test period. Mean urine volume, urine concentrations of Cr and K, urine osmolality, urine-to-plasma osmolality, urine-to-plasma urea nitrogen, and plasma urea nitrogen varied significantly through time periods I to IV (P less than 0.05); however, means for time periods I to IV were not different from 24-hour means.

Urine clearance ratios as a diagnostic aid in equine metabolic disease

Article

Jan 1976

Renal Clearance, Urinary Excretion of Endogenous Substances, and Urinary Diagnostic Indices in Healthy Neonatal Foals

Article

Jan 1991

Urine (U) and serum (S) were obtained every 2 hours during a 12- or 24-hour period from eight healthy 96-hour-old pony or horse foals. Dams' milk samples were obtained concurrently. Urine volume was measured during this 12- or 24-hour period. The mean amount of urine produced was 148 ± 20 ml/kg/day. Baseline urinalyses were evaluated on all foals at two days of age, before any manipulation. Urine generally was dilute (< 1.008) but the specific gravity was as high as 1.027 in one normal foal. Continuous (12 or 24 hour) urinary catheterization resulted in bactiuria but not white blood cells in the urine. Prolonged catheterization did not cause foals to become febrile or exhibit clinical signs of cystitis or other illness. Urinary electrolyte excretion, urinary electrolyte clearances, and fractional electrolyte excretions (FE) were measured. When compared with normal values reported in adult horses, excretion, clearance, and FE were similar for sodium (Na) but higher for potassium (K), phosphorus (P), and calcium (Ca). There were no significant differences between data collected during different time periods, and it was concluded that the use of single sample urine/serum estimates of fractional excretion in the neonatal foal was an appropriate indicator of the renal handling of electrolytes, and when viewed in conjunction with urinalysis and other serum parameters, a valuable aid to evaluating renal function.

The use of creatinine clearance ratios in the prevention of equine rhabdomyolysis: A report of four cases

Article

Dec 1988

Reliability of single-sample phosphorus fractional excretion determination as a measure of daily phosphorus renal clearance in equids

Article

Apr 1983

In 4 healthy horses and 1 Welsh pony, fractional renal excretions of phosphorus (FEp) determined from 9 hourly time collections taken over a 24-hour period were compared to assess whether a single-sample collection would be an accurate indicator of the daily FEp. The mean FEp for each animal varied from 0.115% to 0.302%; the 2 animals with the highest values were significantly different (P less than 0.05) from the 3 with the lowest values. Individual variation within animals was not great, however, because it was calculated that the 24-hour FEp value could be found within +/- 0.087% of the single sample value 95% of the time in a given animal.

Percent creatinine clearance ratios

Article

May 1980
Vet Med Small Anim Clinician

J Coffman

Urinary indices for differentiation of prerenal azotemia and renal azotemia in horses

Article

Mar 1982
JAVMA-J AM VET MED A

The urine urea nitrogen/plasma urea nitrogen ratio (Uun/Pun), urine creatinine/plasma creatinine ratio (Ucr/Pcr), urine osmolality/plasma osmolality ratio (Uosm/Posm), and fractional excretion of filtered sodium (FENa) were evaluated in 16 horses with acute azotemia to ascertain the significance of each index in the differentiation of prerenal azotemia from renal azotemia. Renal azotemia was diagnosed when renal biopsy or postmortem histologic examination demonstrated evidence of organic renal disease or when azotemia was found in the presence of isosthenuria. The diagnosis of prerenal azotemia was based on the absence of renal histologic lesions or stabilization of blood urea nitrogen and serum creatinine soon after therapy. In 10 horses with renal azotemia, Uun/Pun was 2.1-14.3, Ucr/Pcr was 2.6-37.0, Uosm/Posm was 0.8-1.7, and FENa was 0.08-10.0. In 6 horses with prerenal azotemia, Uun/Pun was 15.2-43.7, Ucr/Pcr was 51.2-241.5, Uosm/Posm was 1.7-3.4, and FENa was 0.02-0.50. The values for each of these indices differed significantly between the 2 groups of horses (P less than 0.05). It was concluded that these indices were of value in the early classification of renal failure in the horse and that this information could be utilized in planning of therapy of acute azotemia in the horse.

Assessment of the Calcium and Phosphorus Nutrition in Horses by Analysis of Urine

Article

May 1982

Studies were made to determine if a practical assessment of the calcium and phosphorus nutrition of horses could be obtained from an analysis of urine samples. The concentrations of Ca and P in urine samples changed markedly when groups of 4 mares were fed diets containing from 1.0 to 3.9 g Ca/kg and from 1.5 to 6.1 g P/kg, but serum concentrations of Ca and P remained relatively constant. The concentrations in single urine samples were considered unreliable indicators of excretion of the minerals because of variations in water excretion, and two methods to overcome this problem were examined. In one method, the creatinine clearance ratios (%Cr) of Ca and P were calculated. The other method was simpler, and concentrations of the minerals were expressed as the ratio of the total solute concentration. Both of these methods appeared to give reliable estimates of the excretion of Ca and P in urine, and there were significant relationships between the values obtained for horses fed diets containing a wide range of Ca and P. When the horses were fed adequate Ca, the Ca‐%Cr was greater than 2.5% and P‐%Cr was less than 4%. The corresponding ratios of mineral concentration to solute concentration were greater than 15 μmole Ca/mosmole and less than 15 μmole P/mosmole. When a low Ca (1.0 g/kg) and high P (4 g/kg) diet was fed, the excretion of Ca and P had changed markedly after 3 days and could be monitored in single samples of urine by either method. It was concluded that a practical assessment of the Ca and P nutrition of horses could be obtained from an analysis of urine samples to determine if the diet is either low, adequate or high in Ca, and high in P.

Potassium concentrations in muscle, plasma and erythrocytes and urinary fractional excretion in normal horses and those with chronic intermittent exercise-associated rhabdomyolysis

Article

Aug 1993
RES VET SCI

Potassium concentrations were measured in semimembranosus muscle, plasma and erythrocytes, and the urinary fractional excretion determined in normal horses and those that had chronic intermittent exercise-associated rhabdomyolysis. Muscle from the rhabdomyolysis horses was also evaluated microscopically. The horses with rhabdomyolysis had a lower muscle potassium concentration on a dry weight basis. Although the wet weight potassium content was also lower, the difference was not significant. Urinary fractional excretion of potassium (and also sodium and chloride) did not differ significantly between the two groups although the rhabdomyolysis group had a lower percentage excretion of potassium. Erythrocyte potassium concentration was similar for both groups. Low grade to moderate degenerative myopathy or absence of lesions was seen on microscopic sections of muscle from horses with rhabdomyolysis; only one had a vacuolar myopathy and potassium content was not determined. These results suggest that altered muscle potassium content may be a factor in rhabdomyolysis.

Practical use of urinary fractional excretion

Abstract

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