Urinary Orotic Acid Research Articles

In vivo assessment of mutations in OTC for dominant-negative effects following rAAV2/8-mediated gene delivery to the mouse liver

Mutant proteins have the potential to exert dominant-negative effects that might limit the therapeutic efficacy of their wild-type counterparts after gene transfer. For ornithine transcarbamylase (OTC) deficiency, in vitro studies have suggested the presence of dominant-negative effects, however, supporting in vivo studies have not been conducted. In this study, we exploited the capacity of recombinant adeno-associated virus (rAAV) 2/8 vectors to deliver transgenes to the mouse liver with high efficiency to determine whether expression of selected OTC mutant proteins exert inhibitory effects on endogenous wild-type OTC enzymatic activity. Using site-directed mutagenesis we constructed three OTC mutants with a theoretical or reported in vitro capacity to exert dominant-negative effects, and delivered these to the liver using rAAV2/8. Each mutation had been earlier identified in patients with OTC deficiency. Treated mice showed no increase in urinary orotic acid levels or reduction in OTC activity despite supra-physiological expression of the mutant proteins, consistent with an absence of dominant-negative effects. These data have important implications for the development of gene therapy strategies for OTC deficiency and validate a model system in which potential dominant-negative effects of specific mutations in prospective patients can be examined empirically before gene therapy.

Orotic Acid Excretion and Arginine Metabolism

The urinary excretion of orotic acid, an intermediate in the pyrimidine biosynthetic pathway, is markedly increased in many inborn errors of the urea cycle and in a number of other disorders involving arginine metabolism. Carbamoyl phosphate, which accumulates within hepatic mitochondria in patients with ornithine transcarbamoylase deficiency, can diffuse to the cytosol and enter the pyrimidine pathway, resulting in greatly increased orotic acid production and excretion. This orotic aciduria also occurs in inborn errors of the mitochondrial ornithine/citrulline transporter, arginase, argininosuccinate synthetase, and argininosuccinate lyase. Increased orotic acid excretion is also found in a number of hypoargininemic states, such as lysinuric protein intolerance. However, orotic aciduria should not be used uncritically as an index of arginine deficiency because it is found in patients with arginase deficiency who exhibit hyperargininemia. Increased orotic acid excretion can also arise as a result of impairments of pyrimidine synthesis, whether brought about by a genetic defect (e.g., in UMP synthase) or by drugs that inhibit the terminal part of the pathway (e.g., allopurinol or 6-azauridine). When used appropriately, measurement of urinary orotic acid is a valuable tool for the study of many derangements of arginine metabolism, including arginine depletion, and to assess the efficacy of therapies used to replete this amino acid.

Renal Fanconi syndrome with ultrastructural defects in lysinuric protein intolerance

Renal Fanconi syndrome developed rapidly in a 3-year-old Moroccan girl with established lysinuric protein intolerance. She was hospitalized because of lowered consciousness, uncoordinated movements and hepatosplenomegaly after a febrile period. Laboratory investigations revealed plasma ammonia 270 micromol/L (normal <70 micromol/L), ferritin 159 micromol/L (normal 2-59 micromol/L), LDH 1180 U/L (normal 26-534 U/L). LPI was diagnosed based on the findings of reduced plasma ornithine, arginine and lysine, and an increased level of glutamine. Urinary orotic acid (645 micromol/mmol creatinine; normal <3.6) was strongly increased. A defect in the SLC7A7 amino acid transporter was established (homozygous c.726G > A mutation). Detailed renal function tests including an acid challenge test, bicarbonate loading, and tubular maximal reabsorption of glucose showed complex tubular dysfunction. No evidence of respiratory chain defects was found in muscle or kidney tissue. No morphological abnormalities were demonstrated in the mitochondria. Ultrastructural analysis of proximal tubular cells showed vacuolization and sloughing of the apical brush border (Fig. 1). Renal involvement in LPI has only been described in a few reports; however, no detailed studies of the renal acidification mechanism were performed. Our patient had evidence of a full-blown Fanconi syndrome. Surprisingly, a metabolic acidosis was found with a moderately increased serum anion gap combined with repeatedly normal plasma organic acid values. This finding is in contrast with the diagnosis of renal tubular acidosis. Patients with hyperlysinaemia have a similar heavy load on the renal tubules; they never develop a renal Fanconi syndrome. Therefore, we consider the intratubular accumulation of lysine an unlikely candidate for the development of the renal Fanconi syndrome.

Low citrulline may not be diagnostic of ornithine transcarbamylase deficiency: A case report

A newborn boy with family history of severe ornithine transcarbamylase (OTC) deficiency was investigated prospectively and managed aggressively at birth based on an existing protocol for at risk neonates. Undetectable citrulline levels at birth suggested that the infant was affected; however, normal plasma glutamine and urine orotic acid levels confused the diagnosis to some extent. Mutation testing confirmed that the patient did not have OTC deficiency. Thus the low plasma citrulline level did not validate our initial biochemical suspicion of OTC deficiency, and this highlights the importance of considering all available clinical, biochemical and molecular evidence in determining disease status.

Citrin Deficiency: A Novel Cause of Failure to Thrive That Responds to a High-Protein, Low-Carbohydrate Diet

The proband was born at 36 weeks, appropriate for gestational age, to nonconsanguineous white parents. There was no evidence of hyperbilirubinemia or intrahepatic cholestasis in the neonatal period, and she had normal newborn screen results. She presented with 3 episodes of life-threatening bleeding and anemia. The diagnostic evaluation for her bleeding diathesis revealed an abnormal clotting profile with no biochemical evidence for hepatocellular damage. She was incidentally noted to have severe growth deceleration that failed to respond to 502 kJ/kg (120 kcal/kg) per day of protein-hydrolyzed formula. An extensive diagnostic workup for failure to thrive, which was otherwise normal, included plasma amino acid analysis that revealed hyperglutaminemia and citrulline levels within the reference range. Testing of a repeat sample revealed isolated hypercitrullinemia. No argininosuccinic acid was detected. Her ammonia level and urine orotic acid were within the reference ranges. Subsequent plasma amino acid analysis exhibited a profile suggestive of neonatal intrahepatic cholestasis caused by citrin deficiency with elevations in citrulline, methionine, and threonine. Western blotting of fibroblasts demonstrated citrin deficiency, and a deletion for exon 3 was found in the patient's coding DNA of the SLC25A13 gene. On the basis of the experience with adults carrying this condition, the patient was given a high-protein, low-carbohydrate diet. The failure to thrive and bleeding diathesis resolved. When compliance with the dietary prescription was relaxed, growth deceleration was again noted, although significant bleeding did not recur. This is the first report of an infant of Northern European descent with citrin deficiency. The later age at presentation with failure to thrive and bleeding diathesis and without obvious evidence of neonatal intrahepatic cholestasis expands the clinical spectrum of citrin deficiency. This case emphasizes the importance of continued dietary control and growth monitoring in children with neonatal intrahepatic cholestasis caused by citrin deficiency and identifies a new metabolic entity responsible for failure to thrive.

The diagnostic utility of a genetics evaluation in children with pervasive developmental disorders

Purpose: A genetics evaluation of children with pervasive developmental disorders (PDDs) identifies a diagnosis in 6% to 15% of cases. However, previous studies have not measured the incidence of genetic disorders among children with autistic-like features who do not necessarily meet the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition criteria for PDD.Methods: We identified 101 patients at our institution referred for PDD, autism, Asperger syndrome, or autistic features. Seventy-eight were males and 23 were females, giving a male-to-female ratio of 3.4:1. No diagnosis was identified on examination alone, although Rett syndrome was suspected in six females. Seventeen patients did not undergo any type of testing because of noncompliance.Results: Of the remaining 84 patients analyzed, seven (8.3%) were found to have abnormalities on testing. Three chromosomal anomalies were found: one with 5p duplication, one with low-level mosaicism for trisomy 21, and one with an unbalanced 10;22 translocation. Three females were diagnosed with Rett syndrome after MECP2 analysis identified a disease-causing mutation. The remaining patient was found to have an elevated urine orotic acid, with a normal ammonia level, of unknown significance.Conclusion: On the basis of our series, the yield of a genetics evaluation in patients with features of PDD who do not necessarily meet the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition criteria is 8.3%. Approximately half of these were the result of a chromosomal abnormality. Three cases of Rett syndrome were identified for which autistic behaviors are a well-described feature. These findings suggest that a high-resolution karyotype provides the greatest diagnostic yield for patients with autistic-like features. MECP2 analysis should be considered for females who present with autistic behaviors.

健常新生児および尿素サイクル異常症における尿中ピリミジン分析

Pyrimidinea ppea rst o be especiallyi mportanti n the neonatal period, but the reference ranges for urinary pyrimidines have not been reported. We measured urinary pyrimidines in 23 healthy newborns on 6 successive days after birth (from day 0 to day 6) and at 1month of age. We also analyzed newborns with urea cycle disorders including ornithine transcarbamylase (OTC) deficiency. We measured urine samples using high-performancel iquid chromatographyw ith column switching. The reference ranges for urinary orotic acid, uracil and pseudouridine were determined. Orotic acid was greatly increased in OTC deficiency cases, but not in carbamoyl phosphate synthetas I deficiency. We speculate that urinary pyrimidine comcentrations is a useful index for diagnosis in the neonatal period.

Analytical derivatization–a tool for determination of orotic acid

Derivatization of orotic acid (OA) into various forms (trimethylsilylderivate, alkyl ester and per-methylated derivate) and their evaluation by GC/MS is described. The tested approach includes ion-exchange SPE clean-up, evaporation and chemical reaction with different types of derivatization agents (N,O-bis-(trimethylsilyl)trifluoroacetamide with trimethylchlorosilane, butanol with acetylchloride and ethereal solution of diazomethane). Derivate originated in the reaction with diazomethane was used for determination of urinary orotic acid by GC/MS. Detection limit of 0.28 μmol l −1 was reached using the ion 82 m/ z in single ion monitoring (SIM) mode. Linearity of the method was tested within the range of 3.4–2503.4 μmol l −1 covering physiological and pathological levels of orotic acid in urine sample. Recoveries were within the range 93.7–110.6%. Application of the method on the patient with defect of ornithine transcarbamylase (OTC) was demonstrated as well.

Rapid determination of orotic acid in urine by a fast liquid chromatography/tandem mass spectrometric method.

Quantification of orotic acid (uracil-6-carboxylic acid) in urine is an important tool to diagnose some inherited diseases, such as urea cycle disorder (OTCD) and hereditary orotic aciduria. New rapid analytical methods are necessary to provide high-throughput orotic acid analyses. A new analytical method has been developed for the rapid analysis of orotic acid in urine by liquid chromatography coupled with ion spray tandem mass spectrometry (LC/MS/MS). After a sample dilution 1:20, the analysis was performed in the selected reaction monitoring mode in which orotic acid was detected through the transition m/z 155 to 111. The retention time was 3.9 min in a 4.5-min analysis. Daily calibration between 0.5-5.0 micromol/L of orotic acid, corresponding to 10-100 micromol/L in urine before the 1:20 dilution, offered consistent linearity and reproducibility. Interassay coefficient of variance (c.v.) was 4.97% at a mean concentration of 10.99 micromol/L. The sensitivity and specificity of tandem mass spectrometry permitted a high volume of analyses of orotic acid. The sample preparation is simple, inexpensive and not time demanding.

Rapid Determination of Orotic Acid in Urine by Liquid Chromatography–Electrospray Tandem Mass Spectrometry

Orotic acid (ORA) is an important biochemical marker for uridine monophosphate synthase deficiency, an autosomal recessive disease characterized by macrocytic hypochromic megaloblastic anemia, growth retardation, orotic aciduria, and crystalluria (1). In addition, patients with urea cycle diseases excrete increased amounts of urinary ORA (2). Thus, ORA aciduria is observed in patients with ornithine carbamoylasetransferase deficiency (OCTD), an X-linked disorder, and could reveal heterozygosity after a protein load, and in citrullinemia, argininosuccinic aciduria, and argininemia (2)(3). Currently there are two widely accepted approaches to the determination of urinary ORA, stable-isotope-dilution gas chromatography–mass spectrometry (GC/MS), and ion-exchange HPLC methods with ultraviolet detection, each of which has difficulties and limitations (4)(5)(6)(7). Ito et al.(8) recently described a liquid chromatography–electrospray tandem mass spectrometry (LC-ESI-MS/MS) method for a large number of urinary metabolites, including ORA. In the present work we describe a more specific, high-throughput, sensitive stable-isotope-dilution LC-ESI-MS/MS method for the determination of urinary ORA. ORA was purchased from Sigma, and [1,3-15N2]orotic acid used as internal standard (IS) was obtained from Cambridge Isotope Laboratories. Acetonitrile and glacial acetic used for HPLC were purchased from Fisher Scientific. Syringe-driven membrane filter units were of LCR type (0.45 μm pore size) obtained from Millipore. Glass autosampler vials (2-mL capacity) and 300-μL vial inserts were purchased from Agilent. Urine samples were from pediatric patients investigated for metabolic diseases. Adult urine samples were from healthy laboratory personnel. All urine samples were stored at −20 °C until analysis. MS/MS analysis was carried out on a Micromass QuattroLC triple quadrupole mass spectrometer interfaced with a Z-spray ESI source and equipped with a Jasco HPLC pump Model PU-980 and a Jasco Model AS-950 autosampler. The ESI source was operated in the negative-ion mode with the source kept at 150 …

Plasma urea-cycle-related amino acids, ammonium levels, and urinary orotic acid excretion in short-bowel patients managed with an oral diet

Background and Aims: The small intestine contains several enzymes involved in arginine synthesis and converts glutamine to citrulline, the major compound for endogenous arginine synthesis. This study was conducted to assess the plasma status of urea-cycle intermediates and orotic urinary excretion in short-bowel patients. Methods:Thirteen stable short-bowel syndrome patients (7 men; 60.2±15.2 years) were studied. Patients were divided into moderately resected (Group A; n=6) and severely resected (Group B; n=7) according to their remnant bowel length (Group A: 61–150 cm; Group B: ≤60 cm). All subjects were consuming an oral diet plus dietetic supplements. Plasma urea-cycle amino acids, ammonium and urinary orotic acid were determined. Results: Plasma glutamine levels were significantly higher in both patient groups than in the control group ( P<0.001). Regarding citrulline, Group B levels were significantly lower vs. controls ( P<0.001). Comparisons between patient groups showed higher arginine in Group A ( P<0.05) and non-statistically lower citrulline in Group B. Blood ammonium and orotic urinary excretion were normal. Conclusions: Although plasma citrulline and glutamine alterations were found, patients showed no hyperammonemia or orotic aciduria, which suggests a certain degree of adaptation in arginine and related amino acid metabolism, when an adequate dietary supply of arginine is provided.

Determination of orotic acid in urine by capillary zone electrophoresis in tandem-coupled columns with diode array detection

Analytical potentialities of capillary zone electrophoresis in the separation system with tandem-coupled columns to the spectral identification and determination of orotic acid (OA) in urine by diode array detection (DAD), coupled to the separation system via optical fibers, were investigated. A very significant “in-column” clean-up of OA from urine matrix was reached in the separation stage of the tandem by combining a low pH (2.8) with complexing effects of electroneutral agents [α- and β-cyclodextrins, poly(vinylpyrrolidone) and 3-( N, N-dimethyldodecylammonio)propanesulfonate]. Due to this, its DAD spectral data could be acquired in the detection stage of the tandem with almost no disturbances by matrix co-migrants. The concentration limits of detection obtained under such working conditions for a 200-nl sample load of OA and 320 μm I.D. capillary tubes were 3.5 μmol/l (218 nm) and 0.4 μmol/l (280 nm). Using chemometry procedures (target transformation factor analysis, fixed size moving window-evolving factor analysis, orthogonal projection approach and fixed size moving window–target transformation factor analysis) in processing of the acquired spectral data, the presence of OA in the loaded urine matrix could be confirmed with confidence when its concentration was 10 μmol/l or slightly less.

Capillary zone electrophoresis of orotic acid in urine with on-line isotachophoresis sample pretreatment and diode array detection

Potentialities of capillary zone electrophoresis with on-line isotachophoresis sample pretreatment and diode array detection (ITP–CZE–DAD) to the separation, detection and identification of trace analytes present in biological matrices were investigated. Urine represented a multicomponent, variable and high ionic strength matrix while orotic acid was chosen as a model analyte of a practical clinical relevance in this investigation. Using the ITP–CZE combination in the column-coupling configuration of the separation system ITP provided an enhanced sample load capacity to the separation system (a 30 μl sample injection volume), concentrated the analyte and served as an on-line sample clean up technique. On the other hand, CZE performed a final separation of the analyte from matrix constituents present in the ITP pretreated sample and provided favorable conditions for its detection and identification by DAD. Using current correction and smoothing procedures analytically relevant DAD spectra of orotic acid could be obtained also in instances when this was injected in a model sample at a 2·10 −7 mol/l concentration (an estimated limit of determination of orotic acid at a 218 nm detection wavelength). ITP–CZE separations of urine samples (based on differences in acid–base properties and host–guest complexations of the analyte and matrix anionic constituents) led to significant sample clean ups. Consequently, DAD spectra of orotic acid matching its reference spectrum, could be acquired also in instances when the acid was present in urine matrices (loaded in 30 μl injection volumes of 20-fold diluted urine samples) at 4–6·10 −7 mol/l concentrations. Here, residual trace matrix interferents prevented a closer approach to the above value attainable for model samples. Although this work was focused only on one analyte and urine matrix it implies very promising potentialities of the ITP–CZE–DAD combination in the identification and quantitation of trace analytes present in biological matrices, in general.

Influence of dose and age on the response of the allopurinol test for ornithine carbamoyltransferase deficiency in control infants.

Measurement of urinary orotidine and orotic acid after an oral allopurinol challenge is an important diagnostic test for ornithine carbamoyltransferase deficiency that is sometimes used in infants (< 1 year of age), although there is little information on normal test results in this age group. We found higher orotidine excretion in normal infants than in older children given the test, whereas orotate excretion was similar in both groups. The increased orotidine excretion appears to be due to the use in the infants of higher allopurinol doses per kilogram of body weight than in the children. The normalized-dose dependency of the orotidine response extends even to adult age. Thus, dose-normalized responses should be used in the test and there is no need for careful age-matching of the controls.

Urinary Orotic Acid Levels in Normal Pregnancy and Pregnancy-Induced Hypertension

Our objective was to study the urinary levels of orotic acid in normal pregnancy and in pregnancy-induced hypertension. Such levels were measured using high-performance liquid chromatography with column-switching. The levels of urinary orotic acid (μmol/g creatinine) in normal pregnancy (n = 14) were 6.9 ± 2.3 (first trimester), 10.1 ± 2.4 (20 weeks) and 12.0 ± 3.7 (30 weeks). In pregnancy-induced hypertension (n = 14), the corresponding levels were 6.5 ± 1.7, 7.8 ± 2.7 and 7.6 ± 2.3, respectively. Normal pregnant subjects individually showed a significant elevation at 20 and 30 weeks of gestation as compared with those in the first trimester (p < 0.01). A high consumption of arginine in nitric oxide production during normal pregnancy may cause a physiological elevation of urinary orotic acid. The absence of an elevation in pregnancy-induced hypertension may be associated with a decrease in nitric oxide production.

Indicators of L-arginine metabolism and cardiovascular risk factors--a cross-sectional study in healthy middle-aged men.

This study examines the relationship between traditional risk factors of coronary artery disease and indicators involved in the metabolism of L-arginine (plasma and urine L-arginine, plasma L-citrulline, serum creatinine and urine orotic acid). Our study population consisted of 40 healthy male volunteers aged between 35 and 55 years. We found an inverse association between serum creatinine and blood pressure, between plasma L-citrulline and blood pressure, as well as between urine L-arginine and blood pressure. We also found a positive association between plasma LDL-cholesterol and urine L-arginine and a negative correlation between plasma L-arginine and LDL-cholesterol. Orotic acid measured from urine was not associated with any of the indicators of L-arginine metabolism. Our results indicate that L-arginine metabolism is of profound significance for cardiovascular health. However, our study does not answer questions relating to causality. Further studies are needed to clarify the causal relationship between cardiovascular risk factors, especially elevated blood pressure and high LDL-cholesterol, and indicators of L-arginine metabolism.

Effect of lysine infusion on urea cycle in lysinuric protein intolerance

Poor intestinal absorption and excessive renal loss of dibasic amino acids result in low plasma concentrations in patients with lysinuric protein intolerance (LPI). Arginine and ornithine deficiency impair the function of the urea cycle and cause hyperammonemia after protein intake, while chronic lysine deficiency may cause growth failure and lead to reduced bone density in such patients. Since high lysine concentrations inhibit several enzymes of the urea cycle in the liver, lysine supplementation may induce hyperammonemia in LPI. We thus studied how LPI patients tolerate high plasma lysine by intravenous (IV) infusion of 3.3 mmol/kg lysine hydrochloride over 90 minutes in 6 adult patients and 4 healthy controls. The plasma lysine concentration (mean +/- SD, range) peaked in the patients (9,114 +/- 1,864, 7,156 to 12,044 micromol/L) and controls (10,185 +/- 2,253, 7,714to 13,122 micromol/L) at 90 minutes. Urinary lysine excretion peaked in the second 2-hour urine collection in the patients (4,582 +/- 1,276, 3,018 to 6,315 micromol/m2 body surface area per hour) and in the first 2-hour collection in the controls (5,373 +/- 1,766, 3,551 to 7,286 micromol/m2/h). Two patients had mild nausea but no hyperammonemia and one patient had moderate hyperammonemia (peak, 112 micromol/L) at the end of the infusion. Orotic acid excretion increased in 2 subjects with a peak excretion rate of 33 and 251 micromol/m2/h in the third 2-hour collection after starting the load. All other subjects remained asymptomatic and showed no change in plasma ammonia or urinary orotic acid excretion. We thus conclude that an acute increase in plasma lysine caused minimal clinical or biochemical untoward effects in patients with LPI. Moderate increases in plasma lysine after low-dose oral supplementation with lysine or well-absorbed lysine derivatives are probably well tolerated in LPI.

Determination of urinary orotic acid and uracil by capillary zone electrophoresis

We describe a simple method for measuring orotic acid and uracil concentration in urine by capillary zone electrophoresis in 20 m M Na-borate buffer, pH 9.2. The method was applied for studying a patient with HHH (hyperornithinemia, hyperammonemia and homocitrullinuria) syndrome. A high value of uracil excretion was found during periods of relatively low orotic acid excretion and normal ammonemia. The orotic acid level in urine was increased by increasing protein intake.

Aberrations of ammonia metabolism in ornithine carbamoyltransferase-deficient spf-ash mice and their prevention by treatment with urea cycle intermediate amino acids and an ornithine aminotransferase inactivator

Sparse fur with abnormal skin and hair (spf-ash) mice are deficient in ornithine carbamoyltransferase (OCT) activity, but their OCT protein is kinetically normal. We administered ammonium chloride to spf-ash mice, in order to analyze ammonia metabolism and to find a rationale for the therapy of OCT deficiency. Ammonia concentration in the liver of spf-ash mice increased to a level much higher than in the control. Ammonium chloride injection caused an increase in ornithine (Orn) 5 min after injection and an increase in the sum of Orn, citrulline (Cit) and arginine (Arg) for at least 15 min in the liver of control mice, but no increase in Orn, Cit and Arg in the liver of spf-ash mice. Treatment of spf-ash mice with Arg 5–20 min prior to the injection of ammonium chloride kept the hepatic ammonia concentration at a level comparable to that without the load. A significant reciprocal relationship between ammonia and Orn concentrations in the liver of spf-ash mice 5 min after an ammonium chloride load with or without Arg strongly suggests that ammonia disposal is dependent on the supply of Orn. In spf-ash mice loaded with tryptone as a nitrogen source, Arg supplementation showed a dramatic decrease in urinary orotic acid excretion in a dose-dependent manner. Similar effects were observed with Cit and Orn at the same dose, and a long-lasting effect with an ornithine aminotransferase inactivator, 5-(fluoromethyl)ornithine, at a much lower dose. The rate of urea formation in liver perfused with ammonium chloride was lower in spf-ash mice than in controls, but with the addition of Orn to the medium it increased to a similar level in control and spf-ash mice. These results indicate that OCT is not saturated with Orn in vivo under physiological conditions and that the administration or enrichment of the urea cycle intermediate amino acids enhances the OCT reaction so that the ammonia metabolism of OCT-deficient spf-ash mice is at least partially normalized.

Urinary orotic acid-to-creatinine ratios in cats with hepatic lipidosis

Abstract Objective To determine urinary orotic acid (OA) conentration and evaluate the urinary OA-to-creatinine ratio (OACR) in cats with hepatic lipidosis (HL). Animals 20 cats with HL and 20 clinically normal cats. Procedure Hepatic lipidosis was diagnosed on the basis of clinical signs, results of serum biochemical analyses, exclusion of other concurrent illness, and cytologic or histologic evaluation of liver biopsy specimens. Urine samples were collected from each cat and frozen at −20 C until assayed. Urine creatinine concentrations were determined, using an alkaline picrate method followed by spectrophotometric assay. Urine OA concentration was determined, using high-performance liquid chromatography. Minimum amount of detectable OA in feline urine was 1 µg/ml. Because of small interfering peaks near the base of the OA peak, the minimum quantifiable concentration of OA was determined to be 5 pg/ml. Urinary OACR was compared in both groups of cats. Results Differences in urinary OACR were not detected between clinically normal cats and cats with HL. Peaks were not detected for urinary OA in any of the 20 clinically normal cats. Of the 20 HL cats, 14 did not have detectable peaks for urinary OA. Of the 6 HL cats that had detectable urinary OA peaks, 3 had values of &lt; 5 µg/ml. Conclusions Apparently, OACR does not increase significantly in cats with HL. Clinical Relevance Urinary OACR is not a useful diagnostic test for HL in cats. (Am J Vet Res 1999; 60:753–754)