Uric acid and diabetes mellitus: an update

The relationship between diabetes mellitus (DM) and high serum uric acid is complex and controversial. Many epidemiological studies have reported a positive association, whereas others have reported an inverse association or none. In the pathogenesis of DM it is the intracellular urate that is more important than the extracellular and dissociation between the two is possible. Evidence suggests that high serum uric acid induces insulin resistance and beta cell failure in animal models. Reduction of intracellular uric acid can be achieved by dietary measures such as reducing fructose and salt intake, and uric acid-lowering drugs. We suggest that in the Western diet, these elements play a crucial role in pathogenesis of DM. To determine the precise and exact interrelationship between intracellular and extracellular uric acid, well-designed studies are required. Besides this, clinical trials are needed to determine whether intracellular and extracellular urate reduction will provide benefit in prevention and treatment of DM and complications associated with it.

Interaction of sex and diabetes on the association between hemoglobin glycation index, hemoglobin A1c and serum uric acid

BACKGROUND

Hemoglobin glycation index (HGI), which is calculated by blood glucose and hemoglobin A1c(HbA1c), reflects the individual discrepancy in HbA1c. This study aimed to investigate the association between HGI/HbA1c and serum uric acid(SUA) stratified by sex and diabetes.

METHODS

The study recruited 33772 participants who underwent physical examinations between April 2016 and August 2021 in Beijing Chao-Yang Hospital. A random subsample of 3000 subjects was utilized to calculate the formula of HGI and data of the remaining 30772 participants were used for analysis. HGI and HbA1c were categorized according to quartiles (Q1, Q2, Q3, Q4), using Q1 as the reference. We used multiple linear regression and restricted cubic splines for data analysis.

RESULTS

30772 participants with a mean age of 44.4 years old were included in the analysis, 48.6% (N = 14944) of which were female and 7.7% (N = 2363) with diabetes. Associations of HGI, HbA1c and SUA were modified by sex and diabetes. The relationship between SUA levels and HGI was positive in women without diabetes, with one unit increase in HGI associating with an 11.3 μmol/L increase in SUA (P < 0.001) after adjusting for other confounders. On average, each one-unit increase in HbA1c was associated with a 14.3 μmol/L decrease in SUA in women with diabetes, a 14.9 μmol/L decrease in SUA in men with diabetes, and a 16.5 μmol/L increase in SUA in women without diabetes (all P < 0.001). The SUA levels in men without diabetes showed a bell-shaped relation with HbA1c, increasing as the HbA1c rose to around 5.7% and then falling with a further increase of HbA1c (P < 0.001).

CONCLUSIONS

SUA levels were inversely correlated with HbA1c in diabetic patients, also in men with prediabetes (HbA1c ≥ 5.7%), but positively correlated with HbA1c and HGI in women without diabetes. Glycemic control may help to reduce the risk of hyperuricemia in non-diabetes women.

Identification of a new mutation in the human xanthine dehydrogenase responsible for xanthinuria type I

Objectives

Hereditary xanthinuria is a rare, autosomal and recessive disorder characterized by severe hypouricemia and increased xanthine excretion, caused by a deficiency of xanthine dehydrogenase/oxidase (XDH/XO, EC: 1.17.1.4/1.17.3.2) in type I, or by a deficiency of XDH/XO and aldehyde oxidase (AOX, EC: 1.2.3.1) in type II.

Methods

We describe a novel point mutation in the XDH gene in homozygosis found in a patient with very low serum and urine levels of uric acid, together with xanthinuria. He was asymptomatic but renal calculi were discovered during imaging.

Results

Additional cases were found in his family and dietary recommendations were made in order to prevent further complications.

Conclusions

Hereditary xanthinuria is an underdiagnosed pathology, often found in a routine analysis that shows hypouricemia. It is important for Laboratory Medicine to acknowledge how to guide clinicians in the diagnosis.

Serum Uric Acid Revealed a U-Shaped Relationship With All-Cause Mortality and Cardiovascular Mortality in High Atherosclerosis Risk Patients: The ASSURE Study

Background: Previous studies have demonstrated an association between hyperuricemia and cardiovascular disease (CVD). The Framingham study confirmed that patients with high atherosclerotic risks (HARs) had worse prognoses. However, after adjusting for confounding factors, the association between serum uric acid (SUA) and all-cause mortality and cardiovascular mortality remains unclear, especially for HAR patients. Objective: The aim of this study was to reveal the relationship of SUA with all-cause and cardiovascular mortality in HAR patients. Methods: This multicenter cohort study enrolled 3,047 participants, and the follow-up was 68.85 ± 11.37 months. Factors related to cardiovascular and all-cause mortality were tested by multivariate Cox regression analysis. Restricted cubic splines (RCSs) with knots were used to explore the shape of the dose-response relationship with SUA and the hazard ratio (HR) of all-cause and CVD mortality. SUA transformed by RCS was added to the Cox regression model as an independent variable, and all-cause and CVD mortality scores were calculated. Survival receiver operating characteristic curves were produced using a regression model predicting the score. Results: SUA demonstrated a "U-shaped" relationship with all-cause and cardiovascular mortality. SUA predicted all-cause and CVD mortality, with cutoff values of values of >370.5 μmol/L for males and >327.65 μmol/L for females and <180.5 μmol/L for males and <165.7 μmol/L for females, respectively. The survival ROC curve indicated that SUA is able to predict all-cause and CVD mortality, with areas under the curve of 0.702 and 0.711, respectively. The HRs of all-cause mortality (male and female) with hyperuricemia and hypouricemia were 2.08 and 2.01 and 2.04 and 1.98, respectively, and the HRs of CVD mortality (male and female) were 2.09 and 1.79, and 2.02 and 1.89, respectively. Conclusion: Abnormal SUA levels were significant and independent risk factors for all-cause and CVD mortality. Hyperuricemia and hypouricemia increased mortality in both males and females. Routine SUA evaluation and intensive management are needed for HAR patients. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03616769.

Renal effects of uric acid: hyperuricemia and hypouricemia

The prevalence of chronic kidney disease (CKD) is increasing worldwide. Although hyperuricemia has been associated with CKD in many studies, it remains controversial whether this is the cause or the result of decreased renal function. Recent observational studies of healthy populations and patients with CKD have reported that uric acid (UA) has an independent role in the development or progression of CKD. Experimental studies have shown several potential mechanisms by which hyperuricemia may cause or promote CKD. However, other reports have indicated an association between hypouricemia and CKD. This opposing effect is hypothesized to occur because UA is a major antioxidant in human plasma and is associated with oxidative stress. In this article, we discuss the potential association between UA imbalance and CKD and how they can be treated.

Uric Acid Is a Strong Risk Marker for Developing Hypertension From Prehypertension: A 5-Year Japanese Cohort Study

Prehypertension frequently progresses to hypertension, a condition associated with high morbidity and mortality from cardiovascular diseases and stroke. However, the risk factors for developing hypertension from prehypertension remain poorly understood. We conducted a retrospective cohort study using the data from 3584 prehypertensive Japanese adults (52.1±11.0 years, 2081 men) found to be prehypertensive in 2004 and reexamined in 2009. We calculated the cumulative incidences of hypertension over 5 years, examined risk factors, and calculated odds ratios (ORs) for developing hypertension after adjustments for age, sex, body mass index, smoking and drinking habits, baseline systolic and diastolic blood pressure, pulse rate, diabetes mellitus, dyslipidemia, chronic kidney disease, and serum uric acid levels. The additional analysis evaluated whether serum uric acid (hyperuricemia) constituted an independent risk factor for developing hypertension. The cumulative incidence of hypertension from prehypertension over 5 years was 25.3%. There were no significant differences between women and men (24.4% versus 26.0%; P=0.28). The cumulative incidence of hypertension in subjects with hyperuricemia (n=726) was significantly higher than those without hyperuricemia (n=2858; 30.7% versus 24.0%; P<0.001). After multivariable adjustments, the risk factors for developing hypertension from prehypertension were age (OR, 1.023; P<0.001), female sex (OR, 1.595; P<0.001), higher body mass index (OR, 1.051; P<0.001), higher baseline systolic (OR, 1.072; P<0.001) and diastolic blood pressure (OR, 1.085; P<0.001), and higher serum uric acid (OR, 1.149; P<0.001). Increased serum uric acid is a strong risk marker for developing hypertension from prehypertension. Further studies are needed to determine whether treatment of hyperuricemia in prehypertensive subjects could impede the onset of hypertension.

Insulin stimulates uric acid reabsorption via regulating urate transporter 1 and ATP-binding cassette subfamily G member 2

Accumulating data indicate that renal uric acid (UA) handling is altered in diabetes and by hypoglycemic agents. In addition, hyperinsulinemia is associated with hyperuricemia and hypouricosuria. However, the underlying mechanisms remain unclear. In this study, we aimed to investigate how diabetes and hypoglycemic agents alter the levels of renal urate transporters. In insulin-depleted diabetic rats with streptozotocin treatment, both UA excretion and fractional excretion of UA were increased, suggesting that tubular handling of UA is altered in this model. In the membrane fraction of the kidney, the expression of urate transporter 1 (URAT1) was significantly decreased, whereas that of ATP-binding cassette subfamily G member 2 (ABCG2) was increased, consistent with the increased renal UA clearance. Administration of insulin to the diabetic rats decreased UA excretion and alleviated UA transporter-level changes, while sodium glucose cotransporter 2 inhibitor (SGLT2i) ipragliflozin did not change renal UA handling in this model. To confirm the contribution of insulin in the regulation of urate transporters, normal rats received insulin and separately, ipragliflozin. Insulin significantly increased URAT1 and decreased ABCG2 levels, resulting in increased UA reabsorption. In contrast, the SGLT2i did not alter URAT1 or ABCG2 levels, although blood glucose levels were similarly reduced. Furthermore, we found that insulin significantly increased endogenous URAT1 levels in the membrane fraction of NRK-52E cells, the kidney epithelial cell line, demonstrating the direct effects of insulin on renal UA transport mechanisms. These results suggest a previously unrecognized mechanism for the anti-uricosuric effects of insulin and provide novel insights into the renal UA handling in the diabetic state.

Prevalence and possible causes of hypouricemia at a tertiary care hospital

BACKGROUND/AIMS

We aimed to investigate the prevalence and possible causes of hypouricemia in the Korean population and to compare our findings with published results of other populations.

METHODS

We examined the serum uric acid levels of 30,757 subjects who had their uric acid values measured at least once during a 1-year period. All individuals with hypouricemia (serum uric acid < 2.0 mg/dL, n = 424) were reviewed with respect to medical drug history and concomitant diseases previously identified as being associated with hypouricemia.

RESULTS

The prevalence of hypouricemia was 4.14% (299/7,223) among inpatients and 0.53% (125/23,534) among outpatients, for an overall prevalence of 1.39% (424/30,757). Possible causes associated with hypouricemia were found to be solid or hematologic malignancies (n = 86), diabetes mellitus (n = 56), and therapeutic drugs (n = 29). The medications were allopurinol (n = 11), angiotensin II receptor blockers (n = 10), salicylates (n = 6), febuxostat (n = 1), and warfarin (n = 1). In the remaining 226 individuals, the cause of hypouricemia was not identified.

CONCLUSIONS

Hypouricemia is relatively common in the Korean population compared to those of other countries. The possible causes associated with hypouricemia are related to underlying diseases and medications.

Characterization of Mesoamerican Nephropathy in a Kidney Failure Hotspot in Nicaragua

BACKGROUND

Mesoamerican nephropathy (MeN) is a kidney disease of unknown cause that mainly affects working-age men in Central America. Despite being a major cause of morbidity and mortality in this region, its clinical characteristics have not been well defined.

STUDY DESIGN

Cross-sectional family-based study.

SETTING & PARTICIPANTS

266 members of 24 families with high chronic kidney disease (CKD) burdens in a MeN hotspot in Northwestern Nicaragua. We compared clinical and biochemical characteristics of affected individuals first with their unaffected relatives and then with NHANES (National Health and Nutrition Examination Survey) participants with CKD in order to reveal identifying features of MeN.

PREDICTOR

CKD defined as serum creatinine level ≥ 1.5mg/dL in men and ≥1.4mg/dL in women.

OUTCOMES

Clinical and biochemical parameters, including serum sodium, potassium, bicarbonate, calcium, magnesium, phosphorus, and uric acid.

RESULTS

Hyperuricemia, in many cases severe, was common among patients with MeN. Uric acid levels in patients with MeN were higher than those in NHANES participants (mean, 9.6 vs 7.4mg/dL for men in each group) despite more frequent use of uric acid-lowering medications in Nicaraguan individuals (71.7% vs 11.2%). In multivariable linear mixed-effects regression analysis, uric acid levels were 2.0mg/dL (95% CI, 1.0-3.0; P<0.001) higher in patients with MeN compared with their NHANES counterparts after adjusting for age, estimated glomerular filtration rate, and uric acid-lowering therapies. In contrast to prior reports, hyponatremia and hypokalemia were not common.

LIMITATIONS

CKD defined by single serum creatinine measurement; population likely not representative of full MeN phenotype spectrum across Central America; major differences between MeN and NHANES groups in important characteristics such as age, ancestry, and recruitment method.

CONCLUSIONS

Hyperuricemia out of proportion to the degree of decreased kidney function was common among Nicaraguan patients with MeN. Our results suggest that rather than being solely a consequence of CKD, hyperuricemia may play a role in MeN pathogenesis, a hypothesis that deserves further study.

An Invert U-Shaped Curve: Relationship Between Fasting Plasma Glucose and Serum Uric Acid Concentration in a Large Health Check-Up Population in China

There are some published studies focus on the invert U-shaped relationship between fasting plasma glucose (FPG) and serum uric acid (UA), while the threshold value and gender differences of this relationship were still obscure. We aimed to explore the dose-response relation between FPG level and serum UA concentration by conducted this epidemiological research in a large health check-up population in China. A total of 237,703 people were collected from January 2011 to July 2014 in our cross-sectional study; 100,348 subjects age 18 to 89 years and without known diabetes were included for the current analysis. One-way analysis of variance, generalized additive models, and 2-piecewise linear regression model were used. The mean concentration of UA with FPG of <6.1, 6.1 to 6.9, and ≥7.0 mmol/L was 240.9, 260.2, and 259.6 μmol/L in women and 349.0, 360.8, and 331.0 μmol/L in men. An invert U-shape with a threshold FPG of 7.5 (women)/6.5 (men) mmol/L was observed in the regression curve of FPG and UA, even after adjusting for potential confounders. The adjusted regression coefficients were 2.4 (95% confidence interval [CI]: 1.5 to 3.4, P < 0.001) for FPG < 7.5 mmol/L, -3.2 (95% CI: -5.0 to -1.3, P < 0.001) for FPG ≥ 7.5 mmol/L in women; while 0.8 (95% CI: -0.4 to 2.0, P = 0.19) for FPG < 6.5 mmol/L, -7.1 (95% CI: -8.0 to -6.1, P < 0.001) for FPG ≥ 6.5 mmol/L in men. Furthermore, the interaction between different FPG level and sex was significant (P < 0.05). An invert U-shape with a threshold of FPG was existed for serum UA level in Chinese adults age 18 to 89 years without known diabetes, and significant gender differences were found. Future researches should pay more attention to this relationship.

Management of Chronic Kidney Disease: The Relationship Between Serum Uric Acid and Development of Nephropathy

Chronic kidney disease (CKD) is increasingly recognized as a global health problem, and new and effective strategies are needed for the management of this condition. Recently, there has been renewed interest in the relationship between serum uric acid (SUA) levels and CKD, and several recent trials have demonstrated a possible link between SUA and the development and/or progression of CKD in patients with and without diabetes. The identification of key urate transporters such as urate transporter 1 and glucose transporter 9 has provided not only insights into the pathophysiology of hyperuricemia, but also possible links to other processes, such as glucose homeostasis. The renewed interest in the role of SUA in CKD has coincided with the development of sodium glucose co-transporter 2 inhibitors for the treatment of diabetes. In addition to improving glycemic control, these agents, acting via the kidneys in an insulin-independent manner, have also been shown to reduce SUA levels and potentially improve some measures of renal function. This review will discuss the role of uric acid in CKD treatment, and how SUA-lowering therapies may prevent or delay the progression of CKD.

FUNDING

Janssen Scientific Affairs.

Hypouricaemia and hyperuricosuria in familial renal glucosuria

Familial renal glucosuria is a rare co-dominantly inherited benign phenotype characterized by the presence of glucose in the urine. It is caused by mutations in the SLC5A2 gene that encodes SGLT2, the Na⁺-glucose cotransporter responsible for the reabsorption of the bulk of glucose in the proximal tubule. We report a case of FRG displaying both severe glucosuria and renal hypouricaemia. We hypothesize that glucosuria can disrupt urate reabsorption in the proximal tubule, directly causing hyperuricosuria.

Regulation of tissue-specific expression of the human and mouse urate transporter 1 gene by hepatocyte nuclear factor 1 alpha/beta and DNA methylation

Expression of Urate transporter 1 (URAT1/SLC22A12) is restricted to the proximal tubules in the kidney, where it is responsible for the tubular reabsorption of urate. To elucidate the mechanism underlying its tissue-specific expression, the transcriptional regulation of the hURAT1 and mUrat1 genes was investigated. Hepatocyte nuclear factor 1 alpha (HNF1alpha) and HNF1beta positively regulate minimal promoter activity of the URAT1 gene as shown by reporter gene assays. Electrophoretic mobility shift assays revealed binding of HNF1alpha and/or HNF1beta to the HNF1 motif in the hURAT1 promoter. Furthermore, the mRNA expression of Urat1 is reduced in the kidneys of Hnf1alpha-null mice compared with wild-type mice, confirming the indispensable role of HNF1alpha in the constitutive expression of URAT1 genes. It was also shown that the proximal promoter region of mUrat1 was hypermethylated in the liver and kidney medulla, whereas this region was relatively hypomethylated in the kidney cortex. These methylation profiles are in a good agreement with the proximal tubule-restricted expression of mUrat1 in the kidney cortex. Taken together, these results strongly suggest that tissue-specific expression of the URAT1 genes is coordinately regulated by the transcriptional activation by HNF1alpha/HNF1beta heterodimer and repression by DNA methylation.

Renal handling of uric acid in patients with type 1 diabetes in relation to glycemic control

BACKGROUND

The aim of the study was to compare the renal handling of uric acid (UA) in 16 patients with type 1 diabetes without renal failure (age 34.8 +/- 13.3 years) and in 15 healthy subjects (age 34.9 +/- 12.6 years).

METHODS

Creatinine clearance (Cr-Cl), clearance of uric acid (UA-Cl), fractional excretion of uric acid (UA-FE), and 24-h urinary UA excretion (UA-U) were determined. Glycemic control was assessed using fasting glucose, glycated hemoglobin and fructosamine tests.

RESULTS

Patients with diabetes had significantly (p < 0.0001) lower serum UA concentrations compared to control group (2.8 +/- 0.7 vs. 5.7 +/- 0.8 mg/dl), and higher urinary UA excretion (813 +/- 107 vs. 423 +/- 40 mg/day), UA clearance (21.9 +/- 7.1 vs. 5.2 +/- 0.9 mL/min) and fractional UA excretion (17.1 +/- 5.5 vs. 4.8 +/- 1.3%), with higher creatinine clearance (129 +/- 16 vs. 111 +/- 12 mL/min, p < 0.005). In patients with diabetes there was a strong negative correlation between serum UA concentration and UA 24-h excretion (R = -0.79; p < 0.001). Fractional UA excretion correlated with fasting glycemia and HbA1c (R = +0.51 and +0.53; p < 0.05).

CONCLUSIONS

In type 1 diabetes there is significant UA renal clearance increase, which is higher with poor glycemic control. It leads to hypouricemia despite an approximately twofold UA excretion increase and therefore despite increased UA synthesis.

Hypouricemia in individuals admitted to an inpatient hospital-based facility

BACKGROUND

Decreased serum uric acid levels resulting from renal urate wasting occasionally are reported in hospitalized patients because of isolated or generalized proximal tubular damage. There are limited recent findings with regard to the incidence and cause of hypouricemia in patients admitted to an internal medicine clinic. The aim of this study is to examine the prevalence of hypouricemia in individuals admitted to our inpatient hospital-based facility and identify underlying causes and pathogenetic mechanisms and any association of hypouricemia and uricosuria with other tubular defects.

METHODS

A total of 7,250 serum urate measurements were available on patients' admission. Hypouricemia is defined as a serum urate level less than 2.5 mg/dL (149 micromo/L). In all hypouricemic cases, a detailed clinical and laboratory investigation was performed.

RESULTS

Hypouricemia was found in 90 patients (1.24%). In all except one patient, hypouricemia was associated with inappropriate uricosuria (urate fractional excretion [FE] > 10%; range, 10.8% to 94%). There was an inverse correlation between serum uric acid level and its FE (r = -0.73; P < 0.0001). The most common causes of hypouricemia were obstructive jaundice of any cause (n = 18), solid or hematologic neoplasias (n = 17), diabetes mellitus (n = 12), drugs affecting urate homeostasis (n = 10), and intracranial diseases (n = 8). Seventeen patients with hypouricemia showed one or more other manifestations of proximal tubular damage, such as glucosuria, inappropriate phosphaturia leading to hypophosphatemia, and kaliuria resulting in hypokalemia.

CONCLUSION

Hypouricemia caused by inappropriate uricosuria is not rare in patients admitted to an internal medicine clinic, is related to underlying diseases, and may be associated with other abnormalities of proximal tubular function.

Hypouricemia and hyperuricemia in type 2 diabetes: two different phenotypes

BACKGROUND AND DESIGN

Conflicting data exist about uric acid levels in type 2 diabetes mellitus, as low levels were found in diabetic patients, while elevated serum uric acid is a feature of hyperinsulinemia and impaired glucose tolerance. The present study was addressed to evaluate the relation between uric acid and metabolic parameters, creatinine clearance and albumin excretion rate in a cohort of type 2 diabetic patients.

RESULTS

Hyperuricemic patients were older and had higher values of body mass index (BMI), systolic and diastolic blood pressure, triglycerides, albumin excretion rate, C-peptide and prevalence of hypertension, metabolic syndrome and macroalbuminuria and lower values of high-density lipoprotein (HDL)-cholesterol, creatinine clearance and glycated haemoglobin (HbA1c). The correlations between uric acid levels and triglycerides, BMI, systolic blood pressure, albumin excretion rate, C-peptide, creatinine clearance, HDL-cholesterol and HbA1c remained significant in a multiple regression analysis after adjustment for age, sex and duration of diabetes. After performing multiple logistic regression analyses, uric acid levels were independently associated with hypertension [odds ratio (OR) = 1.8; 95% confidence interval (CI) 1.6--2], after adjustment for age, sex, duration of diabetes and macroalbuminuria (OR = 1.5; 95% CI 1.1--2.0), after adjustment for age, sex, HbA1c levels, creatinine clearance, duration of diabetes and blood pressure levels and the metabolic syndrome (OR = 1.6; 95% CI 1.5--1.8), after adjustment for age, sex and creatinine clearance.

CONCLUSIONS

In type 2 diabetes, hyperuricemia seems to be associated with the insulin-resistant syndrome and with early onset or increased progression to overt nephropathy, while hypouricemia is associated with worse metabolic control, hyperfiltration and a late onset or decreased progression to overt nephropathy.

Abnormal serum uric acid levels in children

Measurement of the serum uric acid level, most commonly considered in adult patients, is frequently obtained inadvertently for pediatric patients because it is a standard component of many multichannel chemistry profiles offered by clinical laboratories. Most standard references for normal uric acid values do not take into account the impact of the metabolic changes in children at different ages on the uric acid level. A substantial number of childhood conditions may produce perturbations in the serum uric acid level. Knowledge of normal serum uric acid levels and of the conditions affecting those levels in children enables a more focused pursuit of underlying abnormalities.

Uric acid metabolism in children

The renal excretion of uric acid in children differs quantitatively, and perhaps qualitatively, from that in adult humans. The younger the child, the greater the renal clearance of uric acid and the greater the excretion of uric acid expressed as mg per kg body weight. During infancy, the reduced ability to maximally concentrate the urine may protect against precipitation of uric acid crystals within the kidney. Conversely, the extremely high urinary uric concentrations places the very small infant at jeopardy during sudden increases in the filtered load of uric acid. Understanding the pharmacologic and physiologic modulators of renal uric acid clearance will allow the pediatrician to minimize the risk of uric acid nephropathy, and to understand the implications of uric acid in the serum or urine in children with fluid and electrolyte disorders. Certainly evaluation of serum and urinary uric acid concentrations is essential in any child with acute renal failure.

Co-occurrence of hypercalciuria and hypouricaemia in type 2 diabetic patients

The relationship between the urinary excretion of calcium (Ca2+) and uric acid was investigated in 151 Type 2 diabetic patients and 48 normal subjects. In the diabetic patients, uric acid clearance/creatinine clearance (Clurate/Clcr) was higher and the serum level of uric acid was lower than in the normal subjects (Clurate/Clcr: 10.9 +/- 5.8 vs 8.1 +/- 2.6%, p less than 0.001; serum uric acid: 3.4 +/- 86 vs 357 +/- 89 mumol l-1, p less than 0.001). Calcium clearance/Clcr (Clca/Clcr) also increased in the diabetic patients, as did urinary excretion rate, but the serum Ca2+ level was not different to normal control subjects (Clca/Clcr: 2.29 +/- 1.59 vs 1.56 +/- 0.98%, p less than 0.001; Ca2+ excretion rate: 2.24 +/- 1.67 vs 1.63 +/- 1.11 mmol day-1, p less than 0.01; serum Ca2+ level: 2.34 +/- 0.11 vs 2.33 +/- 0.08 mmol l-1). In the diabetic patients, Clcr positively and the serum uric acid negatively correlated with the urinary excretion of Ca2+ (p less than 0.001 for both correlations in the multivariate regression analysis). These data suggest that the diabetic patients have increased fractional excretion of both Ca2+ and uric acid.

Acute renal failure due to uric acid nephropathy in a patient with renal hypouricemia

This report is about a 23-year-old man who required hemodialysis in connection with an acute renal failure resulting from uric acid nephropathy without hyperuricemia. After recovering renal function he showed extreme hypouricemia (0.1-0.3 mg/dl) and elevated uric acid clearance (100-300 ml/min). The fractional excretion of uric acid (Cua/Ccr) could be suppressed by oral pyrazinamide and enhanced by probenecid. As no other renal tubular or metabolic abnormalities were detected, it is suggested that a markedly increased renal tubular urate secretion was responsible for the hypouricemia and also for the rare side-effect of an uric acid nephropathy in this patient.