[Blood uric acid levels in patients with sleep-disordered breathing]

Relationship Between Hyperuricemia-Waist Phenotype and Obstructive Sleep Apnea in Type 2 Diabetes Mellitus

Objective

This study aimed to propose the hyperuricemia-waist (HUAW) phenotype and investigate the relationship between the HUAW phenotype and obstructive sleep apnea (OSA) in type 2 diabetes mellitus (T2DM).

Methods

We enrolled 255 patients with T2DM (165 male and 90 female) from the First Hospital of Qinhuangdao. The sleep test was performed, and serum uric acid (UA) levels and waist circumference (WC) were calculated. The HUAW phenotype was defined as serum UA concentrations ≥420 μmol/L and WC ≥90 cm (male) and ≥85 cm (female). The participants were categorized into four phenotype groups based on the mentioned cutoffs: normal WC and normal UA concentrations (group A); normal WC and elevated UA concentrations (group B); enlarged WC and normal UA concentrations (group C); and enlarged WC and elevated UA concentrations (group D). Among these participants, 17.6% were characterized by the HUAW phenotype, 80.0% had OSA, and 47.0% had moderate-to-severe OSA. The prevalence of OSA was 43.4%, 71.4%, 89.7%, and 97.8% in groups A, B, C, and D, respectively. The prevalence of moderate-to-severe OSA was 7.5%, 28.6%, 56.9%, and 72.7% in groups A, B, C, and D, respectively. After adjusting for age, sex, duration of diabetes, glycosylated hemoglobin A1c, smoking, and drinking, the HUAW phenotype was found to be significantly associated with OSA and moderate-to-severe OSA.

Conclusion

The present study proposed the HUAW phenotype and demonstrated that in T2DM, the HUAW phenotype was associated with OSA, especially with moderate-to-severe OSA. Unlike T2DM without the HUAW phenotype, T2DM with the HUAW phenotype showed a significantly higher prevalence of OSA, especially moderate-to-severe OSA. Thus, early sleep studies should be routinely examined in individuals with T2DM who display the HUAW phenotype.

Assessing the causal associations of obstructive sleep apnea with serum uric acid levels and gout: a bidirectional two-sample Mendelian randomization study

OBJECTIVE

Multiple observational studies have reported the close associations of obstructive sleep apnea (OSA) with serum uric acid (SUA) levels and gout. However, the causal nature and direction remains unclear.

METHODS

A bidirectional two-sample Mendelian randomization (MR) study was performed, based on publicly available genome-wide association studies (GWAS) summary statistics, to investigate whether OSA is causally related to SUA levels, gout and vice versa. The inverse-variance weighted (IVW) was used as the primary analysis approach, supplemented with four sensitive analysis methods applied to assess the robustness of the results. Moreover, multivariable MR (MVMR) was utilized to evaluate the independent causal effect of OSA on SUA and gout after adjusting for body mass index (BMI), hypertension, type 2 diabetes (T2D), coronary artery disease (CAD), and chronic kidney disease (CKD).

RESULTS

Genetically predicted OSA liability was significantly associated with increased levels of SUA (IVW method: β = 0.19, 95% CI = 0.11 - 0.26, P = 7.24 × 10^-7) and risk of gout [IVW method: odds ratio (OR) = 1.75 95% CI = 1.13 - 2.69, P = 0.01] in univariable MR. The MVMR results suggested that OSA retained its significant association with increased SUA levels, whereas the significant association between OSA and gout was attenuated to null after adjusting for BMI and T2D. No causal effect of OSA on SUA levels and gout was found in the reverse direction.

CONCLUSIONS

Our findings suggest that OSA was causally associated with increased levels of SUA, but was not independently associated with gout risk.

Serum uric acid and arterial lactate levels in patients with obstructive sleep apnea syndrome: the effect of CPAP treatment

Objectives: Serum uric acid (UA) and arterial lactate acid (LA) are markers of oxidative stress and tissue hypoxia that are present in patients with obstructive sleep apnea syndrome (OSAS). The aim of the study was to evaluate the associations between UA and LA levels and OSAS characteristics as well as the effect of their levels after continuous positive airway pressure (CPAP) treatment.Methods: This is a retrospective of newly diagnosed patients with OSAS. UA and LA levels were measured the night before the diagnostic sleep study, and 6 months after CPAP therapy.Results: We evaluated 604 individuals with OSAS and 98 controls (i.e. individuals without sleep-related breathing disorders). Baseline median (IQR) serum UA levels were higher in OSAS patients compared to controls; 7.0 (6.4, 8.1) mg/dL vs 6.3 (6.1, 6.4) mg/dL, respectively (p < 0.001). This difference remained significant, after adjustment of serum UA to creatinine ratio (UA/Cr) (p < 0.001). Patients with OSAS had higher LA levels at baseline compared to controls; 2.26 (2.25, 2.31) mmol/L vs 1.90 (1.87, 1.97) mmol/L, respectively (p < 0.001). Both UA and LA levels decreased significantly after CPAP treatment [median (IQR): 7.0 (6.4, 8.1) mg/dL vs 6.4 (6.2, 6.8) mg/dL, p < 0.001 and 2.26 (2.25, 2.31) mmol/L vs 2.08 (2.07, 2.31) mmol/L, p < 0.001]. Several sleep parameters were independent predictors of UA and LA levels.Conclusion: In OSAS patients increased serum UA and arterial LA levels are found. CPAP therapy resulted in significant reductions in levels of both biomarkers.

Confounded by obesity and modulated by urinary uric acid excretion, sleep-disordered breathing indirectly relates to hyperuricaemia in males: A structural equation model

Sleep-disordered breathing (SDB) causes hypoxic stress and can trigger uric acid (UA) overproduction. We comprehensively investigated whether SDB, interacting with components of metabolic syndrome, hepatic and renal dysfunctions, low physical fitness, sedentary lifestyle, disrupted sleep, and chronic systemic inflammation (CSI), is directly associated with hyperuricaemia. In 528 community-based males (mean [SD] age 46.2 [7.4] years), we cross-sectionally analysed measures of anthropometry; self-reported lifestyle habits; overnight sleep polysomnography data; cardiopulmonary exercise tests; and biomarkers of cardiometabolic, hepatic, and renal functions; and CSI, using structural equation modelling. Objective disrupted sleep, C-reactive protein, low physical fitness, and sedentary lifestyle were not related to UA levels in univariate analysis and were excluded. The latent variables (with corresponding manifest variables) obesity (body mass index, waist-hip ratio), hypertension (post-sleep systolic, diastolic blood pressure), dyslipidaemia (total cholesterol, triglyceride/high-density lipoprotein cholesterol), hepatic dysfunction (alanine aminotransferase, aspartate transaminase), and renal dysfunction (blood urea nitrogen, serum creatinine) were positively; and hyperglycaemia (fasting glucose, glycated haemoglobin) was negatively associated with hyperuricaemia (serum UA), except for SDB (Apnea-Hypopnea Index, percentage of oxygen saturation <90% period against total sleep time, oxygen desaturation index) in the one-stage influence model. In the two-stage model, SDB, closely interacting with obesity, was positively indirectly associated with hyperuricaemia through directly linked renal dysfunction and obesity-linked hypertension, inverse hyperglycaemia, dyslipidaemia, and hepatic dysfunction. In conclusion, structural equation modelling reveals that SDB closely interacts with obesity and is positively but indirectly related to hyperuricaemia in males. This suggests that urinary UA excretion modulates and obesity confounds the SDB-hyperuricaemia relationship.

A meta-analysis of the association between gout, serum uric acid level, and obstructive sleep apnea

Previous epidemiological investigations have evaluated the association between gout, serum uric acid levels, and obstructive sleep apnea syndrome (OSAS), but with inconsistent results. We conducted this meta-analysis aiming at providing clear evidence about whether OSAS patients have higher serum uric acid levels and more susceptible to gout. Relevant studies were identified via electronic databases from inception to December 17, 2018. Study selection was conducted according to predesigned eligibility criteria, and two authors independently extracted data from included studies. The hazard ratio (HR) and weighted mean difference (WMD) and their corresponding 95% confidence interval (CI) were derived using random-effects models. We conducted meta-, heterogeneity, publication bias, sensitivity, and subgroup analyses. Eighteen studies, involving a total of 157,607 individuals (32,395 with OSAS, 125,212 without OSAS) and 12,262 gout cases, were included. Results show that serum uric acid levels are elevated in patients with OSAS (WMD = 52.25, 95% CI 36.16-64.33); OSAS did not reach statistical significance as a predictor of gout (but there was a trend, HR = 1.25, 95% CI 0.91-1.70) and that the association between OSAS and serum uric acid was quite robust. OSAS may be a potential risk factor for hyperuricemia and the development of gout and thus, effective OSAS therapy may present as a valuable preventive measure against gout. Still, it is vital to undertake clinical studies with better designing to corroborate these associations and shed new light on it.

The Risk of Gout Among Patients With Sleep Apnea: A Matched Cohort Study

OBJECTIVE

Obstructive sleep apnea (OSA) is associated with a range of serious comorbidities. This study was undertaken to investigate whether people with OSA are more likely to develop gout, in the short and long term, compared to those without OSA.

METHODS

A matched retrospective cohort study was undertaken using the UK Clinical Practice Research Datalink. Individuals age ≥18 years who received a diagnosis of OSA between 1990 and 2010 were identified and matched on age, sex, and practice with up to 4 individuals without OSA; follow-up was until the end of 2015. Hazard ratios (HRs) were estimated using Cox regression adjusted for general health, lifestyle, and comorbidity characteristics. The risk of developing gout was assessed at different time points, and the body mass index (BMI) category-specific results were presented.

RESULTS

The study sample included 15,879 patients with OSA and 63,296 without. The median follow-up was 5.8 years. We found that 4.9% of patients with OSA and 2.6% of patients without the disorder developed gout. The incidence rate per 1,000 person-years was 7.83 (95% confidence interval [95% CI] 7.29-8.40) and 4.03 (95% CI 3.84-4.23) among those with and without OSA, respectively. The adjusted HR was 1.42 (95% CI 1.29-1.56). The risk of developing gout among OSA patients compared to those without was highest 1-2 years after the index date (HR 1.64 [95% CI 1.30-2.06]). This finding persisted among those who were overweight and obese. For those with normal BMI, the highest significant HR (2.02 [95% CI 1.13-3.62]) was observed at 2-5 years after the index date.

CONCLUSION

In this study, patients with OSA continued to be at higher risk of developing gout beyond the first year following the diagnosis. Our results further indicate that peak incidences of gout vary according to BMI.

Evaluation of Inflammatory Markers in a Large Sample of Obstructive Sleep Apnea Patients without Comorbidities

Systemic inflammation is important in obstructive sleep apnea (OSA) pathophysiology and its comorbidity. We aimed to assess the levels of inflammatory biomarkers in a large sample of OSA patients and to investigate any correlation between these biomarkers with clinical and polysomnographic (PSG) parameters. This was a cross-sectional study in which 2983 patients who had undergone a polysomnography for OSA diagnosis were recruited. Patients with known comorbidities were excluded. Included patients (n = 1053) were grouped according to apnea-hypopnea index (AHI) as mild, moderate, and severe. Patients with AHI < 5 served as controls. Demographics, PSG data, and levels of high-sensitivity C-reactive protein (hs-CRP), fibrinogen, erythrocyte sedimentation rate (ESR), and uric acid (UA) were measured and compared between groups. A significant difference was found between groups in hs-CRP, fibrinogen, and UA. All biomarkers were independently associated with OSA severity and gender (p < 0.05). Females had increased levels of hs-CRP, fibrinogen, and ESR (p < 0.001) compared to men. In contrast, UA levels were higher in men (p < 0.001). Our results suggest that inflammatory markers significantly increase in patients with OSA without known comorbidities and correlate with OSA severity. These findings may have important implications regarding OSA diagnosis, monitoring, treatment, and prognosis. This trial is registered with ClinicalTrials.gov number NCT03070769.

Red cell distribution width and uric acid in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA), characterized by recurrent partial or complete pharyngeal closure, resulting in apnea or hypopnea, is closely associated with cardiovascular disorders (CVDs). Elevated red cell distribution width (RDW) and serum uric acid (SUA) levels have also been associated with CVDs and the consequent mortality. The aim of this study is to determine SUA levels and RDW in patients with OSA which is major a risk factor for CVDs.

METHODS

This was a retrospective study involving 600 subjects evaluated by polysomnography. Patients were grouped according to the apnea-hypopnea index (AHI), expressed as control group or as mild OSA, moderate OSA, and severe OSA groups.

RESULTS

The mean RDW and the mean SUA were significantly higher in the severe OSA group than in all other groups (P < .015 and P < .003, respectively, for all). RDW was negatively correlated with minimum S_pO2 (r = -.142, P < .01) and positively correlated with mean oxygen desaturation time (r = .113, P < .05). SUA was negatively correlated with minimum S_pO2 (r = -.229, P < .01). The RDW was significantly higher in the OSA patients with CVDs than in those with OSA only (P < .05), although there was no significant difference between the OSA patients with and without CVDs in terms of the SUA in any of the groups (P > .05).

CONCLUSIONS

Elevated levels of SUA and RDW were associated with OSA severity, as defined by AHI. In addition, RDW was significantly higher in severe OSA with CVDs.

Sleep Apnea and the Risk of Incident Gout: A Population-Based, Body Mass Index-Matched Cohort Study

OBJECTIVE

Sleep apnea is associated with hyperuricemia owing to hypoxia-induced nucleotide turnover. We undertook this study to assess the relationship between incident sleep apnea and the risk of incident gout.

METHODS

Using data from The Health Improvement Network in the UK, we identified individuals with a first-ever physician diagnosis of sleep apnea. For each patient with sleep apnea, up to 5 individuals without sleep apnea were matched by sex, age, birth year, and body mass index (within ±0.5 kg/m(2) ). We estimated the incidence rates of gout and examined the relationship between sleep apnea and the risk of incident gout using a Cox proportional hazards model, adjusting for potential confounders. In addition, we assessed the rate difference in gout due to sleep apnea using an additive hazard model.

RESULTS

Among 9,865 patients with newly diagnosed sleep apnea and 43,598 matched individuals without sleep apnea, we identified 270 incident cases of gout over 1 year of followup, resulting in incidence rates of 8.4 per 1,000 person-years and 4.8 per 1,000 person-years, respectively. The crude and multivariable rate ratios of incident gout in patients with sleep apnea were 1.7 (95% confidence interval [95% CI] 1.3, 2.2) and 1.5 (95% CI 1.1, 2.1), respectively. The corresponding rate differences between patients with sleep apnea and the comparison cohort were 3.6 (95% CI 1.6, 5.6) and 2.8 (95% CI 0.7, 4.9) per 1,000 person-years. The effect of sleep apnea persisted across subgroups.

CONCLUSION

This general population-based study indicates that sleep apnea is independently associated with an increased risk of incident gout. Future research should examine the potential benefits of correcting sleep apnea-induced hypoxia on the risk of hyperuricemia and gout flares.

Serum urate and obstructive sleep apnoea in severe obesity

Obstructive sleep apnoea (OSA) may increase the risk of hyperuricaemia and predispose to gout. The evidence for the effects of OSA on serum urate in severe obesity is limited. This study investigated whether OSA was associated with serum urate in severe obesity and whether continuous positive airway pressure (CPAP) treatment was associated with a fall in urate. Severely obese subjects without known OSA or gout were recruited. Baseline assessments included urate, metabolic parameters, spirometry and overnight polysomnography. OSA patients were initially naive to treatment and were offered CPAP. At follow-up, change in urate was compared between CPAP-treated and non-CPAP-treated subjects. A high urate was defined as greater than the median. Logistic regression was performed to identify associations between (1) OSA and high urate at baseline and (2) use of CPAP and change in urate at follow-up. In total, 92 subjects were recruited (61 (66%) OSA and 31 (34%) non-OSA). Median urate was 345 μmol/L. OSA was associated with high urate in females at baseline after adjusting for confounders (adjusted odds ratio ORadj = 10.2; 95% CI: 1.1, 93.5). At follow-up (14 months), 58 subjects (28 on CPAP and 30 not on CPAP) were reassessed. CPAP was significantly associated with a fall to a low urate category at follow-up ( = 0.017). Regression revealed a trend for a fall in urate category in the CPAP-treated group (ORadj = 9.3; 95% CI: 0.8, 97). Serum urate is associated with OSA in severely obese females and CPAP may reduce levels in patients with OSA. There may be a need to consider and assess for OSA in obese patients with hyperuricaemia and recurrent attacks of gout.

Nocturnal risk of gout attacks

OBJECTIVE

Several plausible mechanisms and anecdotal descriptions suggest that gout attacks often occur at night, although there are no scientific data supporting this. We undertook this study to evaluate the hypothesis that gout attacks occur more frequently at night.

METHODS

We conducted a case-crossover study to examine the risk of acute gout attacks in relation to the time of the day. Gout patients were prospectively recruited and followed up via the internet for 1 year. Participants were asked about the following information concerning their gout attacks: the date and hour of attack onset, symptoms and signs, medication use, and purported risk factors during the 24- and 48-hour periods prior to the gout attack. We calculated the odds ratios (ORs) of gout attacks (with 95% confidence intervals [95% CIs]) according to three 8-hour time blocks of the day (i.e., 12:00 AM to 7:59 AM, 8:00 AM to 3:59 PM [reference], and 4:00 PM to 11:59 PM) using conditional logistic regression.

RESULTS

Our study included 724 gout patients who experienced a total of 1,433 attacks (733, 310, and 390 attacks during the first, second, and third 8-hour time blocks, respectively) over 1 year. The risk of gout flares in the 8-hour overnight time block (12:00 AM to 7:59 AM) was 2.36 times higher than in the daytime (8:00 AM to 3:59 PM) (OR 2.36 [95% CI 2.05-2.73]). The corresponding OR in the evening (4:00 PM to 11:59 PM) was 1.26 (95% CI 1.07-1.48). These associations persisted among those with no alcohol use and in the lowest quintile of purine intake in the 24 hours prior to attack onset. Furthermore, these associations persisted in subgroups according to sex, age group, obesity status, diuretic use, and use of allopurinol, colchicine, and nonsteroidal antiinflammatory drugs.

CONCLUSION

These findings provide the first prospective evidence that the risk of gout attacks during the night and early morning is 2.4 times higher than in the daytime. Further, these data support the purported mechanisms and historical descriptions of the nocturnal onset of gout attacks and may have implications for antigout prophylactic measures.

Epidemiology of gout

Gout is the most prevalent inflammatory arthritis in men. The findings of several epidemiologic studies from a diverse range of countries suggest that the prevalence of gout has risen over the past few decades. Although incidence data are scarce, data from the United States suggests that the incidence of gout is also rising. Evidence from prospective epidemiologic studies has confirmed dietary factors (animal purines, alcohol, and fructose), obesity, the metabolic syndrome, hypertension, diuretic use, and chronic kidney disease as clinically relevant risk factors for hyperuricemia and gout. Low-fat dairy products, coffee, and vitamin C seem to have a protective effect.

Synergistic effects of neck circumference and metabolic risk factors on insulin resistance: the Cardiometabolic Risk in Chinese (CRC) study

OBJECTIVES

Recent studies have associated neck circumference (NC) with insulin resistance (IR). We examined whether such relation was modified by other metabolic risk factors.

METHODS

The study samples were from a community-based health examination survey in central China. A total of 2588 apparently healthy Chinese men and women were included.

RESULTS

Plasma levels of total cholesterol (TC), HDL-C, uric acid (UA) and diastolic blood pressure (DBP) were independently associated with NC after adjusted for age, sex, body mass index (BMI), waist circumference (WC) and hip circumference (HC) (P = 0.009, 0.001, 0.015 and 0.015, respectively). We observed significant interactions of NC with triglyceride (TG) and UA (all the p for interaction = 0.001) in relation to HOMA-IR. It appeared that the associations between NC and HOMA-IR were more evident in those with higher UA or TG level.

CONCLUSIONS

Our data indicate that in apparently healthy Chinese adults, there were synergistic effects of UA, TG and neck circumference on insulin resistance.

Association between uric acid levels and obstructive sleep apnea syndrome in a large epidemiological sample

INTRODUCTION

Recurrent hypoxia, which is associated with obstructive sleep apnea syndrome (OSAS), leads to an increase in the degradation of adenosine triphosphatase into xanthine, which in turn increases uric acid concentrations.

OBJECTIVE

The current study aimed to determine whether an association exists between OSAS and uric acid levels in the peripheral blood from a representative population of Sao Paulo (Brazil).

METHODS

A population-based survey adopting a probabilistic 3-stage cluster sample of Sao Paulo was used to represent the population according to gender, age, and socioeconomic class. A total of 1,042 volunteers underwent polysomnography recordings for OSAS diagnosis, blood pressure assessment, and biochemical blood analysis, and answered questionnaires.

RESULTS

Uric acid levels were correlated with most important risk factors for OSAS, such as AHI, desaturation time and index, minimum oxyhemoglobin saturation (SpO2), blood pressure, cholesterol, BMI, triglycerides and arousal, and with OSAS itself. Also, uric acid was increased in OSAS volunteers even after controlling for all confounders. Hyperuricemic volunteers presented lower mean and minimum SpO2 and increased desaturation index. Importantly, minimum SpO2 was a significant predictor of uric acid levels, which in turn was considered an independent predictor for OSAS in the binary logistic model. However, a ROC curve analysis for establishing cut-off points for uric acid levels as a biomarker of OSAS revealed moderate sensitivity and specificity.

CONCLUSION

A strong association was found between uric acid levels and OSAS in a representative sample of the population of Sao Paulo. Although they do not qualify for a biomarker alone, uric acid levels may be involved in OSAS severity and should be considered in sleep apnea management in the future.

The association of gout with sleep disorders: a cross-sectional study in primary care

BACKGROUND

Both gout and sleep apnoea are associated with the metabolic syndrome. Hyperuricaemia is also prevalent in sleep apnoea syndrome. The objective of this study was to examine the association between gout and sleep apnoea and other sleep disorders.

METHODS

Data were taken from a validated database of general practice records from nine practices in the UK between 2001 and 2008. People consulting for gout were identified via Read codes and each matched with four controls for age, gender, practice and year of gout consultation. Sleep problems and confounding comorbidities were also identified via Read codes. Medications were identified through a linked database of prescription records. The association between gout and sleep disorders was assessed using a logistic regression model, adjusting for ischaemic heart disease, hypertension, diabetes mellitus and diuretic use.

RESULTS

1689 individuals with gout were identified and each successfully matched to four controls. Amongst those with gout, the prevalence of any sleep problem was 4.9%, sleep problems other than sleep apnoea 4.2%, and sleep apnoea 0.7%, compared to 3.5%, 3.2% and 0.3% respectively in controls. Gout was associated with any sleep problem (odds ratio (OR) 1.44; 95% confidence interval (CI) 1.11, 1.87), sleep problems other than sleep apnoea (OR 1.36; 95% CI 1.03, 1.80), and sleep apnoea (OR 2.10; 95% CI 1.01, 4.39). On multivariable analysis, gout remained significantly associated with any sleep problem (OR 1.39; 95% CI 1.06, 1.81) and sleep problems other than sleep apnoea (OR 1.37; 95% CI 1.03, 1.82), however the association with sleep apnoea was attenuated (OR 1.48, 95% CI 0.70, 3.14).

CONCLUSIONS

Gout and sleep problems appear to be associated and clinicians should be aware of the co-existence of these two conditions. Larger prospective epidemiological studies are required to explore causality.

Association between Serum Uric Acid Levels and Sleep Variables: Results from the National Health and Nutrition Survey 2005-2008

Sleep disordered breathing as well as high serum uric acid levels are independent risk factors for cardiovascular disease. However, studies evaluating the relationship between sleep-disordered breathing and hyperuricemia are limited. We examined the 2005-2008 National Health and Nutrition Examination survey's sleep variables and high serum uric acid among 6491 participants aged ≥20 years. The sleep variables included sleep duration, snoring, snorting, and daytime sleepiness. The main outcome was high serum uric acid level, defined as levels of serum uric acid >6.8 mg/dL in males and >6.0 mg/dL in females. We found that snoring more than 5 nights per week, daytime sleepiness, and an additive composite score of sleep variables were associated with high serum uric acid in the age- , sex-adjusted model and in a multivariable model adjusting for demographic and lifestyle/behavioral risk factors. The association was attenuated with the addition of variables related to clinical outcomes such as depression, diabetes, hypertension, and high-cholesterol levels. Our results indicate a positive relationship between sleep variables, including the presence of snoring, snorting, and daytime sleepiness, and high serum uric acid levels.

Highly sensitive determination of uric acid in the presence of major interferents using a conducting polymer film modified electrode

This paper describes the sensitive and selective determination of uric acid (UA) in the presence of important interferences, ascorbic acid (AA), dopamine (DA), tyrosine (Tyr) and methionine (Met) at physiological pH using an electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole on glassy carbon (p-AMTa) electrode. The p-AMTa electrode shows an excellent electrocatalytic activity towards UA. This was understood from the observed higher oxidation current and heterogeneous rate constant (3.24×10(-5)ms(-1)) for UA when compared to bare GC electrode (4.63×10(-6)ms(-1)). The selective determination of UA in the presence of 1000-fold excess of AA was achieved using p-AMTa electrode. Further, the p-AMTa electrode was successfully used for the simultaneous and selective determination of UA in the presence of important interferences, DA, Tyr and Met. Using amperometric method, 40nM UA was detected for the first time. The current response of UA was increased linearly while increasing its concentration from 40nM to 0.1mM and a detection limit was found to be 0.52nM (S/N=3). Finally, the practical application of the present method was demonstrated by determining UA in human urine and blood serum samples.

Serum uric acid and lactate levels among patients with obstructive sleep apnea syndrome: which is a better marker of hypoxemia?

BACKGROUND AND OBJECTIVES

Tissue hypoxia due to repeated sleep apneas leads to increased serum levels of uric acid (UA) and lactate in patients with obstructive sleep apnea syndrome (OSAS). Studies on assessment of serum level of UA in patients of OSAS are available. However, research on simultaneous evaluation of levels of serum lactate and UA is lacking.

DESIGN AND SETTING

Prospective, case-control study in a tertiary care institution.

PATIENTS AND METHODS

Forty patients suffering from OSAS, diagnosed by night polysomnography (PSG), were included in this study. Forty age- and sex-matched subjects in whom the presence of OSAS was ruled out by night PSG were included as healthy controls. Participants underwent a procedure for the measurement of serum UA and lactate before and after sleep.

RESULTS

Both before and after sleep UA levels of patients with OSAS were found to be significantly higher (P=.001 and .002, respectively) as compared to UA levels of controls. A statistically significant (P=.02) overnight (after sleep) rise was observed in the serum lactate level of OSAS patients. The correlation between serum UA values and %TSTs (percentage of total sleep time spent) below 95% SaO2 (arterial oxygen saturation) was statistically significant (P=.02). The correlation was positive with %TSTs below 90% SaO2, whereas it was found negative with normal basal oxygen. No significant correlation was observed between serum UA and the AHI (apnea-hypopnea index). Polysomnographic variables failed to show significant correlation with serum UA on respective multiple regression models controlling for age, body mass index, and waist-hip ratio. However, plasma lactate levels after sleep correlated with %TSTs below 95% of SaO2 and AHI with P values of .02 and .01, respectively.

CONCLUSIONS

Both serum UA and lactate were positively correlated with the degree of hypoxia in OSAS. The plasma UA levels in patients with OSAS did not show an overnight rise. However, the plasma lactate levels were higher in the morning. The measurement of serum lactate level was a better marker of oxidative stress among patients with OSAS.