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uric acid ( ua ) is an end product of purine base metabolism and an antioxidant agent .
serum ua concentration is influenced by several factors such as overproduction , decreased glomerular filtration or renal hypoperfusion , enhanced tubular reabsorption or diminished elimination .
that is degraded by urate oxidase ( urease ) to allantoin , which is freely eliminated in urine .
hyperuricemia is generally defined by ua levels > 6.5 mg / dl or 7 mg / dl in men and > 6 mg / dl in women .
the role of ua as an independent causative or potential risk factor of mortality is controversial in patients with kidney disease , hypertension , obesity , cardiovascular events , diabetes mellitus , ischemic stroke , and cancer disease .
the changes in ua in the clinical setting and pathophysiological events are related to oxidative stress , and provide evidence of impaired plasma antioxidant capacity in severe sepsis .
a correlation has been found between serum ua level and inflammatory markers on population - based cohort studies .
serum ua concentrations can be considered as a marker of severity in critically ill patients without craniocerebral trauma and especially in patients with meningococcal infection .
changes in hypoxanthine , xanthine , ua concentrations , and oxygen transport parameters can be used to assess changes in the functioning of the microcirculatory bed .
it has been established that an increased blood plasma level of hypoxanthine and xanthine may serve as an additional criterion of tissue hypoxia in critically ill surgical patients .
ua level during the 1 day of intensive critical care admission is not an independent risk of mortality in pediatric intensive care unit ( icu ) , although the presence of sepsis and high level of ua have been associated with poor outcome .
a number of scoring systems have been developed that circumvent the complexity and time constraints of traditional scoring systems developed to use in icu setting .
these scoring systems contain many items that should be checked in different times after admission , and sometimes are very time - consuming .
we presumed that ua level at the early hours of admission could predict the mortality of the admitted patients as a simple single test .
this study was conducted to evaluate the validity of serum ua in prediction of mortality in patients in the emergency department .
this is a prospective cohort study which was conducted during june  december 2014 in observation unit of the emergency room of imam khomeini hospital , sari , iran .
the unit has four beds with intensive care facilities . in this study , 120 ( above 18 years old )
patients who needed intensive care for the first time and maintained in the same condition for at least 24 h were included in the study and their blood samples were taken before initiation of any treatment .
the exclusion criteria was ; age under 18 years old , having trauma , acute coronary syndrome , myocardial infarction , hemodialysis , plasma creatinine of above three , any type of cancer , patients with hyperuricemia , and patients taking allopurinol .
this study was accepted and confirmed by the ethics committee of mazandaran university of medical sciences .
the epidemiological and clinical information of the patients was obtained by one physician and confirmed by another .
ua level was measured by using the colorimetric uricase methods in only one selected laboratory of imam khomeini hospital with the instrument selectra e device and ready to use ua toos commercial reagent kits obtained from ua pars azmoon co , iran . for evaluation of the severity of the disease ,
the scores range is between 0 and 27 , with nine items and the scoring system are as follows : respiratory distress ( defined as having respiratory rate above 20/min or o2sat < 90% in the normal room air or needing oxygenation with mask or experiencing apnea ) : three points , septic shock ( clinical symptoms indicative of positive systemic inflammatory response syndrome and suspicious or confirmed infectious foci accompanied with resistance to primary fluid therapy hypotension .
three points , platelet count < 150,000 : three points , bandemia > 5% : three points , age > 65 years : three points , lower respiratory tract infection ( defined as infiltration in chest x - ray or clinical evidence indicative of this diagnosis ) : two points , needing in - home care nursing service : two points , and any change in the level of awareness : this system included nine items , scores ranged 0 - 27 .
these scores explained as following : 04 : very low risk , 57 : low risk , 812 : moderate risk , 1315 : high risk , 15 < very high risk .
mortality in emergency department sepsis score mortality rate of the patients in the first 28 days of hospitalization was considered as the primary outcome .
furthermore , the requirement of using mechanical ventilation and taking vasopressor during the hospitalization time and severity of the disease based on meds score were measured . finally ,
relationship of the serum ua level was evaluated by the cutoff point of 7.3 mg / dl for each outcome .
receiver operating characteristic ( roc ) curve area was used for determination of the validity of ua level test in prediction of mortality . for comparison of the groups below 7.3 mg /
dl ua group and above 7.3 mg / dl ua group , chi - square and independent t - test used p < 0.05 were considered statistically significant .
finally , relationship of the serum ua level was evaluated by the cutoff point of 7.3 mg / dl for each outcome .
receiver operating characteristic ( roc ) curve area was used for determination of the validity of ua level test in prediction of mortality . for comparison of the groups below 7.3 mg /
dl ua group and above 7.3 mg / dl ua group , chi - square and independent t - test used p < 0.05 were considered statistically significant .
sixty - two males ( 51.7% ) and 58 females ( 48.3% ) were included in the study .
the patients were divided into two groups : patients with serum ua level of lower than 7.3 mg / dl and patients with serum ua level of equal or more than 7.3 mg / dl .
each group consisted of sixty patients : 29 ( 48.3% ) males and 31 ( 51.7% ) females in the serum ua < 7.3 mg / dl group , 33 ( 55% ) males and 27 ( 45% ) females in the serum ua 7.3 mg / dl . no significant statistical differences were found according to the gender of patients in these groups . in general , the average age of the patients in the serum ua 7.3 mg / dl group was significantly higher . during the study ,
31 patients underwent mechanical ventilation , from which the number of patients with serum ua levels of higher than 7.3 mg / dl were more than other group , but this difference was not statically significant ( p = 0.061 ) . in patients who needed mechanical ventilation ,
an average of serum ua was 7.82  2.82 ; however , in the patients who did not need mechanical ventilation this amount was 6.16  2.7 , the difference was statically significant [ table 2 ] .
comparison of patients in two groups of high and low uric acid level in according age , gender , requirement of ventilator and vasopressor medicine in the roc analysis with the cutoff point of 6.95  0.73 for ua level , the under the curve area of 0.667 ( 95% confidence interval [ ci ] : 0.5610.774 ) with 71% sensitivity and 55.1% specificity for prediction of patient 's need to use mechanical ventilation were taken into account ( p  0.006 ) [ figure 1 ] .
receiver operating characteristic curve for predicting the need of using ventilator according uric acid level cutoff point during this study , majority of patients who needed to take vasopressor medication had serum acid uric level of above 7.3 mg / dl .
out of 120 participants , 96 patients who did not take vasopressor , the mean serum ua level was 6.39  2.84 .
in the evaluation of meds , most patients having serum ua levels of lower than 7.3 mg / dl had lower meds points ( on average 4.6  3.21 ) in compared to patients with high serum ua levels ( on average 12  2.99 ) .
this difference was found to be statically significant which , indicates the patients with serum ua equal to 7.3 mg / dl or higher , were at higher risk of mortality [ table 3 ] .
comparison of patients mortality in emergency department sepsis score in high and low serum uric acid levels twelve patients expired during the study , 9 of whom were older than 65 years old .
total mean serum ua level was 7.65  3.25 , although , in patients who did not survive during the study it was higher than survived patients ( 6.47  2.76 ) , this difference was not significant ( p  0.171 ) .
furthermore , results showed that expiry of patients underwent mechanical ventilation and took vasopressor , were significantly higher than other patients [ table 4 ] .
comparison of patients mortality rate according serum uric acid level , needing ventilator , and taking vasopressor using serum ua level cutoff point for predicting possibility of patients ' mortality via roc curve was not found to be significant ( area under curve : 0.595 [ ci : 0.4220.770 ] , p = 0.27 ) [ figure 2 ] .
therefore , serum ua level cutoff point could not predict possibility of patients ' mortality in this study .
receiver operating characteristic curve for determination of serum uric acid cutoff point to predict mortality in patients
based on the results of this study , there is no relationship between serum ua level and mortality rate of patients regardless of their underlying diseases .
however , serum ua levels were meaningfully higher in patients who underwent mechanical ventilation . using mechanical ventilation , infusion of vasopressor and age of higher than 65 years ,
ua level is an independent risk factor in the treatment of hypertension and is also associated with the cardiovascular accidents .
ua level is considered as an index in early diagnosis of renal failure and patients with asymptomatic hyperuricemia are at higher risk of progression to end - stage renal disease .
various factors effect on serum ua level and changes in ua level are related to oxidative stress in the clinical situation .
these changes cause disturbance in the antioxidative capacity of plasma , especially in septic patients . by increase in acute physiology and chronic health evaluation
( apache ii ) score , a special pattern is noted in plasma metabolism , and plasma ua amount increases progressively in patients with poor medical conditions . in one study , it has been shown that the level of serum ua in the 1 day of admission in icu was not related to the mortality rate ; however , effects of mechanical ventilation and resistant shock were the main mortality factors regardless of serum ua level .
these research results are in agreement with our findings . however , in a study on fifty critically ill patients the level of serum ua was shown to be higher in nonsurvivor patients compared to the survivors .
the serum ua levels of 7 mg / dl or higher , will extend the hospitalization time of patients in icu and also increases the time of using mechanical ventilation in patients .
the level of serum ua increases in respiratory disorders , especially if hypoxia and systemic inflammation exist .
study , which was done on patients having respiratory diseases , revealed that serum ua level 6.9 mg / dl is an independent predicting factor in 1-month mortality of the patients .
moreover , duration of hospitalization in icu and using mechanical ventilation are longer in these patients in 1 month .
one of the most important findings in our study was the relationship between needing to use the mechanical ventilation and the amount of serum ua ; it means that serum ua level of 6.95  0.73 and above has 71% sensitivity and 55.1% specificity in prediction of demanding mechanical ventilation .
patients with acute respiratory failure who needed mechanical ventilation had a higher amount of ua urea and mortality rate .
similarly , in our study , the mortality rate was higher in patients who underwent mechanical ventilation and took vasopressor . in the hooman et al .
study , needing to administer vasopressor was shown to be an independent variable in poor outcome patients . the level of serum ua has a direct relationship with apache ii score , which means that patients with high apache ii score have higher serum ua levels .
similarly , in our study there was a direct association between serum ua and meds ; however , the mortality rate was not associated with meds . in this study , there were various factors such as dehydration , taking nephrotoxic drugs , severity of the underlying disease , instability of the vital signs , and medical complications during hospitalization ( e.g. , nosocomial infections ) which can influence the outcome of the patients ; therefore , these factors and incidents , when occurring during the hospitalization time can have an effect on the mortality of the patients the same way as the primary condition of the patients . considering this issue and limitations of this study
, the predictive value of serum ua in patients ' mortality can be improved by measuring the serum ua several times , taking into account the medical complications during hospitalization and uniform sampling of the patients .
the serum ua level in the 1 day of hospitalization of a critically ill patient is not an independent indicative factor for mortality ; however , age of above 65 years , requirement of mechanical ventilation and a shock which needs vasopressor infusion , indicate a poor outcome for the patient regardless of his serum ua level .
however , high level of ua reveals critical status of the patient and requires mechanical ventilation .
aim : this study was conducted to evaluate the validity of serum uric acid ( ua ) in prediction of mortality among patients in the emergency department.materials and methods : this is a prospective cohort study which was conducted during 2014 . in this study , 120 critically ill patients who required intensive care unit care services were included . 
 for evaluation of severity of the disease , mortality in emergency department score ( meds ) in the first 24 h of admission , the requirement of using mechanical ventilation , taking vasopressor during the hospitalization time and severity of the disease based on meds score were measured . 
 the patients were divided into two groups : patients with serum ua level lower than 7.3 mg / dl and patients with serum ua level of equal or more than 7.3 mg / dl . 
 for comparison of the mortality rate in groups , chi - square and fisher exact tests were applied.results:in patients , who needed mechanical ventilation , average of serum ua was 7.82  2.82 ; however , in the patients who did not need mechanical ventilation this amount was 6.16  2.7 , a difference was statically significant . 
 we found a statically meaningful difference between serum ua level with requiring mechanical ventilation and the predictive level of ua 6.95  0.73 ( f = 8.52 ; p  0.004 ) . in the evaluation of meds , most patients with serum ua levels lower than 7.3 mg / dl had lower meds points ( on average 4.6  3.21 ) in compared to patients with serum ua level higher than 7.3 mg / dl ( on average 12  2.99 ) . 
 this difference was found to be statistically significant which indicates the patients whose serum ua was 7.3 mg / dl or higher , were at higher risk of mortality.conclusion:the serum ua level in the 1st day of hospitalization of a critically ill patient is not an independent indicative factor in relation to mortality . 
 high level of ua reveals critical status of the patient and requires mechanical ventilation .