
 nowadays , laboratory services play a major role in optimizing patient care . in some circumstances , increased laboratory use is allowed such as : 1 .
the duration of the patient s hospitalization can be shortened ( 1 - 4 ) . 
 

previous test results are not available or the physician does not know about them ( 5 - 8 ) , nevertheless , information technology can display previous test results and reduce useless repeat testing ( 9,10 ) .
a performed test , repeats again for the patient after admission to hospital ( 11 ) .
3 . pre - analytic errors occur and there is a need for re - sampling the specimen ( 12,13 ) .
in the early decades of 1970 , lundberg and his colleagues at the los angeles county / university of southern california medical center introduced the term  panic values  for those kinds of laboratory results that can predict high risk danger for the patients and be life - threatening unless the physicians do some immediate possible intervention .
after some criticism that physicians should not be panic for any cause , they changed it to  critical values 
( 12,13,16 ) . 
 
 in time , reporting of critical laboratory test values became an important operation of clinical laboratory utilization and has been adapted worldwide including some laboratory accreditation agencies , such as the college of american pathologists ( cap ) and the joint commission on accreditation of healthcare organizations ( jcaho ) that have made it part of the requirements for laboratory accreditation ( 17,18 ) .
they require laboratories to define their own list of critical test values according to their national safety conditions and an authentic system to report of such results to patient s caregivers ( 18 - 20 ) . 
 

the jcaho announced improving the process of critical value reporting a national patient safety goal for the years 2004 through 2006 .
also it has defined critical test results as not only laboratory tests but also imaging , electrocardiograms , and other diagnostic proceedings ( 17 ) . 
 
 in the early years of automatic laboratory procedures , there were no advanced laboratory information system ( lis ) technology and instruments with sensitive level sensors and clot detectors .
therefore , it was acceptable to repeat critical test values to prevent inaccurate results created due to common problems such as misidentification of the sample , fibrin clots , or insufficient samples .
but nowadays repeating them is necessary only when we have uncertain results otherwise it is an unnecessary work to do ( 21 ) . as a recent summary of data from a college of american pathologists ( cap )
q - probes survey shows that pre - analytic and post analytic errors representing 85% to 92% of all clinical laboratory related errors , while analytic issues include only 8% to 15% of them ( 22,23 ) .
it also approved that 60.8 percent of laboratories still repeat critical values in chemistry , and 52.6 percent always repeat critical values in hematology ( 24 ) . 
 
 on the other hand
, unnecessary tests may have some disadvantages such as : 1 . performing inappropriate treatments .
2 . causing fear and anxiety in patients by false positive results , or inducing a large number of further unnecessary testing ( 25,26 ) .
3 . increased costs for the patients and health care system which could lead to other incompetencies in health care delivery ( 27 - 31).4 .
delay reporting to caregiver for example , the cap q - probes survey expressed that laboratory routine repeat testing can delay reporting by 10 to 14 minutes without increasing the accuracy of the results ( 24,31,32 ) . 
 

so far , several studies have been conducted recently about the routine repeat testing of critical values in laboratories and its possible effect on increasing accuracy of the results , such as : 1 .
chima et al s study in 2007 on 580 repeated tests in hematology , coagulation , and chemistry testing ( 21 ) .
2 . toll et al s study in 2010 on 500 consecutive critical results in 5 different hematology and coagulation tests ( 31 ) .
3 . deetz et al s study in 2011 on 3162 critical results ( 33 ) .
they all reported that routine repeating critical test values did not offer any advantage over single testing in improving results accuracy . 
 

there has not been any study about determining the effect of routine repeat testing of critical values in laboratory tests in iran .
moreover , the international studies on this subject mostly cover a limited range of laboratory tests .
therefore , we conducted our research in a way that covers various tests to overcome this shortcoming of existing literature .
another incentive for our research is the fact that the majority of laboratories in iran , especially the ones in educational hospitals apply routine repeat testing of critical values as their regular method .
this method is time consuming and expensive , so unless they add significant prognostic information they can be avoided .
our goal was to determine the effect of routine repeat testing of critical values in 13 different hematology , coagulation , and routine chemistry tests . 

specialty services at our hospital include internal medicine , cardiology , neurology , neurosurgery , pediatrics , ophthalmology , ent , gynecology and obstetrics and emergency .
in our hospital we repeat critical laboratory test values routinely to verifying them to ensure their accuracy before reporting them to the physician .
this repeating can be performed on the same collected specimen or on the re - collected one . 
 

tests examined were hemoglobin ( hgb ) , white blood cell count ( wbc ) , platelet count ( plt ) , international normalized ratio ( inr ) , partial thromboplastin time ( ptt ) for hematology laboratory and glucose ( glc ) , potassium ( k ) , sodium ( na ) , phosphorus ( p ) , magnesium ( mg ) , calcium ( ca ) , total bilirubin ( total bil ) and direct bilirubin ( direct bil ) for chemistry laboratory .
hematology tests were performed on ethylenediaminetetraacetic acid ( edta ) -anticoagulated blood specimens on the sysmex kx 21 analyzer . for sodium and potassium tests we used ion selective electrode ( ise ) method on microlyte analyzer .
chemistry tests were performed on serum specimens on the hitachi 902 analyzer , and coagulation tests were performed on citrated blood specimens and analyzed by manual method .
we created a report to retrieve only the repeated critical values tests not any repeated testing .
the data captured in these reports included date , patient i d , age and gender of patients , initial result , repeated result , repeated test was performed in which sample : the same collected specimen or on the re - collected one .
we collect these data for over a year from august 22 , 2011 to august 22 , 2012 . 
 

medical laboratory staff was highly qualified and they have had over five years of experience .
we also directed them on the way that the tests results should be collected and reported . 
 

the critical laboratory test values were collected from patients with a wide variety of clinical complaints including malignancies , infections , autoimmune disorders , traumas , etc . the absolute value and the percentage of change between the 2 test runs for each critical value were calculated and averaged for each test category and then compared to the college of american pathologists / clinical laboratory improvement amendments ( cap / clia ) allowable errors . if the absolute difference or the percentage of change between the repeated value and the initial result was greater than cap / clia allowable error , it was assumed an outlier .
the cap/ clia allowable errors and critical values for the tests are shown in table 1 . 
 

absolute difference , mean , and percentage of change were calculated as follows : 
 
 absolute  diffrence=|ininitial  test  valuerepeated  test  value| 
 
 mean = initial  test  value+repeated  test  value2 
 
 percentage  of  change = absolute  diffrence  initial  test  valueinitial  test  value100 


 all statistical analysis was done by spss19 . absolute difference , mean , and percentage of change were calculated as follows : 
 
 absolute  diffrence=|ininitial  test  valuerepeated  test  value| 
 
 mean = initial  test  value+repeated  test  value2 
 
 percentage  of  change = absolute  diffrence  initial  test  valueinitial  test  value100 


 hemoglobin ( hgb ) : among the 348 hgb critical values , the repeat values of 122 specimens ( 35.06% ) had equal results to the initial test run . 
 
 
white blood cell count ( wbc):among the 469 wbc critical values , the repeat values of 171 specimens ( 36.46% ) had equal results to the initial test run . 
 
 
the repeat values of 95 specimens ( 30.74% ) had equal results to the initial test run . 
 
  international normalized ratio ( inr ) : among the 104 inr critical values , the repeat values of 27 specimens ( 25.96% ) had equal results to the initial test run . in this category ,
69 repeating tests ( 66.35% ) were performed on the re - collected sample . 
 
 
partial thromboplastin time ( ptt):among the 126 ptt critical values , the repeat values of 13 specimens ( 10.32% ) had equal results to the initial test run . in this category ,
86 repeating tests ( 68.25% ) were performed on the same collected sample , and 40 repeating tests ( 31.75% ) were performed on the re - collected sample . 
 
 
phosphorus ( p):among the 82 p critical values , the repeat values of 52 specimens ( 63.4% ) had equal results to the initial test run . 
 
 
glucose ( glc):among the 109 glc critical values , the repeat values of 17 specimens ( 15.6% ) had equal results to the initial test run . 
 
 
potassium ( k):among the 118 k critical values , the repeat values of 62 specimens ( 52.5% ) had equal results to the initial test run . 
 
 
magnesium ( mg):among the 87 mg critical values , the repeat values of 56 specimens ( 64.37% ) had equal results to the initial test run 
 
  sodium ( na):among the 124 na critical values , the repeat values of 76 specimens ( 61.29% ) had equal results to the initial test run . 
 
 
calcium ( ca):among the 106 ca critical values , the repeat values of 36 specimens ( 33.96% ) had equal results to the initial test run . 
 
 
total bilirubin : among the 131 bil total critical values , the repeat values of 22 specimens ( 16.8% ) had equal results to the initial test run . 
 
 
direct bilirubin : among the 120 bil direct critical values , the repeat values of 20 specimens ( 16.67% ) had equal results to the initial test run . 
 

the mean absolute difference and percentage of change between two testing runs for each test category and subgroups of them are tabulated in table 2 . 
 

hgb , hemoglobin ; wbc , white blood cell ; plt , platelet ; inr , international normalized ratio ; ptt , partial thromboplastin time ; p , phosphorus ; glc , glucose ; k , potassium ; mg , magnesium ; na , sodium ; ca , calcium ; bil , bilirubin ; sec , seconds . 
 

the lowest absolute difference was 0.05 mg / dl , obtained for the mg and p results , and the highest absolute difference was 1747.57 per / ml , obtained for the plt results . among the subgroups
the lowest absolute difference was 0.03 mg / dl , obtained for the mg<1 mg / dl results , and the highest absolute difference was 9125 per / ml , obtained for the plt>950000 results . 
 

the lowest percentage of change was 0.37% , obtained for the na results , and the highest percentage of change was 7.99% , obtained for the p results . among the subgroups the lowest percentage of changewas 0.21% , obtained for the na>150 mmol / l results and the highest absolute difference was 7.99% , obtained for the p results . 
 

there was 1 outlier ( 0.2% ) in the wbc test category with the absolute difference of 200 per / ml , and a mean value of 1400 per / ml , 9 ( 2.9% ) in the plt test category with the absolute differences in the range of 1000 to 4000 per / ml , and the mean values in the range of 3500 to 18000 per / ml .
5 ( 4.8% ) in the inr test category with the absolute differences in the range of 0.8 to 1 , and the mean values in the range of 5.6 to 6.5 . 5 ( 4% ) in the ptt test category with the absolute differences in the range of 17 to 18 seconds , and the mean values in the range of 115.5 to 127 seconds , and none in other 9 test categories . 
 
 out of 20 ( 100% ) samples with significant difference ( outlier )
only two ( 10% ) of them were among the tests performed on recollected samples , the rest were performed on the same samples .
both of these cases belong to ptt test which means two of 126 tests ( 1.6% ) and two of 40 recollected samples of this test ( 5% ) showed significant differences .
therefore , we do not have enough evidence to conclude whether recollecting samples have significant effects on the results . 


  international normalized ratio ( inr ) : among the 104 inr critical values , the repeat values of 27 specimens ( 25.96% ) had equal results to the initial test run . in this category ,
69 repeating tests ( 66.35% ) were performed on the re - collected sample . 
 
 
partial thromboplastin time ( ptt):among the 126 ptt critical values , the repeat values of 13 specimens ( 10.32% ) had equal results to the initial test run . in this category ,
86 repeating tests ( 68.25% ) were performed on the same collected sample , and 40 repeating tests ( 31.75% ) were performed on the re - collected sample . 
 
 
phosphorus ( p):among the 82 p critical values , the repeat values of 52 specimens ( 63.4% ) had equal results to the initial test run . 
 
 
glucose ( glc):among the 109 glc critical values , the repeat values of 17 specimens ( 15.6% ) had equal results to the initial test run . 
 
 
potassium ( k):among the 118 k critical values , the repeat values of 62 specimens ( 52.5% ) had equal results to the initial test run . 
 
 
magnesium ( mg):among the 87 mg critical values , the repeat values of 56 specimens ( 64.37% ) had equal results to the initial test run 
 
  sodium ( na):among the 124 na critical values , the repeat values of 76 specimens ( 61.29% ) had equal results to the initial test run . 
 
 
calcium ( ca):among the 106 ca critical values , the repeat values of 36 specimens ( 33.96% ) had equal results to the initial test run . 
 
 
total bilirubin : among the 131 bil total critical values , the repeat values of 22 specimens ( 16.8% ) had equal results to the initial test run . 
 
 
direct bilirubin : among the 120 bil direct critical values , the repeat values of 20 specimens ( 16.67% ) had equal results to the initial test run . 
 

the mean absolute difference and percentage of change between two testing runs for each test category and subgroups of them are tabulated in table 2 . 
 

hgb , hemoglobin ; wbc , white blood cell ; plt , platelet ; inr , international normalized ratio ; ptt , partial thromboplastin time ; p , phosphorus ; glc , glucose ; k , potassium ; mg , magnesium ; na , sodium ; ca , calcium ; bil , bilirubin ; sec , seconds . 
 

the lowest absolute difference was 0.05 mg / dl , obtained for the mg and p results , and the highest absolute difference was 1747.57 per / ml , obtained for the plt results . among the subgroups the lowest absolute difference was 0.03 mg / dl , obtained for the mg<1 mg / dl results , and the highest absolute difference was 9125 per / ml , obtained for the plt>950000 results . 
 

the lowest percentage of change was 0.37% , obtained for the na results , and the highest percentage of change was 7.99% , obtained for the p results . among the subgroups the lowest percentage of changewas 0.21% , obtained for the na>150 mmol / l results and the highest absolute difference was 7.99% , obtained for the p results . 
 

there was 1 outlier ( 0.2% ) in the wbc test category with the absolute difference of 200 per / ml , and a mean value of 1400 per / ml , 9 ( 2.9% ) in the plt test category with the absolute differences in the range of 1000 to 4000 per / ml , and the mean values in the range of 3500 to 18000 per / ml . 5 ( 4.8% ) in the inr test category with the absolute differences in the range of 0.8 to 1 , and the mean values in the range of 5.6 to 6.5 . 5 ( 4% ) in the ptt test category with the absolute differences in the range of 17 to 18 seconds , and the mean values in the range of 115.5 to 127 seconds , and none in other 9 test categories
samples with significant difference ( outlier ) only two ( 10% ) of them were among the tests performed on recollected samples , the rest were performed on the same samples .
both of these cases belong to ptt test which means two of 126 tests ( 1.6% ) and two of 40 recollected samples of this test ( 5% ) showed significant differences .
therefore , we do not have enough evidence to conclude whether recollecting samples have significant effects on the results . 


 as we mentioned before , recent studies showed that the routine repeat testing of critical test values does not have any advantage with recent year s laboratory automated equipments ( 21,31 ) . in a recent study ,
chima et al collected a total of 580 repeated tests for potassium , glucose , platelet count , and activated partial thromboplastin time and expressed that 95.3% of repeated testing for critical values was within their acceptable difference ( 21 ) .
another study examined 500 consecutive critical results for 5 different hematology / coagulation tests . by using their laboratory s acceptable tolerance limits for reruns ( atlr ) ,
toll et al expressed that 0% to 2.2% of the repeated values for these tests were outside of their acceptable range ( 31 ) .
also , in 2011 deetz et al examined 2162 critical results in chemistry laboratory and they found that 2.8% of the repeated values were outside of the cap / clia total allowable errors ( 33 ) .
they all concluded that repeated testing for critical values did not offer an advantage in hematology , chemistry , and coagulation settings . to determine the effect of routine repeat testing of critical values
, we examined 2233 specimens from 13 different hematology , coagulation , and chemistry tests ( 348 hgb critical results , 469 wbc critical results , 309 plt critical results , 104 inr critical results , 126 ptt critical results , 82 p critical results , 109 glc critical results , 118 k critical results , 87 mg critical results , 124 na critical results , 106 ca critical results , 131 total bilirubin critical results , and 120 direct bilirubin critical results ) .
we calculated the absolute difference and the percentage of change between the initial and repeated value for each of them and then compared with cap / clia total allowable errors .
if the absolute difference or the percentage of change between the repeated value and the initial result was greater than cap / clia allowable error , it was assumed an outlier . 
 
 from 2233 repeated test values ,
a total of 20 outliers were detected ( 99.1% ) in which the difference between 2 testing runs exceeded the cap / clia limits for allowable error .
the test results outside this range included : there was only one outlier ( 0.2% ) in the wbc test category , 9 ( 2.9% ) in the plt test category , 5 ( 4% ) in the ptt test category , 5 ( 4.8% ) in the inr test category and none in other test categories .
the significant difference between the initial result and the repeated result in the ptt test category might be attributed to instability of specimens from patients on heparin therapy .
sometimes , heparin inhibition by platelet factor 4 ( released by activated platelets in the specimen ) makes these patient s results poor reproducible ( 34 ) . in the plt test category
, it might be attributed to clot formation in the testing process , and that would decrease the count initially , but because of the poor strength of the clot , it will get a higher count the second time .
another problem with platelet counting is when you get down to really low levels ; debris in the sample ( e.g. ruptured cells , membranes , etc . ) become a significant problem and interferes with the measurement system ( 24 ) . on the other hand , hemolysis due to
the breakdown of red blood cells is important to the laboratory because it can have an effect on laboratory results by increasing them falsely . 
 
 despite our effort ,
first of all , the fact that all of our samples were collected from a single medical laboratory means that our results could be affected by the quality of its instruments , kits and reagents .
secondly , collected data for some tests such as phosphorus and magnesium were limited which could have made some biasness in our results . finally , recollected samples were not available for all of our tests ( they were only available for ptt and inr ) .
therefore , we are not able to make a comprehensive comparison between initial samples and recollected ones . 
 
 as a result of limited time and resources
it will be beneficial for further studies to collect data from different laboratories , which would be more representative . 


 at the end , we can say that the result of our observations is similar to previous studies .
nowadays , with advanced laboratory equipments , the routine repeat testing of critical values has no effect on increasing the accuracy of the results of these tests .
repeat testing may be helpful in some situations , such as when the physician doubts about the accuracy of a result , or when the test result is not consistent with the patient 's condition .
by ignoring the routine repeat testing of critical values we can accelerate the result reporting to caregiver , in addition to , we can reduce the additional test costs . 

 
 background : routine repeat testing of critical laboratory values is very common these days to increase their 
 accuracy and to avoid reporting false or infeasible results . 
 we figure that repeat testing of critical laboratory 
 values has any benefits or not . 

 
 methods : we examined 2233 repeated critical laboratory values in 13 different hematology and chemistry 
 tests including : hemoglobin , white blood cell , platelet , international normalized ratio , partial thromboplastin 
 time , glucose , potassium , sodium , phosphorus , magnesium , calcium , total bilirubin and direct bilirubin . the 
 absolute difference and the percentage of change between the two tests for each critical value were calculated 
 and then compared with the college of american pathologists / clinical laboratory improvement amendments 
 allowable error . 

 
 results : repeat testing yielded results that were within the allowable error on 2213 of 2233 specimens 
 ( 99.1% ) . 
 there was only one outlier ( 0.2% ) in the white blood cell test category , 9 ( 2.9% ) in the platelet test 
 category , 5 ( 4% ) in the partial thromboplastin time test category , 5 ( 4.8% ) in the international normalized ratio 
 test category and none in other test categories . 

 
 conclusion : routine , repeat testing of critical hemoglobin , white blood cell , platelet , international normalized 
 ratio , partial thromboplastin time , glucose , potassium , sodium , phosphorus , magnesium , calcium , total bilirubin 
 and direct bilirubin results does not have any benefits to increase their accuracy . 
 
Introduction
Methods
Statistical analysis
Results
International Normalized Ratio (INR)
Discussion
Conclusion