prostate - specific antigen ( psa ) is one of the most important tools for the early detection of prostate cancer .
an elevated serum psa level is an indication to pursue additional diagnostic evaluation , including ultrasound - guided prostate biopsies , to rule out prostate cancer .
however , the major drawback of serum psa testing is that psa is prostate - specific but not prostate - cancer - specific .
various physiological and benign pathologic processes , including prostatitis , urinary retention , and ejaculation , can affect the serum psa level [ 3 - 8 ] . also , there are limited data on the effect of hospitalization on the serum psa level .
serum psa levels measured at least 24 hours after admission in hospitalized patients have been shown to be decreased compared with those measured in the outpatient department before admission , which suggests that the lack of activity associated with bed rest during hospitalization might decrease serum psa values .
however , there have been no reports comparing serum psa levels measured just after admission with those measured in the outpatient department before admission .
if serum psa levels measured just after admission are decreased compared with those measured in the outpatient department , only the serum psa levels measured in the outpatient department should be considered for the serial monitoring of psa levels in patients with equivocal serum psa values . therefore , in this study , inpatient serum psa ( ipspsa ) values measured just after admission were compared with the preadmission outpatient serum psa ( opspsa ) values to investigate whether hospitalization influences serum psa values .
transrectal ultrasound - guided needle biopsies of the prostate were performed for detecting prostate cancer in 2,017 patients between february 2001 and april 2011 at our institution .
the indications for prostate biopsy were serum psa elevation or abnormal findings on a digital rectal examination or transrectal ultrasonography .
young patients with serum psa elevation usually underwent prostatitis workup and were given oral antibiotic treatment if needed . the decision to biopsy was based on an elevated repeat psa level after a period of time and the patient 's preference despite being informed of the low risk of prostate cancer . among the total 2,017 patients , the patients who underwent prostate biopsies on an outpatient department basis , in whom preadmission opspsa was not measured at ajou university hospital , who had a pathologic diagnosis of prostate cancer , who had recent clinical evidence of acute urinary retention , or who had an interval of more than 1 month between opspsa and ipspsa were excluded .
patients who had been taking 5-reductase inhibitors or phytotherapeutic agents within 6 months of biopsy were also excluded from the analysis . all other medications including -blockers
were allowed to be taken until the day of biopsy , except for antiplatelet drugs and anticoagulants , which were instructed to be stopped or switched to short - acting drugs a few days before .
finally , we retrospectively reviewed the data of 416 patients who were hospitalized for prostate biopsies ; whose opspsa and ipspsa values were measured in our hospital within 1 month of admission and just after admission , respectively ; and whose prostate biopsy results revealed no evidence of cancer .
blood sampling for psa was always instructed to be taken before any procedures that could influence the serum psa level , such as digital rectal examination , prostatic massages , transrectal ultrasonography , and cystoscopy .
five milliliters of blood was collected from an antecubital vein and was immediately sent to our hospital 's central laboratory .
psa was measured in serum samples by using a microparticle enzyme immunoassay in an asym immunoassay analyzer ( abbott diagnostics , abbott park , il , usa ) until 2006 and afterwards by using an electrochemiluminescence immunoassay ( roche diagnostics gmbh , mannheim , germany ) in a modular e170 analyzer ( hitachi , ibaraki , japan ) .
the patients were usually hospitalized at 17:00 to 18:00 in the afternoon for prostate biopsies .
samples were obtained for blood tests , including psa , immediately after admission , and prostate biopsies were performed the next day after admission , irrespective of the serum psa level during hospitalization .
the opspsa and ipspsa measurements were compared according to age , the presence or absence of chronic prostatitis in biopsy pathology , serum psa levels , and prostate size .
statistical analysis was performed by using paired sample t - tests with spss ver . 16.0 ( spss inc . ,
the mean age of the 416 patients included in this study was 61.6 years ( range , 29 to 85 years ) . among all 416 patients , the mean interval between opspsa and ipspsa measurements was 22.2 days ( range , 3 to 30 days ) .
the mean prostate size measured by transrectal ultrasonography was 53.63 ml ( range , 12.8 to 197.9 ml ) . among all 416 patients , the mean ipspsa levels ( 6.69 ng / ml ) were significantly lower than the opspsa levels ( 8.01 ng / ml , p<0.001 ) ( table 1 ) .
when the patients were stratified according to age , mean ipspsa levels were significantly lower than opspsa levels in patients aged 40 to 59 years ( p<0.001 ) and 60 years ( p<0.001 ) .
the mean ipspsa levels were lower than opspsa levels in patients aged 20 to 39 years , but not significantly so ( p=0.141 ) .
when the patients were stratified according to the presence or absence of chronic prostatitis in biopsy pathology , mean ipspsa levels were significantly lower than opspsa levels , irrespective of the presence or absence of chronic prostatitis ( p<0.001 and p=0.001 , respectively ) .
when the patients were stratified according to the serum psa level , mean ipspsa levels were significantly lower than opspsa levels in patients with psa of 4 to 9.9 ng / ml ( p<0.001 ) and 10 ng / ml ( p<0.001 ) .
the mean ipspsa levels were lower than the opspsa levels in patients with psa < 4 ng / ml , but not significantly so ( p=0.116 )
. when the patients were stratified according to prostate size , mean ipspsa levels were significantly lower than opspsa levels , irrespective of prostate size ( table 1 ) .
various physiologic and benign pathologic processes can lead to elevations of the serum psa level .
these factors include nonmalignant diseases of the prostate , such as benign prostatic hyperplasia , acute and subacute prostatitis , prostatic ischemia , and infarction of the prostate .
urinary retention and ejaculation can also lead to increased psa levels in the absence of prostatic diseases .
in addition , physical manipulation of the prostate , such as prostatic massages , cystoscopy , or in rare cases , digital rectal examination , can also increase serum psa levels [ 3 - 8 ] .
there have also been many studies of biological variations in serum psa levels [ 11 - 13 ] .
a more recent survey of 27 published studies suggested that a single measurement of the serum psa level may not be sufficiently precise for screening and diagnosis of prostate cancer , because the mean biological variation of psa is 20% in the range of 0.1 to 20 ng / ml for men over 50 years . with regard to the daily variability in the serum psa level , mermall et al .   reported a circadian variation of serum psa with a nadir value in the early morning and a peak value at midafternoon .
by contrast , tekin et al .   demonstrated a diurnal rhythm in psa with a peak value at 08:00 and a gradual decline throughout the day until midnight .
however , many other studies have reported that the variations in serum psa values during a 24-hour period are random without any diurnal or circadian pattern [ 17 - 20 ] .
therefore , it is unlikely that there is an optimal time point during a 24-hour period at which to measure psa , and blood samples for serum psa values can be drawn from patients at any time of day .
there have also been a few reports about discrepancies between outpatient and inpatient serum psa values in the same man .
stamey et al .   reported that serum psa levels measured 24 hours after admission decreased by a mean of 18% with a maximum of 50% when compared with preadmission levels .
this may be due to the lack of activity associated with bed rest during hospitalization , and physical exertion owing to ambulatory status could cause an increase in serum psa values .
confirmed the findings of stamey et al .   by showing a significant difference between outpatient values and inpatient values measured after a minimum of 24 hours of bed rest .
however , they found that the stressful exercise of cardiac stress testing during hospitalization had no effect on serum psa values .
.   also found that the serum psa levels measured 72 hours after hospitalization significantly decreased by a median of 12% compared with the values obtained immediately before admission . although the reasons for this decrease in the serum psa level are uncertain , it is probable that the lack of activity compared with the preadmission ambulatory status could contribute to the decrease in serum psa levels , because blood samples were obtained 24 to 72 hours after admission in the above 3 studies .
the effect of exercise on the serum psa level is controversial . whereas exercises such as bicycle riding increased the serum psa levels in some reports
, exercises such as bicycle riding or high - altitude trekking did not affect the serum psa levels in others .
in the most recent study by loprinzi and kohli , participants were 16% more likely to have an elevated serum psa level for every 1-hour increase in sedentary behavior , and were 18% less likely to have an elevated serum psa level for every 1-hour increase in light physical activity .
therefore , those authors suggested that individuals who engage in more sedentary behavior and lower levels of light physical activity have higher serum psa values . in the current study , we obtained the blood samples for ipspsa testing just after admission and found that the ipspsa values were decreased compared with the preadmission levels .
therefore , the effects of resting and sedentary behavior did not seem to influence the results .
the reasons for the decrease in serum psa levels after hospitalization are still not certain .
the decrease in ipspsa levels compared with opspsa levels , although not significant , in patients aged 20.39 years and with psa < 4 ng / ml might have been due to the small sample size of these subgroups compared with the other subgroups .
psa variability may be related to analytical variation according to the methods of psa measurement , sample handling , and laboratory processing .
therefore , we excluded patients in whom opspsa was not measured in our hospital to eliminate the effects of analytical variation .
serum psa was measured by using two different immunoassay systems according to the period of psa testing in our hospital . however , because our focus of analysis was the comparison of opspsa and ipspsa in the same man with an interval between the two psa measurements of within 1 month , and opspsa and ipspsa in the same man were measured by using the same immunoassay system , there should be no analytical variation according to the laboratory processing .
we also excluded patients with an interval of more than 1 month between opspsa and ipspsa measurements to minimize the possible effect of biological variation in serum psa levels .
we also excluded patients who had a pathologic diagnosis of prostate cancer , because the serum psa level might be influenced during the time interval between the opspsa and ipspsa . in our previous report
about short - term ( median interval , 29 days ; range , 7 to 90 days ) psa velocity before prostate biopsy in 670 patients with serum psa levels of 2.5 to 20 ng / ml , median short - term psa velocity ( ng / ml / mo ) , which was defined as ( [ ipspsa - opspsa]/interval [ days])30 , was significantly different between patients with benign histology and those with prostate cancer ( -0.70 and -0.20 , respectively ; p=0.021 ) .
the factor of recent ejaculation , which can affect the serum psa level , was not analyzed in this study .
another limitation of our study is that the time of blood sampling was different for opspsa and ipspsa .
the blood sampling for the former was mostly done in the morning or early afternoon , whereas that for the latter was done in the late afternoon .
as discussed earlier , the influence of the timing of psa measurement within a day is controversial .
moreover , the steps following the blood sampling , i.e. , from the handling of samples until the analysis , were identical for both , excluding any possible influence from preanalytical differences . nevertheless , we believe that the ipspsa levels were decreased compared with opspsa levels ; thus , the hospitalization itself decreased the serum psa levels . therefore , serum psa values should be measured on an outpatient basis for the serial monitoring of psa . a larger prospective
hospitalization decreases serum psa values compared with those measured on an outpatient basis in patients with benign prostatic diseases .
therefore , serum psa values should be measured on an outpatient basis for the serial monitoring of psa levels .
 purposeto investigate whether hospitalization influences serum prostate - specific antigen ( psa ) values.materials and methodstransrectal ultrasound - guided prostate biopsies were performed for detecting prostate cancer in 2,017 patients between february 2001 and april 2011 at ajou university hospital . of those patients , 416 patients who were hospitalized for prostate biopsies , whose serum psa values were measured at the outpatient department within 1 month of admission and also just after admission , and who had negative prostate biopsy results were included in the present study . 
 we retrospectively reviewed the data of the 416 patients and compared the serum psa values measured in the outpatient department with those measured during hospitalization.resultsamong all 416 patients , the interval between the two psa measurements was 22.2 days ( range , 3 to 30 days ) and the prostate size measured by transrectal ultrasonography was 53.63 ml ( range , 12.8 to 197.9 ml ) . among all patients , 
 mean serum psa levels measured during hospitalization were significantly lower than those measured in the outpatient department ( 6.69 ng / ml vs. 8.01 ng / ml , p<0.001 ) . 
 when stratified according to age , the presence or absence of chronic prostatitis in the biopsy pathology , serum psa levels , and prostate size , the serum psa levels measured during hospitalization were significantly lower than those measured in the outpatient department in all subgroups , except in cases aged 20 to 39 years and those with psa < 4 ng / ml , in whom no significant differences were shown.conclusionshospitalization decreases serum psa values compared with those measured on an outpatient basis in patients with benign prostatic diseases . therefore , serum psa values should be checked on an outpatient basis for serial monitoring . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS