Usefulness of dipstick test for determining leukocytes and bacteria in urine]

The value of a simple dipstick test (BMtestLN, Boehringer Mannheim-Shionogi) for determination of leukocytes and bacteria in urine was examined. This test consisted of detection of esterase, an enzyme present in leukocytes and the nitrate reduced by bacteria. A total of 666 clinical urine specimens were tested with both tests. The evaluation of leukocytes in urine was compared with microscopic examination, and the identification and measurement of strains was performed using a semiquantitative plate culture method as a reference. The leukocyte esterase test had a sensitivity of 85.3%, a specificity of 67.3%, positive predictive value of 54.7% and negative predictive value of 90.8%. The range of the sensitivity value of nitrate test was 25.7% for the detection of bacteriuria (bacteria greater than or equal to 10(4) CFU/ml). This test had a specificity of 99.6%, positive predictive value of 94.8% and negative value of 82.9%. We concluded that this dipstick test is not useful for determination of the slight change of pyuria, but sensitive for the determination of acute and untreated urinary tract infections.     

Nitrite and leukocyte dipstick testing for urinary tract infection in individuals with spinal cord injury

OBJECTIVE: To determine sensitivity, specificity, and positive and negative predictive values of nitrite (NIT) and leukocyte esterase (LE) testing in relation to laboratory evidence of significant bacteriuria and urinary tract infection (UTI) in persons with spinal cord injury (SCI). DESIGN: Monthly urine cultures were compared with results of dipstick testing. SETTING: Community based. METHODS: Fifty-six people with SCI were evaluated on a monthly basis with dipstick testing for NIT and LE as well as urine cultures. Participants reported whether they believed that they had a UTI and, if so, whether they were treated for the UTI and what symptoms they had experienced. RESULTS: The sensitivity rate for the most comprehensive criteria--defined as positive NIT test, a positive LE positive, or both a positive NIT test and positive LE test--was 0.64 and the specificity rate was only 0.52. No single type of bacteria was found to occur in more than 30% of the urine samples. CONCLUSION: Reliance on dipstick testing for NIT and LE in individuals with SCI can lead to high rates of overtreatment for UTI, given the fact that regular catheterization is associated with significant bacteriuria. Individuals with SCI should be evaluated with urine culture to ensure proper treatment.     

尿干化学分析与尿液沉渣检查对尿路感染诊断价值的比较

目的:探讨尿路感染(UTI)检验的较好方法。方法:以UTI诊断的金标准为参照,对124例UTI住院患者中段尿进行尿干化学分析和尿沉渣WBC计数检验,并作对比分析。结果:尿沉渣镜检的灵敏度、阴性预计值、准确率分别为79.6%、88.5%、81.7%,而尿液干化学分析亚硝酸盐(NIT)或WBC的灵敏度、阴性预计值、准确率分别为63.3%、81.2%、76.8%。结论:在UTI的尿筛查试验中,尿沉渣镜检WBC计数比尿干化学分析NIT、WBC的诊断价值为优。     

Nitrite and Leukocyte Dipstick Testing For Urinary Tract Infection in Individuals With Spinal Cord Injury

Abstract

Objective: Todetermine sensitivity, specificity, and positive and negative predictive values of nitrite (NIT) and leukocyte esterase (LE) testing in relation to Iabaratory evidence of significant bacteriuria and urinary tract infection (UTI) in persons with spinal cord injury (SCI).

Design: Monthly urine cultures were compared with results of dipstick testing. Setting: Community based.

Methods: Fifty-six people with SCI were evaluated on a monthly basis with dipstick testing for NIT and LE as weil as urine cultures. Participants reported whether they believed that they had a UTI and, if so, whether they were treated for the UTI and what symptoms they had experienced.

Results: The sensitivity rate for the most comprehensive criteria-defined as positive NIT test, a positive LE positive, or both a positive NIT test and positive LE test-was 0.64 and the specificity rate was only 0.52. No singletype ofbacteria was found to occur in more than 3 0% of the urine samples.

Conclusion: Reliance on dipstick testing for NIT and LEin individuals with SCI can Iead to high rates of overtreatment for UTI, given the fact that regular catheterization is associated with significant bacteriuria. lndividuals with SCI should be evaluated with urine culture to ensure proper treatment.     

Flow meter urine testing: a practical proposition in patients attending for urodynamics?

OBJECTIVE: To find a practical way of detecting urinary tract infection (UTI) before invasive urodynamic testing, as UTIs after urodynamics are well documented, but there are no standard guidelines about when urine should be analysed before urodynamics. PATIENTS AND METHODS: Before urodynamics all patients are asked to provide a free urine flow; the patient is then catheterized to obtain a catheter-specimen of urine that is tested for infection by a urine dipstick. If the dipstick is found positive for nitrites and/or leukocytes, the test is abandoned and the sample sent for microscopy, culture and sensitivity. In the present study, patients were asked to provide a free urine flow into the flowmeter as usual. Between patients, the flowmeter was washed with soap and water and dried, so that there would be no cross-contamination between patients' urine results. Urine was collected as usual and tested using a dipstick, the patient was then catheterized and another dipstick test done on the catheter specimen of urine (CSU), to compare results. RESULTS: Pairs of urine samples, when positive for nitrite were 100% consistent, and 89% of pairs positive for leukocytes were the same before and after catheterization. The remaining 11% (all women) of the positive leukocyte group had leukocytosis on testing the flowmeter urine but not on the CSU, possibly due to contamination from the vagina. CONCLUSION: Testing urine by dipstick in the sample from the flowmeter is a feasible option, thus saving the patient an inappropriate catheterization, with the risk of bacteraemia during urodynamics, and allowing the flowrate to be measured.     

Bacteriuria in patients with an orthotopic ileal neobladder: urinary tract infection or asymptomatic bacteriuria?

OBJECTIVE

To investigate the prevalence of asymptomatic bacteriuria (ABU) and urinary tract infection (UTI), and the local and systemic inflammatory response, in patients with ileal neobladder.

PATIENTS AND METHODS

The study included 40 patients who had a radical cystectomy and ileal neobladder. Two urine samples, one for chemical and physical analysis, and cytofluorimetry, and one for urine culture, were collected every 3 months for 9 months after surgery.

RESULTS

Of 119 urine cultures, 69 (57%) were positive for bacteria. Only nine of the 40 patients had no bacteriuria on urine culture. Escherichia coli strains were cultured from eight of 10 patients with persistently positive urine. The incidence of bacteriuria was different according to gender. There was a high concentration of leukocytes (0–6 µL) in 118 of 119 samples. The mean concentration of leukocytes in sterile urine culture was 1181/µL, while in patients with ABU the mean was 491 (P < 0.05).

CONCLUSION

A positive urine culture is a very common finding in patients with an orthotopic bladder. The most interesting results was the absence of elevated inflammatory indices and/or symptoms, even in those patients with high levels of bacteriuria. Probably this is due to the completely different inflammatory response of ileal mucosa against bacteria than has bladder mucosa. Indeed, the leukocyte concentration detected in urinary sediment was inversely association with bacterial growth in urine cultures. These findings suggest a redefinition of ABU and UTI in patients with an orthotopic neobladder.     

Proteinuria and renal disease: prognostic value of urine dipstick testing for leukocytes

Proteinuria is utilized to screen for underlying kidney disease and serves as a marker of disease progression. The aim of this study was to test the hypothesis that patients with proteinuria will have a higher frequency of urine dipstick positive for leukocytes as an index of noninfectious renal inflammation. In this retrospective analysis, 1,099 urine specimens were evaluated from 676 patients. Proteinuria was present in 39% of the samples and leukocyturia in 5.1%. The percentage of urines that were dipstick positive for leukocytes was similar in those specimens with or without proteinuria. However, in patients with proteinuria and concomitant leukocyturia, the mean serum creatinine concentration was higher (P=0.003) and the calculated GFR was lower (P=0.01) compared to those without this additional abnormality. These differences were noted despite similar age, gender distribution, and array of underlying diseases in these two groups. Based on these findings, urine dipstick testing for leukocytes as a primary means of screening otherwise healthy children for serious renal disease is of little value. However, in patients with established proteinuria, a positive dipstick result for leukocytes is a simple means of identifying those with more prominent noninfectious renal inflammation, a process which may promote kidney disease progression. This finding may serve as an early marker of the severity of renal injury, regardless of whether the primary process is glomerular or tubular.     

Trimethoprim versus gentamicin for the prevention of bacteriuria following transrectal biopsy of the prostate--do patients need additional anaerobic cover?

OBJECTIVES: To study the incidence of aerobic and anaerobic bacteriuria in patients undergoing transrectal ultrasound-guided biopsies of the prostate. A comparative assessment of efficacy of trimethoprim with gentamicin for the prevention of bacteriuria following the transrectal biopsy of the prostate. To assess the need for additional prophylaxis against anaerobes for patients undergoing transrectal biopsies of the prostate gland. PATIENTS AND METHODS: In a pilot study during 1995-1997, all the patients undergoing transrectal ultrasound-guided biopsy of the prostate were randomised to receive either trimethoprim or gentamicin prophylaxis prior to the procedure. Midstream urine (MSU) samples were taken just prior to biopsy and 72 h later. A patient questionnaire to determine the symptoms of urinary tract infection (UTI) accompanied the 72-hour MSU request form. Urine samples were cultured aerobically, using a semiquantitative technique if dipstick analysis revealed the presence of blood, pus cell or nitrite. In addition to the routine aerobic culture, post-biopsy samples were also cultured for anaerobes by direct and enrichment methods. Bacteriuria was defined as a pure or mixed growth of 10(5) colony-forming units/ml. Fisher's test of exact probability was used for statistical analysis. RESULTS: 115 patients were available for final analysis. 53 had received gentamicin and 62 trimethoprim. Four patients had pre-existing bacteriuria (3.5%), 3 in the trimethoprim group and 1 in the gentamicin group. Post-operative bacteriuria developed in 5 patients given gentamicin (9.4%) and 1 given trimethoprim (1.6%). This difference was not statistically significant (p = 0.085). Post-procedure bacteriuria was asymptomatic in all but 1 case. Anaerobes were detected in only 5 MSUs (4.3%) post-biopsy. CONCLUSION: Though there was no statistical significant difference in the rates of bacteriuria following administration of trimethoprim and gentamicin, data appear to favour trimethoprim prophylaxis. Further studies are warranted. Transrectal biopsy of the prostate is associated with a low incidence of anaerobic UTI. In view of the very low incidence of anaerobic bacteriuria, routine antibacterial prophylaxis against anaerobes does not appear to be justified.     

Are true-negative nitrite results affected by a two-hour delay in dipstick/pad analysis of urine in incontinence pads?

OBJECTIVES: To determine if true-negative nitrite results of a urine dipstick pressed into an incontinence pad (dipstick/pad method) are affected by a 2-hour delay in analysis. DESIGN: A quantitative study. SETTING AND SUBJECTS: Clean-catch urine specimens from a convenience sample of clinic patients, staff, and long-term care facility residents. INSTRUMENT: Changes from negative to positive for each group of urine specimens were evaluated using percentages within the groups. METHODS: Urine specimens were collected and a portion was cultured. Urine specimens negative for a urinary tract infection were included in the study. A portion of the specimen was poured into an incontinence pad. Initial nitrite results were determined using a dipstick pressed into an incontinence pad. Pads with true-negative dipstick/pad nitrite results were tested 2 hours later in the same manner. Urine culture results determined groups: mixed colonies; 50,000 to 75,000 colony-forming units per milliliter of a single type of uropathogen; greater than or equal to 50,000 cfu/mL diphtheroids; no significant growth; and no growth. RESULTS: Of the 443 urine cultures negative for a urinary tract infection, 441 initial dipstick/pad nitrite results were negative. Two initial true-negative nitrite dipstick/pad results, or 0.5%, changed from negative to positive over the 2-hour period: 1 in the "mixed colonies" group (0.4%) and 1 in the "no growth" group (0.7%). CONCLUSIONS: Results of this study indicate that true-negative nitrite results of a dipstick pressed into urine in an incontinence pad do not appear to be affected by a 2-hour delay in analysis.     

Pyuria: its predictive value of asymptomatic bacteriuria in ambulatory elderly men

A total of 664 urine samples collected from 254 asymptomatic, ambulatory, elderly men was examined for pyuria with a standardized glass slide microscopy method. The presence or absence of more than 10 polymorphonuclear leukocytes per high power field was highly predictive of the presence or absence of significant bacteriuria, respectively. The determination of pyuria in this select population may be a useful and inexpensive test to screen for bacteriuria.     

Urine analysis performed by flow cytometry: reference range determination and comparison to morphological findings, dipstick chemistry and bacterial culture results--a multicenter study

AIM: To validate whether quantitative flow-cytometric analysis of particulate matter in urine would allow for accurate and rapid enumeration of red blood cells (RBC), leukocytes (WBC), squamous epithelial cells (EC), casts, and bacteria, a Sysmex UF-100 analyzer was tested in a multicenter study. MATERIAL AND METHODS: At first, reference values were established and found to be < 14 for RBC, < 16 for WBC, < 9 for EC, < 2 for casts and < 173 for bacteria, respectively (counts per microl; 97.5 percentile). Due to the wide use of dipstick and microscopic sediment analysis in routine urine diagnostics, comparative studies on 950 random urine samples were performed. Bacterial counting combined with WBC enumeration was further compared in 266 routine urinary microbiologic cultures. RESULTS: Good correlations were found comparing UF-100 results of RBC (r = 0.89), WBC (r = 0.94), and EC (r = 0.74) with Fuchs-Rosenthal Chamber (FRC) counts. However, some misclassification of casts (r = 0.32) could be observed. Correlations of UF-100 with dipstick and sediment testing was significant (p < 0.001), but the scatter of the latter two methods is too wide to consider them as quantitative methods. Promising results further revealed that the analyzer has a good negative predictive value (NPV) for microbiologically negative cultures, especially for cultures with bacterial counts of 10(5)/l (NPV = 95%). CONCLUSION: The analyzer is capable of providing rapid and reliable urine analysis of cellular particles avoiding the known imprecision of dipstick and sediment methodology. Thus, when used in an algorithm, combined with dipstick or quantitative urine chemistry analysis (for hemoglobin, esterase, protein, glucose, etc.), this analyzer might serve as a rapid and accurate screening tool in routine urine analysis, thereby reducing manual reviewing rate as well as the number of missed samples, compared to screening with dipstick alone.     

Bacteriuria and pyelonephritis,diagnosis and treatment

According to Kass, a significant bacteriuria means that there are more than 10⁵ germs/ml in the urine. Every bacteriuria needs intensive therapy, otherwise, even if asymptomatic, in a high percentage pyelonephritis will develop. A comparative investigation of 1167 urine samples showed that of the screening tests the modified Griess test was the most reliable (91.8%). The TTC test was positive in 76%. More than 90% positive results were obtained by Gram staining of centrifuged urine. Midstream collection of urine was used in every case. The results in chronic pyelonephritis and pregnancy with bacteriuria emphasize the necessity of intermittent long-term treatment. For this therapy schedule was developed. Preconditions for a successful treatment are: a differentiation of germs and the preparation of an antibiogram.     

Assessment of haematuria: automated urine flowmetry vs microscopy.

BACKGROUND: Microscopy of the urine sediment may be a useful method in the distinction between a glomerular and a non-glomerular source of urinary bleeding. However, microscopic techniques are time consuming and hampered by inter-observer variations. In the present study we have therefore compared bright-field microscopy with automated urine flowmetry (Sysmex UF-100), examining their ability to differentiate between glomerular and non-glomerular haematuria. METHODS: Fresh urine samples were obtained from 112 patients with a well-defined, single cause of a positive dipstick test. Their urine specimens were examined within 4 h in a blinded manner. Of them, 79 specimens had a positive dipstick for blood and thus could be evaluated for haematuria. RESULTS: The Sysmex UF-100 had a sensitivity and specificity of 0.83 and 0.94 respectively in detecting non-glomerular bleeding. The positive and negative predictive values were 0.95 and 0.78 respectively. The corresponding values of microscopy were 0.79 and 0.90 respectively, and 0.93 and 0.74 respectively. CONCLUSIONS: Automated flowmetry can be used in the distinction between glomerular and non-glomerular haematuria.     

A new automated system for urine analysis: a simple, cost-effective and reliable method for distinguishing between glomerular and nonglomerular sources of haematuria.

OBJECTIVE: To determine the ability, reliability and accuracy of a new automated system of urine analysis in differentiating glomerular from nonglomerular bleeding in the initial investigation of haematuria, and compare its efficacy with conventional phase-contrast microscopy (PCM). PATIENTS AND METHODS: One hundred and six urine samples from patients in whom the final diagnosis was available were analysed using electrical flow impedance to detect, enumerate and size red blood cells in a conductive fluid (the cellfacts analyser, Microbial Systems Ltd, Coventry, UK). All the samples were also tested using a dipstick method and PCM was carried out for comparison on 45 of the 106 urine specimens. The results of cellfacts analysis were correlated with the final diagnoses to assess sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of this method; the costs were also analysed. RESULTS: Sixty-nine urine samples tested positive for blood on dipstick urine analysis and all these were confirmed to have red blood cells on cellfacts analysis. The remaining 37 samples were negative for blood on dipstick testing and cellfacts analysis, although seven patients had been referred with previously detected microscopic haematuria, none of whom were found to have any detectable pathology in the urinary tract on clinical examination and investigations. The remaining 30 patients were diagnosed to have urological or nephrological conditions with no haematuria. In the positive group, 20 (29%) patients were from the glomerular group, with a mean (range) red blood cell size of 4.25 (4-5.1) micrometer, and 49 (71%) from the nonglomerular group, with red blood cells of 5.47 (4.67-5.70) micrometer. These ranges overlapped at 4.67-5.1 micrometer at the decision threshold of 4.75 micrometer, the distribution of dysmorphic and eumorphic red blood cells for the glomerular group was 18 (90%) and two (10%), respectively, and for the nonglomerular group was 2 (4%) and 47 (96%), respectively. The sensitivity, specificity, PPV and NPV were 90%, 96%, 90% and 96%, respectively. Consumable and labour costs were very low. CONCLUSIONS: Cellfacts analysis is a simple, rapid, objective and cost-effective method for differentiating glomerular from nonglomerular urinary red blood cells, especially when few such cells are present.     

The presence of microscopic hematuria detected by urine dipstick test in the evaluation of patients with renal colic

Urolithiasis is a common diagnosis in patients presenting at our hospital with flank pain. One of the most important steps in the diagnostic algorithm of renal colic is the presence of hematuria, but this fact has been challenged by authors reporting a negative urinalysis for microscopic hematuria in about 9–18% of such patients. Our aim was to investigate whether the same results are obtained when a sample of urine is tested with a urine dipstick test (UDT) at the time of the initial examination. Data from patients with the clinical diagnosis of renal colic examined at the emergency department of our hospital were reviewed, and the sensitivity of hematuria in urine samples tested by UDT was recorded in a group consisting of patients for whom imaging showed evidence of a stone >3 mm in size. In cases in which UDT was negative, or showed only traces of red blood cells (RBCs), a formal urinalysis was performed. A total of 609 patients were finally included in the study, with a mean age of 49.2 years. Average stone size was 5.8 mm, located mainly in the lower part of the ureter. Dipstick analysis was positive for hematuria in 92.9%. A urinalysis, with a cut-off point of less than three red blood cells per high power field, was used as a means to verify the results of the UDT in 17.8% of cases: in 7.1% of UDT negative patients and 10.7% of patients with traces of blood. The urinalysis was negative in 5.1% of patients, adding only 2% to the diagnostic accuracy of UDT. Therefore, our findings suggest that the sensitivity of a UDT for hematuria in cases of suspected renal colic has a high degree of accuracy when performed at the emergency department, and can be used as a first-line, low cost examination. A microscopic analysis may be useful when the UDT is negative or not clear enough, to verify the results.     

The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy

Background  

Many studies have evaluated the accuracy of dipstick tests as rapid detectors of bacteriuria and urinary tract infections (UTI). The lack of an adequate explanation for the heterogeneity of the dipstick accuracy stimulates an ongoing debate. The objective of the present meta-analysis was to summarise the available evidence on the diagnostic accuracy of the urine dipstick test, taking into account various pre-defined potential sources of heterogeneity.     

Is sexual intercourse a significant cause of haematuria?

OBJECTIVES: To determine whether recent sexual intercourse might be a cause of microscopic haematuria in patients referred to a urological unit following dipstick detection of urinary haemoglobin. SUBJECTS AND METHODS: Forty-eight volunteers (24 men and 24 women) consented to have heterosexual intercourse with their regular partner, and to provide samples of urine for testing before and from the first void on the morning after intercourse. After appropriate instruction, volunteers tested their own urine for the presence of blood using standard dipsticks. Any volunteer with haematuria either before or after intercourse was offered a standard haematuria assessment. The results were analysed using the chi-squared test. RESULTS: None of the volunteers tested positively for haematuria immediately before sexual intercourse; six of the 24 women (25%), but no men, became positive after intercourse (P < 0.01). Only one of the six women accepted the offer of a haematuria evaluation and no pathology was identified. CONCLUSION: These results suggest that up to a quarter of women develop microscopic haematuria as a direct result of sexual intercourse. A history of recent sexual intercourse should therefore be considered when assessing the clinical significance of microscopic haematuria in women.     

Cost-effective screening for urinary tract infections in urogynaecological patients

This study aims to test the cost-effectiveness of reagent-strip urine nitrite compared with microbiological laboratory testing for screening of urinary tract infections (UTI). The study is a retrospective review of 708 female patients who underwent cystometry during a 1-year period. Urine dipstick nitrite was used as a screening test for UTI while urine cultures were taken as an outcome. Symptoms of UTI were noted. Of 708 patients screened, 70 (9.9%) had a significant UTI. Only 32 (4.5%)of 708 patients were nitrite positive. Urine dipstick nitrite has sensitivity of 40%, specificity of 99%, positive predictive value (PPV) of 88 % and negative predictive value (NPV) of 94%. If the screening test included symptoms for UTI together with urine nitrite, the results are: sensitivity 89%, specificity 31%, PPV 12% and NPV 96%. A combination of screening with urine nitrite and UTI symptoms can increase sensitivity to 89%. A total of 29% of specimens (screen negative=nitrite negative/asymptomatic) can then be excluded from UFEME/culture testing, thus resulting in cost savings.     

Detection and significance of microscopic hematuria in patients with blunt renal trauma

Detection of hematuria is paramount in establishing injury to the urinary system. In 339 patients with blunt renal trauma in whom radiographic studies defined the severity of injury we compared the degree of microscopic hematuria determined by dipstick and microscopic urinalysis. The overall correlation between the 2 methods was low (Pearson's coefficient 0.41). However, more than 80 per cent of the urine samples with 50 to 100 red blood cells per high power field corresponded to a dipstick result of 3+. The dipstick method had greater than 97.5 per cent sensitivity and specificity for detection of microscopic hematuria. Only 7 of the 339 patients (less than 2 per cent) had a discharge diagnosis of other than renal contusion: 5 had renal artery thrombosis or avulsion of the renal vessels and 2 had minor cortical lacerations that were managed nonoperatively. Although microscopic hematuria may be quantified more accurately by microscopic analysis, it can be detected reliably with a high degree of sensitivity and specificity by dipstick analysis.     

Antibiotic prophylaxis in percutaneous nephrolithotomy: prospective study in 81 patients

PURPOSE: To compare single-dose and short-course antibiotic prophylaxis protocols in percutaneous nephrolithotomy. PATIENTS AND METHODS: Eighty-one patients with sterile urine preoperatively who underwent percutaneous nephrolithotomy were divided into two groups. The first group (N = 43) received a single intravenous dose of antibiotic (200 mg of ofloxacin) during anesthetic induction, and the second group (N = 38) received treatment doses of antibiotic (400 mg of ofloxacin per day) until the nephrostomy catheter was removed. The two groups were identical according to demographic and treatment characteristics. For each patient, microbiologic evaluation of extracted stones and urine samples was done. If patients developed fever in the postoperative period, blood and urine cultures were taken. Factors that might have affected the development of postoperative fever and infection were analyzed. RESULTS: Nine patients in the first group had postoperative fever. Three had bacteriuria, and one had bacteremia. In the second group, eight patients had fever. One had bacteriuria and bacteremia. Nineteen patients (eleven in the first group, eight in the second) had positive stone cultures. No statistical difference was observed between the two groups in terms of bacteriuria, bacteremia, positive stone cultures, or postoperative fever. The febrile patients had longer operations with the use of more irrigation fluid and longer postoperative hospital stays. CONCLUSIONS: In patients whose preoperative urine cultures are sterile, short-term prophylaxis has no advantage over single-dose prophylaxis as a means of preventing infection. The duration of surgery and the amount of irrigation fluid are significant risk factors for postoperative fever.