Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Primary Study Investigators

STUDY OBJECTIVE: To (1) determine appropriate decision thresholds and diagnostic accuracies for pleural fluid (PF) tests that discriminate between exudative and transudative pleural effusions, and (2) evaluate the quality of the primary investigations. DESIGN: Formal meta-analysis of studies that report the diagnostic value of pleural fluid tests. SETTING: Data collected from international academic medical centers. PATIENTS: Hospitalized patients undergoing thoracentesis for pleural effusions. INTERVENTIONS: Primary investigators were requested to transmit original data from patients described in their studies. MEASUREMENTS AND RESULTS: Eight primary studies described 1,448 patients with one or more of the following tests: protein (P)-PF, P-PF/serum ratio (R), bilirubin (BILI)-R, lactate dehydrogenase (LDH)-PF, LDH-R, cholesterol (C)-PF, C-R, and albumin gradient. We found that all eight tests had similar diagnostic accuracies when evaluated by receiver operating characteristic (ROC) analysis except for BILI-R, which was less diagnostically accurate. Decision thresholds determined by ROC analysis differed from previously reported values for LDH-PF (>0.45 upper limits of normal) and C-PF (>45 mg/dL). Paired and triplet test combinations tended to have higher diagnostic accuracies compared with individual tests, but examination of the odds ratios with 95% confidence intervals did not identify a clearly superior test combination. Limitations of the primary studies presented a high likelihood of bias affecting their results. CONCLUSIONS: Several strategies exist for clinicians in utilizing PF tests to classify effusions as exudates or transudates but accurate interpretations of these test results will require better designed studies.     

Ethnic and sex bias in primary care screening tests for alcohol use disorders

BACKGROUND: The use of self-report screening tests for alcohol use disorders in the primary care setting has been advocated. OBJECTIVE: To test for ethnic and sex bias in three self-report screening tests for alcohol use disorders in a primary care population. DESIGN: Cross-sectional study with patients randomly selected from appointment lists. SETTING: University-based family practice clinic. PATIENTS: Probability sample of 1333 adult family practice patients stratified by sex and ethnicity. MEASUREMENTS: Patients completed 1) a diagnostic interview to determine the presence of a current alcohol use disorder and 2) three screening tests: the CAGE questionnaire, the Self-Administered Alcoholism Screening Test (SAAST), and the Alcohol Use Disorders Identification Test (AUDIT). RESULTS: The areas under the receiver-operating characteristic (ROC) curves for the CAGE questionnaire and the SAAST ranged from 0.61 to 0.88 and were particularly poor for African-American men and Mexican-American women. For the AUDIT, the area under the ROC curves was greater than 0.90 for each patient subgroup. The sensitivity of the CAGE questionnaire and the SAAST at standard cut-points was lowest for Mexican-American women (0.21 and 0.13, respectively). Positive likelihood ratios for the AUDIT were similar to or higher than those for the other screening tests, whereas negative likelihood ratios were lowest for the AUDIT (<0.33), indicating the superiority of this test in ruling out a disorder. CONCLUSIONS: A marked inconsistency in the accuracy of common self-report screening tests for alcohol use disorders was found when these tests were used in a single clinical site with male and female family practice patients of different ethnic backgrounds. The AUDIT does not seem to be affected by ethnic and sex bias.     

Significance and possibilities of histopathologic diagnosis in breed-specific skin diseases

In modern medicine, sophisticated laboratory tests and imaging studies are often emphasized at the expense of history and physical examination, rather than complementing clinical assessment. Ancillary testing often fails to advance the diagnostic process, and increases patient risk and the expense of medical care. The relative value of clinical evaluation and technological methods is rarely considered, and the power of the clinical evaluation is therefore underestimated. The likelihood ratio (LR) is a semiquantitative measure of the performance of diagnostic tests which indicates how much a diagnostic procedure modifies the probability of disease, and is calculated from the sensitivity and specificity of the test (or directly from the change in probability associated with the test result). We review the performance of frequently-used tests by their LRs, and compare them to the power of clinical assessment, with clinical cases to illustrate the application of LRs in the diagnostic process. The discriminative power of clinical assessment and ancillary tests is often similar, and the combination of the two greatly increases accuracy in the diagnostic process. Clinical assessment is indeed frequently more informative than current technical modalities. LRs assist in putting the value of testing in proper perspective. Practice in evaluating pre-test probabilities of disease and in the application of LRs should be enhanced in medical training.     

Serendipity in diagnostic imaging: magnetic resonance imaging of the breast

BACKGROUND: Magnetic resonance imaging (MRI) of the breast has been proposed as a noninvasive diagnostic test for evaluation of suspicious ("index") lesions noted on mammography and/or clinical breast examination (CBE). However, women may have incidental ("serendipitous") lesions detected by MRI that are not found on mammography or CBE. To understand better whether or not biopsy procedures should be performed to evaluate serendipitous lesions, we estimated the breast cancer risk for women with this type of lesion. METHODS: A decision analysis model was used to estimate the positive predictive value (i.e., the chance that a woman with a serendipitous lesion has cancer) of MRI for serendipitous lesions in women who had an abnormal mammogram and/or CBE suspicious for cancer (where a biopsy procedure is recommended). We restricted the analysis to data from women whose index lesions were noncancerous and used meta-analysis of published medical literature to determine the likelihood ratios (measures of how test results change the probability of having cancer) for MRI and the combination of CBE and mammography. The positive predictive value of MRI was calculated using the U.S. population prevalence of cancer (derived from registry data) and the likelihood ratios of the diagnostic tests. RESULTS: Under a wide variety of assumptions, the positive predictive value of MRI was extremely low for serendipitous lesions. For instance, assuming sensitivity and specificity values for MRI of 95.6% and 68.6%, respectively, approximately four of 1000 55- to 59-year-old women with serendipitous lesions would be expected to have cancer (positive predictive value = 0.44%, 95% confidence interval = 0.24%-0.67%). CONCLUSION: In women with a suspicious lesion discovered by mammography and/or CBE that is found to be benign, serendipitous breast lesions detected by MRI are extremely unlikely to represent invasive breast cancer. Immediate biopsy of such serendipitous lesions may, therefore, not be required.     

Perioperative assessment and management of risk from coronary artery disease

PURPOSE: To summarize available evidence on preoperative cardiac risk stratification so that the internist may 1) use clinical and electrocardiographic findings to stratify a patient's perioperative risk for myocardial infarction and death; 2) decide which tests provide useful additional risk-related information; and 3) understand the benefits, risks, and evidence surrounding the decision to undertake coronary revascularization before elective noncardiac surgery. DATA SOURCES: A MEDLINE search and review of the reference lists of identified articles. Sensitivities, specificities, and likelihood ratios for diagnostic tests were calculated, and a quality rating for study methods was applied. DATA EXTRACTION: Myocardial infarction and mortality were the major outcomes considered, and a quality rating for study methods was applied. DATA SYNTHESIS: Clinical and electrocardiographic findings, organized by multivariate prediction indices, accurately identify patients as having low, intermediate, or high risk for myocardial infarction or death. Pharmacologic stress imaging with thallium or echocardiography probably improves risk stratification for intermediate-risk patients having vascular surgery. These tests have not been shown to be effective prognostic indicators for patients having nonvascular surgery. No studies of angiography for risk prediction have been reported. Decision analyses and retrospective series suggest that the risks incurred by doing coronary angiography and revascularization before elective surgery outweigh the benefits. Prospective, controlled studies of coronary revascularization are lacking. Evidence from a randomized, controlled trial has shown a survival benefit with the perioperative use of beta-blockers in patients at risk for coronary artery disease. CONCLUSIONS: Evaluation of all surgical patients by use of clinical indices is recommended. Low-risk patients need no further evaluation before surgery. High-risk patients need optimal management of their high-risk problems, including (if appropriate) beta-blocker use, and may need to have their elective procedures canceled. Intermediate-risk patients probably benefit from further noninvasive stress testing, especially if they are having vascular surgery. Further clinical trials are needed for most areas of concern.     

Relation between sampling device and detection of abnormality in cervical smears: a meta-analysis of randomised and quasi-randomised studies

OBJECTIVE: To assess the diagnostic yield of different sampling devices used in cervical screening. DESIGN: Meta-analysis of randomised and quasi-randomised studies. SETTING: All randomised and quasi-randomised studies comparing the yield of cytological or histological abnormalities when two or more different sampling devices were used. SUBJECTS: 85,000 patients included in 29 studies reported in 28 papers. MAIN OUTCOME MEASURES: Pooled relative risk and 95% confidence interval of the yield of mild dysplasia or worse in smears recovered by each sampling method versus each other method with which it was compared; sensitivity or positive predictive value, or both, of cytological versus histological results in six studies from which sufficient data were available. RESULTS: There were no substantial differences in the yield of cytological abnormalities between the Ayre spatula, the Cytobrush, and the cotton swab used alone. There were also no substantial differences in the yield of cytological abnormalities between the extended tip spatula, the Ayre spatula combined with the Cytobrush or cotton swab, or the Cervex brush. The Ayre spatula, Cytobruah, or cotton swab used alone generally performed significantly worse than the combinations, the extended tip spatula, or the Cervex brush. There were no substantial differences in sensitivity or positive predictive value between the sampling methods. CONCLUSIONS: These results support the use of either the extended tip spatula, a combination of any spatula plus the Cytobrush or cotton swab, or the Cervex brush for cervical screening.     

Improvement of specificity in PSA-based screening by using PSA-transition zone density and percent free PSA in addition to total PSA levels

BACKGROUND: The clinical value of prostate-specific antigen (PSA) density in differentiating between prostate cancer and benign prostatic hyperplasia has been the subject of several studies. In this context the question has been raised about the diagnostic benefit of PSA transition-zone density (PSA-TZ density = total PSA/transition-zone volume) in the detection of prostate cancer. In the following study the value of PSA-TZ density alone and in combination with free PSA was investigated. METHODS: Between August 1995-May 1996, 308 first-line screening volunteers with elevated total PSA levels ranging from 2.5-10.0 ng/ml were evaluated. All patients underwent digital rectal examination, transrectal ultrasound, and transrectal ultrasound-guided biopsy of the prostate. Prior to these investigations, serum was obtained and total as well as free PSA levels were obtained. PSA transition-zone density (PSA-TZ density) was defined as follows: PSA-TZ density = total PSA/transition-zone volume. RESULTS: ROC curve analyses for PSA-TZ density showed that by using a PSA-TZ density of more than 0.22 ng/ml/cc as a biopsy criterion, 24.4% of negative biopsies could be avoided; ROC curve analyses for free PSA showed that by using percent free PSA <20% as a biopsy criterion, 45.5% of negative biopsies could be eliminated. When combining these two diagnostic tests, 54.2% of negative biopsies could be avoided. CONCLUSIONS: We conclude that PSA-TZ density, in addition to total and free PSA, is a new opportunity which renders it possible to calculate the likelihood of detecting prostate cancer on repeat biopsies in an individual patient.     

Meta-analysis of the relationship between risk perception and health behavior: The example of vaccination.

Background: Risk perceptions are central to many health behavior theories. However, the relationship between risk perceptions and behavior, muddied by instances of inappropriate assessment and analysis, often looks weak. Method: A meta-analysis of eligible studies assessing the bivariate association between adult vaccination and perceived likelihood, susceptibility, or severity was conducted. Results: Thirty-four studies met inclusion criteria (N = 15,988). Risk likelihood (pooled r = .26), susceptibility (pooled r = .24), and severity (pooled r = .16) significantly predicted vaccination behavior. The risk perception-behavior relationship was larger for studies that were prospective, had higher quality risk measures, or had unskewed risk or behavior measures. Conclusions: The consistent relationships between risk perceptions and behavior, larger than suggested by prior meta-analyses, suggest that risk perceptions are rightly placed as core concepts in theories of health behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A population perspective on diagnostic criteria for Parkinson's disease

For Parkinson's disease (PD), little is known about how the choice of diagnostic criteria affects research results. Using data on PD from three community studies (from Argentina, the Netherlands, Italy), we compared the impact on prevalence of several sets of diagnostic criteria. Each set was based on cardinal signs--resting tremor, bradykinesia, rigidity, impaired postural reflexes--and required that other parkinsonism be excluded. Some sets had additional requirements related to duration of symptoms, asymmetry of signs, or response to medication. In terms of prevalence, much lower estimates were associated with the requirements of asymmetry of signs and response to medication. The assessment of these clinical features may not be practical in community studies. Impaired postural reflexes, as a cardinal sign, seemed superfluous. For community studies of PD, we recommend the following diagnostic criteria: at least two of resting tremor, bradykinesia, or rigidity, in the absence of other apparent causes of parkinsonism.     

Mood (affective) disorders (F3). Results from the ICD-10 field trial of the Diagnostic Criteria for Research in German-speaking countries

The present study reports results of the ICD-10 research criteria trial concerning the diagnosis of affective disorders (section F3). On the basis of written case reports and videotapes a total of 451 clinicians from 34 centres in German-speaking countries prepared 2.228 diagnostic ratings on 39 different psychiatric patients. Three of the 39 cases met the diagnostic criteria for affective disorders, and 248 of the diagnostic assessments referred to these cases. The majority of clinicians rated the reliability, the ease and the suitability of the diagnostic criteria positively. The reliability of the affective disorders was extremely good, with a kappa of 0.93 in the range of 2-character diagnoses. The reliability of the 3-character categories was much smaller: Kappa values for depressive episode (F31) and recurrent depressive disorder (F33) were 0.68 and 0.54, respectively. The lowest concordance had a kappa value of 0.22 and was found in the case report of dysthymia (F34.1). Therefore a more precise definition of the diagnostic criteria for dysthymia would be desirable.     

Evaluating diagnostic tests in the pleural space. Differentiating transudates from exudates as a model

Physicians have a staggering variety of diagnostic tests available for directing their diagnostic and therapeutic decisions. Technologic advances in laboratory science have increased the sophistication of new tests and accelerated their rate of adoption into clinical practice. Unfortunately, studies that report the value of new diagnostic tests often fail to follow accepted methodologic standards for unbiased test assessment or provide clinicians with sufficient information for the intelligent evaluation of a test's performance and applicability. The following review of pleural fluid tests that discriminate between exudative and transudative effusions serves to highlight important methodologic considerations in the assessment of diagnostic tests.     

Regression-line analysis of trimethoprim-sulfamethoxazole activity against Neisseria gonorrhoeae

A standardized disk diffusion test was developed and used to test the susceptibility of 102 strains of Neisseria gonorrhoeae to combinations of trimethoprim and sulfamethoxazole (TMP/SMX) by relating zone diameters of inhibition to minimal inhibitory concentrations (MIC's). MIC's for TMP/SMX in ratios of 1:20 ranged from 0.08/1.52 to 2.5/47.5 mug/ml and zones of inhibition ranged from 34 to 10 mm. The coefficient of correlation (r) was -0.75. For comparison, a regression line was similarly calculated for ampicillin. MIC's ranged from 0.02 to 0.32 mug/ml and zones of inhibition ranged from 50 to 31 mm; r was -0.71. With establishment of MIC breakpoints to define the categories, susceptible, intermediate, and resistant, the disk duffusion test would be as reliable for estimating susceptibility of gonococci to TMP/SMX as for estimating susceptiblity to ampicillin.     

Nonword repetition and child language impairment

A brief, processing-dependent, nonword repetition task, designed to minimize biases associated with traditional language tests, was investigated. In Study 1, no overlap in nonword repetition performance was found between a group of 20 school-age children enrolled in language intervention (LI) and a group of 20 age-matched peers developing language normally (LN). In Study 2, a comparison of likelihood ratios for the nonword repetition task and for a traditional language test revealed that nonword repetition distinguished between children independently identified as LI and LN with a high degree of accuracy, by contrast with the traditional language test. Nonword repetition may have considerable clinical utility as a screening measure for language impairment in children. Information on the likelihood ratios associated with all diagnostic tests of language is badly needed.     

Wasp venom immunotherapy changes IgG antibody specificity

OBJECTIVE: To evaluate the quality of studies seeking to establish measurement properties (reliability and validity) of ultrasonic estimation of urinary bladder volume. DESIGN: Online searching of the MEDLINE database between 1966 and 1995, and scanning of bibliography of known studies on ultrasonic bladder volume estimation. Study selection and study quality assessment were performed independently by two reviewers. Each article was evaluated for suitability of the reference standard, adequacy of reported blinding of the observers and appropriateness of the statistical index of concordance. The last two of these guidelines were applied to reliability studies (evaluating the relation among observed ultrasonic estimations), and all three guidelines were applied to validity studies (evaluating the relation of ultrasonic estimation with a definitive measurement). POPULATION: One hundred and twenty-five participants enrolled in the five reliability studies and 769 participants in the 27 validity studies selected for appraisal of their quality. MAIN OUTCOME MEASURE: Rate of study compliance with preset criteria for high quality. RESULTS: None of the studies complied with all of the criteria for high methodologic quality. In the five reliability studies, investigators did not report adequate blinding of observers in three (60%) and an appropriate index of reliability was not used in any. Among the 27 validity studies, there was a lack of a suitable reference standard in 6 (22%), an inadequate blinding in 25 (93%), and an inappropriate index of validity in all (100%). CONCLUSION: Based on our guidelines for quality assessment, a large proportion of studies on measurement properties was found to have inadequate methods, raising concern about the credibility of the reliability and validity estimates reported. These deficiencies highlight the lack of rigour employed in the design, conduct and analysis of reliability and validity studies, which has the potential for leading to patient mismanagement due to biases in the assessment of measurement variability in clinical investigations.     

Utility of scintigraphic methods in patients with fever of unknown origin

BACKGROUND: We assessed the utility of scintigraphy with indium 111-labeled polyclonal human IgG scintigraphy in patients with fever of unknown origin that fulfilled the criteria of temperature of 38.3 degrees C or more for at least 3 weeks and no diagnosis during 1 week of hospital admission. We compared the utility of this technique with results of scintigraphic techniques reported in the literature. METHODS: Data for all patients seen at our university hospital in whom 111In-IgG scanning was performed were analyzed and checked for the criteria for fever of unknown origin. The literature on the utility of scintigraphic techniques in patients with fever of unknown origin was reviewed. RESULTS: We studied 24 patients with fever of unknown origin. In 13 patients, focal 111In-IgG accumulation was observed. In nine (38%) of those, the positive 111In-IgG scintigram led to the final diagnosis; in the other four patients (17%), the scintigraphic findings were not helpful. In the 11 patients with negative 111In-IgG scans, extensive diagnostic workup produced no infection as the final diagnosis in nine patients (38%), one had an abscess in a renal cyst that was detected several months later, and in the other the cause of fever was an infected intravenous line. The overall sensitivity and specificity of 111In-IgG scintigraphy were 81% and 69%, respectively. The positive predictive value was 69% and the negative predictive value was 82%. CONCLUSIONS: Our results show that 111In-IgG scintigraphy significantly contributed to the diagnostic process in patients with fever of unknown origin. A positive scan increased the likelihood of finding the cause of the fever, and a negative scan ruled out an inflammatory component with a high degree of certainty. These data compare favorably with data in the literature concerning other radiopharmaceuticals; a larger prospective evaluation of this technique is indicated.     

Convergence of scores on the interview and questionnaire versions of the Eating Disorder Examination: A meta-analytic review.

Significant discrepancies have been found between interview- and questionnaire-based assessments of psychopathology; however, these studies have typically compared instruments with unmatched item content. The Eating Disorder Examination (EDE), a structured interview, and the questionnaire version of the EDE (EDE–Q) are considered the preeminent assessments of eating disorder symptoms and provide a unique opportunity to examine the concordance of interview- and questionnaire-based instruments with matched item content. The convergence of EDE and EDE–Q scores has been examined previously; however, past studies have been limited by small sample sizes and have not compared the convergence of scores across diagnostic groups. A meta-analysis of 16 studies was conducted to compare the convergence of EDE and EDE–Q scores across studies and diagnostic groups. With regard to the EDE and EDE–Q subscale scores, the overall correlation coefficient effect sizes ranged from .68 to .76. The overall Cohen's d effect sizes ranged from .31 to .62, with participants consistently scoring higher on the questionnaire. For the items measuring behavior frequency, the overall correlation coefficient effect sizes ranged from .37 to .55 for binge eating and .90 to .92 for compensatory behaviors. The overall Cohen's d effect sizes ranged from ?0.16 to ?0.22, with participants reporting more binge eating on the interview than in the questionnaire in 70% of the studies. These results suggest the interview and questionnaire assess similar constructs but should not be used interchangeably. Additional research is needed to examine the inconsistencies between binge frequency scores on the 2 instruments. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Evaluation of the diagnostic value of a test. Main information indices

Evaluating a new diagnostic test is an essential step required before using a new examination technique. The information concerning the disease provided by the test must be examined in terms of diagnostic value and cost. A test can be evaluated using several indexes. For tests giving binary results, the main information indexes were defined and the calculation of the index was illustrated by an example. The sensitivity, specificity, the Youden index, and the positive and negative predictive values were presented together with the likelihood and odds-ratio. For tests giving quantitative results, the analysis of the ROC curves was discussed. Indexes were interpreted in terms of disease prevalence, the modalities (diagnosis, screening) for applying the test, the sampling technique for the tested population, the gain in diagnosis, and cost of the examination.     

Evaluation of the diagnostic contribution of a test. Main information indices

Evaluating a new diagnostic test is an essential step required before using a new examination technique. The information concerning the disease provided by the test must be examined in terms of diagnostic value and cost. A test can be evaluated using several indexes. For tests giving binary results, the main information indexes were defined and the calculation of the index was illustrated by an example. The sensitivity, specificity, the Youden index, and the positive and negative predictive values were presented together with the likelihood and odds-ratio. For tests giving quantitative results, the analysis of the ROC curves was discussed. Indexes were interpreted in terms of disease prevalence, the modalities (diagnosis, screening) for applying the test, the sampling technique for the tested population, the gain in diagnosis, and cost of the examination.     

The mental health of hospital nurses in Tasmania as measured by the 12-item General Health Questionnaire

The goal of this study was to examine the clinical and economic outcomes of alternative diagnostic strategies for differentiating benign from malignant adrenal masses. METHODS: We used cost-effectiveness assessment derived from decision analysis and the economic perspective of the payer of health care services. One-time evaluation with fine-needle aspiration (FNA) and combinations of chemical-shift MRI, noncontrast CT, 131I-6beta-iodomethylnorcholesterol (NP-59) scintigraphy, with or without FNA, in a hypothetical cohort of 1000 patients with incidentally discovered unilateral, nonhypersecretory adrenal masses. We calculated and compared the diagnostic effectiveness, costs and cost-effectiveness of the alternative strategies based on estimates from published literature and institutional charge data. RESULTS: At an assumed baseline malignancy rate of 0.25, diagnostic utility varied from 0.31 (CT0) to 0.965 (NP-59) and diagnostic accuracy from 0.655 [noncontrast CT using a cut-off attenuation value of > or = 0 (CT0)] to 0.983 (NP-59). The average cost per patient per strategy ranged from $746 (NP-59) to $1745 (MRI +/- FNA). The best and worst potential cost-to-diagnostic utility ratios were 773 (NP-59) and 2839 (CT0) and 759 (NP-59) and 1982 (MRI +/- FNA) for cost and diagnostic accuracy, respectively. The NP-59 strategy was the optimal choice regardless of the expected outcome examined: cost, diagnostic utility, diagnostic accuracy or cost-effectiveness. Varying the prevalence of malignancy did not alter the cost-effectiveness advantage of NP-59 over the other diagnostic modalities. CONCLUSION: Based on available estimates of reimbursement costs and diagnostic test performance and using reasonable clinical assumptions, our results indicate that the NP-59 strategy is the most cost-effective diagnostic tool for evaluating adrenal incidentalomas over a wide range of malignancy rates and that additional clinical studies are warranted to confirm this cost-effectiveness advantage.     

Lymphoscintigraphic identification of sentinel lymph nodes: clinical evaluation of 0.22-micron filtration of Tc-99m sulfur colloid

PURPOSE: To evaluate the use of 0.22-micron filtration of technetium-99m sulfur colloid particles in the optimization of lymphoscintigraphy. MATERIALS AND METHODS: Forty-one consecutive lymphoscintigraphic studies obtained with 0.22-micron filtration of Tc-99m sulfur colloid in 41 patients (26 men, 15 women; average age, 55.4 years) and 41 consecutive studies obtained with 5.0-micron filtration in 41 patients (20 men, 21 women; average age, 54.5 years) were retrospectively, randomly reviewed. Studies were evaluated for lymphatic channel depiction and sentinel lymph node depiction. Studies included immediate flow images (obtained at 10 seconds per frame) and multiview static images obtained up to 2 hours after intradermal Tc-99m sulfur colloid injection. RESULTS: The number of drainage beds visualized was 52 with 5.0-micron filtration and 51 with 0.22-micron filtration (P = .570). The number of lymphatic channels visualized was 45 with 5.0-micron filtration and 75 with 0.22-micron filtration (P = .006). The number of lymph nodes visualized was 102 with 5.0-micron filtration and 123 with 0.22-micron filtration (P = .123). The number of studies judged as optimal (i.e., depicted lymphatic channels leading to sentinel nodes) was 10 with 5.0-micron filtration and 19 with 0.22-micron filtration (P = .038). The number of studies with depicted lymph nodes but no depicted lymphatic channel was 15 with 5.0-micron filtration and six with 0.22-micron filtration (P = .023). CONCLUSION: The use of 0.22-micron filtration in the preparation of Tc-99m sulfur colloid substantially improves study quality and increases the diagnostic certainty in the identification of sentinel lymph nodes.