Test-negative Patients Research Articles

Efficacy and safety of the monoclonal anti-tumor necrosis factor antibody F(ab′)2 fragment afelimomab in patients with severe sepsis and elevated interleukin-6 levels*

To evaluate whether administration of afelimomab, an anti-tumor necrosis factor F(ab')2 monoclonal antibody fragment, would reduce 28-day all-cause mortality in patients with severe sepsis and elevated serum levels of IL-6. Prospective, randomized, double-blind, placebo-controlled, multiple-center, phase III clinical trial. One hundred fifty-seven intensive care units in the United States and Canada. Subjects were 2,634 patients with severe sepsis secondary to documented infection, of whom 998 had elevated interleukin-6 levels. Patients were stratified into two groups by means of a rapid qualitative interleukin-6 test kit designed to identify patients with serum interleukin-6 levels above (test positive) or below (test negative) approximately 1000 pg/mL. Of the 2,634 patients, 998 were stratified into the test-positive group, 1,636 into the test-negative group. They were then randomly assigned 1:1 to receive afelimomab 1 mg/kg or placebo for 3 days and were followed for 28 days. The a priori population for efficacy analysis was the group of patients with elevated baseline interleukin-6 levels as defined by a positive rapid interleukin-6 test result. In the group of patients with elevated interleukin-6 levels, the mortality rate was 243 of 510 (47.6%) in the placebo group and 213 of 488 (43.6%) in the afelimomab group. Using a logistic regression analysis, treatment with afelimomab was associated with an adjusted reduction in the risk of death of 5.8% (p = .041) and a corresponding reduction of relative risk of death of 11.9%. Mortality rates for the placebo and afelimomab groups in the interleukin-6 test negative population were 234 of 819 (28.6%) and 208 of 817 (25.5%), respectively. In the overall population of interleukin-6 test positive and negative patients, the placebo and afelimomab mortality rates were 477 of 1,329 (35.9%)and 421 of 1,305 (32.2%), respectively. Afelimomab resulted in a significant reduction in tumor necrosis factor and interleukin-6 levels and a more rapid improvement in organ failure scores compared with placebo. The safety profile of afelimomab was similar to that of placebo. Afelimomab is safe, biologically active, and well tolerated in patients with severe sepsis, reduces 28-day all-cause mortality, and attenuates the severity of organ dysfunction in patients with elevated interleukin-6 levels.

Immediate contact reactions to fragrance mix constituents and Myroxylon pereirae resin.

We have studied patients who have positive-patch test reactions to fragrance-allergic screening substances fragrance mix (FM) or Myroxylon pereirae resin (balsam of Peru) for immediate contact reactions to the standard FM, the constituents of the FM and Myroxylon pereirae resin. In the fragrance-positive subjects (n = 60), there were positive immediate contact reactions to Myroxylon pereirae resin in 56.6% and to FM in 11.6%. In a control group (n = 50) of eczematous, patch test-negative patients there were positive immediate reactions to Myroxylon pereirae resin in 58.0% subjects and to FM in 12.0%. The absence of a significant difference between the fragrance-allergic group and control group is in keeping with a non-immunological basis for the majority of the immediate reactions seen.

The role of atopy in Maltese patients with chronic rhinitis.

The global prevalence of allergic rhinitis has been on the increase and recent clinical experience in Malta has shown a similar trend. The aim of this study was to investigate the role of atopy in 415 patients presenting with rhinitis of at least 3 months duration, and to identify the common allergens responsible. Presenting clinical features, past and family history of seasonal allergic symptoms, exposure to cigarette smoking, pet ownership and occupation were analysed. All patients were skin tested for common allergens. Fifty-five per cent of patients were atopic, the main allergens responsible being house dust mite, cat dander and grass pollen. Rhinorrhoea and sneezing were significantly more common in atopic patients, who were more likely to have a past history and family history of seasonal asthma, eczema or rhinoconjunctivitis. Skin test-negative patients with idiopathic rhinitis were mostly females and tended to present a decade later. Differentiation between atopic and idiopathic chronic rhinitis may be helpful in the clinical setting in order to help predict response to treatment.

Detection of specific IgE to quinolones

Rationale Immediate adverse reactions to quinolones (IARQ) like urticaria, angioedema and shock are observed with increasing frequency. Our aim was to assess if these reactions are IgE-mediated. Methods We studied 55 patients with IARQ. Sixty-two percent of the patients recalled a previous exposure to quinolones. Two control groups were tested: 22 atopic individuals without history of ADR and 10 individuals who tolerated quinolones. We did not perform skin tests because they induce false positive results. Because of the severity of the reactions no provocation test was performed. IgE to quinolones was tested by a RIA using epoxy-activated sepharose 6B as solid phase, to which quinolones (ciprofloxacin, cinoxacin, lomefloxacin, ofloxacin, pipemidic acid, pefloxacin, norfloxacin, nalidixic acid, rufloxacin) were covalently coupled. Results The test yielded positive results in 30 patients (54.5%), tested 1-48 months after the reaction, and negative in the controls. In atopic patients, the quinolone-specific IgE seems to persist longer. The test negative patients may have lost drug specific IgE with time, reacted with an epitope of the quinolone not detectable in the test system or had actually pseudoallergic reactions. Inhibition of the uptake by various quinolones, but not by non related molecules (amoxicillin, penicillin G, cefuroxim, rifampicin and 4-aminoantipirin) demonstrated the specificity of binding of IgE to quinolones. These inhibition studies also allowed to identify a common epitope, which might explain the broad serological and clinical cross-reactivity. Conclusions A substantial part of IARQ appear to be IgE-mediated. Cross-reactivity is frequent and suggests that all quinolones should be avoided in these patients.

IgE antibody to Aspergillus fumigatus recombinant allergens in cystic fibrosis patients with allergic bronchopulmonary aspergillosis.

Allergic bronchopulmonary aspergillosis (ABPA) in cystic fibrosis (CF) is characterized by a heightened Th2 CD4+ T-cell response to Aspergillus fumigatus (Af) allergens and a hyper-immunoglobulin E (IgE) state compared with cystic fibrosis patients without ABPA. The IgE serologic differentiation of ABPA from atopic CF patients can be difficult. We propose as the reactivity with purified antigens varies qualitatively and quantitatively and that the antibody response is more specific than with crude Af antigen extract, the IgE responses to purified recombinant Af allergens may differentiate ABPA from atopic CF patients. Serum IgE reactivity to seven recombinant purified allergens and to a crude extract of Af was measured in 15 ABPA, in 23 Af skin test positive (ST+), and in 19 Af skin test negative (ST-) CF patients. Four of the ABPA CF patients were studied before and after developing ABPA. Nine ABPA patients were studied during flares and remissions of ABPA. Allergic bronchopulmonary aspergillosis patients had significantly increased IgE reactivity to Asp f2, f3, f4, f6, and f16 compared with the Af ST+ and ST- non-ABPA CF patients. In the ABPA patients studied before and after developing ABPA, IgE reactivity also increased to Asp f2, f3, f4, and f6, and to the crude extract. In ABPA CF patients, IgE reactivity to Asp f1, f2, f3, and f6 significantly increased during periods of ABPA flares compared with periods of remission. Analysis of the receiver operating curve demonstrated that IgE reactivity to Asp f3 and f4 gave the best sensitivity and specificity and were better than IgE reactivity to a crude extract of Aspergillus. Furthermore, in ABPA patients studied during periods of remission the IgE reactivity to Asp f3 and f4 remained significantly elevated compared with Af ST+ non-ABPA patients. The IgE responses when considered either to be positive or negative to Asp f3 and f4 significantly differentiated ABPA from Af ST+ and ST- non-ABPA CF patients. In contrast, IgE reactivity was considered positive to the crude extract in 89% of ABPA, 61% of Af ST+, and 0% of Af ST- non-ABPA CF patients. Immunoglobulin E reactivity to a panel of purified Af allergens, especially to Asp f3 and f4, differentiates ABPA from atopic Af ST+ non-ABPA CF patients. Serial determinations of IgE reactivity to individual purified Aspergillus antigens, especially Asp f3, demonstrates that increases in IgE reactivity may provide improved distinction between stages of flares and remission compared with changes in IgE reactivity to a crude Aspergillus extract.

Periimplantar cobalt-specific DTH reaction in a patch test negative patient with failure of hip arthroplasty

Rationale Hypersensitivity reactions to metal implants have been reported mostly under the picture of local or systemic eczema or impaired wound and fracture healing. In addition, in arthroplasty non infectious complications like swelling, pain or loosening cannot be always explained by mechanical factors. We report on a patient with local seroma and loosening of his hip endoprosthesis, in whom patch testing was negative but periimplantar tissue showed cobalt-specific DTH. Methods Patch testing was done with a standard and an implant constituent series. Immunohistochemistry, RT-PCR for cytokine expression and lymphocyte transformation tests (LTT) were performed. Results Patch test gave no reactions. Immunohistochemistry of periimplantar tissue obtained at revision surgery showed dense lymphocytic infiltration with marked predominance of CD45RO+ memory T-cells. RT-PCR revealed strong tissue expression of TNF-a and IFN-g, but absence of IL-4 and IL-10. Reactivity of peripheral blood mononuclear cells to nickel, chromium, cobalt, molybdenum was not enhanced. But cells derived and expanded (by IL-2) from periimplantar tissue showed marked proliferative response to cobalt (stimulation index 5.2 and 6.2, CoCl3 10–5 and 10–6 M). Conclusions Metal specific hypersensitivity reactions may arise in the proximity of metal implants and not necessarily coinvolve the skin. Due to missing patch test reactivity, incidence of such conditions may be underestimated.

Oral lichenoid lesions (OLL) and mercury in amalgam fillings.

84 patients with oral lichenoid lesions (OLL) were seen in the contact dermatitis clinic. All these patients had reticulate, lacy, plaque-like or erosive lichenoid changes adjacent to amalgam fillings. Patch testing to metallic mercury, 0.1% thimerosal, 1% ammoniated mercury, 0.1% mercuric chloride, and in some cases 0.05% phenylmercuric nitrate and amalgam discs was undertaken. 33 (39%) patients had positive patch test findings. 30/33 patch test positive patients had replacement of their amalgam fillings, with 28 (87%) patients experiencing improvement of symptoms and signs within 3 months. This confirms that mercury allergy is a factor in the pathogenesis of OLL in some cases. In cases where patch test negative patients improve with amalgam replacement, mercury may be acting as an irritant in the pathogenesis of OLL.

A clinical and patch test study of adult widespread eczema.

The purpose of this study was to investigate the role of contact hypersensitivity (CHS) in adult widespread eczema (WE) and to analyse the aetiology of WE. 108 consecutive adult WE patients were patch tested. 352 patients with suspected localized allergic contact dermatitis (ACD) tested in the same period served as a control. The average age of the patients with WE was significantly greater than the control group (47.6 +/- 15.0 v 39.2 +/- 14.9, p < 0.01, Student's t-test). More male patients were found in the WE group (42.6% vs 25.0%, p < 0.01, chi2-test). 71 (65.7%) of the WE patients were patch test positive. ACD was diagnosed in 29 out of 108 (26.9% of the WE patients and 40.8% of the PT positive patients) WE patients. ACD was also suspected in another 42 patients (39.8%), who had at least 1 positive PT result but the relevance of PT was hard to determine. In the remaining 37 patch test negative patients, 2 cases of food allergy were diagnosed by clinical findings and open food challenge test. 1 case of atopic dermatitis was diagnosed. 34 patients (31.5%) were diagnosed as unclassified endogenous eczema. Most of the WE patients with ACD (15/29, 51.7%) were ACD from widespread contact with hair dye during bathing. Most of the WE patients with hair dye ACD were male (male : female = 2.75). The total positive rates of PT in the WE group were no different to the control (65.7% vs 61.5%, p > 0.05, chi2-test). No significant difference was found for the positive rates of common contact allergens. The rate of atopy was no different between the 2 groups either (6.5% v 5.1%, p > 0.01, chi2-test). These results indicated that contact sensitization was very common in adult WE. Neglected widespread contact with contact allergens, especially hair dye, plays a very important role in our adult WE. The roles of age and sex in WE need to be studied further.

IgE antibodies to penicillin in skin test negative patients.

IgE antibodies to penicillin in skin test negative patients.

Patients with negative skin tests

The aim of this article is to present and discuss the clinical problem of systemic anaphylaxis to Hymenoptera venoms in patients without detectable immunoglobulin E, as it appears in recent literature. Reported at variable frequency in large series of patients undergoing evaluation, systemic anaphylaxis was previously considered to reflect lost sensitization or to involve non-immunoglobulin E mediated mechanisms. Sporadic case-reports drew attention to the fact that severe or even fatal reactions may occur in patients with negative skin tests. A breakthrough article by Golden et al., who performed deliberate stings on skin test negative venom anaphylaxis patients, demonstrated that clinical sensitivity was still present in a subset of these subjects and pointed out to the limitations of present diagnostic methods or reagents. New immunobiochemical methods and highly specific recombinant allergens--when all clinically relevant Hymenoptera venom allergens have been identified, cloned, sequenced and expressed in the proper system--are anticipated to increase the diagnostic yield. Non-specific mechanisms causing anaphylactoid reactions will probably explain some enigmatic, skin test negative radioallergosorbent test negative cases in the future. Occult mastocytosis, predisposing patients to anaphylactoid reactions, has been reported with increasing frequency among skin test negative patients. Lastly, other causes mimicking venom anaphylaxis may on rare occasions contribute to the problem. With the present understanding of venom allergy, the practising clinician is not infrequently faced with the dilemma of the skin test negative patient. Once other identifiable causes have been carefully ruled out, referral to a specialized center for deliberate sting-challenges appears in selected cases to be a medically appropriate and ethically justified management approach.

Circulating, Mycobacterium tuberculosis-specific lymphocytes from PPD skin test-negative patients with tuberculosis do not secrete interferon-gamma (IFN-gamma) and lack the cutaneous lymphocyte antigen skin-selective homing receptor.

Individuals with a negative intradermal reaction to tuberculin PPD have long been described in the Mycobacterium tuberculosis exposed, immune-competent population. Here, we studied PPD-specific blood T lymphocytes from these subjects for phenotypic markers relevant to skin migration, including the expression of the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen (CLA). Out of 82 patients with active tuberculosis we identified four subjects who were repeatedly PPD skin test-negative. CD4 T lymphocytes specific to mycobacterial antigens were derived from these individuals, which (i) proliferated in vitro to M. tuberculosis antigens comparably to those from PPD+ patients; (ii) secreted comparable amounts of IL-2 but lower amounts of IFN-gamma; (iii) were confined within the CLA-negative T cell subset. We conclude that the negative tuberculin reaction in a small subset of patients exposed to mycobacteria is associated with impaired production of IFN-gamma by circulating PPD-specific T cells that are lacking CLA expression. On this basis in vitro proliferation to PPD can discriminate bona fide non-responders from infected patients with a deficit in the margination of M. tuberculosis-specific T lymphocytes.

Discontinuing venom immunotherapy.

The decision to discontinue venom immunotherapy requires a great deal of clinical judgement because of the potential for a life-threatening reaction to a sting. The risk of recurrence is a combination of the frequency of reaction and the severity of reaction. Early studies reported a relapse rate of 8-14% in radioallergosorbent test-negative patients when therapy was stopped after 3 years. Unfortunately, the venom skin test or radioallergosorbent test becomes negative in only 25% of patients after 5 years of treatment. An alternative criterion for stopping treatment after 5 years regardless of the skin test has been equally successful, with most post-treatment reactions being much milder than pre-treatment reactions. There was no evidence of a rebound of venom sensitivity when therapy was stopped, even when patients were stung. The level of venom-specific IgE antibodies is better suppressed by 5 than by 3 years of treatment. The risk of relapse is higher in honeybee-allergic patients and in patients who had a systemic reaction (to a sting or an injection) during therapy. The frequency of reaction may be low, but patients who had very severe pre-treatment reactions have a greater chance of the reaction being severe again, and should remain on therapy for life. Long-term observations show that the incidence of systemic reaction to a sting remains 10% for each sting that occurs, even 10-15 years after stopping treatment. Because patients may not react to one sting and then subsequently react to another sting, the cumulative frequency of sting reactions is approximately 17% after 10 years off treatment. Moreover, negative venom skin tests are not a guarantee of safety because there is almost the same 10% frequency of reaction in patients who appear to lose sensitivity. It is not yet clear whether some low-risk patients (children, mild reactors) could discontinue treatment after just 3 years.

The Editors’ Choice

The Editors’ Choice

Noninvasive tests as a substitute for histology in the diagnosis of Helicobacter pylori infection

Background: Rapid urease tests for Helicobacter pylori have a sensitivity of 80% to 90%. Therefore histologic examination of gastric biopsies is recommended as a “backup” diagnostic test in rapid urease test–negative patients. However, noninvasive tests (urea breath test, serology, whole blood antibody tests) may provide a more rapid diagnosis and be less expensive but offer similar accuracy. Methods: Sixty-seven patients (no prior treatment for H pylori, no proton pump inhibitors, antibiotics, or bismuth within 4 weeks) undergoing endoscopy for evaluation of dyspepsia symptoms and testing rapid urease test–negative by antral biopsy were enrolled. All had the following tests: gastric biopsies (2 antral, 1 fundus; H&E and Alcian Yellow stain) examined for gastritis and H pylori ; 13C-UBT; capillary blood for whole blood rapid antibody tests: FlexSure HP, QuickVue, AccuStat, and Stat-Simple Pylori; serum for FlexSure HP; HM-CAP enzyme-linked immunoassay. H pylori infection was diagnosed (reference standard) if chronic gastritis was present on histology and at least 2 of the 3 following tests were positive: urea breath test, H pylori organisms unequivocally demonstrated in biopsies on special stain, and/or enzyme-linked immunoassay. The test and treatment costs per patient were calculated. Results: Of 67 patients with a negative rapid urease test, 4 were positive for H pylori. None had active peptic ulcer disease. Histology only identified 1 patient with organisms visible on special stain. Using chronic active gastritis (neutrophilic and mononuclear infiltrate) as a diagnostic criterion for H pylori, 6 patients would have been judged positive. However, only 2 of these were truly positive by the reference standard (positive predictive value 33%). Negative predictive value for presence of organisms and chronic active gastritis was 95% and 97%, respectively. All of the noninvasive tests identified all 4 truly positive patients correctly. Urea breath test and FlexSure whole blood assay yielded a substantial number of false-positive results (positive predictive value 31% and 36%, respectively); positive predictive value for the other tests ranged from 50% to 80%. All tests except histology had a negative predictive value of 100%. Histology was the most costly test (p < 0.001 compared with all other tests), followed by urea breath test and HM-CAP serology (p < 0.001 compared with all rapid antibody tests). Conclusions: Whole blood or serum antibody testing is a rapid, accurate, and cost-effective means for establishing H pylori status in rapid urease test–negative patients. Whole blood or serology rapid antibody testing should substitute for histology when the patient has not been previously treated for H pylori. (Gastrointest Endosc 2000;52:20-6.)

Positive atopy patch test reactions to Pityrosporumorbiculare in atopic dermatitis patients

Pityrosporum orbiculare, although a part of our normal cutaneous microflora, can cause skin infections and induce specific immunoglobulin (Ig) E antibodies in atopic dermatitis patients. P. orbiculare is therefore considered to be one of the trigger factors for atopic dermatitis. To investigate if P. orbiculare can induce an eczematous reaction in atopic dermatitis patients, seborrhoeic dermatitis patients and healthy controls. Fifteen atopic dermatitis patients, eight seborrhoeic dermatitis patients and eight healthy controls were patch tested with extract of P. orbiculare on non-lesional, tape-stripped skin of the back. NaCl was used as a negative control. The patch tests were evaluated after 24, 48 and 72 h. Skin biopsies were taken from P. orbiculare patch test sites at 24 h and 72 h, from NaCl patch test sites at 72 h, from non-lesional skin and, in the atopic dermatitis patients, also from lesional skin. The skin biopsies were investigated with immunohistochemical techniques. P. orbiculare-specific IgE in serum was analysed with RAST. Specific IgE to P. orbiculare was found in serum from 13/15 atopic dermatitis patients and in eight of them a positive patch test reaction to P. orbiculare was observed, with a maximal reaction at 48 h. Significantly higher serum levels of P. orbiculare-specific IgE were detected in patch test-positive compared with patch test-negative atopic dermatitis patients (P < 0. 01). The seborrhoeic dermatitis patients and healthy controls were RAST and patch test-negative for P. orbiculare. In the patch test-positive atopic dermatitis patients an infiltration of CD4+ T cells and eosinophils was observed at the P. orbiculare patch test sites together with an upregulation of ICAM-1 and HLA-DR expression. P. orbiculare can induce an eczematous reaction in sensitized atopic dermatitis patients and may be an important trigger factor in these patients. The P. orbiculare patch test can be of diagnostic value in this subgroup of atopic dermatitis patients.

Hyperventilation as a Specific Test for Diagnosis of Coronary Artery Spasm

The hyperventilation test has been used as a clinical tool to induce coronary spasm. However, its diagnostic and prognostic values have not been fully elucidated. This study was designed to establish the sensitivity and specificity of the hyperventilation test and to clarify the characteristics of hyperventilation test-positive patients. We examined 206 patients in whom coronary spasm was documented by angiography (spasm group), and 183 patients without angina at rest in whom acetylcholine failed to induce spasm (nonspasm group). All patients performed vigorous hyperventilation for 6 minutes in the early morning. Of the spasm group patients, 127 showed positive responses to the test, including ST elevation (n = 111), ST depression (n = 15) and negative U wave (n = 1). None in the nonspasm group showed any ischemic electrocardiographic change. Thus, the sensitivity and specificity of this test for diagnosis of coronary spasm were 62% and 100%, respectively. In the spasm group, there were no significant differences between hyperventilation test-positive and test-negative patients in age, sex, the prevalence of hypertension, diabetes mellitus, obesity, smoking, and the number of diseased vessels. When clinical characteristics were compared, the proportions of the patients with high disease activity (≥5 attacks a week), with severe arrhythmias (second- or third-degree atrioventricular block and/or ventricular tachycardia) during attacks, and with multivessel spasm were significantly higher in the hyperventilation test-positive patients than in the negative patients (69% vs 20%, p <0.0001; 31% vs 11%, p <0.005; and 58% vs 34%, p <0.01, respectively). These findings imply that hyperventilation is a highly specific test for the diagnosis of coronary artery spasm, and that hyperventilation test-positive patients are likely to have life-threatening arrhythmias during attacks and multivessel spasm.

Selecting Skin Testing Reagents to Predict Amoxicillin and Cephalosporin Allergy

Objectives This study assessed the accuracy of a panel of skin testing reagents to detect immunoglobulin E sensitivity to amoxicillin and oral cephalosporins. Methods One hundred and eighty-seven children and adolescents experiencing adverse reactions to amoxicillin (or amoxicillin/clavulanate), and/or an oral cephalosporin, that were considered sufficient to preclude further use were studied. Skin testing with penicillin G, commercial benzylpenicilloyl phosphate, penicillin minor determinant mixture (MDM), ampicillin, cefazolin, cefuroxime, and ceftriaxone was performed according to the suspected drug allergy, followed by an oral challenge, repeat skin testing, and prospective follow-up if no reactions were observed. Results Fifty-four (33.5%) of 161 patients with suspected amoxicillin reactions and 13 (50%) of 26 suspected cephalosporin reactions had positive skin tests or oral challenges. Positive reactions to only the MDM reagent occurred in 9 amoxicillin- or cephalosporin-allergic patients, to only the ampicillin reagent in 4 amoxicillin-allergic patients, and to only a cephalosporin reagent in 3 cephalosporin-allergic patients. No reactions to oral challenge were severe after negative skin testing. During prospective follow-up, one (0.9%) of 107 patients suspected of amoxicillin allergy who completed our skin testing—oral challenge repeat skin test protocol without a reaction and two (1.8%) patients with borderline reactions subsequently developed urticaria 8-16 months later while taking a course of amoxicillin. Reactions were mild. No test negative patients suspected of cephalosporin allergy developed a reaction with a subsequent course of a cephalosporin. Amoxicillin reactors with positive skin tests or oral challenges (N = 54) received 83 treatment courses of cephalosporins uneventfully in prospective follow-up. Conclusions Elective amoxicillin and cephalosporin skin testing and oral challenge protocols are helpful in identifying patients at very low risk for developing subsequent hypersensitivity reactions.

Clinical prediction rules to optimize cytotoxin testing for Clostridium difficile in hospitalized patients with diarrhea

Although routine testing of hospitalized patients with diarrhea for Clostridium difficile cytotoxin has been advocated as a high-yield procedure, the rationale for this practice has been questioned. To target a low-yield subgroup for whom routine testing could be deferred, we derived a clinical decision rule for predicting results of the C difficile cytotoxin assay in hospitalized adults with diarrhea. We hypothesized a priori that two variables, antibiotic use (within 30 days prior to testing) and history of significant diarrhea (new onset of > 3 partially formed or watery stools per 24 hour period), would be highly predictive of cytotoxin results, and obtained these data on 480 consecutive patients who underwent diagnostic testing for C difficile at a university hospital and affiliated Veterans Affairs medical center. For more detailed modelling, we recorded symptoms, signs, comorbidity, and other potential causes of diarrhea for 68 test positive patients (cases) and 265 randomly selected test negative patients (controls) within the study cohort. The overall prevalence of positive cytotoxin assays was 14%. Prior antibiotic therapy (OR = 9.0, 95% CI 2.1-38.4), significant diarrhea (OR = 2.2, 95% CI 1.1-4.7), and abdominal pain (OR = 1.9, 95% CI 0.96-3.7) were independent predictors of cytotoxin assay results. The model discriminated patients with positive and negative assays with a receiver operating characteristic (ROC) area of 0.68; observed and predicted probabilities of a positive cytotoxin assay were well correlated over the entire range of observed probabilities (r2 = 0.86). A decision rule (defined as positive if prior antibiotic use and either significant diarrhea or abdominal pain are present) demonstrated sensitivity and specificity of 86 and 45%. When applied to the entire dataset (N = 480), a simplified a priori rule, defined as positive if both prior antibiotic use and history of significant diarrhea are present, demonstrated sensitivity, specificity, positive and negative predictive value of 80, 45, 18 and 94%, respectively (6% of those predicted to be cytotoxin-negative actually tested positive). Use of this rule would have averted 39% of cytotoxin assays in our study population. Patients without prior antibiotic use and either significant diarrhea or abdominal pain are unlikely to have positive C difficile cytotoxin assay results, and may not routinely require cytotoxin testing.

Ibopamine in glaucoma diagnostics: a new pharmacological provocative test

Ibopamine is used when performing provocative tests, thanks to its pharmacological property of increasing ocular pressure in eyes with outflow system impairment. This study summarizes the latest results that we have achieved with reference to its clinical-diagnostic use. 175 (250 eyes) POAG patients, 101 (190 eyes) glaucoma suspects with mild ocular hypertension, 39 (64 eyes) NTG patients and 163 (326 eyes) healthy volunteers underwent an ibopamine provocative test. Among the POAG and the glaucoma suspects, 49 (92 eyes) and 20 (38 eyes) patients were selected who, starting from the performing of ibopamine test, had at least one year of perimetric follow-up. These patients have been assessed for the perimetric defect progression in relation to the (negative or positive) response to ibopamine. the ibopamine test was positive for 92% of the glaucomatous patients, 61% of the glaucoma suspects, 52% of the NTG patients and 0% of the healthy volunteers. It was observed that 28% of the ibopamine-positive glaucoma suspects showed a perimetric deterioration during an average 2.5-year follow-up. No perimetric deterioration was found on ibopamine-negative glaucoma suspects (Fisher's exact test: p = 0.038). Among glaucomatous patients, 46% of the test-positive individuals showed a progressive trend of the perimetric defect, as against about 8% of glaucomatous test-negative patients (Fisher's exact test: p = 0.003). We believe that the ibopamine provocative test can be usefully applied especially to epidemiological screening studies to identify patients who might develop ocular hypertension or glaucoma and in the follow-up of glaucoma suspects, to identify individuals who have a greater risk of developing perimetric defects.

Problems in selecting the adequate patient population from existing data files for assessment studies of new diagnostic tests

Assessment of new diagnostic tests should be carried out in a population with suspicion of disease. This ‘indicated’ population may comprise all patients for whom the target disease is part of the differential diagnosis. To investigate this empirically, data from a study on ultrasonography for scrotal pathology diagnosis was used for assessment of ultrasonography for epididymitis. The population could be selected according to several inclusion criteria, varying from patients with epididymitis mimicking diseases in their differential diagnosis, to patients with only epididymitis mentioned in their differential diagnosis. Different methods of population gathering led to large variations in the test characteristics of ultrasonography (sensitivity 76–83%, specificity 79–97%, prevalence of epididymitis for test-negative patients 56-5%). These results suggest selection bias depending on the true disease status. We advocate prospective assessment studies in populations with disease suspicion, as defined by signs, symptoms and complaints. Constituting an indicated population from an existing file of retrospectively gathered data may pose problems.