Cut-off Value Set Research Articles

Effect of transportation, time of sampling, and lymphocyte numbers on gamma interferon response toMycobacterium bovisin cattle at time of slaughter

Adapting the gamma interferon (IFNγ) assay for tuberculosis screening at points-of-concentration of cattle would improve global efforts to eradicate bovine tuberculosis. Two separate studies were conducted to evaluate if transportation of cattle, the time of blood collection, and total lymphocyte count affects the retention of a positive IFNγ assay result during slaughter of cattle experimentally sensitized with inactivated Mycobacterium bovis. Study 1 evaluated IFNγ assay responses to M. bovis and Mycobacterium avium stimulations in 5 cows (4 sensitized and 1 control) at the housing facility, after a 30-min transport to the slaughter facility, immediately before stunning, at commencement of exsanguination, and at 5 min after exsanguination commenced. Study 2 evaluated IFNγ assay responses to Mycobacterium antigen stimulations and total lymphocyte count in blood collected from 5 steers (4 sensitized and 1 control) at the housing facility, at commencement of exsanguination and at 2 successive 1-min intervals. The results indicated that blood obtained from sensitized cattle at commencement of exsanguination was more likely to remain positive than blood collected at successive time points; hence the time of blood collection is crucial to obtaining a useful IFNγ assay result for bovine tuberculosis at slaughter. The lymphocyte count progressively declined following exsanguination, and this decline might contribute to the reduction in the measured IFNγ. To compensate for the reduction in IFNγ production, a different set of positive cutoff values might be needed for blood collected at exsanguination. The current findings provide useful preliminary information necessary for making changes to the interpretation of the IFNγ assay on blood collected during exsanguination.

235: Heart rate variability in the first five minutes of the tilt test to predict syncope?

Vasovagal syncope mechanisms, diagnostic tools and treatments are currently strongly explored and debated. The aim of this study is to specify the early cardiac autonomic adaptations to tilt test in negative and positive (cardio-inhibitory and vasodepressor) subjects. Healthy men (n=81) from 18 to 35 years old underwent a 45 min 80° tilt test after a 15 min rest. Three clinicians independently classified each test results according to the VASIS classification: negative (NEG), mixed, cardio-inhibitor (CI) or vasodepressive (VD) syncope. Only three groups were studied: the NEG (n=13), CI (n=11) and VD (n=8). ECG recorded during 5 min of resting (Rest5) and the first 5 min of the tilt test (Early5) were compared within and between groups. ECG signals were analysed with the validated algorithm Segmenta (LTSI, Rennes) to calculate usual HRV parameters: Ptot, LF, HF, LFnu, HFnu. First , within group comparisons showed that in NEG subjects from Rest5 to Early5, HF and HFnu decreased (p<0,01) and LF (p<0,05) and LFnu (p<0,01) increased. VD subjects showed similar responses (p<0,05), except for HF indices (NS). In CI subjects LF and HF indices weren’t significantly different between Rest5 and Early5. Second , between groups comparisons of the relative adaptations (%) from Rest5 to Early5 showed that the increase in LFnu was higher in NEG (+180±80%) than in CI (+66±50%) (p<0,01). HFnu decrease was also higher in NEG (-66±5%) than in CI (-38±9%) (p<0,05). Our results suggest a lack of sympatho-vagal balance activation in the first 5 min of tilt test in subjects with vasovagal syncope. CI and VD syncope groups show a lower decrease of HF indices in the Early5. Moreover, CI group shows a lower increase of LF indices. A perspective of this work is the set of cut-off values from data recorded over the first 5 min of tilt test to estimate the risk and the type of vasovagal reaction, based on a bigger population. Figure (abstract 235) – LFnu and HFnu variations (%) in NEG and CI

Population-based screening for colorectal cancer using an immunochemical faecal occult blood test: A comparison of two invitation strategies

Background: To date, there is no screening programme for colorectal cancer (CRC) in Flanders, Belgium. However, The European Code Against Cancer (2003) recommends a population-based approach for CRC screening. This study aimed to obtain information about potential participation rates for a population-based screening programme for CRC in Flanders, and to compare two invitation strategies. Methods: In 2009, a trial programme for CRC screening was set up in three Flemish areas for all average-risk people aged 50–74 years, using an immunochemical faecal occult blood test (iFOBT) with a cut-off value set at 75ng/ml of haemoglobin. The faecal sampling set was sent at random by post (mail group) or provided by the general practitioner (GP group). Results: In total, 19,542 people were invited to participate. Of these, 8229 provided a faecal sample, resulting in an overall participation rate of 42.1%. Participation by mail and through the GP was 52.3% (95% CI, 51.3–53.2) and 27.7% (95% CI, 26.7–28.6), respectively. The difference of 24.6% was statistically significant (95% CI, 23.3–25.9, p<0.001). Before the reminder letter was sent and the other invitation strategy was offered, the overall participation rate was 26.5% (n=5176); 36.4% (95% CI, 35.5–37.4) for the mail group and 16.6% (95% CI, 15.8–17.3) for the GP group. The odds of participating in CRC screening was almost three times higher for people invited by mail as opposed to people invited through a GP (OR=2.96, 95% CI, 2.78–3.14, p<0.001). Women were more likely to participate in CRC screening than men (OR=1.22, 95% CI, 1.15–1.30, p<0.001). In addition, we found that inhabitants from residential (OR=1.98, 95% CI, 1.85–2.11) and rural (OR=2.90, 95% CI, 2.66–3.16) areas were more likely to participate than those in urban areas. Of the 8229 people who submitted a faecal sample, 435 (5.3%) had a positive iFOBT, and of those, CRC was diagnosed in 18 (5.7%) individuals. Compliance for follow-up colonoscopy was 72.9%, and did not differ between the mail (72.4%, 95% CI, 67.5–77.3) and GP groups (74.3, 95% CI, 66.2–82.5). Conclusion: Inviting people for CRC screening by means of a direct-mail invitation, and including a faecal sampling set (iFOBT), results in much higher participation rates than inviting people through the GP.

Methylation of the CpG sites only on the sense strand of the APC gene is specific for hepatocellular carcinoma.

Hypermethylation of the promoter of the tumor suppressor gene, adenomatous polyposis coli (APC), occurs in various malignancies, including hepatocellular carcinoma (HCC). However, reports on the specificity of the methylation of the APC gene for HCC have varied. To gain insight into how these variations occur, bisulfite PCR sequencing was performed to analyze the methylation status of both sense and antisense strands of the APC gene in samples of HCC tissue, matched adjacent non-HCC liver tissue, hepatitis, cirrhosis, and normal liver tissues. DNA derived from fetal liver and 12 nonhepatic normal tissue was also examined. These experiments revealed liver-specific, antisense strand-biased CpG methylation of the APC gene and suggested that, although methylation of the antisense strand of the APC gene exists in normal liver and other non-HCC disease liver tissue, methylation of the sense strand of the APC gene occurs predominantly in HCC. To determine the effect of the DNA strand on the specificity of the methylated APC gene as a biomarker for HCC detection, quantitative methylation-specific PCR assays for sense and antisense strand DNA were developed and performed on DNA isolated from HCC (n = 58), matched adjacent non-HCC (n = 58), cirrhosis (n = 41), and hepatitis (n = 39). Receiver operating characteristic curves were constructed. With the cutoff value set at the limit of detection, the specificity of sense and antisense strand methylation was 84% and 43%, respectively, and sensitivity was 67.2% and 72.4%, respectively. This result demonstrated that the identity of the methylated DNA strand impacted the specificity of APC for HCC detection. Interestingly, methylation of the sense strand of APC occurred in 40% of HCCs from patients with serum AFP levels less than 20 ng/mL, suggesting a potential role for APC as a biomarker to complement AFP in HCC screening.

Development and evaluation of Indirect Hemagglutination Antibody Test (IHAT) for serological diagnosis and screening of bovine cysticercosis in Ethiopia

The study was conducted to develop and evaluate an Indirect Hemagglutination Antibody Test (IHAT) for the serological diagnosis of Cysticercus bovis in live animals. IHAT was set-up in-house and used to test serum samples of cattle against sheep red blood cell (SRBC) coated with crude extracts of C. bovis cyst. Serum samples for screening were collected from Addis Ababa abattoir (n=522), a dairy farm from the suburbs of Addis Ababa (n=101), and a traditional extensive farm (n=109). Postmortem inspection was conducted on a total of 522 animals slaughtered in Addis Ababa Abattoir, out of which 39 (7.5%) were positive for C. bovis. Thirty-seven of these had viable C. bovis cysts. IHAT titres were determined from serially diluted sera, with a cut-off value set at a titre of 1:64. Cross reaction with other helminths was either absent or very low. Sensitivity and specificity of the IHAT were 100% and at least 90%, respectively. Based on this test, 149 cattle (28.5%) from the Abattoir, 33 cattle (30.3%) from the extensive farm and 8 cattle (7.9%) from the dairy farm were positive for C. bovis. The difference in prevalence between the dairy farm and extensive farm was significant (P

Diffusion-weighted magnetic resonance imaging in focal breast lesions: analysis of 78 cases with pathological correlation

This study assessed the usefulness of magnetic resonance diffusion-weighted imaging (DWI) in distinguishing between benign and malignant breast lesions. Gadolinium-enhanced magnetic resonance imaging (MRI) and DWI with determination of the apparent diffusion coefficient (ADC) were performed on 78 women, each with a focal breast lesion at least 7 mm in diameter, which was studied by cytology or histology. Final diagnoses were obtained by cytology in 29 cases and histology in 49 (11 percutaneous biopsies and 38 surgical specimens). There were 43 benign lesions (13 fibrocystic disease, eight fibroadenoma, seven adenosis, five normal breast tissue, four inflammatory lesions, three intramammary lymph nodes, two scleroelastosis and one fat necrosis) and 35 malignant lesions (30 invasive ductal carcinoma, two invasive lobular carcinoma, one ductal carcinoma in situ, one carcinomatous mastitis and one metastasis from neuroendocrine carcinoma). The mean ADC values were 1.677±0.151 for benign lesions and 1.298±0.129 for malignant lesions (p<0.001). With an ADC cutoff value of 1.48, DWI had 88.6% sensitivity [confidence interval (CI) 78.1%-99.1%] and 95.3% specificity (CI 88.9%-100%), with 31 true positives, four false negatives (three invasive ductal carcinoma and one carcinomatous mastitis), 41 true negatives and two false positives (one fat necrosis and one fibroadenoma). With the cutoff value set at 1.52, DWI sensitivity (35 true positive, no false negative) was 100% and specificity was 86% (CI 75.7%-96.3%) due to 37 true negatives and six false positives (an additional two fibroadenoma and two fibrocystic disease compared with those recorded with the cutoff set at 1.48). The overall accuracy of DWI considering both cutoff values (72 correct evaluations out of 78 cases) was 92.3% (CI 86.4%-98.2%). DWI is a reliable tool for characterising focal breast lesions.

Genetic diversity assessment of anoxygenic photosynthetic bacteria by distance-based grouping analysis of pufM sequences

To assess how completely the diversity of anoxygenic phototrophic bacteria (APB) was sampled in natural environments. All nucleotide sequences of the APB marker gene pufM from cultures and environmental clones were retrieved from the GenBank database. A set of cutoff values (sequence distances 0.06, 0.15 and 0.48 for species, genus, and (sub)phylum levels, respectively) was established using a distance-based grouping program. Analysis of the environmental clones revealed that current efforts on APB isolation and sampling in natural environments are largely inadequate. Analysis of the average distance between each identified genus and an uncultured environmental pufM sequence indicated that the majority of cultured APB genera lack environmental representatives. The distance-based grouping method is fast and efficient for bulk functional gene sequences analysis. The results clearly show that we are at a relatively early stage in sampling the global richness of APB species. Periodical assessment will undoubtedly facilitate in-depth analysis of potential biogeographical distribution pattern of APB. This is the first attempt to assess the present understanding of APB diversity in natural environments. The method used is also useful for assessing the diversity of other functional genes.

Metabolic risk-factor clustering estimation in children: to draw a line across pediatric metabolic syndrome

The diagnostic criteria of the metabolic syndrome (MS) have been applied in studies of obese adults to estimate the metabolic risk-associated with obesity, even though no general consensus exists concerning its definition and clinical value. We reviewed the current literature on the MS, focusing on those studies that used the MS diagnostic criteria to analyze children, and we observed extreme heterogeneity for the sets of variables and cutoff values chosen. To discuss concerns regarding the use of the existing definition of the MS (as defined in adults) in children and adolescents, analyzing the scientific evidence needed to detect a clustering of cardiovascular risk-factors. Finally, we propose a new methodological approach for estimating metabolic risk-factor clustering in children and adolescents. Major concerns were the lack of information on the background derived from a child's family and personal history; the lack of consensus on insulin levels, lipid parameters, markers of inflammation or steato-hepatitis; the lack of an additive relevant effect of the MS definition to obesity per se. We propose the adoption of 10 evidence-based items from which to quantify metabolic risk-factor clustering, collected in a multilevel Metabolic Individual Risk-factor And CLustering Estimation (MIRACLE) approach, and thus avoiding the use of the current MS term in children. Pediatricians should consider a novel and specific approach to assessing children/adolescents and should not simply derive or adapt definitions from adults. Evaluation of insulin and lipid levels should be included only when specific references for the relation of age, gender, pubertal status and ethnic origin to health risk become available. This new approach could be useful for improving the overall quality of patient evaluation and for optimizing the use of the limited resources available facing to the obesity epidemic.

Making the case for objective performance metrics in newborn screening by tandem mass spectrometry

The expansion of newborn screening programs to include multiplex testing by tandem mass spectrometry requires understanding and close monitoring of performance metrics. This is not done consistently because of lack of defined targets, and interlaboratory comparison is almost nonexistent. Between July 2004 and April 2006 (N=176,185 cases), the overall performance metrics of the Minnesota program, limited to MS/MS testing, were as follows: detection rate 1:1,816, positive predictive value 37% (54% in 2006 till date), and false positive rate 0.09%. The repeat rate and the proportion of cases with abnormal findings actually been reported are new metrics proposed here as an objective mean to express the overall noise in a program, where noise is defined as the total number of abnormal results obtained using a given set of cut-off values. On the basis of our experience, we propose the following targets as evidence of adequate analytical and postanalytical performance: detection rate 1:3,000 or higher, positive predictive value>20%, and false positive rate<0.3%.

Neural Network Using Combined Urine Nuclear Matrix Protein-22, Monocyte Chemoattractant Protein-1 and Urinary Intercellular Adhesion Molecule-1 to Detect Bladder Cancer

We developed a neural network to identify patients with bladder cancer more effectively than hematuria and cytology. The algorithm is based on combined urine levels of nuclear matrix protein-22, monocyte chemoattractant protein-1 and urinary intercellular adhesion molecule-1. A randomized double-blinded study of voided urine from 253 patients undergoing outpatient cystoscopy was performed. Of the patients 27 had bladder cancer on biopsy and 5 had muscle invasion. Urine tumor markers were measured using sandwich-enzyme-linked immunosorbent assay kits. Urine from patients with bladder cancer on cystoscopy was compared to urine from controls with negative cystoscopy results. An algorithm was created with 3 sets of cutoff values modeled to be 100% sensitive for superficial bladder cancer, 100% specific for superficial cancer and 100% specific for muscle invasive cancer, respectively. We compared our model to hematuria and cytology. For the hematuria dipstick test sensitivity, specificity, positive and negative predictive values were 92.6%, 51.8%, 18.7% and 98.2%, respectively. For atypical cytology sensitivity, specificity, positive and negative predictive values were 66.7%, 81%, 29.5% and 95.3%, respectively. For the sensitive model set sensitivity, specificity, positive and negative predictive values were 100%, 75.7%, 32.9% and 100%, respectively. For the specific model set sensitivity, specificity, positive and negative predictive values were 22.2%, 100%, 100% and 91.5%, respectively. For the muscle invasive model set sensitivity, specificity, positive and negative predictive values were 80%, 100%, 100% and 99.6%, respectively. The standard bladder tumor evaluation of 253 patients costs 61,054 US dollars but 36,450 US dollars using our model. Our algorithm is superior to conventional screening tests for bladder cancer. The model identifies patients who require cystoscopy, those with bladder cancer and those with muscle invasive disease. It provides possible savings over current screening methods. The potential loss of other information by not performing cystoscopy was not evaluated in our study.

Monte Carlo calculation of the radiation field at aircraft altitudes.

Energy spectra of secondary cosmic rays are calculated for aircraft altitudes and a discrete set of solar modulation parameters and rigidity cut-off values covering all possible conditions. The calculations are based on the Monte Carlo code FLUKA and on the most recent information on the interstellar cosmic ray flux including a detailed model of solar modulation. Results are compared to a large variety of experimental data obtained on the ground and aboard aircraft and balloons, such as neutron, proton, and muon spectra and yields of charged particles. Furthermore, particle fluence is converted into ambient dose equivalent and effective dose and the dependence of these quantities on height above sea level, solar modulation, and geographical location is studied. Finally, calculated dose equivalent is compared to results of comprehensive measurements performed aboard aircraft.

Predictors of mortality in patients treated with continuous hemodiafiltration for acute renal failure in an intensive care setting.

We performed this study to identify predictors of mortality in critically ill patients treated with continuous venovenous hemodiafiltration (CVVHDF) for acute renal failure in an intensive care setting. It was an uncontrolled, observational study that took place in a general intensive care unit in a university hospital. Forty-one patients undergoing CVVHDF for acute renal failure in a consecutive sample of 1,018 ICU treatments were studied. The underlying disease included 25 postsurgical cases and 16 medical cases. Between survivors (n = 23) and nonsurvivors (n = 18), the following factors were assessed: demographic data; the number and type of failed organs; Acute Physiology and Chronic Health Evaluation (APACHE) II scores; urine production; pH; base excess; serum creatinine levels; bilirubin levels; lactate levels; platelet counts; and hemodynamic variables, including cardiac index and central venous pressure. On univariate analyses, the number of failed organs (p < 0.01), presence of hepatic failure (p < 0.01), APACHE II scores (p < 0.01), pH (p < 0.01), base excess (p < 0.001), average urinary production before the initiation of CVVHDF (p < 0.05), and serum bilirubin (p < 0.01) and lactate levels (p < 0.001) were significantly different. Multiple regression analysis identified serum bilirubin (p < 0.01) and lactate levels (p < 0.01) as the predictors of hospital mortality. Presence of hepatic failure was also predictive of hospital mortality (p < 0.01) in the analysis of the type of organ failure. The cut-off value set at bilirubin levels > 10 mg/dl or arterial lactate levels > 3.5 mmol/L provided 83.3% sensitivity and 90.9% specificity in the prediction of hospital death. The crucial factors in predicting outcome of critically ill patients undergoing CVVHDF for renal failure are elevated serum bilirubin and lactate levels at the onset of CVVHDF. Presence of hepatic failure, defined as both jaundice and coagulopathy, may also worsen outcome of critically ill patients undergoing CVVHDF for renal failure. The cut-off value set at bilirubin levels > 10 mg/dl or arterial lactate levels > 3.5 mmol/L may serve as beneficial predictors of hospital mortality.

Prediction of mean pulmonary wedge pressure using Doppler pulmonary venous flow variables in hypertrophic cardiomyopathy

We examined whether pulmonary venous flow variables, assessed by transthoracic Doppler echocardiography, could predict mean pulmonary wedge pressure in hypertrophic cardiomyopathy. Forty-four patients with no left ventricular systolic dysfunction (left ventricular fractional shortening ≥25%) were studied. Forty patients with systolic dysfunction (dilated cardiomyopathy group) served as control. Mitral and pulmonary venous flow velocity curves were recorded with the pulsed-Doppler method and were related to mean pulmonary wedge pressure obtained by right heart catheterization. In hypertrophic cardiomyopathy group, the systolic ( r=−0.15, P=0.335) and diastolic ( r=0.35, P=0.022) forward flow velocity were poorly related to mean pulmonary wedge pressure, whereas the velocity of atrial reversal ( r=0.68, P<0.001) correlated well with mean pulmonary wedge pressure. In dilated cardiomyopathy group, the systolic ( r=−0.51, P=0.001) and diastolic ( r=0.60, P<0.001) forward flow velocity were strongly related to mean pulmonary wedge pressure. With the cut-off value set at the velocity of atrial reversal >30 cm/s in hypertrophic cardiomyopathy group, the sensitivity for predicting mean pulmonary wedge pressure >15 mmHg was 79% and the specificity was 73%. In conclusion, the atrial component of the pulmonary venous flow can be used to predict mean pulmonary wedge pressure in hypertrophic cardiomyopathy.

Caesarean section rates in an African country

The use of caesarean section (C.S.) has been analysed in the 12 hospitals of the Midlands Province of Zimbabwe during a 2-year period. Maternal mortality rate, perinatal mortality rate, low birthweight rate, percentage of high risk pregnancy, C.S. rate and instrumental delivery rate have been extracted for each hospital. The rate of C.S. delivery varied between 2.2 and 16.8 per 100 deliveries but was not correlated with the number of high-risk pregnancies. Increased use of C.S. was not linked to better perinatal results. An important determinant of the C.S. rate appears to be the physician and the ratio between the rate of instrumental deliveries (ID) and C.S. differentiated the 12 hospitals into two groups. Although there was no difference in the number of high risk patients in these two groups, outcomes were much better in the hospitals with a high ID rate than in the hospitals with a high C.S. rate, suggesting that attitudes of medical staff can influence both the mode of delivery and the perinatal outcome in a developing country.

Evaluation of the serum level of immunosuppressive substance in oral cancer patients

The serum level of immunosuppressive substance (IS) was studied in 40 patients with primary oral cancer and in 79 patients without cancer. Its usefulness was evaluated as a parameter for monitoring therapy as well as recurrence of the tumors. Mean values for serum IS in patients with cancer and patients without were 687 ± 284 μg/mL and 464 ± 153 μg/mL, respectively. Normal healthy controls had a mean value of 431 ± 105 μg/mL, with the cutoff value set at 641 μg/mL (mean +2 SD). Patients without cancer who had a severe infectious disease showed conspicuously high serum IS levels, and these values were closely correlated with their C-reactive protein values. The positive rate of IS increased in all patients with oral cancer was 58%. The mean level of serum IS in cancer patients was significantly higher than that of the controls ( P < .01), and the level was found to be more elevated as the stage of the disease advanced (stage I to III, 48%; stage IV, 68%). Histologic analysis of the tumor cells in patients with squamous cell carcinoma (SCC) showed that the mean serum IS level of those who had poorly differentiated SCC was much higher (937 ± 181 μg/mL) than that of patients with well-differentiated SCC (616 ± 159 μg/mL). Patients who had recurrent or metastatic cancer, or those who died from the cancer exhibited marked elevation of the serum IS levels, whereas patients who remained free of cancer in the follow-up period showed significantly lower serum IS levels. The rise and fall of the serum IS level was closely correlated with the disease progression and/or remission. These data strongly suggest that serum IS is a useful parameter for monitoring the disease stage as well as the effect of therapy on patients with oral cancer.

Metabolic Effect of Hemipancreatectomy in Donors: Preoperative Prediction of Postoperative Oral Glucose Tolerance

Between November 1977 and January 1987, 55 transplantations of pancreas segments from living donors related to their recipients were performed at the University of Minnesota. A preliminary analysis of metabolic test results in donors tested 1 yr after hemipancreatectomy showed an increase in mean glucose and a decrease in mean insulin values during oral glucose tolerance tests (OGTTs) in 18 donors, a 14% increase in the mean of the mean glucose levels during 24-h metabolic profiles in 12 donors, and a decrease of 45% in the mean 24-h urinary C-peptide excretion in 21 donors. Including the studies performed postdonation, 11 of 31 (35%) donors developed an abnormal OGTT result. In a retrospective analysis, preoperative results of intravenous glucose tolerance tests (IVGTTs) and cortisone-stimulated OGTTs were found to be statistically significant predictors of an abnormal OGTT after hemipancreatectomy. The mean of the 5- to 50-min IVGTT insulin values was the best predictive test. With the cutoff value set at 62 microU/ml, this test result had a sensitivity of 100%, a specificity of 83%, and a positive predictive value of 75% for identifying donors who developed an abnormal OGTT. The sum of the 5- and 10-min IVGTT insulin (cutoff 140 microU/ml) had a sensitivity of 100%, a specificity of 67%, and a predictive value of only 60%, whereas the delta-insulin had values of 86, 71, and 60%, respectively. Both the IVGTT mean insulin and the sum of the 5-min and 10-min insulin test results were 100% predictive of an abnormal test (0% risk), but the IVGTT mean insulin excluded the lowest proportion of otherwise suitable donors (a low "false-alarm" rate). The IVGTT mean insulin can be used to identify or exclude potential donors who would develop an abnormal OGTT result should hemipancreatectomy be performed.

IV. Geographically smoothed geomagnetic cutoffs

Detailed calculations of effective vertical-trajectory cutoff rigidities have failed to eliminate a discontinuity in the neutron-monitor latitude variation in the vicinity of Mexico City noted after the 1965 survey described in paper I of this set of five papers. Since a similar discontinuity appears when the vertical cutoffs are plotted against geographical latitude, the irregularity seems to be a function of the vertical rigidity cutoffs. Extensive calculations of cutoffs at, intervals of one degree of latitude along meridians 260 °E and 285° E have delineated the systematic nature of the irregularity. A set of cutoff values, which orders the observations satisfactorily for the analysis in the present papers, was obtained by smoothing a 5° latitude by 15° longitude grid of calculated values within a sector of the northern hemisphere bounded by meridians 195 °E and 285 °E.