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Biomedical subjects

M J McFarlane

Publications and source records attributed to M J McFarlane.

At least 19 recordsLinked to original sources
PubMed1994

Use of the alveolar-arterial oxygen gradient in the diagnosis of pulmonary embolism.

BACKGROUND: Arterial blood gas (ABG) values and the alveolar-arterial oxygen (A-a) gradient are sensitive indicators of pulmonary pathology. Alone, they are not diagnostic of pulmonary embolism (PE), but they may be useful in excluding the diagnosis of PE if their values fall within the normal range. The purpose of this study was to determine the diagnostic value of a normal A-a gradient in ruling out PE. PATIENTS AND METHODS: The Derivation Set came from the records of all patients at Cleveland MetroHealth Medical Center who received a ventilation/perfusion (V/Q) scan for suspected PE in 1988 or 1989. Demographic and clinical data were obtained that included risk factors, symptoms, signs, and laboratory tests. A-a gradients were calculated using a standard equation; a normal gradient was defined as less than or equal to (age/4 + 4). The A-a gradient was examined before and after controlling for PE risk factors. The Validation Set was comprised of patients who had V/Q scans in 1987 and 1990. RESULTS: Among the 873 patients in the Derivation Set, 540 had simultaneous room air ABG determinations. Of these patients, 109 (20%) had a discharge diagnosis of PE. Only 1 of 57 (1.8%; 95% confidence interval [CI]: 0.9%-10.7%) patients without a history of PE or deep venous thrombosis (DVT) and with a normal A-a gradient had PE. Among the 805 V/Q patients in the Validation Set, 489 had simultaneous room air/ABG determinations. Of these, 75 (15%) had PE. Only 1 of 54 (1.9%; 95% CI: 0.1%-11.2%) patients without a history of PE or DVT and with a normal A-a gradient had PE. CONCLUSIONS: A normal A-a gradient among patients without a history of PE or DVT makes the diagnosis of PE unlikely. Further diagnostic evaluation may be unnecessary in this subgroup of patients.

Adult↗
PubMed1993

Gallstones, cholecystectomy, and colorectal cancer.

PURPOSE: To examine the controversial association of gallstones, cholecystectomy and colorectal cancer. Methodologic explanations for the association include ascertainment bias, unequal diagnostic testing, and necropsy selection bias. Necropsy screening, which eliminates unequal diagnostic testing and ascertainment bias and reduces necropsy selection bias, was used to study this controversy. METHODS: Adult necropsies at the University of Kansas Medical Center from 1950 to 1984 were reviewed. Patients with colorectal cancer, gallstones, or who had cholecystectomy during life were excluded. The remaining patients were those in whom neither colorectal cancer nor gallstones were suspected during life (reducing selection bias). The occurrence of gallstones and colorectal cancer among these individuals was then determined (reducing ascertainment bias and unequal diagnostic testing). RESULTS: Of 7485 persons receiving necropsy, 239 had colorectal cancer diagnosed during life and an additional 604 had gallstones or cholecystectomy, leaving 6642 patients available for study. Overall, no association between colorectal cancer and gallstones was found. In women, gallstones were associated with colorectal cancer; 6/447 (1.3%) with gallstones had colorectal cancer compared with 11/2259 (0.4%) without gallstones who had colorectal cancer, p = 0.048, odds ratio 2.78 (95% CI 0.84-8.25). A stronger association was found between right-sided colorectal cancer and gallstones (odds ratio 6.79, 95% CI 1.14-46.46). CONCLUSIONS: These data suggest an association between gallstones and colorectal cancer among women. Gallstones may indicate patients at higher risk for colorectal cancer. Studies associating cholecystectomy with colorectal cancer may be explained--not by ascertainment bias--but, rather, by susceptibility bias. The reason for the cholecystectomy (gallstones) may be the correct association and not the cholecystectomy itself.

Adult↗
PubMed1992

Meningiomas are not significantly associated with breast cancer.

We studied 283 meningiomas seen at the University of Kansas, Kansas City, from 1948 through 1984, identifying all additional nonmeningeal malignancies and primary brain tumors in these patients and calculating the expected number of additional tumors by the use of a person-year method from age and sex-matched cancer incidence data. We determined expected numbers of total neoplasms in our meningioma population as well as the expected numbers in each major organ system for the sexes independently and together. We then calculated standard morbidity ratios and 95% confidence intervals for each tumor type. The number of breast cancers did not reach statistical significance. We found a significantly increased number of second primary brain tumors in women (standard morbidity ratio, 8.0; 95% confidence interval, 2.2 to 20.4) and an increased number of thyroid cancers in both sexes (standard morbidity ratio, 7.5; 95% confidence interval, 1.5 to 21.9).

Adult↗
PubMed1991

The epidemiologic necropsy for abdominal aortic aneurysm.

The epidemiologic necropsy measures the occurrence of unsuspected disease through the examination of necropsy records. The estimates of unsuspected disease should approximate what occurs in the living population. The necropsy records of the University of Kansas Medical Center (Kansas City) from 1950 to 1984 were examined for the occurrence rate of abdominal aortic aneurysms. Each adult patient was categorized as (1) without abdominal aortic aneurysm, (2) abdominal aortic aneurysm discovered as a necropsy surprise, or (3) abdominal aortic aneurysm diagnosed or suspected during life. Necropsy detection rates of unsuspected abdominal aortic aneurysms were compared with those found in five published screening surveys. The necropsy detection rate in men was 81 (0.019) of 4155 and was 28 (0.009) of 3142 in women, a difference that was statistically significant. When the necropsy series was adjusted to reflect the same demographic composition as the screening surveys, the results from necropsy and screening were statistically similar. In particular, two surveys from the United Kingdom showed screening detection rates among white men of 0.072 compared with a necropsy detection rate of 0.058. These results further support the use of the epidemiologic necropsy as a research tool for estimating the reservoir of disease in the population.

Adult↗
PubMed1989

More lung cancer but better survival. Implications of secular trends in "necropsy surprise" rates.

In previous research, we have demonstrated the value of using necropsy "surprise" lung cancer cases, in those in whom lung cancer was not suspected during life, to estimate the size and composition of the "reservoir" of undetected lung cancer in the general population. The current research was done to determine the characteristics and consequences of secular changes over time in the composition of the lung cancer "reservoir." The results suggest that further advances in diagnostic technology will enhance detection during life of the large "reservoir" of resectable lung cancer, particularly in women. With the increased detection of these reservoir cases during life, the statistical occurrence rates for lung cancer will seem to increase, but survival rates will seem to improve because more of the detected cases will be resectable.

Autopsy↗
PubMed1989

Clinical diagnosis is not a source of bias in selection for necropsy.

Recent reports have suggested a minimal difference in demographics between hospital deaths undergoing necropsy and those that do not. In order to assess whether the clinical diagnosis at death influenced the decision to request necropsy in deaths occurring in the hospital, a 10% sample of all adult necropsies at the University of Kansas Medical Center (Kansas City) from 1962 through 1981 was obtained. These patients (cases) were matched by age, race, sex, and date of death to hospital deaths not undergoing necropsy (controls). The charts were reviewed, and the primary diagnosis at death was ascertained and categorized into one of the 14 categories of the International Classification of Diseases. There were 412 case-control pairs, with 237 men and 175 women in each group. Most patients were classified under the headings Circulatory (142 cases vs 140 controls) and Neoplasm (143 cases vs 148 controls), followed by Respiratory (21 cases vs 33 controls) and Digestive (44 cases vs 28 controls). Overall, no statistically significant differences were observed between cases and controls. There were no gender-specific differences in all but two of the categories. In men, the controls had more patients classified under the heading injury (19 vs seven). In women, the control group had more patients classified under the heading Respiratory (14 vs four). Because of multiple comparisons, these findings could have occurred by chance. These data suggest that the primary diagnosis at death is not a source of bias in the selection for necropsy. Consequently, necropsy-selection bias, if it exists, may be due to other factors, such as the complexity of the patient's clinical course.

Autopsy↗
PubMed1988

A clinical index to predict survival in acute renal failure patients requiring dialysis.

Recent advances in technology have not substantially changed the relatively low survival rate associated with acute renal failure (ARF). Several clinical prognostic variables and multivariate models have been reported to predict survival in individual patients, but these are either cumbersome to use or restrictive in their application. A straightforward clinical index has been developed to predict survival in ARF based on data obtained for all patients receiving dialysis for ARF at the University of Kansas Medical Center from November 1979 through October 1985. During this period, 126 patients received dialysis for ARF, with an overall survival of 25% (32/126). There were no significant differences between survivors and nonsurvivors in age, gender, or indication for dialysis. Eleven variables were statistically related to survival, and were reduced to five when clinically similar variables were combined or eliminated. A clinical survival index was based on these five easily determined variables that were significantly related to survival: systolic blood pressure less than or equal to 110 mm Hg, assisted ventilation, congestive heart failure, proven or suspected sepsis, and gastrointestinal (GI) dysfunction (bleeding, ileus, obstruction, or recent abdominal surgery). Survival was directly related to the number of factors present: zero, 62% (8/13); one, 44% (8/18); two, 30% (10/33); three, 19% (5/26); four, 0% (0/20); and five, 6% (1/16). This straightforward index, derived from easily obtained clinical data, is useful for judging survival prognosis in patients with ARF severe enough to warrant treatment with dialysis.

Acute Kidney Injury↗
PubMed1987

Female patients with meningioma of the sphenoid ridge and additional primary neoplasms of the breast and genital tract.

Of 283 meningioma patients seen at the University of Kansas from 1948 to 1984, eight women acquired two primary extraneural cancers in addition to their meningiomas. Of these eight patients, six (75%) had sphenoid ridge meningiomas compared with 15% of meningioma patients overall (P less than 0.001). Seven (87.5%) had at least one breast or genital cancer (P less than 0.001). Of the six with sphenoid ridge meningiomas, five (83.3%) had both of their additional tumors in these two organ systems, and the sixth had one such tumor. It is proposed that this grouping of sphenoid ridge meningioma, breast cancer, and genital cancer represents a unique constellation of neoplasms in women.

Adult↗
PubMed1987

Lung carcinoma in the elderly population. Influence of histology on the inverse relationship of stage to age.

Unlike most cancers, lung carcinoma is more likely to be localized at the time of diagnosis in older age groups when compared to those who are middle-aged. In an attempt to explain this inverse age-stage relationship we studied 9062 histologically confirmed cases of lung carcinoma occurring from 1975 to 1984 obtained from the regional cancer registry for Kansas and western Missouri. They were analyzed according to histologic type, age, sex, and stage at diagnosis. The data suggest that the proportion of squamous cell carcinoma rises and that of adenocarcinoma and small cell undifferentiated carcinoma falls with increasing age. The proportion of staged lung carcinoma with local disease at the time of diagnosis increases with age. In males this trend occurred in all cell types except large cell undifferentiated carcinoma but was most significant for squamous cell carcinoma. Squamous cell carcinoma was the only group to show a significant trend among females. The rise in squamous cell and fall in small cell carcinoma may partially explain the increased prevalence of local stage disease with advancing age.

Adenocarcinoma↗
PubMed1987

The 'epidemiologic necropsy'. Unexpected detections, demographic selections, and changing rates of lung cancer.

When rising rates of occurrence are reported for a particular disease, clinicians often cannot determine whether the disease has increased in actual occurrence or in the improved detection provided by better diagnostic technology and expanded access to medical care. The epidemiologic use of necropsy data, which might help answer these questions, has been inhibited by fears of bias in demographic and clinical selection of patients for necropsy. The demographic problem can be managed by suitable adjustment and standardization of the disease rates found at necropsy, and the clinical problem can be reduced or avoided by studying the rates with which the disease is found unexpectedly in necropsies performed for other, unrelated clinical reasons. The results, obtained in population groups "screened" via necropsy, can suggest the magnitude of the "undetected reservoir" that coexists and supplements the rates of reported occurrence for a disease. In a study of necropsies at Yale-New Haven (Conn) Hospital from 1972 to 1981, the necropsy detection rates for lung cancer were slightly higher for women than for men, and were substantially higher for both genders than the customarily reported rates in the general population. The results suggest that the reported rates may continue to rise in both genders until they become essentially equal at a size approximating that of the currently undetected reservoir. The "epidemiologic necropsy" offers a potentially valuable method to help distinguish the true occurrence rates of disease from the changes attributable to improved diagnostic detection with modern technology.

Adult↗
PubMed1987

Absence of demographic bias in selection for necropsy.

The epidemiologic use of necropsy data has been inhibited by the belief that the information is demographically biased. This study was undertaken to investigate whether patients who have died and who have undergone a necropsy are representative of hospital deaths. In a review of all hospital and necropsied deaths from 1962 to 1981 in adult patients at the University of Kansas Medical Center, Kansas City, it was found that 7393 hospital patients died and 4122 underwent necropsy (56%), with similar proportions in both men and women. The mean age of those undergoing necropsy was slightly younger: 60 years vs 62 years in men and 57 years vs 59 years in women. The proportion of necropsies performed was relatively similar for whites (57%) and nonwhites (51%). Although the large sample size made all these differences "statistically significant," there were no clinically relevant differences with regard to gender, age, or race. These findings confirm a previous study at another institution and suggest that a demographic bias does not distort necropsy population data compared with data of the population of hospital deaths.

Adult↗
PubMed1986

Diethylstilbestrol and clear cell vaginal carcinoma. Reappraisal of the epidemiologic evidence.

The association between DES and the development of clear cell vaginal carcinoma may have several alternative explanations rather than a cause- and-effect relation. One important possibility is that susceptibility bias, arising from reasons for use of the drug in a problem pregnancy, is a prime source of the observed effect in the case-control studies. Rather than being a cause of clear cell vaginal carcinoma, exposure to DES would serve as a prognostic "marker" to identify women born of problem pregnancies that increased their risk for development of the disease. Since medical advances in prenatal and perinatal care allowed these problem pregnancies to be carried to the term delivery of a viable child, DES may have been associated with an increased occurrence of clear cell vaginal carcinoma--without causing the disease. Another alternative hypothesis is needed to account for the high rates of reported previous exposure to DES in the case subjects of the two case-control studies. These rates may have been elevated by some form of interviewer bias or recall bias. The relatively high incidence of clear cell vaginal carcinoma that would be expected from the results of these case-control studies has not been observed in cohort studies. No instances of clear cell vaginal carcinoma have thus far been found in suitably assembled cohorts of women exposed to DES in utero. The history of science contains abundant examples of fervently held beliefs about cause- and-effect relations that were later found to be erroneous. The existing evidence of a DES/vaginal cancer relation is currently too weak for the causal role of DES to be regarded as established. To get better evidence, the problems of biased comparison and biased data can be addressed in at least three ways. The first is to carry out an appropriately objective new case-control study, with suitably chosen control subjects; the second is to study the issue of susceptibility bias by getting additional information about the occurrence of problem pregnancies in the mothers of patients with clear cell vaginal carcinoma who were not exposed to DES; the third is to review past tissue specimens from previously diagnosed genital adenocarcinomas, searching for clear cell cancers that may have been unrecognized. Until the suspected biases are addressed and either confirmed or refuted, the relation between DES and clear cell vaginal carcinoma remains a statistical association that is unaccompanied by the quality of evidence required for scientific conclusions.

Adenocarcinoma↗
PubMed1986

Clinical features of lung cancers discovered as a postmortem "surprise".

Despite improved modern diagnostic techniques, many patients with primary lung cancer escape detection of their disease during life. In a review of postmortem records at a university hospital, 28 percent of 153 primary lung cancers found at necropsy had not been diagnosed while the patient was alive. The male/female ratio was 1.3 in this undetected group, compared with 2.3 in the detected group. The main clinical features that seemed to lead to nondiagnosis were a terminal clinical state in patients who were too sick for further diagnostic searches, the absence of suggestive primary symptoms, a chest x-ray film interpreted as not showing primary lung cancer, and the absence of cigarette smoking. Among the patients with lung cancer at necropsy, the proportion of nonsmokers was higher in the previously undiagnosed group than in the group with antemortem diagnoses, even when patients were stratified for primary symptoms. The findings suggest the need for diagnostic alertness to the possibility that curable lung cancer can occur in patients who have a positive chest-film lesion but who are nonsmokers and who lack typical symptoms.

Adult↗
PubMed1986

Necropsy evidence of detection bias in the diagnosis of lung cancer.

The correct diagnosis had not been made during life in 26% of 153 patients with lung cancer found in necropsies performed between 1971 and 1982. The likelihood of a correct antemortem diagnosis showed distinctive gradients in relation to the patients' history and amount of cigarette smoking, symptomatic manifestations, and anatomic extensiveness of the cancers. However, cigarette smoking still exerted a diagnostic effect in patients with similar symptoms and similar degrees of anatomic spread. Furthermore, if a lesion was present, chest films were more likely to be radiologically interpreted as a cancer in smokers. The results suggest that smokers receive preferential consideration regarding the diagnosis of lung cancer. This detection bias can have adverse scientific consequences in depriving nonsmokers of suitable therapy, in leading to falsely high estimates of the true magnitude of the smoking/lung cancer association, and in distracting etiologic attention from other agents that may cause lung cancer.

Adult↗
PubMed1985

The role of susceptibility bias in epidemiologic research.

Because prognostic adjustment in epidemiologic studies of disease etiology has usually been limited to matchings or stratifications based on demographic characteristics, clinical sources of susceptibility bias have received little attention. This may have led to an incorrect association in two prominent epidemiologic relationships: that between clear-cell vaginal carcinoma and the use of diethylstilbestrol to treat women with bleeding or previous pregnancy loss; and that in the conflicting results of the studies linking sex steroids to the risk of birth defects. The recognition and management of susceptibility bias requires attention to the patients' clinical status at the time of exposure to the alleged causative agent, and also requires collecting and analyzing clinical data excluded or ignored in most epidemiologic studies. To avoid susceptibility bias, data about bleeding, threatened abortion, and other clinical reasons for prescribing therapy are needed for the appropriate matchings or stratifications.

Abnormalities, Drug-Induced↗