False-negative Readings Research Articles

A comparison of five methods of temperature measurement in febrile intensive care patients

A clinically useful temperature measurement method should correlate well with the body's core temperature. Although previous investigators have studied temperature readings from different sites in hypothermic and normothermic patients, none have compared methods specifically in febrile patients. To compare temperature measurement methods in febrile intensive care patients. Temperature readings were obtained in rapid sequence from an electronic thermometer for oral and axillary temperature, rectal probe, infrared ear thermometer on "core" setting, and pulmonary artery catheter, approximately every hour during the day and every 4 hours at night. The sample consisted of 13 patients with pulmonary artery catheters and with temperatures of at least 37.8 degrees C. Rectal temperature correlated most closely with pulmonary artery temperature. Rectal temperature showed closest agreement with pulmonary artery temperature, followed by oral, ear-based, and axillary temperatures. Rectal and ear-based temperatures were most sensitive in detecting temperatures greater than 38.3 degrees C. Likelihood ratios for detecting hyperthermia were 5.32 for oral, 2.46 for rectal, and 1.97 for ear-based temperature. Rectal and ear-based temperatures had the lowest negative likelihood ratios, indicating the least chance of a false negative reading. Axillary temperature had a negative likelihood ratio of 0.86. Rectal temperature measurement correlates most closely with core temperature. If the rectal site is contraindicated, oral or ear-based temperatures are acceptable. Axillary temperature does not correlate well with pulmonary artery temperature. These results underscore the importance of consistency in method when establishing temperature trends, and of awareness of method when interpreting clinical data.

Optimization of the L-M cell bioassay for quantitating tumor necrosis factor α in serum and plasma

In attempting to quantitate TNF-α in body fluids using current bioassay protocols, we discovered several factors which adversely affect reliability, sensitivity and specificity. The objective of this study was to establish an optimum assay for use with serum and plasma samples. While adopting the commonly used L-M cell bioassay to test serum and plasma samples, we noted non-specific staining of cell debris and protein by crystal violet dye, even if the wells were washed prior to staining. However, when we replaced crystal violet with tetrazolium salts to measure cell viability, we discovered that both serum and plasma, from a variety of species, non-specifically reduced both MTT and XTT tetrazolium salts to a colored formazan product resulting in absorbance values significantly higher than those of medium and serum controls. This effect was particularly pronounced with fetal bovine serum which showed significant color development with as little as 6% serum in the test wells. Maximum sensitivity can only be obtained by eliminating these false negative readings. Therefore the serum or plasma containing supernatant must be removed from the test wells and replaced with fresh serum-free medium prior to addition of the substrate. This finding should be applicable to other body fluids such as urine, milk, and synovial fluid as well as any tetrazolium based assay for cell viability which uses serum-supplemented culture medium. Additionally, when the substrate XTT, which reduces to a water-soluble formazan product, was compared to MTT which reduces to a water-insoluble product, XTT was found to be superior since elimination of the solubilization process resulted in reduction of assay time. Also, overall absorbance readings using XTT were higher than with MTT, without any loss of sensitivity. There were no differences in detectability of TNF-α between serum and plasma and use of preservative-free heparin was found not to have adverse effects on TNF-α assay. Heat treatment of both serum and plasma seemed to inactivate factors that contributed to the non-specific lysis of the L-M cells when their concentrations exceeded 25%.

Office arthroscopy: A diagnostic alternative

Twenty patients with enigmatic knee symptoms were selected for evaluation by both magnetic resonance imaging (MRI) and office arthroscopy. Office arthroscopy was performed in a standard examination room using a miniature (1.7 mm) fiberoptic arthroscope under local anesthesia. All MRI scans were performed on a state-of-the-art 1.5-T magnet unit, and included specialized cartilage sequences in 7 patients. In 14 patients, 26 areas showed articular cartilage changes by arthroscopy (grade 2–3). Only nine of these areas were detected by MRI (sensitivity 34.6%). There were five false-positive and four false-negative readings of meniscal tears by MRI as compared with office arthroscopy. These results improved when postoperative menisci were excluded. Only one of three anterior cruciate ligament (ACL) disruptions identified by MRI could be verified by arthroscopy. The one posterior cruciate ligament (PCL) disruption was confirmed by both techniques. MRI was superior to arthroscopy in identifying bone contusions, subchondral sclerosis, and medial cruciate ligament (MCL) sprains. Office arthroscopy is an accurate and cost-efficient alternative to MRI in diagnostic evaluation of knee pathology in patients with enigmatic symptomatology.

Latex agglutination test for cytomegalovirus antibody screening of transplant donors important aspects

In a retrospective study, false negative readings of CMV Scan results were detected. In a following prospective survey of 72 transplant donor sera, CMV Scan had a sensitivity and a negative predictive value of >95%. Although CMV Scan is a rapid and useful test, a higher reliability can be achieved if results are controlled by another sensitive test or, at the least, CMV Scan is read by two different persons.

A prospective evaluation of glucose reagent teststrips in the prehospital setting

Reagent teststrip determination of blood glucose has been shown to be accurate for hospital and home testing and is commonly used in prehospital care despite the lack of studies in this arena. This prospective, multicenter study examines the ability of glucose reagent teststrips to detect hypoglycemia when used under field conditions compared with simultaneously drawn control samples for laboratory glucose determination. Also examined was the accuracy of the teststrips in the laboratory glucose range ≤200 mg/dL. One hundred eighty-one pairs of data were analyzed. Hypoglycemia was defined as laboratory glucose ≤60 mg/dL. The teststrips correctly identified 31 of 33 patients in this range (sensitivity = 94%), and 125 of 148 patients without hypoglycemia (specificity = 85%). The two false negative readings were 70 and 90 mg/dL. Reagent teststrips were within ±40 mg/dL of the laboratory value in 70% of cases. The correlation coefficient (Spearman r) between teststrip and laboratory glucose in the range ≤200 mg/dL was. 80. Using teststrip readings of 90 mg/dL or less as a measure of hypoglycemia yields 100% sensitivity with a specificity of 57%. We conclude glucose reagent teststrips are a useful adjunct for use in the prehospital setting and may be valuable for the detection of hypoglycemia.

Prospective evaluation of radiologically directed fine-needle aspiration biopsy of nonpalpable breast lesions

The application of fine-needle aspiration biopsy (FNAB) to the diagnosis of nonpalpable breast lesions was evaluated with a new method which uses standard needle localization under mammographic guidance to assure accurate sampling by FNAB. This method was prospectively applied to 100 mammographically detected breast lesions in 100 women (mean age, 53 years). All 100 patients underwent surgical excision of these nonpalpable lesions after cytologic aspiration. Sufficient aspirated material was obtained for cytologic diagnosis from 91 patients (91%). The histologic and cytologic interpretations were then compared. Twenty malignancies were ultimately diagnosed by histology (12 invasive ductal carcinoma, six ductal carcinoma in situ, and two lobular carcinoma in situ), of which 17 had been cytologically diagnosed. There were no false-positive diagnoses of malignancy by FNAB. False-negative readings (3.3%) included two cases of lobular carcinoma in situ and one case of ductal carcinoma in situ. This technique thus demonstrated a sensitivity of 85%, specificity of 100%, and overall diagnostic accuracy of 96.7% for the nonsurgical detection of malignancy in nonpalpable breast lesions. These results suggest that the established safety, reliability, and cost-effectiveness of FNAB can be maintained in this clinical setting. This procedure may obviate the need for open surgical biopsy in those patients with an unequivocal diagnosis of malignancy. It can also be done using standard techniques and equipment available in many community hospitals.

Methods for screening the naturally acquired and vaccine-induced immunity to the mumps virus

Since the introduction of the measles, mumps and rubella (MMR) vaccine in Sweden in 1982, a yearly evaluation of the immunity pattern and seroconversion rate of 12-year-old children has been carried out. To be able to realize large-scale, follow-up studies, techniques have to be used which are not too labour-intensive and time-consuming but are sensitive enough to detect past immunity and post-vaccination titres. We report tests with haemolysis-in-gel (HIG) technique and an enzyme-linked, immunosorbent assay (ELISA) compared with neutralization (NT) for the detection of mumps antibodies. This study comprises 226 paired serum samples obtained between 1985 and 1989. One hundred and forty-one of the paired samples had been selected because they had given negative or borderline readings, using HIG technique. The remaining samples were consecutive pre- and post-vaccination sera obtained in 1989 from 85 vaccinees from one area in Sweden. HIG technique gave both false positive and false negative readings, compared with NT as also the false positive sera were detected. Non-inactivated sera could not be used in the NT test against mumps virus, owing to unspecific NT reactions. No differences between non-inactivated and inactivated sera by NT were seen, as against other paramyxoviruses. Cross-reactivity between mumps and parainfluenzae in NT tests was not demonstrated. The ELISA test proved more reliable and specific than HIG and was more sensitive than NT. Some post-vaccination sera from vaccinees who failed to seroconvert by NT contained high levels of mumps antibody detectable by the ELISA. Late post-vaccination sera which were negative by the NT also showed high levels of mumps-specific antibody detectable by the ELISA. Using ELISA test it was demonstrated that sera from children naturally immunized with mumps virus had significantly higher ELISA values than post-vaccination sera from children earlier vaccinated ( P < 0.001). A significantly higher booster effect after vaccination was also seen by the ELISA compared with the NT test.

The effect of incubation with Staphylococcus aureus Cowan I on subsequent determinations of IgG, IgM, and IgM rheumatoid factor by ELISA

Staphylococcus C(Urem Cowan I strain (SAC) is a polyclonal B-cell activator used for in vitro lymphocyte stimulation studies [l]. Its cell wall is rich in protein A, which reacts with the Fc fraction of IgG [2,3], but may also react with Fab fractions [2,4,5], and with IgM [6]. The B-cell stimulation is mediated through protein A interaction with their surface immunoglobulins (Ig) [7], and is T-cell independent [8], although subsequent maturation into Ig-secreting cells is T-cell dependent [8]. SAC in concentrations of 0.0005 to 0.1% has been shown to stimulate lymphocytes in vitro to secrete IgG, IgM, and IgM RF [8-121. The Ig responses in these studies are measured by enzyme-linked immunosorbent assay (ELISA). SAC may potentially interfere with subsequent ELISA readings of Ig concentrations in supernatant of such lymphocyte stimulation assays: Protein A on the SAC cells might bind IgG (and other Ig) secreted by lymphocytes, lowering their concentration in the supernatant. Furthermore, protein A could elute off SAC cells [13] then bind to IgG in the solid phase of the ELISA. This may result in either inhibition of Ig binding causing false negative readings, or binding of protein A to the enzymelabelled Ig, causing false positive readings. To determine whether SAC in concentrations used to stimulate lymphocytes, inteferes significantly with determination of Ig concentration by ELISAs, we have studied in vitro the effects of preincubation of SAC with IgG, IgM, and IgM rheumatoid factor (RF), on the subsequent determination of these Ig by ELISA.

Evaluation of Simple Tests for Detection of HIV Antibodies: Analysis of Interobserver Variation in Tanzania

200 sera were tested for HIV antibodies with different tests in Tanzania. The results were interpreted by 5 different observers with different laboratory experience. There was considerable variation between observers and between testing methods. HIV-Chek was easiest to perform with little interobserver variation, but a few probably false negative readings were seen. Serodia gave many false positives. Western Blots gave more diverging results due to indeterminate sera and lack of training. HIV-Chek seems best when time, facilities, and training are limited and if combined with Serodia false negative results can be excluded.

Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa.

A cross-sectional radiological survey of 2,245 men who were employed in South African asbestos mines was conducted in 1976. Since 1976, the lungs of 172 of these men who died have been examined to establish the presence of asbestosis or other pneumoconiosis. The x-ray readings (ILO/UC 1971) were compared with the pathological findings. A high prevalence of false positive readings, particularly for two of the three readers, was found. False negative readings were also very prevalent. Detailed information about asbestos and other mining exposure, smoking habit, age, height, and weight were examined to determine what influence they may have had in inducing false positive findings. Other dust exposure and smoking appeared to be possible factors, whereas age and obesity were probably not. It is suggested that the term "small irregular opacities" requires more precise definition.

Suction rectal biopsy in the diagnosis of Hirschsprung's disease and chronic constipation

Suction rectal biopsy has gained increased acceptance as the means of definitively diagnosing Hirschsprung's disease as well as excluding this diagnosis when evaluating the child with chronic constipation. During the 11-year period from 1 July 1974 through 30 June 1985 at the University of Michigan, Mott Children's Hospital, 309 suction rectal biopsy specimens were evaluated. Of these, 293 were done for the evaluation of chronic constipation and/or Hirschsprung's disease. The remaining 16 were performed as a part of the work-up in patients with neuromuscular, glycogen storage, inflammatory bowel, or other diseases. Forty-two (14%) of the 293 patients were diagnosed as having Hirschsprung's disease at an average age of 14.4 months. This diagnosis was ruled out in the remaining 251 patients, whose age at biopsy averaged 2.7 years. There was one false-negative reading representing an incidence of 0.3%, with no false-positives. There were no complications. The suction rectal biopsy is a bedside or clinic procedure that reliably provides pathologic material adequate for the accurate diagnosis or exclusion of Hirschsprung's disease and offers a number of advantages over manometric, radiographic, histochemical, and open, full-thickness biopsy techniques.

Incidental Hydronephrosis on Bone Scintigraphy: Sonographic Verification

We studied 98 kidneys in 55 patients with bone scintiscans and renal sonography. Among the 29 kidneys in which hydronephrosis was suspected on bone scintiscans only 12 were truly hydronephrotic by renal ultrasound. In the other 17 cases extrarenal pelves, postural stasis, early urinary tract obstruction or renal parenchymal disease may have contributed to the discrepant findings. By ultrasound criteria there were no false negative readings for hydronephrosis on scintiscan. While it is safe to interpret absence of hydronephrosis caution should be used in diagnosing hydronephrosis, since less than half of the cases actually will have the disease when suspected on a bone scintiscan.

Inadequate hemolysis of erythrocytes on reagent strips at low pH causes false-negative readings.

Patients' urines gave an unexpectedly high percentage of false-negative results for erythrocytes on a reagent strip, even when the test field for ascorbic acid indicated that none of this substance was present to inhibit the test reaction. By adding known amounts of erythrocytes to normal urines, we found that this phenomenon was time-dependent and occurred with three different brands of reagent strips in urines having a pH below 6.0. Hemolysis of erythrocytes was totally inhibited below pH 5.1 after 4 h of incubation with 50 X 10(6) erythrocytes per liter. The inhibition is apparently caused by shrinkage of the erythrocytes, rending them insensitive to the hemolytic agents in the different reagent strips tested.

Detection of specific IgM antibodies to toxocaral ES antigen: Effect of absorption of sera with protein A Sepharose

The activity of both the IgG and IgM antibodies to ES antigen from Toxocara canis larvae was tested before and after absorption of sera by protein A Sepharose 4B (PASB). For this purpose, the ELISA technique was applied to the sera from 12 dogs and 6 infants. The effect of absorption of sera by PASB was as follows. The average values before and after absorption in dog sera were 0.11 and 0.02, respectively. The same effect was observed in the infant sera. Of the 12 dog sera tested, four had a elevated IgM activity and three were considered to be false positive. Also, two adult dogs in chronic infection had a IgM antibody. Of the six infant sera tested, one had a slightly elevated IgM activity and no false positive and negative readings were found. The results of this work indicated that the absorption of sera with protein A might be useful in detecting the IgM antibodies to ES antigen. Although the false positive readings appeared without absorption of sera, misreadings hampered by the amount of IgG could be eliminated after absorption.

The Estimation of Bladder Volume by Sonocystography

Real-time ultrasonography was used to measure bladder volumes. Volumes were calculated as the product of 3 internal bladder diameters (height, width and depth). The true bladder volume was obtained from the voided volume or by catheterization. There was a good correlation between calculated and true volumes provided a correction factor of 0.6 was applied. It also was found that a simpler method using only 2 diameters and a correction factor of 0.15 was nearly as reliable. The accuracy of this quantitative method was shown to be limited to an average error of plus or minus 25 per cent for bladder volumes between 100 and 500ml. Smaller volumes could be assessed only qualitatively. False negative readings were common for bladder volumes less than 50ml.

BILIARY PRESSURE MEASUREMENT

Aim: To demonstrate that measurement of biliary pressure can aid in the management of patients with internal biliary drainage catheters. Methods: Twenty-five patients (13 male, 12 female) on internal biliary drainage for diverse etiologies were followed for up to 2 years (1 m-2 years). A measurement of the pressure in the biliary system was performed through the drainage catheter after insertion and when clinically indicated thereafter. Bile was allowed to flow freely up a venotube connected to the end of the drainage catheter and pressure obtained in cm. of water with zero at the level of the common bile duct. Results: In all patients with an adequately draining catheter, the biliary pressure was consistently below 20 cm. of water. There were no false positive or negative pressure readings. A pressure higher than 20 cm. of water was found to indicate some element of obstruction. Vigorous flushing with saline often relieved the obstruction and restored adequate drainage. Examination of obstructed catheters removed for exchange revealed that sludge first obstructs the distal side holes. After catheter exchange biliary pressure returned to normal in all cases. Conclusion: Biliary pressure measurements accurately reflect catheter patency. This test indicates the status of the drainage catheter and its need for replacement.

Evaluation of the anaplasmosis rapid card agglutination test for detecting experimentally-infected elk.

Anaplasma marginale was experimentally transmitted from cattle to elk to cattle. Six intact adult elk (Cervus canadensis canadensis) inoculated with freshly collected heparinized blood from cattle chronically infected with A. marginale became asymptomatic carriers. Although the elk did not develop clinical or hematologic evidence of infection, they became seropositive by the serum(SRCA) and plasma rapid card agglutination (PRCA) tests. Blood from the experimentally-infected elk produced disease in splenectomized bovine calves and the carrier state persisted for at least one year. Infection did not occur when two elk were inoculated with 0.5 ml of frozen blood from known bovine carriers. The blood had been frozen for four weeks in liquid nitrogen with 6% dimethyl-sulfoxide. The bovine SRCA and PRCA tests were adapted for use with elk serum. To obtain accurate test results, serum collected from clotted elk blood had to be held for at least 72 h at 21-27 C before performance of the SRCA test. Comparative serologic and infectivity studies indicated that the carrier (reactor) status of elk was accurately identified with the serologic tests in 61 of 68 samples evaluated. Incorrect serologic results with the SRCA and PRCA tests were false-negative readings. In no case were uninfected elk identified as seropositive.

The sacral tubercle--a cause for hot spots on bone scan.

The sacral tubercle, S1 posterior spinous process, can appear as intense as the sacroiliac joints on posterior bone scan in 4% of normal adult male patients. Due to sexual differences in anatomy, the scan appearance of the sacrum can cause false-positive readings. The converse, false-negative readings, can occur if the sacral intensity is taken as a constant when comparing ratios of sacroiliac joint intensities and sacral intensities on bone scans of patients with sacroiliac disease. This study demonstrates the normal anatomy of the sacrum and presents a sequence of tests to diagnose disease in the sacrum.

Scintillation camera nonuniformity: effects on cold lesion detectability.

Abstract Based on these data it is concluded that false negative and true negative readings decrease with increasing nonuniformity causing a severe decrease in physicians' ability to distinguish normals. False positive readings increase with increasing nonuniformity showing physicians' reading accuracy to be seriously affected by field nonuniformity. On this basis, the maintenance of scintillation camera performance is critical to the quality of clinical nuclear medicine practice. An expansion on this study including the parameters of spatial distortion and resolution, is currently underway at the Johns Hopkins University Applied Physics Laboratory under auspices of the Food and Drug Administration's Bureau of Radiological Health.

Lymphangiography as an aid in staging bladder carcinoma.

Eighty patients with histologically proven carcinoma of the urinary bladder had pedal lymphangiography as part of their assessment for metastatic disease. Results were correlated with surgical findings within three months of the lymphangiographic interpretation in 49 patients. There were no false-positive lymphangiograms, and only five (10%) false-negative readings were recorded. The finding of positive lymphangiograms in 9% of patients with stage B disease, 16% of patients with stage C disease, and 57% of patients with a fixation of the tumor to the pelvic or abdominal wall emphasizes the value of the procedure in limiting unnecessary surgical exploration.