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This prospective trial demonstrated that the best possible definition for a positive leukocyte esterase test (Chemstrip 9) is + or ++. With use of this definition, the sensitivity in detecting significant leukocyturia is 83% and the specificity is 70%. The use of this test strip could reduce screening costs in registering obstetric patients.
We have compared the specific gravity (S.G.) determined by the N-Multistix method with that obtained from the Total Solids (TS) meter. Overall, 88.7% of the specific gravity results obtained with the reagent strip method were within 0.005 of those obtained with the TS meter. There was a good correlation between the methods and there was no bias for the group means obtained by either method. A good correlation was also found between the S.G. on the strip and osmolality (correlation coefficient of 0.955). The results obtained with the reagent strip for urinary specific gravity therefore appear acceptable for routine laboratory purposes.
Four indirect approaches, based on inquiry into a past history of haematuria, visual inspection for blood in the urine specimens, and the use of reagent strips to detect haematuria and proteinuria, were evaluated to identify persons with Schistosoma haematobium infection. These approaches were applied individually and in three different screening sequences on two populations in Ghana and Zambia in order to identify infected children and adults for subsequent treatment in both areas. Detection of haematuria using reagent strips was the single approach with the highest sensitivity and specificity. The observation of gross haematuria (bloody urine), followed by detection of blood by reagent strips, identified 87% of infected children in both areas. This screening sequence showed the highest combined sensitivity and specificity in the identification of infected children as well as adults for treatment in both areas. Differences in the results between the two countries are discussed. This study emphasizes the need for evaluation of indirect screening procedures for the diagnosis of S. haematobium infection in each endemic area so as to establish criteria for their interpretation, prior to large-scale field application.
In a nationwide survey of schistosomiasis conducted in Mali from 1984 to 1989, 56265 individuals from 323 villages had their urine examined parasitologically using a filtration technique. From a sample of 242 children in 3 villages, aged 7 to 14 years, urine samples were collected and tested for haematuria using reagent strips. Analysis of the age-specific prevalence rates of Schistosoma haematobium infection showed a strong positive correlation between the prevalence rate in the 7-14 year-old age group, and both the overall prevalence (r = 0.90; P < 0.001) and the prevalences at other ages. An index was derived from this relationship using the equation: overall prevalence = -1.14 + 0.74 (prevalence in 7-14 year-olds). The sensitivity and specificity of reagent strip testing for microhaematuria as compared to urine filtration were 73.3% and 83.2% respectively. We conclude that reagent strip testing of urine samples collected from a sample of individuals aged 7-14 years would be sufficient to estimate the overall prevalence of Schistosoma haematobium infection in a Malian community and suggest that this assessment procedure be used at the peripheral level of primary health care to decide on treatment regimes.
I describe the mechanism whereby ascorbic acid can hamper test systems involving a peroxide-generating system, peroxidase, and a benzidine-type indicator. In test media such as urines, abnormally high concentrations of ascorbic acid may give rise to false negatives in the determination of analytes such as glucose. Absorbance measurements in solution or reflectance measurements on commercially available paper reagent strips demonstrate either inhibition of visible activity by ascorbic acid or a lag time in the development of oxidized indicator color. The duration of the lag time is proportional to the ascorbic acid concentration, is inversely proportional to the enzyme concentration, and is also affected by concentrations of hydrogen peroxide and o-tolidine indicator. The same results were seen in both citrate buffer pH 5 and phosphate buffer pH 7. Because the complete system (o-tolidine indicator, hydrogen peroxide, and peroxidase) must be present if the ascorbate is to be oxidized rapidly, this indicates that ascorbic acid inhibits color development by re-reducing oxidized indicator as fast as it is formed; the o-tolidine then acts catalytically in oxidizing ascorbic acid. Added Cu2+ and Fe3+, both known to react with ascorbic acid, had measurable but small effects on the system. In contrast, Hg2+ abolished the ascorbic acid-elicited lag time, even when present in near-stoichiometric concentration. Hg2+ showed little inhibitory effect on the activity of either glucose oxidase or peroxidase. Presumably it rapidly oxidizes ascorbic acid to dehydroascorbate. The reaction of mercuric ion with ascorbate was measured by reflectance measurements of paper reagent strips in addition to absorbance measurements of solution assays; equivalent results were obtained. Incorporation of Hg2+ into reagent strips can thus render both strips and solution diagnostic tests insensitive to interfering substances such as ascorbic acid.
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Researchers evaluating the accuracy of rapid blood glucose monitoring (RBGM) techniques have often concluded that RBGM was sufficiently accurate for clinical use. However, investigators of patients' use of RBGM have more often reported unacceptable levels of accuracy and have shown individual differences between patients in the level of accuracy attained. Responsibility for excessive errors has commonly been attributed to patients' inadequacy in using RBGM. The logic of such attributions is questioned. Data are presented which indicates that errors attributed to patient inaccuracy may actually be due to (a) inaccuracy of reference blood glucose determinations used to evaluate patients' accuracy and (b) variable accuracy of RBGM techniques dependent on the range of blood glucose levels: some patients may appear to be less accurate than others simply because their blood glucose levels fall into a range less accurately measured by the RBGM technique. Furthermore, data presented reveal batch to batch variation in accuracy of the particular reagent strips used. Such variation between batches may help to account for inconsistencies between RBGM evaluation studies in which apparently identical reagent strips were used.
393 primary school children were screened for Schistosoma haematobium using four indirect techniques (a) history of haematuria, (b) visual appearance of urine and use of chemical reagent strips to detect presence of (c) blood and (d) protein in urine. Results showed that the use of chemical reagent strips for the detection of blood was the most specific and sensitive method, even in areas of lower prevalence and intensity. History of haematuria, protein in urine and visual appearance were respectively next in order in terms of specificity and sensitivity. The implications of these findings for further studies have been made.
A method of testing for bacteriuria with multiple reagent strips for blood, nitrite, and leucocyte esterase was evaluated. Of 669 urine specimens tested, 267 were negative on the reagent strips and so would ordinarily be discarded, creating a reduction in the workload of culturing urine specimens of 40%. Thirteen of these were false negative results, however, which represented 10% of all the samples with definite bacteriuria. Additional time was required for the screening test which reduced potential savings in manpower. Overall, we found costs to be slightly increased. In our laboratory this screening test was not economic and would produce an unacceptable rate of false negative results.
Measurements of blood alcohol concentration (BAC) were made on patients who presented to an accident and emergency department with acute alcohol intoxication. A correlation of r = 0.418 was noted to exist between BAC as measured by sampling saliva and blood. Blood alcohol concentrations as measured by salivary reagent strip (ALCO-SCREEN, Chem Elec.) were significantly lower (p less than 0.0001) than those determined by gas chromatography of serum. Although such reagent strips offer a rapid measurement of BAC, it is concluded that they are unreliable for the quantitative measurement of BAC in accident and emergency departments.
We evaluated the operation of the Yellow Springs Instrument Co. (YSI) glucose analyzer (model 23A) by clinical nurses for the measurement of blood glucose in the intensive care nursery. In vitro performance was determined with the use of aqueous standards; with a 2-point calibration of 0.0 and 200 mg/dl, a precision of better than 1.0% of each standard (25, 50, 100, 200 mg/dl) was achieved, and the linearity was excellent (Y = 0.99X - 0.49, r = 0.99). The YSI correlated well with a manual spectrophotometric glucose oxidase method (r = 0.99) and the Kodak Ektachem analyzer (r = 0.98) using human umbilical cord blood samples. Five trained clinical nurses performed all YSI and glucose reagent strip analyses, including all in vitro and patient samples. Four reagent strip methods were compared with the YSI from 104 neonatal heel-stick blood samples: Glucometer II with memory (r = 0.73), Glucostix (r = 0.74), Dextrostix (r = 0.70), and Chemstrip bG (r = 0.83). We conclude that clinical nurses can and do learn to use the YSI with excellent precision and that the YSI represents an improved method for measuring glucose concentrations in the newborn intensive care nursery.
Disorders of glucose metabolism are commonly seen by practicing emergency physicians. Reagent strips such as Visidex and Chemstrip are useful as a quick and accurate method of glucose estimation provided the procedure is followed correctly. These reagent strips are particularly useful for rapid screening in the unresponsive patient. The accuracy of glucose analysis obtained from the clinical laboratory is improved when methods to prevent glycolysis are used and when enzymatic methods of glucose analysis are used. The common and important indications for routine glucose analysis include evaluation of symptomatically ill patients with known diabetes or patients with altered mental status or coma of unknown etiology; patients on insulin or sulfonylureas; sick neonates; patients with a variety of drug intoxications; and patients suffering from significant systemic illness or injury likely to manifest with physiologic stress expressed as glucose intolerance.
The effect of changes in packed cell volume was studied in two commonly used reagent strip methods (Dextrostix and Reflotest) of measuring blood glucose and in a filter paper blood spot method. It was found that the results with both the reagent strip methods were greatly haematocrit-dependent. Attention is drawn to the possibility of false diagnoses of hypoglycaemia in haemoconcentrated patients and of normoglycaemia in anaemic patients.
The reliability of a chemical test for haematuria has been evaluated in patients referred for investigation of suspected renal or urological disease. Red blood cells in concentrations of 10/microliter or greater were found in 24% of urines giving a negative dipstick result, 82% of urines giving a trace positive result and nearly 100% of urines giving dipstick results greater than this. The accuracy of the reagent strip in predicting the presence or absence of significant haematuria was improved by testing several urines from each patient. On the basis of this study, if significant haematuria is present, reagent strip urine testing is an efficient method for its detection.
The accuracy of four techniques of home blood glucose monitoring in hemodialysis patients was compared. Arterial-venous blood samples were collected from 23 patients undergoing hemodialysis and analyzed for serum glucose concentrations using an automated laboratory method. Capillary-blood glucose concentrations were also determined in each patient by visual readings of the Chemstrip bG and Dextrostix reagent strips and by reflectometer readings of the StatTek Glucose and Dextrostix reagent strips. Readings of glucose concentration obtained by each of the four techniques were compared with laboratory-determined values, and the true and absolute deviations in these values for each technique were recorded. The effect of patient hematocrit on deviations in glucose concentration readings was evaluated by analysis of variance. The mean glucose concentration readings obtained using the visual and reflectometer (Dextrometer) readings of Dextrostix were substantially less accurate than the other two techniques when compared with serum glucose concentrations determined by the laboratory. The StatTek technique gave the smallest mean absolute deviation from laboratory-determined values. No correlation was found between the patient's hematocrit and either the true or absolute deviations in glucose concentrations. The Chemstrip bG and StatTek techniques are reasonably accurate methods for home monitoring of blood glucose concentrations in diabetic patients undergoing hemodialysis.
Two diabetic patients presented in coma to the accident and emergency department. Although they were hypoglycaemic, the initial blood glucose reagent strip readings were high. We postulate that glucose contamination of their fingers occurred and resulted in spuriously high readings. A small survey highlights the problems resulting from such contamination. Correct handling of blood glucose reagent strips is stressed and we advise venous blood samples in all diabetic emergencies presenting to the accident and emergency department.
Reference interval upper limits for glucose in urine from non-fasting pregnant women, estimated by a glucose dehydrogenase method are higher than for non-pregnant women (1.4 mmol/l) and increase with gestational age: week 10-20, 2.0 mmol/l (n = 158); week 21-30, 2.3 mmol/l (n = 124) and week 31-42, 2.7 mmol/l (n = 245). The reagent strip Tes-Tape correctly identified glucosuria above a clinical decision limit of 7 mmol/l and reacted in two-thirds of urine samples with from upper reference interval to 8 mmol/l of glucose. The reagent strip Uristix in no case gave a positive reaction.
In 148 patients after major surgical procedures urinary endotoxin levels were determined and compared with bacteriological results. The study was designed as a screening study. Urine samples were collected once by suprapubic or transurethral catheters. In a first series of 49 patients urine bacteriology was positive (mainly, Gram-negative rods were found) in 3 cases. However, endotoxin determination was positive in these 3 patients and in a further 10 patients receiving antibiotic therapy for other reasons. Therefore, the following 99 patients were studied also by urinalysis by reagent strips for leukocytes and nitrite. In the second series, 12 urine cultures positive for bacteria were observed. Eleven samples were also endotoxin positive. Five more patients were endotoxin positive and had pathological but unspecific reagent strip results. These patients were treated with antibiotics for other reasons. Patients with candida found in the urine culture (n = 5) were endotoxin negative. Thus, endotoxin determination in urine obtained by suprapubic or transurethral catheters proved to be a very sensitive method for diagnosis of bacterial contamination, even during antibiotic treatment.