| Abstract|| |
Context: The provision of initial treatment to a patient with suspected meningitis depends greatly on early recognition and rapid diagnostic evaluation of cerebrospinal fluid (CSF) leukocytes, proteins, and glucose. The diagnosis is time critical and timely intervention has an implication on the prognosis and outcome. Reasonably, sound laboratorial setups are not available in our country in the primary health-care level and, even in the settings where they are available, long waiting periods precede the availability of results. Aims: We conducted this study to emphasize the role of urine reagent strip test as a rapid diagnostic tool in CSF analysis. Settings and Design: This is a prospective single-blinded study on 100 consecutive CSF samples received with in 1h of tap. Subjects and Methods: All the 100 samples were subjected to definitive test being CSF microscopy and biochemical analysis of proteins and sugar and index test being a semi quantitative analysis of CSF leukocytes, proteins, and sugar by urinary reagent strips. Statistical Analysis Used: The diagnostic accuracy of the reagent strip for different cutoff levels was estimated and tabulated in the form of sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio. Results: 77% of cases were in the pediatric age group and 23% cases were adults. The sensitivity and specificity for leukocytes by the strip method for ≥15 cells/cumm were 89.28% and 98.61%, respectively, which increased to 100% with an increase in the counts. The reagent strip test had a sensitivity of 85.71% and a specificity of 95.65% for the protein levels >30 mg/dl which increased to 100% with an increase in protein levels. The reagent strip test for glucose was highly specific (100%) but less sensitive. Conclusions: The results indicate that urine reagent strip is instrumental in bedside CSF analysis and has a future stand in the diagnosis of meningitis.
Keywords: Cerebrospinal fluid, meningitis, urine reagent strips
|How to cite this article:|
Mazumder S, Ramya B S, Biligi DS. Utility of urine reagent strips in cerebrospinal fluid analysis: An aid to bedside diagnosis of meningitis. Indian J Pathol Microbiol 2018;61:356-9
|How to cite this URL:|
Mazumder S, Ramya B S, Biligi DS. Utility of urine reagent strips in cerebrospinal fluid analysis: An aid to bedside diagnosis of meningitis. Indian J Pathol Microbiol [serial online] 2018 [cited 2021 Jun 13];61:356-9. Available from: https://www.ijpmonline.org/text.asp?2018/61/3/356/236631
| Introduction|| |
Meningitis, the infection of the brain and spinal cord, is a medical emergency and its timely identification and treatment is essential for preventing permanent neurological deficits and death.,
Neonatal meningitis continues to contribute substantially to neurological deficits worldwide. At the same time, conditions such as febrile seizures, especially in the pediatric population, make allusions to meningitis, resulting in a diagnostic dilemma for the clinicians.
Cerebrospinal fluid (CSF) cell counts and protein and sugar estimation, along with microbiological studies, are required to make the diagnosis of meningitis. The presence of an experienced pathologist and the availability of a reasonably sound laboratorial setup are indispensable for the estimation of cell count and protein and sugar estimation. These facilities may not be present in the rural setup and, even in the settings where they are available, the turnaround time period for laboratory-based CSF analysis is long. Although many authors have studied the role of urinary reagent strips (a well-known semi-quantitative method used widely for urine analysis) in the diagnosis of meningitis, this method has not yet gained the popularity it deserves.,,,,, The reagent strip test could prove to be a rapid bedside diagnostic test for CSF pleocytosis and glucose and protein estimation until further substantiation by laboratory results occurs.
The present study is undertaken to evaluate and establish the role of urinary reagent strip method in the analysis of CSF to assist the clinician in the bedside diagnosis or exclusion of meningitis.
| Subjects and Methods|| |
We conducted a prospective single-blinded study, after ethical committee clearance on 100 consecutive CSF samples received in our laboratory within an hour of tap. Hemorrhagic taps were excluded from the study. Age and sex were recorded and all the samples were subjected to both index and definitive tests.
Index test was done by one of the investigators using urinary reagent strips which can detect ten parameters including protein, glucose, and leukocyte esterase. With the help of a pipette, 2–3 drops of undiluted CSF were added to patches of proteins, glucose, and leukocyte esterase, and the color change was recorded and interpreted using the manufacturer-provided color grading.
The reagent strip is designed to detect the range of leukocytes from 15to 500 cells/mm 3. It detects the leukocytes by estimation of leukocyte esterase. Depending on the color change, leukocytes are graded as negative for the cell count of <15 cells/cumm, 1+ for 15–70 cells/cumm, 2+ for 70–125 cells/cumm, and 3+ for 125–500 cells/cumm.
For proteins, the interpretation of the colors on the reagent strips was as follows:<30 as negative, 30–100 was graded as 1+, 100–300 was graded as 2+, and 300–2000 was graded as 3+. We determined if the protein was <30(normal), >30mg/dl, >100mg/dl, or >300mg/dl based on the color change.
For sugars, the readings are as follows: no color change for sugars <50mg/dl, traces for 50–100mg/dl, 1+ for 100–250mg/dl, 2+ for count between 250 and 500, and 3+ for counts between 500 and 1000. Using the strip, we determined if the values were above or below 50mg/dl with the interpretation being no change in color as <50mg/dl and any change in color as >50mg/dl.
Definitive tests were done by an independent blind observer. The tests done were cell count by Neubauer's chamber followed by differential counting on two centrifuged smears: one stained with hematoxylin and eosin stain and the other with Leishman stain along with protein and sugar estimation by an automated analyzer.
The diagnostic accuracy of the reagent strip versus the standard tests was estimated using standard statistical tests and tabulated in the form of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV), and positive and negative likelihood ratios.A receiver operating curve (ROC) curve showing the relationship between sensitivity and specificity as a function of the strip color cutoff was plotted and the area under the curve (AUC) along with its standard error was calculated using the SPSS statistical software package.
| Results|| |
The study was conducted on 100 consecutive CSF samples. There was a fairly equal distribution of males (52%) and females (48%).77% of cases were in the pediatric age group and 23% of cases were adults. 41% of the cases were neonates [Table 1].
Three cardinal parameters, leukocytes, proteins, and glucose tests of the reagent strip, were compared with those of the reference standard. The sensitivity and specificity for leukocytes by the strip method for ≥15 cells/cumm were 89.28% and 98.61%, respectively. The accuracy increased to 100% with higher cutoffs of cell count[Table 2].
The reagent strip test had a sensitivity of 85.71% and a specificity of 95.65% for the protein levels >30 mg/dl. For a cutoff level of the proteins of >300 mg/dl, both the sensitivity and specificity increased to 100%[Table 2].
The reagent strip test for glucose at cutoff levels of <40 mg/dl and <50 mg/dl was highly specific with a specificity of 100% but it was less sensitive (71.42% and 48.2%, respectively) [Table 2].
For each stripcolor's cutoff value, the positive and negative likelihood ratioswerealso derived [Table 3]. The ROC curves with AUC for leukocytes >15, protein >30, and sugar <50 are shown in [Figure 1], [Figure 2], [Figure 3], respectively.
|Figure 1: Receiver operating curve for cells >15. Area under the curve = 98.7%, standard error = 1%|
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|Figure 2: Receiver operating curve for proteins >30 area under the curve = 92.9%, standard error = 3.1%|
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|Figure 3: Receiver operating curve for sugar <50 area under the curve = 92.8 with standard error = 2.8%|
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| Discussion|| |
Meningitis is defined as inflammation of the leptomeninges. It is associated with high mortality and psychoneurological sequelae due to damage to the neurological structures. Delay in the treatment of meningitis in neonates and infants can lead to significant problems in them in the future with respect to language, motor function, cognition, vision, hearing, and even behavioral problems., It is imperative to initiate treatment within 3 h to reduce the morbidity and mortality. The diagnosis greatly depends on the estimate of CSF pleocytosis and glucose and protein levels of the CSF.
Chikkannaiahet al. have used urinary strips for the semi-quantitative analysis of CSF cellularity and chemistry and have observed high sensitivity (96.6%) and specificity (94.5%) in leukocyte estimation. The strip showed a sensitivity of 96% and a specificity of 87.1% for proteins at a cutoff ≥100 mg/dl, while the strip was less specific at a cutoff of ≥30 mg/dl. With respect to glucose, the strip was highly specific (100%) and less sensitive at both the cutoff levels (<40mg/dl and <50mg/dl). Joshi et al. using the reagent strip conducted a similar study and observed a sensitivity of 85.2% and a specificity of 89.6% for leukocytes >10 cells/cumm. For proteins, at a cutoff of ≥30 mg/dl, the sensitivity was high (98.1%) but the specificity was low (57.1%);however, at a cutoff of ≥100 mg/dl, both the sensitivity and specificity were acceptable. The strip-based analysis for glucose at a cutoff of ≤40 mg/dl had high specificity (96.5%) than sensitivity (61.1%); and, even at a cutoff level of ≤50 mg/dl, the test had high specificity (98%) than sensitivity (46.2%). Our study was comparable, in terms of all the three parameters, with the above studies. We also observed that with respect to proteins, we had 11 false-negative cases(<30mg/dl as per strip method),10 out of which actually had laboratory values of proteins <45mg/dl, which is the standard biochemical cutoff for normal CSF proteins. Thus, if a strip is designed for this cutoff level, the accuracy can improve remarkably.
Romanelli et al. compared the results of reagent strips and those of the standard cytological and biochemical assays and obtained values for sensitivity, specificity, PPV, and NPV(90.7%, 98.1%, 95.1%, and 96.4%, respectively) in the diagnosis of bacterial meningitis. Kumar et al. observed a positive correlation between the strip and the laboratory values for the diagnosis of meningitis with κ = 0.94, 0.819, and 0.819 for cells, protein, and glucose, respectively, with P < 0.0001, which was statistically significant. Maclennan et al. in their study observed that additional information maybe obtained with the nitrate patch test and they concluded that the nitrate patch, which is also a component of 10-parameter urinary reagent strip, will become positive in bacterial meningitis in situ ations where the granulocytes are increased but have not released the esterase enzyme.
In our study, we additionally observed that the accuracy of the tests increased with increase in the values of cell counts and proteins and decrease in sugar reaching 100% accuracy for very high test results. This is significant as bacterial meningitis shows very high CSF cell counts and protein levels with very low sugars as compared to aseptic meningitis and thus the strip test proves to be of great relevance in identifying these cases.
We also observed that the specificity of all the three tests was very high nearing 100% and is thus instrumental in ruling out meningitis in doubtful cases. In the era of antibiotic resistance, this test can be very beneficial in terms of avoiding unnecessary overtreatment in children with febrile seizures or neonates with hypoxic seizures where again the differential diagnosis of meningitis is considered. This is significant in our setup as we receive the majority of CSF analysis in our laboratory from patients in the pediatric age group.
This procedure is easy to perform, does not require any technical expertise, and is a boon to the primary health-care centers and rural setups where no laboratory facilities exist. The operators can be trained very easily and competency of the operators can be monitored prior to routine use.
The only shortcoming is the slight variation in the cutoff normal values of protein and sugar in CSF as compared to urine which has added to the few false negatives and false positives in our study. This can be overcome by designing strips specific for CSF analysis, at the manufacturer's level.
| Conclusion|| |
Therefore, in light of our study and with reference to the results obtained in similar studies by various observers, we can conclude that urinary reagent strips can be used to facilitate therapeutic decisions in cases of suspected meningitis, especially in resource-constrained settings. Further studies with larger numbers and comparison with different manufacturer strips can be undertaken. If standardized, this method can revamp the entire diagnostic protocol of meningitis.
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Conflicts of interest
There are no conflicts of interest.
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Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]