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Diagnostic accuracy of urinary reagent strip to determine cerebrospinal fluid chemistry and cellularity
Deepti Joshi1, Keerthi Kundana, Apurva Puranik
1Department of Pathology, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, India.
Background:
The gold standard for diagnosis of meningitis depends on cerebrospinal fluid (CSF) examination by microscopy, biochemistry, and culture, which require an experienced microscopist and laboratory support. We conducted this study to determine if urinary reagent strip is useful to make a semi-quantitative assessment of protein, glucose, and presence of leukocyte esterase in CSF.
Materials And Methods:
All consecutive CSF samples were evaluated in a blinded fashion. CSF was tested using Combur-10 urinary reagent strip as an index test, and CSF microscopy and biochemistry as reference standards. Combur-10 (Boehringer Mannheim) is a urinary reagent strip used to estimate ten parameters including protein, glucose, and leukocytes. We estimated diagnostic accuracy of each index test using corresponding cut-off levels (glucose 1 + vs. CSF glucose >50 mg/dL; protein 1 + and 2 + vs. CSF protein >30 mg/dL and >100 mg/dL; leukocyte esterase positivity vs. >10 granulocytes in CSF sample). We constructed receiver operating curves (ROC) to evaluate overall performance of index tests and estimated area under the curve (AUC).
Results:
CSF samples of 75 patients were included in the study. All the three indicator tests (CSF cells, protein, and glucose) were normal in 17 (22.6%) samples. Of the three tests, diagnostic accuracy of protein estimation (1 + or more on reagent strip) was best for detection of CSF proteins greater than 30 mg/dL [sensitivity 98.1% (95% CI 90.1-100%); specificity 57.1% (95% CI 34-78.2%)], with AUC of 0.97. Sensitivity and specificity for 2 + on reagent strip and CSF protein > 100 mg/dL were 92.6% (95% CI 75.1-99.1) and 87.5% (95% CI 74.8-95.3), respectively, with AUC of 0.96 (95% CI 0.92-1.01). Leukocyte esterase positivity by test strip had a sensitivity of 85.2 (95% CI 66.3-95.8%) and specificity of 89.6 (95% CI 77.3-96.5%) for detection of CSF granulocytes of more than 10/mm(3).
Conclusion:
Existing urinary reagent strips can be used to diagnose meningitis in low-resource settings.
