Indian journal of medical microbiology
October 21, 2026 · via Europe PMC
Determining an Optical Density (OD) cut-off value of IgM Enzyme-Linked Immunosorbent Assay (ELISA) for the diagnosis of Scrub typhus in the selected states of Northeast India.
Yumlembam B, Devi KR, Bidyarani K, Bidyalakshmi Y, Manojkumar RK, Majumdar T, Christina S
AI summary — for doctors, generated from the abstract only
An optical density cut-off of 0.562 gave excellent discrimination for scrub typhus IgM ELISA in Northeast India.
What was studied
Multicentre diagnostic study in Manipur and Tripura using 300 sera (100 healthy, 100 other febrile illness, 100 scrub typhus) tested with the InBios IgM ELISA and ROC analysis.
Key findings
- ROC analysis identified two possible cut-offs, 0.331 and 0.562.
- The higher cut-off performed better, with AUC 0.992.
- The cut-off was set using a clinical reference standard.
Clinical relevance
Region-specific cut-offs can reduce over-diagnosis from background seropositivity while avoiding missed cases in endemic areas.
Who should care
Limitations
The reference standard was clinical rather than independent, and the case-control sampling may overstate performance.
Consider local cut-offs when interpreting IgM ELISA, pending prospective validation.
This is an AI-generated summary of the published abstract, not a clinical recommendation. It may not reflect the full text or subsequent updates — verify against the original source before acting on it.
Abstract
PURPOSE
Scrub typhus, an acute febrile illness caused by the obligate intracellular bacterium Orientia tsutsugamushi, is increasingly reported across Northeast India. IgM enzyme-linked immunosorbent assay (ELISA) remains the most commonly used and cost-effective serological test for diagnosis. However, the performance of IgM ELISA is highly dependent on region-specific optical density (OD) cut-off values to minimise both over-diagnosis due to background seropositivity and missed cases in endemic areas. The present study was undertaken to establish an appropriate OD cut-off for Scrub typhus IgM ELISA in Northeast India using Receiver Operating Characteristic (ROC) curve analysis.
METHODS
This multicentric study, conducted across centers in Manipur and Tripura, collected 300 serum samples over two years (2021-2022). The samples comprised three equal groups of 100 each: healthy volunteers with no recent febrile illness, patients with unrelated febrile illnesses (clinically suspected enteric fever or dengue), and scrub typhus cases. All samples were tested using the Scrub Typhus Detect™ ELISA kit (InBios), and the resulting optical density values were analyzed by ROC curve to determine the optimal diagnostic cut-off.
RESULTS
ROC curve analysis identified two potential OD cut-off values (0.331 and 0.562). The higher cut-off demonstrated improved diagnostic performance, with an area under the ROC curve (AUC) of 0.992, indicating excellent discriminatory ability.
CONCLUSIONS
An OD cut-off value of 0.562 was identified for the InBios Scrub Typhus Detect™ IgM ELISA using a clinical reference standard in samples from Manipur and Tripura in Northeast India. Although the proposed cut-off demonstrated good diagnostic performance, the findings should be interpreted in light of the study limitations. Prospective multicentric validation using independent reference standards is required.
DOI
10.1016/j.ijmmb.2026.101322
PMID
42906691
Research metadata (titles, abstracts, authors, publication dates) is sourced from Europe PMC, which aggregates content from PubMed/MEDLINE, PubMed Central, and other providers under the U.S. National Library of Medicine (NLM/NCBI). NLM does not claim copyright on abstracts; the original journal publishers or authors may hold rights to the full articles. AI-generated summaries are derived only from the abstract, never the full text, and are always labeled as AI-generated.
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