India ink test

India ink test

A diagnostic test used to detect the cryptococcal organism C. neoformans. A dye, called India ink, is added to a sample of CSF fluid, and if the fungi is present, they will become visible as the dye binds to the capsule surrounding the fungus.
Mentioned in: Cryptococcosis
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* The rapid India ink test was interpreted as positive--presence of large irregular sized, budding yeast colonies, surrounded by a larger unstained capsule, with a clear halo against a micro-particulate background; see Figure 2.
The India ink test and the culture had positive comparable results; the authors indicated because the rapid India ink was 60% sensitivity, it should always precede the culture test.
Limitations of the three rapid tests recognize (a) processing within 90 minutes of collection, because of degradation of cellular elements in the CSF, (b) the India ink test may report false negative results, because of infrequent testing (Coovadia, et al., 2015), (c) the cell count with too many RBC may obscure visibility of the yeast, producing a false negative test, and (d) if the infection is early, no cells may be seen in the gram stain or the unspun cell count, producing false negative result.
Firstly, laboratory-based surveillance programmes are likely to identify a substantial proportion of patients with CC because the predominant manifestation of meningoencephalitis is severe headache, which makes health-seeking behaviour by patients inevitable; the diagnosis of CC cannot be made clinically and lumbar puncture with laboratory testing is required; incident cases of cryptococcal meningitis are not treated empirically, unlike bacterial meningitis; and the inexpensive India ink test is readily available in all laboratories in South Africa and has excellent sensitivity in national surveillance compared with culture to identify cases of cryptococcal meningitis.
* Cryptococcal antigen (CrAg) detection should be requested only if the India ink test is negative.
The India ink test has good sensitivity (80-98%) (7,21) and specificity in ARV-naive and fluconazole-naive populations, but may have lower sensitivity in patients who are receiving fluconazole for other reasons (commonly mucocutaneous candidiasis), who present early in the course of disease and who have low fungal burden in the CSF.
Because more reliable results are obtained with the cryptococcal antigen test, it should replace the India ink examination or be performed in addition to the India ink test.

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