Coagglutination (COA) test for the rapid diagnosis of cryptococcal meningitis

Cryptococcus coagglutination (COA) test reagent was prepared locally and showed no cross reactions with different species of bacteria or yeasts or with 75 control sera including 25 that gave positive results for RA factor. We used the COA test to detect cryptococcus antigen in the CSF and we could confirm the diagnosis of 11 out of 115 suspected cases of fungal meningitis; the titre varied from 4 to 128. A four-fold rise in titre confirmed the diagnostic value and a steady fall in titre in three patients on therapy indicated the prognostic value of the test. The earliest confirmation was in a renal transplant patient on the eighth day after onset of symptoms. The COA test was negative with the CSF of 118 patients with chronic meningitis. Cryptococcal colony forming units (cfu) in CSF varied from 100 to greater than 100,000/ml and correlated well with microscopy and with the COA antigen titre in CSF. Four out of the 11 patients who had cryptococcaemia, had 50,000-100,000 cfu/ml in the CSF. Cryptococcus antigen was detected by COA in the serum of all 11 patients, even in those with only 100 cfu/ml in CSF. In the three post-renal transplant patients, who were being monitored regularly, the diagnosis was made early and all three recovered on antifungal therapy with no relapse to date (1-2 years). All the others, including the two primary CNS infections, succumbed to the disease because they presented late for diagnosis and therapy. The cryptococcus COA test is a simple and specific test that can be used as a rapid test to confirm early diagnosis and permit prompt therapy, which should improve the prognosis in CNS and other forms of systemic cryptococcosis. Moreover, it is reproducible and cost-effective, particularly in countries where the latex and other expensive test reagents are not generally available.