TABLE 3.

Common fixatives used to preserve ova and parasites in stool

Preservative	Downstream preparations	Downstream assaysa	Potential for single-vial use	Notes
Formalin, 5% or 10%	Only concentrated wet mount	EIA, FA, IC	Poor	Poor NAT potential, poor trophozoite preservation
SAF	Permanent stained smear and concentrated wet mount	EIA, FA, IC	Fair	Poor NAT potential, suboptimal trophozoite morphology
Mercury-based fixative with PVA	Permanent stained smear and concentrated wet mount (rare)	NAT	Poor	Immunoassays not possible, fixative is highly toxic
Modified Schaudinn's (copper, zinc, or other fixative with PVA)	Permanent stained smear and concentrated wet mount (rare)	NAT	Fair	Immunoassays not possible, concentrated wet mounts are uncommonly performed, suboptimal trophozoite morphology
Single -vial proprietary fixative formulations	Permanent stained smear and concentrated wet mount	Some immunoassays are possible; most NATs	Good	Suboptimal trophozoite morphology, not all immunoassays are possible

^aAbbreviations: EIA, enzyme immunoassay; FA, fluorescent antibody; IC, immunochromographic test; NAT, nucleic acid amplification test.