Toxic Fungi of Western North America

by Thomas J. Duffy, MD

The Wieland-Meixner qualitative test for amatoxins

This is a simple and fairly accurate screening test for the presence of amatoxins if done correctly. Wieland-Meixner testing should never outweigh the clinical findings or another identification of an amatoxic species. The Weiland-Meixner test is often done incorrectly. Hospital laboratories notoriously obtain false negatives by using dilute hydrochloric acid or by performing the test on low lignin paper such as filter paper. The reaction is an acid-catalyzed one (using concentrated HCl acid) with the lignin present in low-grade paper, such as newspaper. A grayed greenish blue color appears with dried amatoxin. Dr. Theodor Wieland first studied the test on high-lignin paper, but Dr. Axel Meixner's article of 1979 (41) specifically noted that it would work on ordinary newspaper and the test is usually referred to simply as the “Meixner test”. The color change was actually noted first on wood chips by W. Dilger, while working on a thesis in Mainz, Germany. (42)

The test should be done on a surface away from high heat or sunlight. A control spot of concentrated HCl turns bluish when exposed to direct sunlight or to a temperature range of 85 to 95°F over a 20-30 minute period. Left in the sun longer, these bluish control spots slowly turn light pink. The Meixner test can be done with a hair drier held at a distance, but overheating is difficult to avoid.

Avoiding sunlight or high heat, a small circle is made on newspaper (or other high-lignin paper) with a pencil. A small amount of mushroom juice is then squeezed on to this and left to dry at room temperature. When dry, a single tinydrop of 8-16 concentrated hydrochloric acid is placed in the center of the circle. The grayed bluish-green that is typical of amatoxins slowly appears over 1-3 minutes, but the test sheet should be observed up to 20 minutes. The color on high lignin paper is usually 25B3-5 in the Methuen Handbook of Colour (43), but may vary from 25B3-5 to 25B5-26B4. There has been considerable concern about false positives. (44) However, if done with reasonable knowledge of colors seen with various genera, falsely positive tests are not of great concern.

The test results from California were combined with taxa presumably identical to those in North America, but collected in Germany and reported by Ruth Seeger. (45,46) The group total was 526 tests, but there were 56 species in common so that the total number of different species tested was 470. Many mushrooms gave an array of colors from yellow, orange and red to green, blue and even violet. Nine species of Agaricus gave a color change from yellowish to reddish, but only twenty nine species of this common genus were tested. There was a 15% false positive result for the total species tested, but this included some easily distinguished genera such as Russula, Lactarius and Coprinus. Excluding these and very bright blue or green colors, the number of false positives drops to 6.8%.

There were a few anomalous single Meixner tests. Galerina marginata was positive for amatoxins in two of the three specimens tested. One specimen of presumed Conocybe filaris was negative, although two other specimens gave a positive test. Lepiota helveola Bres. and Lepiota josserandii Bon & Boiffard were positive as expected.