Methanol as an alternative fixative for cytological smears

Abstract

Ninety-five percent (95%) ethanol is the standard cytological fixative used in many laboratories. Commercially available ethanol is expensive and not freely available in some institutions. Methanol, a tissue dehydrant, is also known to be a cytological fixative. However its efficacy has not been assessed or documented in the literature. One hundred and eight consecutive fine needle aspiration biopsies (FNAB) of thyroid performed at the Department of Pathology, Faculty of Medicine, Colombo were included in a study to assess the efficacy of methanol as a cytological fixative. Aspirated material was smeared on at least 2 slides, one fixed in ethanol and the other in methanol, and stained with haematoxylin and eosin (H&E). The 2 smears were separately assessed for preservation of colloid and cells (nuclei and cytoplasm), as determined by the staining quality with the H&E stain. A score was given for each smear and the final scores for ethanol and methanol were statistically compared. The evaporation rates for ethanol and methanol were calculated. The total score for preservation of colloid was 294/300 (98%) for methanol and 291/300 (97%) for ethanol (p = 0.4). The total score for preservation of cells (nuclear and cytoplasmic) was 276/279 (98.9%) for methanol and 274/279 (98.2%) for ethanol (p = 0.7). The evaporation rates per 100 ml when the bottles used for fixation were kept closed and open per 24 hours were 1 and 37 for methanol and 0 and 17 for ethanol. Literature search did not show inhalational side effects of methanol in humans under standard laboratory conditions. We conclude that methanol is as effective as ethanol for fixation of smears and cheaper.