[Abnormalities in cervical smears stored in plastic bags: potential cause of false negatives].

Introduction: Cervical smear is the most economic and efficient diagnostic tool for the screening of cervical cancer. However, since plastic bags have been used in Guanajuato to transport and store smears, we have observed cytological abnormalities which difficult the diagnosis and lead to false negatives.

Objective: To describe those abnormalities.

Methods: Out of 340 women registered in a primary care center in Mexico, 68 were selected through systematic random sampling during 2007. A cervical smear was obtained and placed on two slides. The first sample was allowed to dry but the second one was placed into the plastic bag immediately after fixation. After 15 days all the smears were stained with the Papanicolaou technique. A certified pathologist, blinded about the variable of study, interpreted the samples according to the Bethesda system, and evaluated the presence of necrosis, edema, holes, and opportunistic microorganisms.

Results: Of the 68 smears exposed to a humid storage, 36 (53%) were inadequate for diagnosis (Fisher's exact probability < 0.001). From them, 36 (53%) had holes or lagoons, 34 (50%) had edema, 31 (46%) had necrosis, and 15 (22%) had fungus. On the other hand, the 68 dried cervical smears were all adequate for diagnosis and none had the changes or cytological abnormalities.

Conclusion: The humid transport and storage of cervical smears produced abnormalities in the normal morphology that could lead to false negative results. The guideline for the handling of cervical smears must stress the importance of allowing the smears to dry completely after fixation and before storing them in plastic bags.