Parasitology Evaluation of potassium hydroxide for wet mount preparation of stool for detection of intestinal parasites Subhash Chandra Parija*, Mandya Rudramurthy Shivaprakash Department of Microbiology, Jawaharlal Institute of Postgraduate Medical Education & Research, Pondicherry 605 006, India Received 15 March 2001; accepted 30 August 2001 Abstract Potassium hydroxide (KOH) is widely used in the wet mount preparation of various clinical specimens for demonstration of fungi and fungal elements. In the present study we have evaluated the use of KOH in the wet mount preparation of fresh stool specimens for the demonstration of intestinal parasites. The KOH wet mount of stool was compared with saline, iodine and lacto-phenol cotton blue (LPCB) wet mount preparations of stool. A total of 855 fresh stool specimens were examined in the study of which 419 specimens were found to be positive for either trophozoites, cysts, ova or larvae of different parasites by all these methods. A total of 309 stool specimens were positive by KOH preparation of stool, while 289, 245 and 208 stool specimens were positive by LPCB, iodine and saline preparations respectively. The KOH was found to be effective in lysing the faecal debris, faecal mass and other artifacts without affecting many of the parasitic ova, cysts and larvae in the stool smears. The parasitic ova, cysts and larvae were impacted by the use of 10% KOH and could be easily visualized, detected and identified against a clear background in the stool smear I hr after preparation of KOH wet mount. From these findings we recommend the routine use of KOH wet mount of stool for demonstration of intestinal parasites in a parasitology laboratory. © 2001 Elsevier Science Inc. All rights reserved. 1. Introduction Intestinal parasitic infections are prevalent worldwide. The specific diagnosis of the condition is made by demon- stration of protozoal cysts or trophozoites; helminthic ova, or less frequently adult worms or larvae in the stool smears by microscopy (Parija, 1993). Wet mount preparation of stool is extensively used in stool microscopy in a parasitol- ogy laboratory for the diagnosis of intestinal parasitic in- fections (Parija & Srinivasa, 1999). Saline, Quensel stain, Nairs’ buffered methylene blue, Lugols’ iodine solution, D’Antonie’s iodine stain and recently introduced lacto-phe- nol cotton blue (LPCB) are the agents frequently used in the wet mount preparation of stool (Parija & Prabhaker, 1995). Preparation of a stool smear on a microscope glass slide that is neither too thin nor too thick is an important consideration in the preparation of a wet mount of stool for examination by microscopy. Because, if a very thin stool smear is pre- pared by taking a little volume of stool, then the possibility of the presence and detection of parasitic ova or cysts become very less thereby giving rise to false negative re- sults. In contrary, if a very thick stool smear is made by taking relatively a large volume of stool, the smear becomes too thick to be examined. This is due to a dense background formed by faecal mass and faecal debris, bacterial flora and other faecal artifacts thereby masking the parasitic ova and cysts that are present, thus making their detection very difficult (Parija, 1996). An agent which can lyse all the faecal debris, faecal mass and bacteria flora in a thick faecal smear, but without af- fecting the parasitic ova, cysts or trophozoites would be an ideal agent in the preparation of a wet mount preparation of stool. Such a lytic agent would make the back ground in a stool smear clear, thereby facilitating for better detection and identification of parasitic ova and cysts in a stool smear. Potassium hydroxide (KOH) is widely used in the wet mount preparation of various clinical specimens for dem- onstration of fungi and fungal element. KOH preparation of a specimen is prepared by mixing clinical materials such as skin scales, hair stuffs, nail scrapings or other specimens with a few drops of 10% KOH on a microscope glass slide. The KOH digests protienaceous debris and bleaches pig- * Corresponding author. Tel.: +91-413-253016 E-mail address: parijasc@vsnl.com (S. C. Parija). www.elsevier.com/locate/diagmicrobio Diagnostic Microbiology and Infectious Disease 41 (2001) 127–130 0732-8893/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0732-8893(01)00300-5