Which test is used to visualize cysts and trophozoites in stool samples?

The microscopic examination is the appropriate test for visualizing cysts and trophozoites in stool samples. This method allows for the direct observation of parasitic forms under a light microscope, where trained personnel can identify the distinctive morphological features of cysts and trophozoites. This is crucial for diagnosing various parasitic infections, such as those caused by Giardia lamblia or Entamoeba histolytica.

Other methods such as stool culture are primarily used for bacterial isolation and are not suited for observing protozoan forms. Urinalysis pertains to analyzing urine samples and does not apply to stool samples. Serological testing involves the detection of antibodies or antigens and is not used for direct visualization of parasites. Thus, microscopic examination is the most effective method for observing and diagnosing parasitic infections in stool samples.