From the Guidelines
A saline wet mount is a laboratory technique used to examine biological specimens under a microscope, involving a small sample of material, a drop of normal saline solution, and a coverslip, allowing for the observation of living microorganisms in their natural state. This technique is particularly useful for detecting motile parasites like Trichomonas vaginalis, intestinal protozoa, or examining white blood cells, as seen in the diagnosis of infections such as bacterial vaginosis, trichomoniasis, or intestinal parasitic infections 1. The procedure is quick, inexpensive, and requires minimal equipment, making it valuable for point-of-care diagnostics.
Key Points
- The saline solution maintains the osmotic balance of cells without distorting their appearance, unlike water which could cause cells to burst through osmosis.
- Saline wet mounts are commonly used in clinical settings to diagnose infections, with a sensitivity of wet mount between 40% and 80% 1.
- The technique involves placing a small sample of material on a glass slide, adding a drop of normal saline solution, and covering it with a coverslip.
- It is essential to submit the specimen in saline, with a transport time of 30 minutes to 2 hours for optimal results, as stated in the 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology 1.
Diagnostic Uses
- Bacterial vaginosis: wet mount and 10% KOH are used for diagnosis, with a quantitative Gram stain being the most specific procedure 1.
- Trichomoniasis: saline wet mount, rapid antigen test, DNA hybridization probe, and culture are used for diagnosis, with a sensitivity of wet mount being poor due to the requirement of live organisms to visualize movement 1.
- Yeast vaginitis: saline wet mount and 10% KOH are used for diagnosis, with a culture being considered in recurrent cases and when wet mount/KOH is negative 1.
From the Research
Definition of Saline Wet Mount
A saline wet mount is a laboratory technique used to diagnose various infections, including vaginal and intestinal parasitic infections. It involves placing a sample of fluid or tissue onto a glass slide with a coverslip, and then examining it under a microscope.
Components of a Saline Wet Mount
- A sample of fluid or tissue, such as vaginal discharge or stool
- A glass slide
- A coverslip
- Saline solution, which is used to prepare the sample for examination
Uses of Saline Wet Mount
- Diagnosis of vaginal infections, such as trichomoniasis and bacterial vaginosis 2, 3, 4
- Diagnosis of intestinal parasitic infections, such as those caused by protozoa and helminths 5, 6
- Examination of samples for the presence of motile organisms, such as Trichomonas vaginalis 2
Preparation and Examination of Saline Wet Mount
- The sample is placed onto the glass slide and a coverslip is applied
- The sample is then examined under a microscope, usually at a magnification of 400× 2
- The examiner looks for the presence of motile organisms, such as Trichomonas vaginalis, or other diagnostic features, such as bacterial vaginosis or yeast cells 3
Advantages and Limitations of Saline Wet Mount
- Advantages: rapid, inexpensive, and easy to perform 2, 3
- Limitations: may not always be accurate, especially if the sample is not fresh or if the examiner is not experienced 2, 4
- Comparison with other diagnostic methods, such as Giemsa staining and PCR, has shown that saline wet mount has lower sensitivity but high specificity 4