01. Characteristics of Starch Granules 

Starch granules are round, oval, or polygonal in shape, with variable sizes. In saline smears, they often exhibit concentric refractive stripes, are colorless, and have a certain degree of refractivity (Picture 1). 

When iodine is added, they turn blue-black; if partially hydrolyzed to dextrin, they appear brown.

picture 1

How can we remember it? Looking at Picture 2, there are many growth rings – and starch granules resemble these rings closely.

picture 2

However, not all starch granules are concentric circles (Picture 3). Starch granules in picture 3 vary in size, appear round or irregularly shaped, and with slightly yellow-green shading.

picture 3

02. Identification Techniques 

 When encountering samples which could hardly identified, try to add the iodine solution to stain them for identification. This method is simple and highly specific. As shown in the figure 4, after adding iodine solution, the starch particles appear blue&black.

picture 4

The molecular gaps of starch will be reduced after dehydration, and iodine molecules will be squeezed out of the dried smear. In this case,the structure of the iodine-starch complex will disintegrate, and the purple&blue will fade to the original brown-red color of iodine(picture5).

picture 5
Starch particles are also found in vaginal secretion smears in gynecological clinics.

03.Clinical significance
Starch granules are rare in the feces of healthy people. Starch granules can be seen in diarrhea, chronic pancreatitis, pancreatic insufficiency, gastrointestinal dysfunction caused by various reasons, and infants&children diarrhea. However, starch granules are sometimes easily confused with fat droplets and food residues, it is necessary to distinguish them.

04.Identification analysis
 Fat in feces is divided into neutral fat, free fatty acids, and bound fatty acids. Common fat droplets refer to neutral fat, which are small spheres of varying sizes, round, and strong light-shielding properties. Usually, it can be seen in infant feces caused by poor digestion and absorption(picture 6).

picture 6

Stain the sample, if it is difficult to distinguish from starch granules in terms of morphology. Neutral fat droplets are vermilion or orange-yellow spheres of varying sizes after Sudan III staining(picture 7)

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picture 7