Sunday, October 15, 2017

Answer to Case 464

Answer: Uric acid crystals

As many of you indicated in your comments, these are NOT Schistosoma haemotobium eggs, despite the superficial resemblance and location in urine, and instead are most consistent with crystals (specifically uric acid crystals). Uric acid crystals can be found in urine in a number of conditions and can be differentiated from S. haematobium eggs using the following features:
  1. Uric acid crystals vary in size and shape and are often much smaller than S. haematobium eggs. In contrast, S. haematobium eggs are regular in size and shape, and quite large (approximately 150 micrometers in length).
  2. Uric acid crystals commonly have points on both ends instead of the single 'pinched-off' spine of S. haematobium eggs. They can also have lateral points or take on other shapes.
  3. There are no internal parasite structures in crystals
  4. Finally, crystals often fracture and break, and may have irregular contours.
I'd encourage you to look at last week's Case 463 to see a good example of S. haematobium eggs. Also, here is a nice side-by-side comparison of a Schistosoma haematobium ovum (left) and a uric acid crystal (right), both stained with Papanicoloau:

I've featured uric acid crystals several times before on this blog, so I thought I would take this opportunity to highlight images from past cases. As you can see from the images below, there is a variety of appearances that uric acid crystals can take in urine:

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