An add-on test was ordered for a patient's serum sample. Upon its retrieval from a refrigerator, the sample appeared as a milky white suspension with no visible aggregates or gel-like structures. When the sample was warmed to 37 °C, the color and the appearance of the sample did not revert to those of normal serum. Crystals were observed when the sample was analyzed microscopically (Fig. 1).

Fig. 1.


  1. What caused the change in the serum?
  2. Which diseases cause this phenomenon?
  3. Can the add-on tests be performed on such a sample?

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