The random urine sample shown in Fig. 1 was collected from a 43-year-old woman with systemic lupus erythematosus. A routine urinalysis (Aution Max AX-4280; Iris Diagnostics) revealed no remarkable findings and, specifically, was negative for protein. The corresponding urine protein concentration, however, was 448 mg/dL (reference interval, ≤12 mg/dL) as measured with a turbidimetric assay (Cobas c701; Roche Diagnostics). Protein concentrations in urine samples previously collected from this patient were undetectable.

Control (on left) and case study (on right) urine samples photographed with bright-field (A) and dark-field (B) lighting.


  1. What is responsible for the unique appearance of this urine sample?
  2. Why did the substance interfere with testing on one platform but not the other?
  3. What precautions should be taken to prevent this interference in urine testing?
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