Leukocyte Lysis in Dilute Urine

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The influence of urine concentration on the cells we observe during urine microscopy is well known.

Concentrated urine specimens with a high urine specific gravity (SG) preserve nucleated cellular morphology the best, however, some cellular structures (e.g.: erythrocytes) can become shrunken and appear crenated.

On the other hand, dilute specimens with a low SG will result in poor preservation of cellular structures. This is because water enters the cells making it swollen with eventual lysis of the cell. Usually both erythrocytes and leukocytes can be destroyed in dilute urine with low SG.

WBC Lysis Video

The video shows how exactly the leukocytes are destroyed (the ones that became dark in the video) in a urine with a low SG (less than 1.010).

Figure 1: Same microscopic field observed immediately after slide preparation (left) and observed after 2-3 minutes (right) in a sample presenting a lot of leukocytes and SG<1.010. Phase contrast microscopy. Original magnification 400x. Basically all leukocytes on the slide were destroyed within 2-3 minutes.

The photos (Figure 1) shows the same microscopic field immediately after sample preparation, with the leukocytes perfectly viewed with their usual morphology and how these cells became totally different within 2-3 minutes.

The use of phase contrast increases the ability to view this. Using Only bright field, the dead leukocytes are basically ghosts, almost impossible to be seen.

Sample conditions like SG (and pH) impacts in the quality of the information that can be observed during microscopic examination of the urine sediment. Leukocytes, erythrocytes and urinary casts are the most affected, being specially destroyed in dilute urines with low SG and alkaline pH.

Keep in mind to always check urine SG and pH When performing urine sediment analysis.

Post by José Antonio Tesser Poloni

Reviewed by Matthew A. Sparks


  1. Specific gravity and pH are unfortunately very often ignored by clinicians.

  2. Great information to keep in mind. Best regards from Chile.

  3. Thanks for this informations about the effects of specific gravity on the morphology of cells

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