>40 x 106/L white cells suggests infection;
>10 x 106/L red blood cells indicates haematuria;
presence of dysmorphic red cells indicates glomerular origin;
>10 x 106/L squamous epithelial cells indicates skin/mucosal contamination of the sample.
Other microscopic findings:
red cell casts may be seen in glomerulonephritis;
white cell casts and mixed cell casts indicate renal disease; the presence of granular and/or hyaline casts, as an isolated finding, is of uncertain clinical significance. They may be seen in patients with dehydration.
Although crystals are seen frequently, they are not usually of any clinical significance.
Infection can be diagnosed in symptomatic patients if bacterial colony count >106/L (pure growth).
The findings on microscopy should also be considered in interpretation.
Increased leucocytes and a pure culture favour infection, while increased squamous epithelial cells and mixed culture suggest contamination.
In patients without symptoms, 'asymptomatic bacteriuria' is defined as a colony count of ³106/L.
In catheter or bladder aspirate specimens any growth indicates infection.
Testing for antibacterial activity is commonly performed and will influence interpretation.