The distinction between amorphous urates and amorphous phosphates is often made on the urinary pH basis but the following can help in differentiation:
- Phosphate is seen in alkaline pH
- Urate is seen in acidic pH
- The precipitate of phosphate is white
- The precipitate of amorphous urate is pink (known as brick dust).
- Amorphous phosphate is soluble in acetic acid
- Amorphous urates are insoluble in acetic acid (by acidification it converts to uric acid)