What are the contents of a hydrocele testis?

Relatively large, uninfected hydroceles of the testis were investigated as to the composition of their fluid. The fluid was different from serum and urine, having the urea nitrogen, uric acid, Na and K levels comparable to but the total protein and inorganic phosphorus levels higher than in normal serum. The analysis of hydrocele contents may be useful in ruling out the possibility of another retention tumor, but not useful in determining whether a hydrocele is communicating with the peritoneal cavity.