ABSTRACT
Gross blood in urine is defined as blood visible to the naked eye. Gross blood may be present in large enough amounts to give the specimen a definite red appearance, or it may be only enough to give a "smoky" appearance to the specimen. Occult blood is defined as blood detectable only by some chemical or physical procedure. Chemical reactions detect both intact red blood cells and free hemoglobin as well as myoglobin. In contrast, microscopic examination of urine sediment will detect only intact erythrocytes. Blood in urine can be described as hemoglobinuria or hematuria. Hemoglobinuria is the presence of free hemoglobin in urine. Chromogens which have been used most often as oxygen acceptors in the reaction include guaiac, benzidine, and orthotolidine. There are many advantages to testing for occult blood in urine in that such testing leads to early detection of the variety of diseases and dysfunctions.
