Urine culture

Urine culture is said to be significantly positive if there are more than 100,000 organisms per ml of urine and an abundance of white blood cells.

Ideally culture should be obtained before therapy is commenced; however in some situations, such as the infant with sepsis, empiric therapy is indicated.

There are two very important additional factors to consider:

• a specimen without bacterial growth but a significant number of white cells may indicate that the patient is on antibiotic therapy or there is another cause of the infection such as tuberculosis or a stone.
• the method of collection is very important. These rules apply to a clean catch - for example a mid stream urine. It is probably true to say that any growth from a suprapubic aspirate is significant, but that much growth in the absence of white cells from a bag urine should be regarded with caution.