Do you culture all urine samples that arrive into your microbiology laboratory?
If so, why?
Is it for reimbursement purposes? I know this is necessary for some parts of the world.
..or is it because you are scared not to?
…or is it because you think it is in the patient’s best interests?
Now that automated urine microscopy analysers are commonplace, some microbiology laboratories selectively culture urine samples based on various microscopy parameters, of which the leucocyte count is a principal criterium.
In addition some urines are cultured based on clinical criteria and regardless of microscopy findings; e.g. pregnancy, immunocompromise, neonates, etc.
In my microbiology laboratory just over 50% of urine samples that arrive into the laboratory find their way onto culture plates. The rest do not get any culture whatsoever.
Do I feel nervous about not culturing half of all the urine samples?
Not in the slightest….
Many “positive” cultures with low numbers of white cells simply represent contamination and can thus lead to overdiagnosis, overinvestigation and overtreatment, not to mention the potential for resistance selection.
It is simply a question of sensitivity v specificity for true infection. By altering the microscopy parameters you can make the urine cultures more sensitive but less specific for true urinary tract infection, or vice versa.
There are no right or wrong thresholds for culture.
And on the ones we don’t culture, we always give the clinicians the option of getting back to us by telephone if they feel culture is strongly indicated despite the microscopy findings.
But they very rarely do…