Use of Urinalysis in the Diagnosis of Kidney Disease
Published: April 2013
Hot Topic Q&A is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.
The following questions were submitted by viewers and answered by the presenter, John C. Lieske, MD, medical director of the Renal Testing Laboratory in the Department of Laboratory Medicine and Pathology at Mayo Clinic in Rochester, Minnesota.
Questions are presented as submitted (unedited).
- For microscopic analysis is there a limit for when the urine should be analyzed in relation to collection time?
In general, the urine should be analyzed as soon as possible to minimize the chance of degradation of urinary elements. The College of American Pathologists (CAP) recommends examination within 2 hours. Samples can potentially be stabilized by refrigeration at 4 degrees C if it is not possible to examine them within the 2-hour time frame.
- Who should perform microscopic urinalysis?
As with all clinical testing, proper training is essential. Most often technologists in a clinical lab perform urinalyses. At the Mayo Clinic in Rochester, MN, technologists performing the microscopic urinalysis are trained for about 6 weeks before they can independently release results. All technologists also have regular competency evaluations. Our educational specialist also trains clinical chemistry fellows, pathology residents and nephrology fellows in urinalysis microscopy during rotations in the Mayo renal laboratory, and all trainees are required to pass practical exams as a part of this training.
- Under what circumstances should microscopic urinalysis be performed?
A microscopic exam can be useful in individuals with a high clinical suspicion of kidney or urinary tract disease, for example persons with lower urinary tract symptoms (eg, frequency, urgency, dysuria) or with systemic conditions associated with risk of kidney disease (eg, systemic lupus, ANCA vasculitis, diabetes). In the Mayo Clinic Renal Laboratory, we use an IRIS to screen urine for microscopic findings. The following criteria are used to pull urines for manual microscopy (ie, not rely on the IRIS):
- Any sample with a protein of 50 mg/dL or greater.
- Any sample that’s red, amber, has abundant mucus, is milky looking, etc. Basically, any sample that looks abnormal macroscopically.
- Any time a possibly pathologic finding is observed in the IRIS. Examples include any casts (except hyaline casts), renal cells, dysmorphic RBC’s, and abnormal crystals.
- Is there any concern that a patient's urine may contain casts (hyaline, granular, waxy...) but have a negative protein result by dipstick?
Generally, you won’t find casts (with the exception of hyaline) in samples with truly negative protein dipstick. Hyaline casts are often seen in otherwise normal urine samples, since they tend to form in concentrated urine.