Accurate Kidney Stone Analysis
Expires: November 4, 2022
Paul Jannetto, Ph.D., is the Director for the Clinical and Forensic Toxicology Laboratory, Clinical Mass Spectrometry Laboratory, and Metals Laboratory for the Department of Laboratory Medicine and Pathology at Mayo Clinic. He holds an academic rank of Assistant Professor of Laboratory Medicine and Pathology.
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Transcript and References
Hi, I’m Matt Binnicker, the Director of Clinical Virology and Vice Chair of Practice in the Department of Laboratory Medicine and Pathology at Mayo Clinic. In this month’s Hot Topic, Dr. Paul Jannetto discusses the proper procedures for collecting and processing kidney stones in order to provide accurate, cost-effective analysis of the stones in a timely manner. I hope you enjoy this month’s Hot Topic, and I want to personally thank you for allowing Mayo Clinic the opportunity to be a partner in your patients’ health care.
Thank you for the introduction.
I have nothing to disclose.
At Mayo Clinic Laboratories, we have a long history of providing accurate and rapid kidney stone analysis. Our lab analyzes more than 90,000 kidney stones per year. Today, I am here to update you on the proper procedures for collecting and processing kidney stones in order to provide accurate, cost-effective, and timely analysis of patients’ kidney stones.
Kidney stones are quite common in the worldwide population. In the United States of America, it is estimated that 1 out of 10 people will develop a kidney stone during their lifetime. Epidemiology also indicates that the incidence of kidney stones is increasing.
If you have ever had a kidney stone, you realize the trauma and pain they can cause. I cannot stress enough that the proper handling and labeling of kidney stone samples is critical to accurate stone composition analysis.
Given the irretrievable nature of the stone, we have one chance of obtaining an accurate compositional analysis. Hence, we must take all the utmost precaution to ensure that the information is not lost. Each step of the analytic process is key to ensure the accuracy of the data.
Thus, kidney stones should be given the same procedure policies as surgical specimens to ensure that proper identification and analysis results are maintained. Information about the stone can easily be lost if the specimens are not labeled or are labeled incorrectly.
Clinical Importance of Kidney Stone Analysis
After the passage or removal of the kidney stone, accurate analysis of the urinary stone composition is the most crucial laboratory diagnostic procedure for the treatment and recurrence prevention in the stone-forming patient.
The causes of kidney stones are complex, resulting from a combination of genetic, dietary, and lifestyle factors. From the lab’s point of view, we can aid in determining the cause by careful examination of the urine and stone constituents. Information about the stone composition is used in both medical and surgical interventions.
Kidney Stone Analysis (KIDST)
Proper analysis of stone collections begins with proper collection, handling, and labeling of kidney stones.
Although it is difficult for a patient to know exactly when a stone will pass, the odds of collecting the stone are increased when patients properly filter their urine. Our lab has seen many unique and sometimes odd ways that patients will attempt to collect their stone. To help our clients simplify the process, Mayo Clinic Laboratories offers a collection kit with a filter, vial, and detailed instructions for patients and lab personnel on how to collect kidney stones.
Clients can order kits by logging into mayocliniclabs.com, selecting the Customer Service page, and from there, selecting the Supplies page. Alternatively, orders may be placed by calling customer service at 1-800-533-1710.
After the stone is collected, clean any blood or foreign material from the stone with deionized water.
Afterwards, dry the stone at room temperature (approximately 24 hours) on a tissue/towel and send the entire stone in a screw-capped plastic container that is labeled properly.
Make sure to indicate the source of the stone also (e.g., urine, kidney, ureter, or bladder).
The Kidney Stone Must Be Clean and Dry for Accurate Analysis
Stones need to be clean and dry before analysis.
The analytical method by which we determine the composition absolutely requires the stone to be clean and dry. Excess water in the stone will cause a major interference in the composition analysis and can totally obscure our results. Excess blood and tissue can cause a false determination that the stone is proteinaceous and mask the true composition of the stone. Therefore, we require that all kidney stones be clean and dry before analysis.
Currently, about 50% of the kidney stones arrive like the stones in the left picture. This forces our lab to spend extra time drying the samples before analysis, which will result in an additional $10 handling charge and delayed turnaround time.
Kidney Stone Analysis (KIDST)
Current guidelines state that kidney stone analysis should be performed using modern methods like infrared spectroscopy or X-ray diffraction. At Mayo Clinic, we use Fourier transform infrared spectroscopy (FTIR), which is considered to be the reference method.
In the lab, we begin with a clean and dry kidney stone.
The kidney stone is then crushed into a powder and placed on top of a crystal.
An infrared beam is passed through the crystal, interacting with the powdered kidney stone sample. During this interaction, the molecular bonds within the stone absorb some of the radiation, giving a unique spectrum as seen on the next slide.
Every sample has a unique infrared spectrum, which can serve as a compound’s fingerprint.
Example of Calcium Oxalate Monohydrate
This is an example of a very common stone composition: calcium oxalate monohydrate. The infrared spectral analysis of the stone produces a unique pattern of absorption (fingerprint), which makes the composition identification relatively simple.
Importance of a “Dry Stone”
This is an example of a wet stone. Water has very strong UV absorbance, and the presence of water is masking the unique fingerprint of the stone composition.
Common Types of Kidney Stones
When we look at the types of kidney stones, we see the vast majority (approximately 74%) are calcium oxalate, followed by hydroxyapatite (a form of calcium phosphate), uric acid, struvite (magnesium ammonium phosphate), and brushite (another form of calcium phosphate).
What Should Your Lab Do if You Received a Wet or Dirty Stone from the Patient?
Although the answer to this question may seem rather obvious, there are some special considerations to keep in mind when drying stones. Stones containing obvious blood should be rinsed with deionized water prior to drying. Drying wet stones must not be done at too high of a temperature. For example, struvite stones, which are typically yellow to brown stones that are composed of magnesium ammonium phosphate, if heated too aggressively can eliminate ammonia, thereby changing the composition. We recommend placing the stone on filter paper at room temperature until dry. Once dry, the stone can be placed in the 10 mL tube provided with our collection kit.
Clean and Dry
In summary, proper specimen handling is critical for accurate determination of kidney stone composition. This includes how you process your patients’ specimens prior to submitting them to Mayo Clinic Laboratories. By following the Kidney Stone Analysis Patient Collection Instructions and the Kidney Stone Analysis Packaging Instructions included in the Mayo Clinic Laboratories kit, you can improve the quality of the test results you receive.
Thank you for your attention.