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What is Kidney Stone Analysis? 

A kidney stone, also known as a nephrolith or a renal calculus, is a hard, rock-like substance which can form in one or both of your kidneys if you have high levels of certain minerals in your urine. Depending on the chemical makeup, kidney stones are of four types:

  • Calcium stones: These are the most common type of kidney stones and include calcium oxalate and calcium phosphate stones. They form when extra calcium that is not used by your bones and muscles remains in your kidneys and instead of being flushed out. 
  • Cystine stones: These stones result from cystinuria, a hereditary condition which causes the amino acid cystine to leak into the urine. 
  • Uric acid stones: These stones form when your urine has a high level of uric acid. People who consume a lot of fish, shellfish and meat are at a high risk of developing uric acid stones.
  • Struvite stones: These stones form after a UTI. They usually form suddenly and grow quickly.

Regardless of the type, kidney stones tend to recur, so if you got a stone once, it is important to know what the stone was made of so any future occurrence may be prevented.  

A kidney stone analysis is done to evaluate the chemicals present in a stone after it has been passed in urine (for smaller stones) or has been removed by surgery (for larger stones).

Kidney stones are more often seen in men than in women. The following factors increase the risk of developing kidney stones:

  • History of kidney stones
  • Long-lasting inflammatory bowel disease
  • Blockage in the urinary tract
  • Inadequate water intake
  • Obesity
  • Repeated urinary tract infection (UTI)
  • Kidney disorders like cystic kidney diseases and renal tubular acidosis
  • Gout (painful swelling of the joints)
  • Hypercalciuria (high urinary level of calcium)
  1. Why is a Kidney Stone Analysis performed?
  2. How do you prepare for a Kidney Stone Analysis?
  3. How is a Kidney Stone Analysis performed?
  4. What do Kidney Stone Analysis results mean?

Your doctor may order this test if you show the following symptoms of kidney stones:

This test is mainly done to determine the chemical makeup of a stone and to get information on how to prevent the formation of more stones in the future. If the stone has already passed out through urine and you have kept it, your doctor may ask you to bring it for analysis. He/she will guide you on how to clean and pack the stone.

For larger stones, which cannot be passed through urine, you may require a minor surgical procedure to remove the stone.

If you have symptoms of a kidney stone, your doctor will give you a strainer made of fine mesh or gauze to filter your urine and collect the stone (just in case you pass one or small particles from one). Following are the steps to collect the stone for testing:

  • Filter your urine through the strainer each time you urinate.
  • Check the strainer carefully for small particles.
  • If you see a stone, keep it in a clean container and leave it to dry.
  • Do not contaminate the stone by adding urine or any fluid into the container.
  • Do not cover the stone with tissue or tape, as it can change the test results.
  • Take it to your doctor for analysis.

In case the stone is too large to pass, be prepared for a surgical procedure. 

Both physical and chemical methods are used for a kidney stone analysis. Physical analytic methods are widely used in laboratories because they can identify a diversity of components. Chemical methods are not commonly used, as they fail to analyse stones accurately. The following methods are used for the study of kidney stones:

  • X-ray diffraction and Fourier transform infrared spectroscopy: These are widely used methods that not only help in determining each component of a stone but also provide concentrations of every component. These methods detect both calcium oxalate and calcium phosphate stones and non-calcium stones, such as protein, uric acid, cystine, lipid and struvite stones.
  • Energy Dispersive X-Ray Analysis: It gives an accurate composition of different elements in a stone. This method also helps in identifying the initiation and the formation of stone.
  • Thermogravimetric analysis: This is a simple and quick method that uses increasing temperature to determine the mass of any thing.
  • Wet chemical analysis: This method only works well if the stone is made of a single type of mineral stone and does not give good results for mixed stone.
  • Scanning electron microscopy: This method is used to study the texture and morphology of stones that are 1-5 nanometres in size.
  • Powder X-ray diffraction: Powder X-ray diffraction can identify the constituents of a stone. It can simultaneously distinguish and measure all the crystals in a stone.

The results of a kidney stone analysis show what type of kidney stone you had. Based on the chemical makeup of the stone, your doctor will recommend medicines and measures to prevent the formation of more stones.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

References

  1. National Institute of Diabetes and Digestive and Kidney Diseases [internet]: US Department of Health and Human Services; Definition & Facts for Kidney Stones
  2. Michigan Medicine: University of Michigan [internet]; Kidney Stone Analysis
  3. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; Kidney Stones
  4. Lab Tests Online. Washington D.C.: American Association for Clinical Chemistry; Kidney Stone Testing
  5. Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2018. Stones in the Urinary Tract
  6. National Kidney Foundation [Internet]. New York (NY). U.S. Kidney Stones
  7. University of Chicago Kidney Stone Evaluation and Treatment Program [Internet]. The University of Chicago. Kidney stone types
  8. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Kidney Stone (Urine)
  9. UW Health: American Family Children's Hospital [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2017. Kidney Stone Analysis
  10. Jonathan Cloutier, Luca Villa, Olivier Traxer, and Michel Daudon. Kidney stone analysis: “Give me your stone, I will tell you who you are!”. World J Urol. 2015; 33: 157–169. PMID: 25465911.
  11. Fazil Marickar YM, Lekshmi PR, Varma L, Koshy P. EDAX versus FTIR in mixed stones.. Urol Res. 2009 Oct;37(5):271-6. PMID: 19536531.
  12. Sharma RN, Shah I, Gupta S, Sharma P, Beigh AA. Thermogravimetric analysis of urinary stones. Br J Urol. 1989 Dec;64(6):564-6. PMID: 2627629.
  13. Vivek K. Singh and Pradeep K. Rai. Kidney stone analysis techniques and the role of major and trace elements on their pathogenesis: a review. Biophys Rev. 2014 Dec; 6(3-4): 291–310. PMID: 28510032.
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