What imaging techniques are used to detect kidney stones?

Types of Kidney Stones

Kidney stones are accumulations of crystals or mineral salts that form due to substances in the urine. These stones can vary in size (from a grain of sand to the size of a grape) and composition:

1. Calcium stones: These are the most common and are usually composed of calcium oxalate.
2. Uric acid stones: These form when the urine is too acidic.
3. Struvite stones: These can appear when you have certain types of urinary tract infections that generate crystals in the urine when it is not acidic enough, in which bacteria produce a type of ammonia.
4. Cystine stones: These are formed by a naturally produced substance in the body called cystine. These stones are rare.

How to detect them with imaging studies?

It is not always easy to observe the kidneys, which is why it is important for the patient to be in a conscious state that allows them to move into different positions.

Generally, most kidney stones can be seen with an ultrasound; almost all will appear as highly reflective structures. This observation can be difficult when the stone is very small. In these cases, a urography or CT scan1¹ should be performed.

There are different imaging studies that can be performed²:

• Plain abdominal X-ray: if this test is not complemented with anything else, its sensitivity or ability to detect the pathology may decrease by up to 59%. This can be due to the size of the stone (not visible if less than 2mm), the type of stone (not visible if it is uric acid), the superposition of intestinal gas, or the interposition of bone, among other factors.
• Abdominal ultrasound: this is one of the most commonly used techniques, along with X-rays, as it detects all types of stones (including uric acid stones) and can detect if there is a urinary obstruction. Despite this, it only detects stones larger than 4mm. It has a low detection capacity, between 20-45% if performed in isolation.
• Intravenous urography: this is a test with high sensitivity (detection capacity) and specificity (87-90%). It cannot be performed during the acute phase of colic because the contrast that needs to be injected could take hours to be eliminated.
• CT scan with and without contrast: this is the most sensitive and specific test (between 94 and 100%) for stone detection. It allows visualization of small and radiolucent stones (such as uric acid stones), it is a brief and simple process, and it does not require intestinal preparation. On the other hand, it is very radioactive, so it cannot be performed on children or pregnant women.

1. Drink a minimum of 2-3 liters of water daily
2. Maintain a healthy diet.
3. Maintain urinary pH at appropriate levels (5.5-6.2). You can modify your pH with the Lit-Control food supplements and their pH Meter which will allow you to maintain proper monitoring!
4. Maintain an active lifestyle, which helps you maintain an adequate weight and avoid obesity.

References:

*1 https://diplomadomedico.com/errores-y-dificultades-en-la-exploracion-ultrasonografica-del-rinon/

*2 https://www.urologosmalaga.com/tratamientos/litiasis-calculos/4-1-litiasis-calculos-evaluacion-y-diagnostico/