Assessment for Kidney Stones

The symptoms associated with kidney stones mentioned above (loin / back ache, blood in the urine or urinary tract infection) may have other causes than kidney stones such as back and spine issues as well as a number of other urological and non-urological conditions. Since these symptoms are not an emergency, the best way to find the cause of them is to arrange an appointment for a discussion and any further investigations with your GP. The symptoms of acute ureteric colic, from a stone in the ureter, are more of an emergency, partly to help deal with the intensity of the pain with adequate pain relief (which might require injections), but also because urgent imaging is often needed to assess the situation rapidly and to determine whether the stone can be left to pass spontaneously or if admission to hospital for urgent intervention to treat the stone actively might be needed. Patients with acute uretetic colic, particularly if it is their first episode, will often need to be seen in an A/E department as an emergency for both analgesia (pain relief) and imaging to make the diagnosis, and exclude any other cause for the sudden onset of their severe abdominal pain. A full clinical history is important to assess whether your symptoms are most likely to be due to kidney stones, whilst making additional enquiries about your general health in case it becomes apparent that your symptoms might be better explained by an alternative condition, or that there is something of importance that “flags up” that should be investigated as the priority. As far as kidney stones are concerned, expect to be asked about your diet, time spent in a hot dry climate, your fluid intake and whether there is a family history of stones. A full physical examination, including assessment of your abdomen, will normally be performed and your blood pressure may be taken as part of the assessment. Some first line tests to help assess the likelihood you have stones and not another cause for your symptoms are then likely to be arranged as follows:
  • General Blood TestsIt is common to measure the overall kidney function, blood sugar, and to make additional general checks on the blood for anaemia or other problems. As far as stones are concerned, measuring the level of calcium, phosphate and uric acid is useful to see if these are high, and therefore potentially linked to the formation of a kidney stone.
  • Urine TestsYour urine will normally be tested for blood (most patients with a stone have a trace of blood in the urine) and the pH (acidity) measured. If there are features of infection (white blood cells or nitrites on the test, particularly if the history suggests symptoms consistent with infection) the urine sample can be sent to the laboratory for culture and to check which antibiotics would be suitable if an infection is found.
  • ImagingThe best way to diagnose stones is to have some form of imaging. Depending on the likelihood that you have a stone, and recent prior imaging, either a Renal Tract Ultrasound or a CT scan will be suggested. The advantage of Ultrasound is that it does not require X-rays, so can be used as a first line investigation in all patients. If there is a stone, the implications of it and the treatment options can be discussed in more detail (see below). Most patients who are referred to a Urologist will either have been seen by their GP and had a renal tract ultrasound that showed a stone, or have been seen in the relevant hospital A/E department with symptoms suggesting acute ureteric colic, for which a CT scan will have been performed there and then.
  • Imaging with CT ScanAssuming you have been referred by your GP, the urologist is likely to arrange a CT scan as the next test, not only to confirm the diagnosis, but to give more accurate additional information about your stone that will help you and your Urologist reach an agreement over how it should be best managed for you. The CT that will most commonly be performed is known as a “non-contrast CTKUB” – this means it does not require intravenous contrast (i.e. no injection is needed), and the images taken cover the urinary tract from top to bottom (i.e. the Kidneys, Ureters and Bladder). The CT images will inform your Urologist where in the urinary tract the stone is and how many stones there are (sometimes there are multiple stones on one side, and can also be present in both kidneys at the same time). The stones’ size is also an important factor in deciding between treatment options. Additional information such as the approximate “hardness” of the stone can be gleaned from CT, which can be useful in choosing Shock Wave Lithotripsy (SWL) if the stone seems “soft” enough on CT.
  • Additional Specialist TestsWhilst not usually possible to test a stone for its biochemical composition at the first visit (unless you pass one spontaneously between your referral by the GP or A/E), a fragment of stone (either passed spontaneously following ureteric colic, as a result of SWL, or actively retrieved at one of the surgical procedures) can be analysed to determine the stone biochemistry. This is useful for guiding future preventative advice, and may also trigger a “metabolic stone screen” if the stone is a particular kind (such as a cystine stone, or a pure calcium phosphate stone for example). A “metabolic stone screen”, involving at least one 24-hour urine collection may be recommended to analyse the urinary constituents in more detail to help inform more bespoke preventative advice. This is not needed for all patients but might be arranged if you have risk factors for future recurrence such as being young (less than 30) when you made your first stone, having a strong family history of stones, or already having made multiple or bilateral stones. It may also be organised based on the specific biochemistry of your stone, or if you have anatomical risk factors that cannot be straightforwardly during the treatment of the stone itself.
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