Kidney stones: symptoms, diagnosis and management

Introduction

Kidney stones, or renal calculi, are hard deposits made of minerals and salts that form inside the kidneys^​1​. They originate in the kidneys but can be found at any point in the urinary tract^​1–3​. The stone may block urinary flow and pain arises from the obstruction of the kidneys collecting system (causing renal colic) or the ureter (causing uretic colic) as it attempts to pass out of the body^​1–3​.

Many people may not experience symptoms; in 2010, results from one population study (n= 5,047) demonstrated an asymptomatic prevalence of 8%^​4​. Acute presentations have an annual incidence of  one to two cases per 1,000 people in the UK; it is estimated that 12% of men and 6% of women will have one episode of associated colic at some stage during their life^​5​. Although preventable, more than half of those diagnosed with kidney stones will develop another within five to ten years^​6​.

Peak age incidence for men is 40–60 years — two-thirds of whom are likely to have recurrent stones — and the peak age incidence is late 20s for women^​5​. Hormonal differences, such as the protective effect of oestrogen, as well as a gender difference seen in urinary pH, calcium excretion and metabolic disorder prevalence, are thought to contribute to the lower incidence in females^​7​.

Around 80% of kidney stones can be passed spontaneously without intervention; however, depending on the size of stone and patient factors (e.g. the anatomy of the patient), medication or surgical interventions may be required^​5,8​. 

Global incidence of kidney stones is increasing^​9​. This increasing prevalence and potential for prevention of stones in working age adults makes this an area in which pharmacists can have an impact in identifying, triaging and supporting patients^​10,11​.

Causes and pathophysiology 

The exact pathophysiology of stone formation is still debated; however, it is thought to be a heterogeneous process^​1​. Stones are more likely to form when the urine is concentrated and there is an excess of waste products, such as minerals, which crystallise, nucleate and grow to form stones^​1​.

Composition of the stone may allow for causes and risk factors to be identified; see Table^{​1,2,8,12​}.

Risk factors

Some patients will be more at risk of kidney stones; non-modifiable risk factors include:

• Male sex: the incidence is 2.5:1 male to female, but this gap looks to be narrowing^​10,13​;
• White ethnicity: in 1994, US study data showed the highest prevalence in white men followed by Hispanic, Asian and Black men^​14​; 
• Family history: those with a family history of kidney stones are more likely to develop multiple stones and experience early recurrence^​1​; 
• Medical history: several conditions increase the risk of stone formation, including anatomical abnormalities of the kidney or urinary tract, genetic conditions affecting metabolism (e.g. adenine phosphoribosyltransferase [APRT] deficiency, cystinuria, Dent disease), gastro-intestinal conditions affecting absorption (e.g. inflammatory bowel disease), conditions that alter urinary pH (e.g. chronic nephritis, gout), volume or concentration^{​3,8,11,15–17​}.

There is some evidence that occupational exposure to heat increases risk, although evidence is weaker in this area^​5​. Occupational exposure to cadmium and lead is associated with stone formation^​5​. Prevalence of kidney stones also increases with increasing weight/BMI^​14​.

Signs and symptoms 

Although some patients will be asymptomatic, patients with larger stones are likely to experience renal or ureteric colic pain and present to a healthcare professional for assistance in a community pharmacy, GP or acute care setting. 

Pain is severe, intense and abrupt in onset; it is unilateral, originating in the loin or flank radiating down to the groin/testicles in men or labia in women, see Figure^​8​. Pain is caused by increased intraluminal pressure stretching the nerve endings of the collecting system or ureter^​1​. Other contributors to pain may include local inflammatory mediators, hyperperistalsis (i.e. excessive or excessively vigorous peristalsis of ureters), mucosal irritation and oedema^​1​. 

Wes Mountain/The Pharmaceutical Journal

Pain occurs in spasms (with intervals of dull ache or no pain) that can last anywhere between minutes to hours^​1,8​. A patient may describe it as the worst pain that they have ever experienced. At its most severe, the pain may be accompanied by nausea and vomiting. A standard scoring system can be used to monitor pain and the STONE score (online calculator can be found here) can be used to determine the risk of stone presence and prevent re-imaging in those with a previous history^​18​. 

If the stone irritates the detrusor muscle or blocks the vesico-ureteric junction, patients may experience increased urinary frequency, pain on urination or straining^​8​.

Patients will require immediate hospital admission if:

• There are signs of systemic infection (e.g. fever or sweats) or sepsis; 
• They have pre-existing conditions that increases risk of acute kidney injury (e.g. chronic kidney disease, transplanted kidney);
• They are dehydrated and can no longer take oral fluids owing to nausea/vomiting^​8​.

Diagnosis 

All patients with suspected renal colic should be referred urgently (within 24 hours) for non-contrast CT imaging to confirm diagnosis^​3​. Ultrasound can be used as an alternative for pregnant women^​8​. Blood tests (full blood count, urea and electrolytes) to confirm kidney function and potential precipitating conditions should be completed in tandem^​1​. 

The CT scan will confirm the diagnosis, number, location and size of stones, as well as anatomical abnormalities associated with recurrent stones^​8​. Women of childbearing age should have a pregnancy test to rule out ectopic pregnancy, which may have overlapping symptoms, such as pelvic pain and urinary symptoms^​1​.

The location and the type of pain can help to distinguish kidney stones from other conditions, such as appendicitis, where the pain is in the right lower quadrant and is typically more persistent and accompanied by fever^​1​. Patients with renal colic may be more restless and unable to lie still unlike the pain in peritonitis, which is an infection in the thin layer of tissue in the abdomen^​8​.

There may be haematuria (blood in the urine) present on a urinary dipstick, which should be undertaken to rule out the diagnosis of a urinary tract infection or pyelonephritis^​1,8​. 

Management

Supportive care

Patients with kidney stones will need assistance with pain relief. The National Institute for Health and Care Excellence recommends that a non-steroidal anti-inflammatory drug (NSAID) should be used as first-line treatment by any route^​3​. However, renal function should be checked before prescribing an NSAID as some patients may develop acute kidney injury from the stone and NSAIDs are contraindicated in renal failure^​19​. Intravenous paracetamol can be used if NSAIDs are contraindicated or do not offer sufficient relief, with opiates being a third-line option^​3​. Anti-emetics can assist with nausea^​1​. Antibiotics should be given if urinary cultures are positive^​1​.

Stone removal

Symptoms, size and placement of stones determine the management route taken to remove the stone:

• Asymptomatic stones less than 5mm: watchful waiting employed as spontaneous stone passage is more likely with smaller stones^​11​;
• Asymptomatic stones larger than 5mm: watchful waiting with patient agreement as to risks and benefits^​8​. These stones should not affect quality of life if the patient has limited symptoms and may not need intervention, but there is the risk of location change and obstruction, bleeding and the development of symptoms^​3​;
• Symptomatic stones less than 10mm: may benefit from medical expulsive therapy, which is where a medication is used to help patients pass the stone spontaneously. Alpha blockers are used for this indication (unlicensed [e.g. Tamsulosin]), with 400 micrograms daily until stone expulsion^​20​. Inhibition of smooth muscle contraction in the ureter assists the passage of the stone into the bladder^​21​.

Stones unlikely to pass, where the pain is ongoing (48 hours) or not tolerated, may be candidates for a procedure for removal^​3​. The choice of procedure is based on anatomy, stone size and patient factors:

• Shockwave lithotripsy: uses shock waves to break up the stone into easier to pass fragments^​8​; 
• Percutaneous nephrolithotomy: endoscopy of kidney during which the stone is broken down by instruments or lasers and removed^​2​;
• Ureteroscopy: endoscopy of the ureter with instruments or energy waves for break down the stone for removal^​8​;
• Open surgery: rarely used, but remains an option for when the above procedures fail or are unlikely to be successful^​11​.

Once passed, the stone can be sent for analysis to determine composition; this can help tailor future prevention advice to the patient^​10​.

Advice on prevention

Given the high risk of reoccurrence, pharmacists can have a role in counselling patients on lifestyle modifications to reduce risk of new stone formation. The BMJ has produced an article on dietary management that may be useful when stone analysis has been performed to tailor the advice to the patient based on the stone composition^​10​. Despite calcium being the most prevalent element found in kidney stones, restriction of dietary calcium actually adversely affects stone reoccurrence^​10​. For patients unsure of their usual calcium intake, the online chart by the Bone Health and Osteoporosis Foundation can be used^​22​.

If lifestyle advise fails, patients with recurrent stones that are predominantly (more than 50%) calcium oxalate may benefit from potassium citrate or thiazide treatment^​2​. Patients taking medications that can induce kidney stone formation should have their use reviewed, considering the patient holistically and whether any metabolic or dietary factors have since resolved. Lifestyle adjustments may prevent reoccurrence, and drug removal may not be required^​23​.

General prevention advice for patients is shown in the Box below^{​8,10,11​}.

Complications

Suspected kidney stones should not be ignored. Complications include obstruction of urinary flow and infection; persisting obstruction reduces renal blood flow and may cause kidney damage and chronic kidney disease^{​1,8,11,24,25​}. Presence of kidney stones is also associated with coronary heart disease, stroke and renal cancer^​26,27​.

Patient case study

A 48-year-old male (95kg) presents to the community pharmacy after experiencing back pain for two days that comes on at night and lasts for approximately four hours. Paracetamol has been tried but did not provide any relief.

The pharmacist asks the patient the following questions:

• Where is the location of the pain?
• Is there any pain or change in urination?
• Has there been any injury to the back or any strenuous activity?
• Is the pain only at night?
• Are there any other symptoms?

The patient reported pain in the upper back on the right-hand side only. They had not noticed any changes in urination but admitted their urine was generally on the darker side. They had not experienced any injuries or completed any activities that could have resulted in muscle damage. They felt some slight throbbing during the day, but the pain at night was the worst thing they have ever experienced and they were vomiting as they were in so much pain. Vomiting did not relieve the pain.

Based on the further description of the patient, the pharmacist recommended that they seek an urgent medical appointment as they may need a referral for a potential kidney stone.

The patient saw their GP that day, was referred to accident and emergency with a letter for an urgent CT. The CT scan showed a small luminous mass of 4mm in the right kidney consistent with kidney stones. The patients GFR was 45mL/minute. The patient was admitted overnight and received paracetamol and codeine for pain. Owing to stone size, they were discharged and told to drink two to three litres of water per day to promote removal, with a follow-up planned for further imaging in five days’ time.

The patient passed their stone three days after discharge from hospital. Further imaging confirmed absence of the stone. Advice was given on weight reduction and fluid management to prevent reoccurrence.