Flank Pain

The protocol for Flank Pain:

Flank Pain


Let’s break it down!

Flank pain is a common chief complaint that can differentiate into any number of disease processes. For our purposes, we’re mainly focused on two in particular: Pyleonephritis (inflammation of the kidney due to infection) and Renal Colic (pain associated with kidney stones). Testicular torsion is also one of our differentials, but you can find more information about that in the Testicular Pain protocol


Pyelonephritis is a urinary tract infection (UTI) at the highest level.  Most UTIs begin and stay in the bladder (cystitis), but if left untreated it can progress into the kidneys. It’s typically caused by bacteria, specifically Escherichia Coli (commonly found in feces).  UTI’s are responsible for an estimated 2-3 million ED visits every year. Although most are relatively harmless with treatment, pyelonephritis carries a mortality of up to 40% for patients over the age of 65. For more on the physiology, check out the following video:


Renal Colic

Renal colic is not a condition by itself, it just represents the pain associated with nephrolithiasis, or “kidney stones“. When these stones form an obstruction in the ureters, they cause the ureters to spasm and elicit a colicky flank pain sensation to the patient, thus the name renal colic.

Kidney stones are extremely common; the current lifetime prevalence of kidney stones is 10-13% for men and 7% for women. In hot arid climates such as certain areas in the middle east, the prevalence can be as high as 25%. Although kidney stones are incredibly painful, mortality is rare. Death typically only occurs from complications of sepsis or renal failure. For more on the pathophysiology of kidney stones, check out the video below:


Back pain and flank pain can be found in both renal colic and pyelonephritis since both involve inflammation of the renal organs. Renal colic is a very peculiar type of pain though.  Kidney stones elicit spasmodic pain in the urinary tract that’s mostly constant and slow to change.  You’ll find that patients with kidney stones will sort of thrash about, struggling to find a comfortable position.

Nausea/vomiting is often associated with kidney diseases as well because the GI tract and the kidneys share many of the same nerves

Frequency, urgency, dysuria (pain/discomfort urinating), and hematuria (blood in the urine) all represent the symptoms of a urinary tract that’s irritated or inflamed, whether that’s from obstruction or infection.  

The presence or absence of fever is something critically important to note.  This is more common with pyelonephritis, but if someone with kidney stones has a fever, that can indicate that the patient has an infected stone and could develop sepsis/renal failure.

We spoke a bit about CVAT (Costovertebral Angle Tenderness) in the Urinary Tract Infection (UTI) review.  If you discover this in a patient, it doesn’t necessarily mean that they have a kidney stone, but it’s a pretty good indicator of Pyelonephritis.  Here’s the CVAT exam video again if you haven’t seen it already:


Antibiotics are not typically indicated for kidney stones/renal colic, but if a fever is present, then that would indicate an infected stone or pyelonephritis. Either way, aggressive antibiotic treatment is warranted.

The most common causative bacteria for kidney infections are typically the same ones found in lower urinary tract infections. This includes  E. Coli, Klebsiella pneumoniae, and Pseudomonas Since the risk of decompensation is so high, we typically treat these infections with broad-spectrum antibiotics.

For PO antibiotics, we have two within the combat medic formulary that you can choose from:

  • Moxifloxacin (broad-spectrum fluroquinoline antibiotic; not typically preferred due to low urinary levels)
  • Amoxicillin/Clavulanic Acid (broad-spectrum penicillin/beta-lactam antibiotic; typically used in conjunction with IV antibiotics)

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If PO antibiotics fail or cannot be give, these are our IV antibiotic choices:

  • Ceftriaxone (broad-spectrum cephalosporin antibiotic; frequently used for pyelonephritis)
  • Ertapenem (broad-spectrum carbapenem antibiotic; commonly used as an alternative to ceftriaxone)

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3. Treat per Pain Management protocol

Renal colic and pyelonephritis can both be extremely painful and can potentially require narcotic medications. However, since ureteral spasms are prostaglandin-mediated, NSAIDs have been found to particularly useful for renal colic. In fact, several randomized control trials have shown NSAIDs to be opiates and paracetamol in the first 30 minutes. Of the many NSAIDS, Ketorolac is particularly effective and frequently used.

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4. Treat per Nausea/Vomiting protocol

As discussed earlier, the GI tract and the kidneys share many of the same nerves. For these patients, the best medications would be Ondansetron or Promethazine

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5. Treat per Dehydration protocol

These patients are frequently dehydrated, which is often why they developed kidney stones in the first place. Persistent nausea makes it especially difficult to hold down PO fluids. IV fluids are frequently given to these patients. For kidney stones, the goal will often be to hydrate the patient enough to help facilitate effective urination to flush the deposit out. This could take anywhere between a few hours to several weeks for the patient, but it helps to get them started.

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Although young patients will typically have a good prognosis with prompt treatment, renal diseases pose a particularly high risk for soldiers in austere environments and they may need several weeks to recover.  In addition, some kidney stones may be unable to pass, thus often requiring advanced procedures to remove.  A Priority evacuation will always be needed for these patients.


Good luck out there!


Brandon Simpson, PA-C
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