Case
A 39-year-old woman presented to the ED with a chief complaint of intermittent right flank pain that radiated into her groin area. She stated the pain had begun suddenly, 4 hours prior to arrival, and was accompanied by nausea and vomiting. The patient said that she had taken acetaminophen for the pain, but had received no relief. Regarding history, according to the patient, her last menstrual period ended 2 days earlier. She denied any urinary symptoms, diarrhea, or constipation. She had no history of abdominal surgery and was currently not on any medications.
The patient’s vital signs at presentation were: temperature 98.7°F; blood pressure, 130/90 mm Hg; heart rate, 110 beats/minute; and respiratory rate, 18 breaths/minute. Oxygen saturation was 98% on room air. On physical examination, she appeared to be in mild distress, pacing around the room. There was moderate right costovertebral tenderness on percussion; the abdomen was soft and nontender.
Incidence
As ED visits for nephrolithiasis are increasing, so too are the health-care costs associated with this condition. Between 1992 and 2009, emergent-care presentations for nephrolithiasis rose from 178 to 340 visits per 100,000 individuals.1 Approximately 1 in 11 people in the United States will be affected by nephrolithiasis during their lifetime.2 Estimated health-care costs associated with these complaints were roughly $2 billion in 2000—an increase of 50% since 1994.2
Evaluation and Diagnosis
Laboratory Evaluation
Urinalysis is one of the initial studies for patients with suspected nephrolithiasis. Although hematuria is a classic finding associated with renal calculi, its sensitivity on microscopic analysis is around 84%. Therefore, the absence of hematuria does not exclude renal colic in the differential diagnosis.3
In addition to detecting hematuria, urinalysis can also reveal an underlying infection. One study by Abrahamian et al4 found that roughly 8% of patients presenting with acute nephrolithiasis had a urinary tract infection (UTI)—many without any clinical findings of infection. The presence of pyuria, however, has only moderate accuracy in identifying UTIs in patients with kidney stones.4 If an infected stone cannot be excluded clinically, computed tomography (CT) is indicated.
Mild leukocytosis (ie, <15,000 cells/mcL) is another common finding in patients with acute renal colic.5 A leukocyte count >15,000 cells/mcL is suspicious for infection or other pathology. A blood-chemistry panel to evaluate renal function is appropriate as a baseline—particularly for patients in whom treatment with a nonsteroidal anti-inflammatory (NSAID) drug is anticipated.
Unenhanced Computed Tomography
With the ability to visualize renal calculi (Figure 1), the use of noncontrast CT has become a standard initial imaging modality in assessing patients with renal colic. Between 1992 and 2009, the use of CT to evaluate patients presenting with flank pain for suspected renal colic more than tripled from 21% to 71%.6 An analysis performed by the American College of National Radiology Data Registry7 shows the mean radiation dose given by institutions for renal colic CT is unnecessarily high, and that few institutions follow CT-stone protocols aimed at minimizing radiation exposure while still maintaining proper diagnostic accuracy. A typical CT of the abdomen and pelvis is equivalent to over 100 two-view chest X-rays.8 Though controversial, data from a white paper by the American College of Radiology suggest that the ionizing radiation exposure from just one CT for renal colic causes an increase in lifetime cancer risk.9
Despite the increase in CT imaging to evaluate patients presenting to the ED with nephrolithiasis/flank pain, the proportion of patients diagnosed with a kidney stone remained the same between 2000 and 2008, with no significant change in outcomes.10-12 Moreover, the use of CT as an initial imaging modality in patients presenting with flank pain—but with no sign of infection—is unlikely to reveal important alternative findings.13
Regarding the sensitivity of CT in detecting nephrolithiasis, one study demonstrates a sensitivity of 100% and a specificity of 94% for noncontrast CT.14 Controversy, however, still exists regarding the necessity and utility of CT in diagnosing nephrolithiasis,15 and CT is one of the top 10 tests included in the American College of Emergency Physicians (ACEP) 2014 Choosing Wisely campaign. In this campaign, ACEP recommended emergency physicians (EPs) avoid abdominal and pelvic CT in otherwise healthy patients younger than age 50 years who present with symptoms consistent with uncomplicated renal colic and who have a known history of nephrolithiasis or ureterolithiasis.15 The ACEP also noted that CTs in this context do not often change treatment decisions and are associated with unnecessary radiation exposure and cost.15
While keeping the aforementioned recommendations in mind, if an EP intends to refer a renal colic patient to a urologist a CT scan is necessary either in the ED or as an outpatient. In all cases (except perhaps in patients in whom there is a history of renal stones), the urologist will need this study to determine the size and location of the stone in order to provide recommendations for management.
Ultrasound
