Blog | Wednesday, August 13, 2014

A clinical prediction rule for kidney stones

Kidney stones (nephrolithiasis) affects 1 in 11 people in the U.S. Some say it’s the worst pain they have ever experienced. There are a number of causes for these stones, including diet, hereditary, chronic urinary infections, gastric bypass surgery or inflammatory bowel disease, and other medical conditions. Sometimes we just don’t know the cause, although they are more prevalent in men than in women.

Patients with acute flank pan often show up in the emergency department with severe pain. Because other things can cause abdominal or back pain, patients will often undergo lots of tests (cat scans, ultrasounds, etc.) to determine the cause. The British Medical Journal has published a study that shows a clinical prediction rule that proved valid in determining that the patient did, in fact, have a kidney stone. Here is what they found:

Eight factors were associated with the presence of a ureteral stone. Each of them was assigned points:
• male sex (2 points)
• duration of pain-greater than 24 hours (0 points)
• duration of pain-6-24 hours (1 point)
• duration of pain less than 6 hours (3 points)
• non black race (3 points) (stones are rare in black race)
• nausea alone (1 point)
• vomiting alone (2 points)
• microscopoic hematuria (3 points) (blood in urine)

Add up the points and if 0-5, there is a low probability (10%) for a kidney stone; 6-9 points is moderate probability (50%); and 10-13 points is high probability (90%).

Alternative causes (non-stone) were found in 1.6% of the high-probability group. These causes were diverticulitis, appendicitis, mass, pyelonephritis, cholecystitis, pneumonia, bowel obstruction, colitis, aortic aneurysm and pancreatitis.

This algorithm was tested and validated in an emergency setting and it could help physicians with diagnosis and help prevent unnecessary testing.

This post originally appeared at Everything Health. Toni Brayer, MD, FACP, is an ACP Internist editorial board member who blogs at EverythingHealth, designed to address the rapid changes in science, medicine, health and healing in the 21st Century.