Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
^ Jump up to: a b c d e f Qaseem, A; Wilt, TJ; McLean, RM; Forciea, MA; Clinical Guidelines Committee of the American College of, Physicians. (4 April 2017). "Noninvasive Treatments for Acute, Subacute, and Chronic Low Back Pain: A Clinical Practice Guideline From the American College of Physicians". Annals of Internal Medicine. 166 (7): 514–530. doi:10.7326/M16-2367. PMID 28192789.
Kidneys — The kidneys are a matched pair. One painful kidney can cause back pain on one side or the other. Kidney pain can feel like back pain, and may occur on only one side. It is usually quite lateral, and just barely low enough to qualify as “low” back pain. However, when kidney stones descend through the ureters, they can cause (terrible) pain in the low back. Kidney stone pain is often so severe and develops so rapidly that it isn’t mistaken for a back pain problem.
While a sharp pain in the hip, groin, pelvis, or thigh is an obvious sign of a hip flexor injury, pain in the lower back and leg are easy to misdiagnose. After all, it’s natural to assume that radiating pain in the leg or lower back originate from these areas. Unfortunately, diagnosing the source of a patient’s pain is not always straightforward. In fact, it’s possible for patients to go years with a misdiagnosed injury.
The problem is that these muscles aren't designed to be prime movers—they're designed to support the action of the glutes. Inability of activating the glutes can result in low back pain (low back muscles compensating), hamstring strains (overacting hamstrings), hip pain (resulting from hamstring-dominant hip extension) and knee pain (poor glute medius strength).
The presence of certain signs, termed red flags, indicate the need for further testing to look for more serious underlying problems, which may require immediate or specific treatment.[5][36] The presence of a red flag does not mean that there is a significant problem. It is only suggestive,[37][38] and most people with red flags have no serious underlying problem.[3][1] If no red flags are present, performing diagnostic imaging or laboratory testing in the first four weeks after the start of the symptoms has not been shown to be useful.[5] 
Enthoven WT, Geuze J, Scheele J, et al. Prevalence and "Red Flags" Regarding Specified Causes of Back Pain in Older Adults Presenting in General Practice. Phys Ther. 2016 Mar;96(3):305–12. PubMed #26183589. How many cases of back pain in older adults have a serious underlying cause? Only about 6% … but 5% of those are fractures (which are serious, but they aren’t cancer either). The 1% is divided amongst all other serious causes. In this study of 669 patients, a vertebral fracture was found in 33 of them, and the chances of this diagnosis was higher in older patients with more intense pain in the upper back, and (duh) trauma. BACK TO TEXT
Some of these red flags are much less red than others, especially depending on the circumstances. For instance, “weight loss” is common and often the sign of successful diet! (Well, at least temporarily successful, anyway. 😃) Obviously, if you know of a harmless reason why you have a red flag symptom, it isn’t really a red flag (duh!). But every single actual red flag — in combination with severe low back pain that’s been going on for several weeks — is definitely a good reason to get yourself checked out.
