How Gout Is Diagnosed

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While gout may seem pretty self-evident based on the appearance alone, a doctor will often want to perform tests to confirm the diagnosis and rule out other causes. As a disease characterized by the deposit of uric acid crystals in the joints, the doctor may want to look for evidence of this by drawing out joint fluid with a needle to examine under the microscope.

In some cases, a diagnosis can by comparing symptoms with a series of lab and/or imaging tests.

Physical Exam

In a great many cases, a gout diagnosis can be made based on a review of your symptoms and medical history. In addition a physical exam, your doctor will want to have a description of the attack (including how it started and how long it lasted) and explore any ​risk factors that may have contributed to the attack.​

Certain tell-tale symptoms may be enough to make the diagnosis, such as:

  • A mono-arthritic attack (meaning only one joint is affected)
  • Acute pain in the first metatarsal-phalangeal joint of the big toe
  • Extreme joint inflammation and redness over one day
  • Having more than one attack in the same joint

While this may be all that your doctor needs to draw up a treatment plan, additional evidence may be require d if this is your first attack or if recurrent symptoms have become severe.

Labs and Tests

The gold standard for making a gout diagnosis is by extracting synovial fluid from a joint and searching for evidence of uric acid crystals (called monosodium urate crystals) under a microscope. Synovial fluid is a thick, light-colored substance that lines the joint and lubricates the space between joints.

The procedure, known as a synovial fluid analysis, starts with an injection of a local anesthetic to numb the joint. After a few minutes, the doctor will insert a needle into the joint space to extract a sample of fluid which would then be sent to the lab for analysis.

In addition to searching for monosodium urate crystals, the lab will check for high uric acid levels as well as evidence of tophus, hardened lumps of uric acid found in later-stage disease.

Among the other lab tests that may be ordered:

  • ​A uric acid blood test may be performed to check for acid levels above 6.8 milligrams per deciliter (although people with low levels can also have gout).
  • Urea and creatinine blood tests may also be performed to see if your kidney function has been impaired as a result of hyperuricemia (excessive uric acid).
  • A urinalysis may be used to check uric acid levels in your urine and assess your risk of kidney stones.

Imaging Tests

To assist with the diagnosis, the doctor may order imaging tests to evaluate the characteristics of a swollen joint or to check for subchondral bone cysts indicative of arthritis. Imaging test options include X-ray, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound.

Each test has its benefits and limitations:

  • X-rays may reveal bone and cartilage erosion but are really only useful after a year of uncontrolled disease.
  • CT and MRI scans can help identify inflammation, bone erosion, and cartilage damage but, according to a study published in European Radiology, may be less able to detect early disease.
  • Ultrasounds are beneficial as they are portable, readily available, and don't require ionizing radiation. They can also detect early evidence of crystal deposits, fluid accumulation, and the widening of the joint space. On the downside, they are unable to visualize deeper structures of a joint.

    In practice, ultrasounds are typically used if you have just begun to experience symptoms or recurrent attacks. Other imaging tests may be ordered based on the history of your symptoms or the severity of your condition.

    Differential Diagnoses

    While the symptoms of gout may seem definitive by appearance alone, there are two other conditions doctors will look at that have remarkably similar features: pseudogout and septic arthritis.

    To differentiate, the doctor will look at four things: the synovial fluid analysis (to check for evidence of crystallization), the white blood count (to check for infection), a gram stain culture of the synovial fluid (to check for bacteria), and the location of your joint pain.

    Gout

    Gout will  have certain physical and diagnostic characteristics that separate it from the other diseases, namely:

    • Synovial fluid analysis: needle-shaped crystals
    • White blood cell count: below 50,000
    • Gram stain culture: negative (meaning no infection)
    • Location: primarily the big toe, midfoot, knee, and the lower extremities (with the involvement of the wrist, elbow, hand, or fingers in later-stage disease)

    Pseudogout

    Pseudogout is a condition where calcium crystals (not monosodium urate crystals) develop in the joint space. The disease can be differentiated from gout in the following ways:

    • Synovial fluid analysis: rhomboid-shaped crystals
    • White blood cell count: below 50,000
    • Gram stain culture: negative
    • Location: typically knee, wrist, or big toe

    Septic Arthritis

    Septic arthritis, also known as infectious arthritis, and is usually caused by a bacterial infection and can be fatal if left untreated. It differs from gout in the following characteristic ways:

    • Synovial fluid analysis: no crystals
    • White blood cell count: above 50,000
    • Grain stain culture: positive (confirming a bacterial infection)
    • Location: primarily the knee

    Sources:

    Rettenbacher, T.; Ennemoser, S.; Weirich, H. et al. "Diagnostic imaging of gout: comparison of high-resolution US versus conventional X-ray." Eur Radiol. 2008;18(3):621-30. DOI: 10.1007/s00330-007-0802-z.

    Tuhina, N.; Jansen, T.; Dalbeth, L. et al. "2015 Gout Classification Criteria An American College of Rheumatology/European League Against Rheumatism Collaborative Initiative." Arthritis Rheumatol. 2015; 67(1):2557-68. DOI: 10.1002/art.39254.