Gout is diagnosed through a combination of joint fluid analysis, blood tests, and sometimes imaging. The single most definitive test is examining fluid drawn from the affected joint under a special microscope to look for uric acid crystals. If crystals are found, no further testing is needed. When joint fluid can’t be obtained, doctors use a scoring system that combines blood work, imaging, and clinical symptoms to reach a diagnosis.
Joint Fluid Analysis: The Gold Standard
The most reliable way to confirm gout is a procedure called joint aspiration, where a doctor draws a small sample of fluid from the swollen joint and sends it to a lab. Under polarized light microscopy, a technician looks for monosodium urate crystals, which appear as needle-shaped structures. Finding these crystals inside white blood cells in the fluid is essentially a definitive diagnosis. Results typically come back within one day.
This test also rules out pseudogout, a condition that mimics gout but involves a completely different type of crystal. Pseudogout crystals are diamond-shaped rather than needle-shaped, and they look different under the microscope’s polarized light. The distinction matters because the two conditions affect different joints and respond to different treatment approaches.
Joint aspiration isn’t always possible, though. Sometimes the joint is too small or difficult to access, the fluid volume is too low, or the timing works against you. In about 25% of acute gout attacks, joint aspirates come back negative even when gout is present. In those cases, doctors turn to other tools.
What the Aspiration Procedure Feels Like
If your doctor recommends joint aspiration, here’s what to expect. The skin over the joint is cleaned with antiseptic, then numbed with a local anesthetic injected through a very small needle. Once the area is numb, a slightly larger needle is inserted into the joint space to withdraw fluid. The doctor will try to remove as much fluid as possible, which often provides some immediate pain relief since it reduces pressure inside the joint. Afterward, a bandage goes over the puncture site.
The whole process takes just a few minutes. Ultrasound is sometimes used to help locate the fluid pocket, especially in joints where the swelling isn’t obvious from the outside. Soreness at the needle site is normal for a day or two afterward.
Blood Tests for Uric Acid
A uric acid blood test measures the level of uric acid circulating in your bloodstream. When levels stay consistently above 6.8 mg/dL, uric acid can start forming crystals in joints. No fasting or special preparation is needed before the blood draw.
Here’s the tricky part: a high uric acid level alone doesn’t prove you have gout. Many people walk around with elevated uric acid and never develop symptoms. And during an acute gout attack, uric acid levels can actually drop temporarily into the normal range, which can be misleading. That’s why this test is useful as one piece of the puzzle but isn’t enough on its own. A very low reading (below 4 mg/dL) actually counts against a gout diagnosis in the clinical scoring system doctors use.
Kidney Function Tests
Your doctor will likely order kidney function blood work alongside the uric acid test. This isn’t just routine. There’s a strong connection between gout and kidney disease. Since the kidneys are responsible for clearing most uric acid from the body, declining kidney function leads to higher uric acid levels. Among people with gout, over 70% have at least some degree of reduced kidney function, and about 24% have moderate to severe kidney disease.
Knowing your kidney function also shapes treatment decisions. Several common gout medications need dose adjustments or are unsafe when kidneys aren’t working well, so this information matters for what comes next.
Imaging Tests
When joint fluid can’t be tested, imaging can help detect uric acid deposits directly.
Ultrasound can reveal what’s called a “double contour sign,” a bright line of uric acid crystals coating the surface of cartilage. This finding is fairly specific to gout (about 89% specificity), meaning if the sign is present, there’s a high chance gout is the cause. However, ultrasound only catches it about 58% of the time, so a negative ultrasound doesn’t rule gout out.
A specialized CT scan called dual-energy CT (DECT) is more accurate overall. It uses two different X-ray energy levels to distinguish uric acid deposits from calcium, then color-codes them on the resulting images. A large analysis of multiple studies found DECT has a sensitivity of 87% and specificity of 84% compared to crystal identification under the microscope. In one study of patients with confirmed gout, specificity reached 93%. DECT is particularly useful for detecting deposits in joints that are hard to aspirate or for identifying hidden uric acid collections that haven’t caused symptoms yet. It also clearly distinguishes gout from pseudogout, since calcium pyrophosphate crystals don’t show up as uric acid on the scan.
Standard X-rays are less helpful for early gout but can show joint damage and tophi (visible uric acid lumps) in people who have had gout for years.
The Clinical Scoring System
When aspiration isn’t performed or comes back inconclusive, rheumatologists use a standardized scoring system developed jointly by the American College of Rheumatology and the European League Against Rheumatism. It assigns points across eight categories covering clinical features, lab results, and imaging findings, with a maximum score of 23. A score of 8 or higher classifies someone as having gout.
The system accounts for typical gout patterns: which joints are affected, how quickly the attack came on, whether the skin over the joint is red and warm, whether there are visible tophi, and what your uric acid level is. Notably, the scoring includes negative points. If joint fluid testing is done and no crystals are found, 2 points are subtracted. If your uric acid level is below 4 mg/dL, 4 points are subtracted. These deductions make it harder to be misclassified when evidence points away from gout.
The system can also be used with clinical features alone, without any imaging or lab results, though it’s most accurate when all the data is available. This flexibility matters in primary care settings where advanced imaging or joint aspiration may not be immediately accessible.