What to test for gout

Gout is a very common disease in normal times. It is very harmful to the human body and will bring great inconvenience to our daily life and work. Once gout attacks, it is extremely painful for gout patients. In fact, if you want to reduce the occurrence of gout, it is also very important to do a good job of prevention in life. If you want to diagnose gout, what do you need to test?

What is the gout test?

The characteristic laboratory tests for gout are blood uric acid level and urine uric acid level, which are of great significance in judging hyperuricemia. In addition, to diagnose gouty arthritis, it is also necessary to examine the synovial fluid, that is, the fluid in the joint cavity. Under an optical and polarized light microscope, the synovial fluid can be seen to have diagnostically characteristic sodium urate crystals that are phagocytosed into white blood cells or in a free, needle-shaped, and birefringent state.

In addition to laboratory tests, gout patients also need to undergo joint X-rays and B-ultrasound examinations. In the early stages of acute arthritis, X-rays only show soft tissue swelling. After repeated attacks, the edge of the articular cartilage is destroyed, the joint surface becomes irregular, the joint space becomes narrow, and gradually tophi are deposited in the subchondral bone and bone marrow. Osteoporosis causes perforated bone damage, which can be seen under B-ultrasound as the double-track sign.

What are the examination items for gout?

1. Blood and urine routine tests and erythrocyte sedimentation rate

1. Routine blood test and erythrocyte sedimentation rate test

During the acute attack phase, the peripheral blood leukocyte count increases, usually to (10-20)×109/L, and rarely exceeds 20×109/L. Neutrophil counts increased accordingly. People with decreased renal function may have mild to moderate anemia. The erythrocyte sedimentation rate increases, usually less than 60 mm/h.

2. Urinalysis

There is generally no change in the early stage of the disease. If the kidneys are affected, there may be proteinuria, hematuria, pyuria, and occasionally tubular urine. If complicated with kidney stones, obvious hematuria may be seen, and acidic urinary stones may also be excreted.

2. Blood uric acid determination

During the acute attack period, the serum uric acid level of most patients increases. It is generally believed that the uricase method has diagnostic value when the concentration is 416 μmol/L (7 mg/dl) for men and >357 μmol/L (6 mg/dl) for women. If uricosuric drugs or cortical hormones have been used, the serum uric acid level may not be high. The remission period can be normal. 2% to 3% of patients present with typical gout attacks but have serum uric acid levels lower than the above levels. There are three explanations: ① The temperature gradient between the core body temperature and the peripheral joint temperature is large; ② The body is in a state of stress and secretes more adrenal cortical hormones, which promotes the excretion of serum uric acid, while the sodium urate content in the distal joints is still relatively high; ③ The influence of treatment with uricosuric drugs or corticosteroids.

3. Determination of Uric Acid Content in Urine

In the case of a purine-free diet and without taking medications that affect uric acid excretion, the total uric acid content in the urine of a normal male adult within 24 hours does not exceed 3.54mmol/(600mg/24h). 90% of primary gout patients have uric acid excretion of less than 3.54mmol/24h. Therefore, normal uric acid excretion cannot rule out gout, but uric acid levels greater than 750 mg/24 h indicate excessive uric acid production, especially non-renal secondary gout. When blood uric acid levels increase, uric acid levels also increase significantly.

4. Arthrocentesis

When acute gouty arthritis occurs, fluid may accumulate in the swollen joint cavity. Extracting synovial fluid with an injection needle for examination is of extremely important diagnostic significance. The white blood cell count of synovial fluid is generally (1-7)×109/L, mainly segmented granulocytes. Regardless of whether they receive treatment or not, sodium urate crystals can still be found in the synovial fluid of most patients during the intermittent period.

(I) Polarized light microscopy

When synovial fluid is placed on a glass slide, a slowly vibrating image of birefringent needle-shaped sodium urate crystals can be seen inside or outside the cells. Using a first-stage red compensation prism, urate crystals appear yellow when the direction is parallel to the mirror axis and blue when perpendicular.

(ii) Ordinary microscopic examination

Sodium urate crystals are rod-shaped and needle-like, and the detection rate is only half that of polarized light microscopy. If heparin is added to the synovial fluid, the precipitate is centrifuged and the precipitate is examined under a microscope, the detection rate can be improved.

(III) UV spectrophotometer determination

The most valuable method for gout is to use an ultraviolet spectrophotometer to qualitatively analyze the contents of synovial fluid or suspected gouty nodules to determine sodium urate. The method is to first determine the absorption spectrum of the sample to be tested, and then compare it with the absorption spectrum of known sodium urate. If the two are the same, the substance being measured is a known compound.