Diagnosis of Gout with Laboratory Tests, X-rays and Aspiration Biopsy

Gout is an inflammatory arthritis disease caused by too much of uric acid in the blood. This leads to the deposit of uric acid crystals in the joint, which leads to gout symptoms. The joint that is most affected is the metatarsophalangeal joint of the big toe.

The diagnosis of gout or gouty arthritis as it is also called is based on a series of investigations, which confirm the presence of gout. Most of the times, the presenting symptoms are enough for your doctor to more or less confirm the diagnosis.

Again, harboring of risk factors can also help the doctor to come closer to diagnosing gout. These include:

  • Being overweight or obese
  • Eating purine-rich foods such as asparagus, dried beans, sardines, gravy, beer, and animal organs such as liver
  • Alcohol abuse
  • Certain medications

Nevertheless, laboratory tests for gout are needed to erase any lingering doubt about gout diagnosis. There are more than 200 forms of arthritis, which cause pain, swelling and inflammation of joints and gout has to be identified from amongst them.

Differential diagnosis 

Gout can be mistaken for other conditions, which share similar symptoms. The differential diagnoses include:

  • Rheumatoid arthritis
  • Pseudogout, which is again a crystal-induced arthritis
  • Psoriatic arthritis
  • Arthritis due to bacterial infection
  • Systemic lupus

Rheumatoid arthritis and systemic lupus attack more than one joint while gout usually attacks one joint at one time.

The diagnosis of gout is confirmed by laboratory tests of blood, urine and the fluid that accumulates in the affected joint.

Blood Tests for Gout

Blood serum is tested for uric acid levels. The rise in uric acid levels along with the typical gout symptoms is strongly suggestive of the presence of gout.

However, uric acid levels may be normal even during a gout attack or there may be raised uric acid levels without the presence of gout. It may take four to six weeks after a gout attack for uric acid levels to rise.

Blood is also tested for creatinine levels to rule out renal impairment, which can disturb the excretion of uric acid and subsequently raise its blood levels.

Urine Test for Gout

A 24-hour sample of urine is collected to measure uric acid levels. A rise in uric acid levels in urine is suggestive of excessive production of uric acid in the body. A fall in uric acid levels in urine is suggestive of improper functioning of the kidneys. Gout can be due to both these reasons.

Therefore, any abnormality of urine uric acid levels along with gout symptoms can be suggestive of gout. Any kidney stones (which are seen sometimes associated with gout) formed as a result of high serum uric acid levels will also be detected by urine tests, which will show crystals of monosodium urate.

X-ray to diagnose gout

In the early stages of gout, x-ray of the affected joint does nothing but rule out other causes of pain and swelling of the joints. The x-ray will show soft tissue swelling, which is even otherwise seen by the naked eye.

In chronic cases of gout, x-ray of the affected joint may show crystal deposits and damaged bones and cartilage caused by repeated gout attacks.

Ultrasound

A musculoskeletal ultrasound is sometimes done to detect urate crystals or tophus in the affected joint.

Needle aspiration of joint fluid

This is the only sure shot diagnostic method to confirm the diagnosis of gout. In the joints, there is the synovial fluid inside the synovial sac, which acts as a lubricant to facilitate joint movements.

This joint fluid is aspirated using a fine needle and syringe and tested for the presence of monosodium urate crystals ( derivatives of uric acid). Sometimes in an acutely swollen and painful condition, this test may not be possible.

Summary of gout diagnosis

Diagnosis of gout can be confirmed as follows.

  • Serum uric acid levels are high.
  • Urine uric acid levels are not within the normal range. They may be either raised or lowered as explained above.
  • X ray shows crystal deposits and/or damaged bones and cartilage.
  • Synovial fluid shows the presence of uric acid crystals.
  • Symptoms show that only one joint is affected.
  • Symptoms and signs of gout are similar to the ones explained in gout symptoms.