Uric Acid in the Body: What It Is and What It Does

Uric acid is formed during the breakdown of purines and appears on blood test reports. Understanding where it comes from and what the number means is easier step by step.

What is uric acid

Uric acid (Acidum uricum, C5H4N4O3) is colorless crystals poorly soluble in water. Carl Scheele isolated it in 1776 from urinary stones and called it lithic acid. In humans and primates, it is the end product of purine metabolism: it is formed by the enzymatic oxidation of xanthine by xanthine oxidase, whereas in other mammals it is further converted to allantoin. Small amounts are present in the brain, liver, blood, as well as in urine and sweat.

Where uric acid comes from: purines and metabolism

The body produces purines itself, and some come from food and drinks. Purines are abundant in liver, anchovies, mackerel, red meat, shellfish, dried beans and peas, and beer. When purines break down, uric acid is formed—this is how uric acid metabolism is linked to purine base metabolism. In birds, some reptiles, and most terrestrial insects, it also serves as the end product of protein metabolism.

How uric acid is excreted from the body

Most of the acid dissolves in the blood and goes to the kidneys, from where it is excreted in urine. At physiological pH, urates—its salts—predominate in solution. If the body produces too much acid or removes too little, the blood level rises: this is hyperuricemia. According to some estimates, elevated concentrations occur in about one third of the world's population.

What the accumulation of uric acid affects

The accumulation of acid and its acid salts manifests in various ways: kidney and bladder stones, gouty deposits, hyperuricemia. The deposition of sodium urate crystals in joints is called gout: it is a type of arthritis with sudden severe pain, most often in the big toe, but also in the feet, ankles, hands, elbows, and knees; the skin over the joint is hot, swollen, and red, although redness is less noticeable on dark skin. Without treatment, an attack lasts one to two weeks, subsequent attacks are longer, and over time persistent joint damage develops. With long-term untreated gout, tophi occur—nodules under the skin on the ears, fingers, or elbows—as well as kidney stones and chronic arthritis, although the latter is rare.

Gout itself is not a reason to call an ambulance; 103 or 112—if sudden pain and swelling in a joint are accompanied by very high fever, chills, nausea, or inability to eat, and the pain intensifies: such signs may indicate an infection inside the joint.

Why uric acid rises

There are many causes: dehydration, alcohol, excess weight, kidney disease, psoriasis, certain medications including diuretics, excessive physical exertion, purine-rich food, hypothyroidism, hyperparathyroidism, polycythemia, leukemia. A gout attack can be triggered by a febrile illness, joint injury, dehydration, excess alcohol, or a very heavy meal.

• gout is more common in men, especially with age;
• the risk is higher in people with excess weight and in women after menopause;
• high cholesterol, high blood pressure, kidney disease, osteoarthritis, and diabetes matter;
• sometimes gout runs in families;
• some medications, including diuretics and blood pressure drugs, increase the chances.

How it is determined in a blood test and when to see a doctor

The blood level is examined, and it can also be checked in urine. Blood is taken from a vein on the inner side of the elbow or the back of the hand; do not eat or drink for four hours before the test unless the doctor says otherwise. Reference ranges: 3.0–7.1 milligrams per deciliter in women and 4.0–8.6 milligrams per deciliter in men; in other units—no higher than 360 µmol/L in women and 420 µmol/L in men. Laboratories provide different ranges, so the numbers are discussed with a doctor; for those being treated for gout, a level below 6 milligrams per deciliter or 5 milligrams per deciliter is considered the target depending on the clinical picture.

See a doctor at the first attack of joint pain and if the usual treatment stops helping. At the appointment, they ask about diet and alcohol and order a blood test for uric acid. If the picture is unclear, they refer to a rheumatologist: joint fluid is taken with a thin needle or, when this is impossible, imaging is ordered.

Questions for the appointment: what my number means specifically with my conditions and medications, whether the test needs to be repeated, and which doctor to see next.

This material is for reference and does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer