Uric acid is a natural compound and a waste product generated from the breakdown of purines, which are found in the body’s cells and many foods. This process is known as purine metabolism. Most uric acid dissolves in the blood, travels to the kidneys, and is filtered out into the urine for elimination. Measuring the concentration of this substance in the blood or urine assesses the body’s metabolic function and overall health.
The Role of Uric Acid in the Body
Uric acid is the final product of purine catabolism, starting with the breakdown of nucleic acids (DNA and RNA) from dying cells and purines consumed through diet. The enzyme xanthine oxidase converts purine precursors into uric acid. Though it is a waste product that must be excreted, uric acid also functions as a powerful antioxidant in the bloodstream, protecting cells from damage caused by free radicals. The body maintains a balance between production and excretion, with approximately 70% of the daily total eliminated by the kidneys and the rest cleared through the gastrointestinal tract.
Defining Normal Range and Testing
The level of uric acid in the blood, known as serum uric acid, is the most common measurement used to determine if levels are within a normal range. Reference ranges vary slightly between laboratories, but general guidelines exist for adult men and women.
For adult males, the typical range is approximately 3.5 to 7.2 milligrams per deciliter (mg/dL). For adult females, the normal range is generally lower, falling between about 2.6 and 6.0 mg/dL. This gender difference is due to estrogen, which offers a protective effect that keeps levels lower in premenopausal women. After menopause, women’s levels tend to rise, approaching those of men.
Uric acid levels are measured using a blood test or a 24-hour urine collection. The serum test measures the concentration of uric acid at the time of collection. The 24-hour urine test requires collecting all urine over a full day to measure the total amount excreted by the kidneys. This measurement helps determine if an elevated blood level is due to overproduction or underexcretion by the kidneys. A normal 24-hour urinary uric acid excretion typically ranges from 250 to 750 mg.
Understanding Elevated Uric Acid Levels
When serum uric acid levels consistently rise above the normal range, the condition is known as hyperuricemia. This is often defined as a level above 7.0 mg/dL in men and above 6.0 mg/dL in women. Hyperuricemia results from two main causes: the overproduction of uric acid or its underexcretion by the kidneys. Underexcretion is the dominant mechanism, accounting for the vast majority of cases where the kidneys struggle to eliminate the compound efficiently. Overproduction is less common and is often associated with high rates of cell turnover seen in certain medical conditions.
Sustained high levels are concerning because concentrations above 6.8 mg/dL exceed the physiological saturation threshold in the body. At this point, uric acid can precipitate out of the blood and form monosodium urate crystals. These microscopic crystals primarily deposit in the joints and surrounding tissues, leading to gout, a painful inflammatory arthritis characterized by sudden, severe joint pain, often starting in the big toe.
Chronic hyperuricemia can also lead to the formation of tophi, which are hard deposits of uric acid crystals beneath the skin. Furthermore, elevated uric acid can crystallize within the urinary tract, contributing to the formation of kidney stones. Chronic hyperuricemia is also linked to an increased risk of other health issues, including hypertension, metabolic syndrome, and cardiovascular disease.
Factors Influencing Uric Acid Levels
Uric acid levels are sensitive to biological processes and external influences such as diet and lifestyle. Dietary intake of purine-rich foods is a significant source of the compound, as these purines are broken down into uric acid. High-purine foods that can raise levels include red meat, organ meats, and certain types of seafood and shellfish. Alcohol consumption, particularly beer and liquor, also contributes to elevated levels by increasing production and reducing kidney excretion. Fructose, found in honey, fruit, and sugary beverages, can quickly increase uric acid levels as its metabolism releases purines.
Maintaining proper hydration is important because water helps the kidneys dilute and excrete the compound efficiently. Certain medications, such as some diuretics and low-dose aspirin, can affect the kidney’s ability to excrete uric acid, leading to higher blood levels. Weight management is also a factor, as obesity and a lack of physical activity are associated with elevated uric acid. A low uric acid level, called hypouricemia, is relatively rare and less clinically concerning than hyperuricemia, though it can be associated with genetic conditions or specific medications.