84550

Uric Acid; Blood

CPT code 84550 refers to the quantitative measurement of uric acid levels within a patient's blood sample, typically serum or plasma. Uric acid is the primary metabolic end product of purine catabolism in humans. Purines are nitrogen-containing compounds found in certain foods, such as red meats, organ meats, and shellfish, and are also released during the natural breakdown and turnover of the body's cells. Under normal physiological conditions, uric acid dissolves in the blood, is processed by the kidneys, and is excreted in the urine. However, when the body produces too much uric acid or the kidneys fail to excrete it efficiently, hyperuricemia occurs. This elevation can lead to the precipitation of monosodium urate crystals in joint spaces, causing the inflammatory condition known as gout, or in the renal tubules, resulting in kidney stones (urolithiasis). Conversely, low levels (hypouricemia) may be seen in conditions such as Fanconi syndrome or liver disease. The clinical utility of this test is broad; it is essential for the diagnosis and longitudinal management of gout, the evaluation of renal function, and the monitoring of patients undergoing cytotoxic chemotherapy. In oncology, rapid cell turnover during treatment can lead to Tumor Lysis Syndrome, where a massive release of intracellular purines causes a dangerous surge in serum uric acid levels, potentially leading to acute renal failure. The laboratory process involves a standard venipuncture. Once the specimen is collected, the laboratory utilizes enzymatic methods, most commonly the uricase method. In this reaction, the enzyme uricase catalyzes the oxidation of uric acid to allantoin and hydrogen peroxide. The resulting chemical change is measured spectrophotometrically to determine the concentration, typically reported in milligrams per deciliter (mg/dL).

Clinical Indications

  • Diagnosis and management of gout (gouty arthritis)
  • Evaluation and prevention of uric acid kidney stones (nephrolithiasis)
  • Monitoring patients undergoing chemotherapy or radiation for leukemia or lymphoma (Tumor Lysis Syndrome)
  • Assessment of renal function and chronic kidney disease (CKD)
  • Evaluation of preeclampsia in pregnant women
  • Screening for metabolic syndrome and related cardiovascular risks
  • Investigation of inherited disorders of purine metabolism (e.g., Lesch-Nyhan syndrome)
  • Monitoring the efficacy of urate-lowering therapies such as allopurinol or febuxostat

Procedure Steps

  1. Verify the patient's identity using at least two identifiers.
  2. Perform a standard venipuncture, typically using a serum separator tube (SST) or a heparinized plasma tube.
  3. Allow the SST blood sample to clot for approximately 30 minutes at room temperature.
  4. Centrifuge the specimen to separate the serum or plasma from the cellular components.
  5. Transfer the serum or plasma to a secondary tube if required by laboratory protocols.
  6. Introduce the sample into an automated chemistry analyzer.
  7. Apply the uricase enzyme reagent to the sample to initiate the oxidation of uric acid into allantoin.
  8. Measure the absorbance change spectrophotometrically at a specific wavelength (usually 293 nm or through a colorimetric secondary reaction).
  9. Calculate the uric acid concentration based on the rate of absorbance change compared to a standard.
  10. Review and release the quantitative result via the Laboratory Information System (LIS).

Coding Guidelines

  • Code 84550 should be used for the quantitative measurement of uric acid in blood (serum or plasma).
  • For the measurement of uric acid in a urine specimen, use CPT code 84560 instead.
  • Uric acid (84550) is not a component of the Basic Metabolic Panel (80048) or the Comprehensive Metabolic Panel (80053) and must be reported separately if performed.
  • If the test is repeated on the same day for clinical monitoring (e.g., in acute Tumor Lysis Syndrome), append modifier -91 to the subsequent tests.
  • Ensure that the medical necessity is documented in the patient's record, as screening for asymptomatic hyperuricemia may not be covered by all payers.

Associated ICD-10 Codes