Renal Function Physiology

Laboratory assessement of

Gout is a syndrome caused by the inflammatory response to deposition of monosodium urate crystals (MSU) in and around joints and soft tissues or crystallization of uric acid in the urinary tract. .

Uric acid is the normal end product of the degradation of purine compounds.

Certain foods are high in purines, which increase uric acid production

Beer.Sardines.Dried beans.Red meat.Gravies.Mushrooms .Spinach.

Asparagus.Fish eggs.Anchovies.Herring.Yeast.Organ meat.Cauliflower.

Serum Uric Acid: normal values range from 4.0 to 8.6 mg/dl in men to 3.0 to 5.9 mg/dl in women.

Why It Is Done?: A uric acid blood test is done to: Diagnosis of gout. Check to see if kidney stones may be caused by high

uric acid levels in the body. Follow up of the effect of therapy for gout. Check uric acid levels in people who are undergoing

chemotherapy or radiation therapy. These treatments destroy cancer cells that then may leak uric acid into the blood.

Some medicines may increase the level of uric acid in the blood. These include diuretics, theophylline, low-dose aspirin (75 to 100 mg daily), and pyrazinamide (antituberculous).

The vitamin niacin, high doses of vitamin C, caffeine, and a substance found in chocolate and tea (theobromine) can cause uric acid levels to be inaccurately high.

Excessive use of alcohol, starvation, a high-protein diet, or strenuous exercise can raise the level of uric acid in the blood.

24 urine collection for uric acid determination: is useful in assessing the risk of renal stones and planning for

therapy and useful in patients being considered for uricosuric therapy or if cause of marked hyperuricemia needs investigation .

Urinary levels are normal below 750 mg/ 24h. Urinary levels above 750 mg/dl in 24h in gout or > 1100 mg/dl in

asymptomatic hyperuricemia indicates urate overproduction. Patients who excrete more than 1100 mg in 24 hours should

undergo close renal function monitoring because of the risk of stones and urate nephropathy.

Urinalysis: Patients with gout are at an increased risk of renal stones; therefore, these patients may have a history of hematuria.

Synovial Fluid Aspiration: in acute gout it is inflammatory (>2000 cells/ml); MSU crystals are identified with the polarized light microscope. Needle shaped crystals of monosodium urate monohydrate that have been engulfed by neutrophils .

The MSU crystals do not exclude the possibility of septic arthritis, for this reason it is also recommended to request a Gram smear.

Polarized microscopy, the crystals appear as bright birefringent crystals that are yellow (negatively birefringent).

Uric acid in the sample originates, by means of the coupled reactions described below, a coloured complex that can be measured by spectrophotometry

Uric acid + O2 + 2H2o→ Alantoin + CO2 + H2O2

2H2O2 + 4-aminoantipyrine + DCFS → Quinoneimine + 4 H2O