Can serum uric acid concentration be used to screen for syndrome of inappropriate antidiuretic hormone secretion (SIADH)?

Updated: Aug 16, 2019
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Measurement of the serum uric acid concentration has been suggested as a screening procedure in patients with hyponatremia secondary to SIADH. Hypouricemia (uric acid < 4 mg/dL) is frequently observed in patients with SIADH during the period of hyponatremia. However, hypouricemia lacks sensitivity and specificity for making the diagnosis of SIADH.

Calculation of the fractional excretion of uric acid (FEUA) may prove useful. [28] The FEUA is defined as the percentage of urate filtered by glomeruli that is excreted in urine. The formula is as follows:

(Urinary uric acid [mg/mL] × serum creatinine [mg/mL] ÷ (serum uric acid [mg/mL] × urinary creatinine [mg/mL])  × 100% = FEUA

An increase in FEUA (usually >9%) occurs as a result of volume expansion and a decrease in distal tubular reabsorption. In contrast, the serum uric acid is usually increased in hypovolemia. Hypouricemia and an elevated FEUA may be seen in either salt-wasting syndromes or SIADH. However, hypouricemia and elevation of the FEUA typically resolve after correction of hyponatremia in patients with SIADH, but persist in  those with salt-wasting syndromes.

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