Rapid quantitative method using spin columns to measure porphobilinogen in urine.

BACKGROUND Large increases of urinary porphobilinogen (PBG) indicate acute porphyria, which may be due to acute intermittent porphyria, variegate porphyria, or hereditary coproporphyria. These conditions are relatively rare but share symptoms with more common conditions, such as acute surgical abdomen, and often must be ruled out rapidly. Reported quantitative methods for PBG measurement are time-consuming and inconvenient. We developed a rapid quantitative method that uses resin-packed spin columns to measure PBG in urine. METHOD We applied urine to anion exchange resin in a spin column, then performed centrifugal separation and washing. PBG was eluted in 1 mol/L acetic acid and reacted with Ehrlich's reagent. After 5 min, we measured absorbance at 525, 555, and 585 nm. PBG concentration (mg/L) was calculated as 88 (A(555) - (1/2)(A(525) + A(585))). RESULTS The reportable PBG concentration range was 0.2-15 mg/L. Between-day (total) imprecision (CV) was 8.4% at 1.2 mg/L and 3.5% at 4.4 mg/L. Comparison with our established method (x) yielded a Deming regression equation: y = 1.04x - 0.01 mg/L (R(2) = 0.98; S(y,x) = 0.87 mg/L). No interference was noted from urobilinogen or highly colored urine specimens. CONCLUSIONS This method for PBG measurement is more rapid and precise than other methods. This test can serve as a quick screening test and facilitates batch analysis for routine quantitative testing.