Background: Several acquired and congenital human disorders perturb the concentrations of delta-aminolevulinate (delta-ALA), creatinine and tyrosine in biological fluids. There is currently no facile, sensitive and specific method to measure these analytes simultaneously.
Method: We developed an LC-MS/MS method to quantify delta-ALA, creatinine and tyrosine in urine that requires minimal sample preparation and no derivatization. The method is also applicable to the analysis of tyrosine in plasma.
Results: All calibration plots were linear, with R(2)>or=0.996. Intra- and interday CVs were <10%. The limit of quantitation for delta-ALA was approximately 0.1 micromol/l, and for creatinine and tyrosine it was well below the lowest measured physiological concentrations. The method was applied to analyze urine from 75 healthy volunteers and 43 patients with hereditary tyrosinemia type I (HT I). The mean urinary concentration of delta-ALA in patients (38+/-35 micromol/l, 53+/-30 mg/g creatinine) was higher than that measured in healthy subjects (5.5+/-2.6 micromol/l, 0.9+/-0.2 mg/g creatinine; p<0.001). Treatment with 2-(2-nitro-4-trifluoromethylbenzyl)-1,3-cyclohexanedione (NTBC), an inhibitor of an early step in tyrosine catabolism, decreased urinary delta-ALA (6.4+/-4.8 micromol/l, 13+/-24 mg/g creatinine; p<0.001). The average plasma tyrosine concentration in healthy volunteers (56+/-14 micromol/l) was within normal reference interval used in clinical practice.
Conclusions: The method is simple, specific and precise and allows simultaneous quantitation of delta-ALA, creatinine and tyrosine at concentrations present under physiological or pathophysiological conditions.