Normal reference ranges for urinary δ‐aminolevulinic acid and porphobilinogen levels

Abstract

Acute hepatic porphyria (AHP) is a family of rare, serious, and potentially life‐threatening metabolic disorders caused by mutations in genes encoding enzymes involved in hepatic heme biosynthesis. AHP is characterized by accumulation of neurotoxic heme intermediates, δ‐aminolevulinic acid (ALA), and porphobilinogen (PBG), which are thought to be causal for the disease manifestations. Novel therapeutic treatments such as givosiran, an RNA interference therapeutic that was recently approved for treatment of adults with AHP, are focused on reducing the levels of ALA and PBG in patients toward levels observed in a healthy population. While there are two published reports on the distribution of urinary ALA and PBG levels in healthy subjects, these lacked the required details to enable the calculation of reference limits for ALA and PBG. Therefore, urinary ALA and PBG levels were quantified in 150 healthy subjects using a validated liquid chromatography tandem mass spectrometry (LC‐MS/MS) method that is highly sensitive, specific, accurate, and reproducible. These data were used to establish the upper limit of normal (ULN) values for ALA and PBG as 1.47 and 0.137 mmol/mol Cr, respectively. Relative to these ULN values, baseline urinary ALA and PBG levels in AHP patients were found to be 9.3‐ to 12‐fold, and 238‐ to 336‐fold higher, respectively. Results from this study can serve as a guide to assess the effectiveness of therapeutic interventions in lowering ALA and PBG.

Efficacy and safety of givosiran for acute hepatic porphyria: 24‐month interim analysis of the randomized phase 3 ENVISION study

“…OLE data for 1.25 and 2.5 mg/kg are pooled. Reference ranges: ALA ULN, 1.47 mmol/mol Cr; PBG ULN, 0.14 mmol/mol Cr 52 . ALA, delta‐aminolevulinic acid; Cr, creatinine; DB, double‐blind; OLE, open‐label extension; PBG, porphobilinogen; ULN, upper limit of normal…”

A Drug‐Drug Interaction Study Evaluating the Effect of Givosiran, a Small Interfering Ribonucleic Acid, on Cytochrome P450 Activity in the Liver

“… Upper limit of normal = 1.47 mmol/mol Cr for ALA and 0.137 mmol/mol Cr for PBG based on Agarwal et al 25 …”

“…Mean ALAS1 mRNA levels at baseline in the enrolled CHE subjects were elevated approximately twofold relative to that in healthy adults. 24 Similarly, mean baseline ALA and PBG levels were elevated by 5-fold and 107-fold above the upper limit of normal, 25 respectively (Table 2). Givosiran treatment resulted in a mean reduction in urine ALAS1 mRNA of 64.3% on day 36 relative to baseline.…”

“…The GMR (90% CI) values for the AUC and C max of caffeine were 3.07 (2.13-4.42) and 1.28 (1.09-1.51), respectively, indicative of statistically significant increase in caffeine exposure due to givosiran treatment (Table 3, Figure 4). Exposure of paraxanthine increased after givosiran 25 ALA, delta aminolevulinic acid; ALAS1, 5'-aminolevulinate synthase 1; mRNA, messenger RNA; PBG, porphobilinogen; SEM, standard error of the mean. a ALAS1 levels are presented as ratio relative to healthy adults.…”

Laboratory Diagnosis of Porphyria

“…The difference is probably due to the presence of contaminant molecules in the urine, which react with Ehrlich's reagent. Recently, LC-MS/MS measurements of a large number of healthy subjects established the upper limit of the normal values (ULN) of ALA and PBG as 1.47 and 0.137 µmol/mmol creatinine, respectively [50], and it was reported that during an acute attack, these values could reach 40 and 55 µmol/mmol creatinine, respectively [48]. Moreover, sample preparation using a solid-phase extraction (SPE) system allows the detection of concentrations as low as 0.05 µM [49].…”