The need for vigilance: false-negative screening for adenylosuccinate lyase deficiency caused by deribosylation of urinary biomarkers.

OBJECTIVES: Adenylosuccinate lyase deficiency (dADSL) is a rare inherited metabolic disorder. Biochemical diagnosis of the disease is based on the determination of enormously elevated urinary levels of succinylaminoimidazole carboxamide riboside (SAICA-riboside) and succinyladenosine (SAdo). We report a case of false negative screening for dADSL caused by deribosylation of the urinary biomarkers SAICA-riboside and SAdo. DESIGN AND METHODS: A thin-layer chromatography (TLC) method with Pauly reagent detection of SAICA-riboside was used as a screening method. High-performance liquid chromatography with diode-array detection (HPLC-DAD) and LC-MS/MS methods were used for the identification and quantitative determination of SAICA-riboside, SAdo, succinylaminoimidazole carboxamide (SAICA) and succinyladenine (SA). RESULTS: Following a negative TLC screening in a known case of dADSL, we analyzed urine using HPLC-DAD. The concentration of SAICA-riboside was 2.7mmol/mol creatinine (below the TLC detection limit), and we detected the two abnormal metabolites identified by LC-MS/MS as SAICA and SA. We showed that SAICA and SA were produced by deribosylation of SAICA-riboside and SAdo in the patient's urine. Studies performed by monitoring the production of SAICA and SA after the addition of SAICA-riboside and SAdo to the patient's urine and to urine samples from patients with urinary tract infections suggested that deribosylation is facilitated by bacterial enzymes. CONCLUSIONS: Screening methods for the diagnosis of dADSL may be falsely negative due to bacteria-mediated deribosylation of SAICA-riboside and SAdo. HPLC-DAD or LC-MS/MS analyses allowing for simultaneous detection of SAICA-riboside, SAdo and their deribosylation products SAICA and SA should be preferentially used for the diagnosis of dADSL in urine.

[Detection of urinary tract infection using Uro-Quick system and quantitative dilution method]. / Detekce mocových infekcí systémem Uro-quick a kvantitativní stanovení redicí metodou.

BACKGROUND: Significant bacteriuria is very important marker of urinary tract infection. The standard method for diagnosis of UTI is quantitative urine culture and identification of bacteria. For rapid enumeration of bacteria in urine semiautomatic systems were developed. Aim of the study was to compare the results of the conventional urine culture method with nephelometric enumeration of bacterial cells in urine. MATERIAL AND METHOD: Urine samples were evaluated simultaneously by Uro-Quick and quantitative urine culture. RESULTS: In summary 1 653 urine samples were elaborated, 402 (83.05 %) from 484 positive samples had positive results in Uro-Quick. Sensitivity of Uro-Quick was 0.83, specificity 0.95, positive predictive value 0.85, negative predictive value 0.93 and accuracy 90.68. Culture time extension improved statistical performance characteristic of Uro-Quick. Problem of the method is the detection of the low amounts of microorganisms. Uro-Quick did not detected microbial growth in 16.77 % of samples containing >/= ten to the fourth CFU/ml of microorganisms. The advantage of Uro-Quick is the speed, 73.93 % of the samples with high microbial concentrations (>/= ten to the fifth CFU/ml) were detected in three hours. CONCLUSION: Uro-Quick offers rapid detection of urine samples with high microbial concentrations, but did not replace the quantitative culture of. Nephelometric detection is necessary to complete with agar plate cultivation.