Homogentisic acid interference in routine urine creatinine determination.

Prior research has shown that the Jaffe reaction is commonly used to measure creatinine in urine. However, this method can produce falsely elevated results due to non-creatinine chromogens. No prior work had resolved the impact of alkaptonuria on newer enzymatic methods. This gap motivated the investigation of how homogentisic acid affects enzymatic creatinine measurements. It was already known that alkaptonuric patients excrete high levels of homogentisic acid in urine. The uncertainty remained about whether this compound interferes with enzymatic assays. Previous studies did not address the comparative accuracy of enzymatic versus Jaffe methods in this context. This paper's contribution clarifies the specific interference mechanism in enzymatic assays.

The aim was to assess the impact of homogentisic acid on enzymatic creatinine measurements in alkaptonuric patients. The specific problem addressed was the discrepancy observed when switching from Jaffe to enzymatic methods. This uncertainty arose after implementing the new automated enzymatic method in the laboratory. The motivation stemmed from the need to ensure accurate creatinine quantification in this patient group. The study sought to determine if HGA interferes with the enzymatic method. It also aimed to compare Jaffe and enzymatic results in alkaptonuric urine samples. The goal was to identify the source of the observed creatinine discrepancy. This investigation aimed to inform diagnostic protocols for alkaptonuria patients.

The study compared two creatinine measurement techniques: Jaffe reaction and enzymatic assay. Urine samples from alkaptonuric patients were analyzed using both methods. Homogentisic acid levels were confirmed via gas chromatography-mass spectrometry. The enzymatic method was performed on an automated clinical chemistry analyzer. Jaffe reaction results were obtained using a standard clinical protocol. Sample selection included patients with confirmed alkaptonuria and elevated HGA. Creatinine values were compared between the two methods for each sample. The presence of HGA interference was confirmed by correlating HGA levels with enzymatic creatinine results.

The enzymatic method yielded lower creatinine values than the Jaffe reaction in alkaptonuric samples. This difference was significant in samples with elevated homogentisic acid. Gas chromatography-mass spectrometry confirmed high HGA levels in these samples. The enzymatic method showed a mean creatinine value 25% lower than Jaffe results. This discrepancy was absent in non-alkaptonuric controls. The study found a direct correlation between HGA concentration and enzymatic creatinine underestimation. The Jaffe reaction remained unaffected by HGA presence. These findings suggest HGA specifically interferes with enzymatic creatinine assays.

The authors state that homogentisic acid interferes with enzymatic creatinine measurements in urine. This interference leads to falsely low creatinine values in alkaptonuric patients. The Jaffe reaction remains reliable for this patient population. The enzymatic method is unsuitable for creatinine determination in alkaptonuric urine. These findings suggest continued use of the Jaffe method for this specific patient group. The study confirms prior knowledge about Jaffe chromogen interference but adds new evidence about enzymatic methods. No prior work had demonstrated this specific interference mechanism. The authors propose that diagnostic protocols should account for this methodological limitation.