Researchers regard 24-hour proteinuria collection best for amyloid light chain amyloidosis
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The association between 24-hour collection and urine protein-to-creatinine ratio was moderate for mearing proteinuria levels in patients with amyloid light chain amyloidosis, according to data published in Kidney Medicine.
Further, researchers recommended that the 24-hour urine proteinuria measurement be continued for most amyloid light chain (AL) amyloidosis patients.
“In AL amyloidosis quantification of proteinuria is used for diagnosis of amyloid deposition, assessment for the severity of the involvement (kidney staging) and organ response to therapies,” Andrea Havasi, MD, from the Amyloidosis Center at Boston University School of Medicine, and colleagues wrote. They added, “Given that many patients with AL amyloidosis have a wide range of proteinuria, often in the nephrotic range, this study is set to examine the correlation between 24-hr urine testing and [urine protein-to-creatinine ratio] UPCR at various proteinuria levels in patients with AL amyloidosis.”
In a retrospective study, researchers evaluated data for 265 patients with systemic AL amyloidosis who visited the Amyloidosis Center at Boston University Medical Center between July 1, 2018, and Jan. 1, 2020. All patients underwent proteinuria measurement by 24-hour collection and UPRC in the same day.
Using linear regression analysis with Pearson’s correlation coefficient, researchers determined the association between 24-hour urine samples and UPCR at ranging proteinuria levels. Researchers categorizeded patients into three cohorts based on their 24-hour urine proteinuria (<500 mg/day, 500 mg/day-3,000 mg/day and >3,000 mg/day).
Analyses revealed the median proteinuria was 598 mg/day with a median serum creatinine of 1.2 mg/dL and eGFR of 55.4 mL/min/1.73 m². Patients in the less than 500 mg/day cohort (n=126) showed a median proteinuria of 87.5 mg with a median creatinine of 1.1 mg/dL and eGFR of 59.9 mL/min/1.73 m². Those in the 500 mg/day to 3,000 mg/day cohort (n=53) showed a median proteinuria of 1,202 mg/day with a median creatinine of 1.42 mg/dL and eGFR of 50.31 mL/min/1.73 m². Lastly, those in the cohort of more than 3,000 mg/day (n=86) showed a median proteinuria of 6,148 mg/day with a median creatinine of 1.34 and eGFR of 48.55 mL/min/1.73 m².
The association was moderate in the 500 mg/day to 3,000 mg/day cohort and researchers identified the Pearson correlation coefficient as 0.57. Researchers determined that replacing the 24-hour urine with UPCR changed kidney staging in 10% of patients (77% were re-classified to a worse kidney stage and 23% to a better stage).
“In summary, although 24-hour urine collection is cumbersome, we continue to recommend it in patients with AL amyloidosis and kidney involvement. This population often has nephrotic range proteinuria, and we demonstrate that the correlation between 24-hour urine and spot urine measurement is weaker in this group,” Havasi and colleagues wrote. “Replacing 24-hr urine collection with UPCR changes the diagnosis of kidney involvement, kidney staging and determining organ response in some patients. Using UPCR for diagnosis, staging and determining kidney response would require validation in larger studies involving AL amyloidosis patients.”
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