Increased urinary excretion of the CD80 protein was found in all patients with active kidney diseases, including Alport syndrome, in a recent study, rendering the protein an unreliable diagnostic biomarker to differentiate between renal diseases, the researchers report.
The study, “The utility of urinary CD80 as a diagnostic marker in patients with renal diseases,” was published in the journal Scientific Reports.
Previous reports have suggested that measuring the levels of urine CD80 protein, which is found in certain immune cells, could be used as a potential biomarker to distinguish between patients with different kidney diseases, such as relapsing forms of minimal change disease, from other renal diseases, including focal glomerulosclerosis. However, more recent studies have failed to reproduce these initial findings.
Now, a group of Japanese researchers have investigated the potential diagnostic value of CD80 to differentiate patients with various renal diseases, including Alport syndrome.
The team collected a total of 55 urine samples, including those from 31 patients with minimal change disease, four patients with focal segmental glomerular sclerosis, four patients with inherited nephrotic syndrome, and five Alport syndrome patients.
The levels of CD80 in the urine — measured in nanograms (ng) and relative to grams (g) of creatinine (Cr), another urine-excreted protein — were significantly higher in patients with minimal change disease (mean of 91.5 ng/gCr), focal glomerulosclerosis (mean of 376.2 ng/g Cr), and inherited syndromes (mean of 220.1 ng/gCr) compared with patients with minimal change disease in remission (mean of 29.5 ng/gCr).
In comparing urinary CD80 values between active minimal change disease and other renal diseases, the researchers found no differences.
To better understand if the elevated levels of urinary CD80 could be related to the levels of this protein in the blood, the researchers measured CD80 level in the blood samples of 15 patients. They found no correlation with the amount of protein in these patients’ urine.
Moreover, in patients with higher levels of urinary CD80 (above 1,000 ng/gCr), the protein’s blood levels remained at a normal range (20-320 pg/mL).
Because urinary protein loss, or proteinuria, is a hallmark of renal disease, the team also explored whether CD80 urinary levels were a result of total protein in the urine. A positive correlation was found for samples of minimal change disease in relapse, focal segmental glomerular sclerosis, and inherited syndromes including Alport, which suggests that CD80 level might reflect glomerular damage severity.
In contrast with previous reports, “measuring urinary CD80 levels is not a reliable marker for the differential diagnosis of minimal change disease in relapse and other kidney diseases,” the researchers concluded.