CgA100 - eGFR-adjusted serum chromogranin A

The concentration of chromogranin A in serum (s-CgA) is a general marker of neuroendocrine neoplasms. Unfortunately, s-CgA is increased in several other clinical conditions, including renal failure. The physician who assesses s-CgA values must consider the patients' renal function. How this should be done is not clear. We developed an adjustment formula from the association between median s-CgA and the estimated glomerular filtration rate (eGFR) in 2708 patients where s-CgA was measured by the CgA II KRYPTOR method. We used multivariable fractional polynomial quantile regression with the model ln(s-CgA) = c(0) + c(1) x sex + c(2) x age + c(3) x eGFR, thus accounting for sex and age. The final adjustment formula could be simplified to s-CgA(100) = (eGFR / 100) x s-CgA, where s-CgA(100) is an indication of what s-CgA would be if eGFR in the same patient was 100 mL/minute/1.73 m(2). In patients with eGFR > 100 mL/minute/1.73 m(2) no adjustment was done. We tested the formula on another patient population (n = 1563), where s-CgA was measured by a RIA method. S-CgA(100) proved to be independent of eGFR in that population. The clinical validity of s-CgA(100) must await further investigations.