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) = c₀ + c₁ × sex + c₂ × age + c₃ × eGFR, thus accounting for sex and age. The final adjustment formula could be simplified to s-CgA₁₀₀ = (eGFR / 100) × s-CgA, where s-CgA₁₀₀ is an indication of what s-CgA would be if eGFR in the same patient was 100 mL/minute/1.73 m². In patients with eGFR > 100 mL/minute/1.73 m² no adjustment was done. We tested the formula on another patient population (n = 1563), where s-CgA was measured by a RIA method. S-CgA₁₀₀ proved to be independent of eGFR in that population. The clinical validity of s-CgA₁₀₀ must await further investigations.