ALB and chronic kidney disease: It is possible that the elevated levels of P-NfL are a consequence of impaired renal clearance, as proposed by others.7 However, the similarity in size between NfL (68 kDa16) and albumin (67 kDa) indicates that clearance should mainly be altered in patients with albuminuria and not all patients with CKD because proteins of this size do not normally pass the glomeruli.