We present a case of unusual renal failure in a patient affected by monoclonal component.
A 69-year-old man was admitted in our Nefrology Unit for the work up of a known but cryptogenic renal failure. In 2014 his creatinine was 0,98 mg/dl.
A prerenal o posternal origin of the kidney injury or a drug nephrotoxicity were excluded, and urinalysis was completely normal. A monoclonal gammopathy IgM kappa and lambda IgG is detected, Bence-Jones proteinuria was absent. Renal ultrasound resulted normal. The determination of glucose in plasma resulted always <40 mg/dl. In January 2016 his creatinine was 2,9 mg/dl, and the patient was admitted in our Unit to undergo renal biopsy. Biohumoral analysis confirmed hypercreatininemia (3,1 mg/dl) and showed a low C3 (31 mg/dl) and a complete consumption of C4 (0 mg/dl); other analysis were normal.
We perform a kidney biopsy that showed about 27 glomeruli with normal features and a lymphoid infiltrate predominantly CD20 positive in the interstitium. IF was negative. While waiting for histological examination results, we hypothesized that also the measurement of creatinine was affected by a problem in the analytical phase.
Performing the determination of creatinine on a serum sample, it resulted 1,3 mg/dl, eGRF 56 ml/min/1,73 mq (CKD-EPI 2009).
Alteration in glucose measurement, depending on type of test tube or anticoagulant, made us thinking that also creatinine measurement was altered. In our laboratory an enzymatic method is used and the blood is collected in standard tubes.
IgM interference in creatinine measurement is not well understood. It has been proposed that IgM component complexes with reagents, or causes an increased turbidity.
Performing an alternative method to estimate renal function (dosing Cystatine C or measuring inulin clearance) is not always possible, so, as showed in our case report, creatinine may be dosed in serum sample.
