Detection of impaired renal function

Summary

Aim: Renal function is usually determined by means of creatinine-clearance, and of serum Cystatin C, the latter with increasing frequency. The present study analyses, whether the diagnostic accuracy of ^99mTc-MAG₃ clearance is comparable to that of these modern serologic methods. Patienten, Methods: 71 consecutive adult Caucasian patients (42 female, 29 male; age 50 ± 16 yrs., range 20 – 83) who were referred to a nuclear medicine department for determination of bilateral renal function with ^99mTc-MAG₃ were included. Following sufficient hydration, 10 ml of blood were taken for determination of Cystatin C and creatinine in serum prior to i.v. injection of the radiotracer. According to the recommendations of the National Kidney Foundation, glomerular filtration rate (GFR) was calculated from serum creatinine using either Cockcroft & Gault and Modification of Diet in Renal Disease (MDRD) study equation. These estimates of GFR served as reference. Cystatin C is a low molecular protein produced by all nuclear cells and is eliminated to 85 % by glomerular filtration. Analysis of ^99mTc-MAG₃ clearance was performed by means of Bubeck’s formula. Results: Linear regression analysis produced Pearson’s correlation coefficients of r = 0.68 and r = -0.69 for the comparison of either Cystatin C and ^99mTc-MAG₃ clearance with the Cockcroft & Gault equation. The comparison of Cystatin C and ^99mTc-MAG₃ clearance with MDRD study equation resulted in correlation coefficients of r = 0.755 and r = -0.77. None of these differences were significant. The exclusion of renal impairment or the detection of an at least moderate renal impairment revealed again no significant differences between Cystatin C and ^99mTc-MAG₃ clearance. Conclusions: Cystatin C and ^99mTc-MAG₃ clearance are equally suited to exclude renal impairment or to detect a relevant renal impairment. Differences between both procedures are more likely a result of the applied reference method.

Zusammenfassung

Ziel: Zur Beurteilung der Nierenfunktion wird, neben der Kreatinin-Clearance, zunehmend auch Cystatin C im Serum bestimmt. Die vorliegende Untersuchung geht der Frage nach, ob die nuklearmedizinische Clearance-Bestimmung mit ^99mTc-MAG₃ gegenüber den modernen serologischen Verfahren bestehen kann. Patienten, Methoden: Eingeschlossen wurden 71 konsekutive erwachsene kaukasische Patienten (42 Frauen, 29 Männer; Alter: 50 ± 16 Jahre), die zu einer seitengetrennten Nierenfunktionsuntersuchung mit ^99mTc-MAG₃ überwiesen wurden. Nach ausreichender Hydrierung erfolgte eine Blutentnahme zur Bestimmung von Kreatinin und Cystatin C im Serum sowie die i.v. Injektion des Radiotracers. Entsprechend den Empfehlungen der National Kidney Foundation wurde die glomeruläre Filtrationsrate (GFR) aus dem Serum-Kreatinin nach den Formeln von Cockcroft & Gault und der »Modification of Diet in Renal Disease« (MDRD)-Studie berechnet. Diese GFR-Äquivalente dienten als Referenz. Cystatin C ist ein niedermolekulares Protein, das von allen nukleären Zellen produziert und zu 85% glomerulär filtriert wird. Die Berechnung der ^99mTc-MAG_3-Clearance erfolgte nach Bubeck. Ergebnisse: Die lineare Regressionsanalyse ergab Korrelationskoeffizienten von r = 0,68 und r = -0,69 für den Vergleich von MAG_3-Clearance und Cystatin C mit der nach Cockcroft & Gault bestimmten Kreatinin-Clearance. Für die nach der MDRD Studie bestimmten Clearance betrugen die Korrelationskoeffizienten r = 0,755 und r = -0,77. Diese Unterschiede waren nicht signifikant. Zum Ausschluss einer Nierenfunktionsstörung und zum Nachweis einer zumindest mittelgradigen Nierenfunktionsstörung ergaben sich zwischen Cystatin C und der ^99mTc-MAG₃-Clearance ebenfalls keine signifikanten Unterschiede. Schlussfolgerungen: Cystatin C und ^99mTc-MAG₃-Clearance sind gleichermaßen zum Ausschluss oder zum Nachweis einer relevanten Nierenfunktionsstörung geeignet. Unterschiede ergeben sich vor allem in Abhängigkeit von der jeweiligen Referenzmethode.

Keywords

Creatinine clearance - cystatin C - ^99mTc-MAG₃ clearance

Schlüsselwörter

Kreatinin-Clearance - Cystatin C - ^99mTc-MAG₃ Clearance

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