Reproducibility of 99Tcm-MAG3 clearance in normal volunteers with the two-sample method: comparison with 131I-OIH

Monitoring renal function: a prospective study comparing camera-based technetium-99m mercaptoacetyltriglycine clearance and creatinine clearance

OBJECTIVES

To determine the value and limitations of technetium-99m mercaptoacetyltriglycine (MAG3) clearance measurements obtained using a gamma camera (camera-based MAG3 clearance), a prospective study was conducted to evaluate the reproducibility of camera-based MAG3 clearance compared with that of conventional creatinine clearance.

METHODS

A total of 24 male patients with stable renal function were entered into the study. The mean age was 66.5 +/- 7.9 years, and the mean serum creatinine was 1.38 +/- 0.57 mg/dL. MAG3 renal scans and 24-hour creatinine clearance measurements were performed 11 +/- 8 days apart. A camera-based MAG3 clearance was obtained at each MAG3 scan; no blood samples were required. Bland-Altman plots were constructed to assist in data analysis.

RESULTS

The Pearson correlation for the first and second camera-based MAG3 clearances (mean 151 versus 158 mL/min/1.73 m2, respectively) was 0.965 compared with 0.729 for the two creatinine clearance measurements (mean 62 versus 72 mL/min/1.73 m2, respectively). Even with the omission of two outliers, the creatinine clearance would have to change by 58.2% compared with the baseline measurement before the clinician could be confident the change exceeded the error of measurement. In contrast, the change required for the camera-based MAG3 clearance was 30.8%.

CONCLUSIONS

The results of this study have demonstrated that MAG3 clearance obtained using a camera-based technique shows greater precision than the conventional creatinine clearance and is superior to the conventional creatinine clearance for monitoring changes in renal function.

Reproducibility of technetium-99m mercaptoacetyltriglycine clearance in patients with impaired renal function

BACKGROUND

The aim of this study was to determine the reproducibility of technetium-99m mercaptoacetyltriglycine (99mTc-MAG3) clearance in patients with a 99mTc-MAG3 clearance below 100 ml/min/1.73 m2.

METHODS

Two separate multi-sample clearance studies were performed in 16 patients at a 1 week interval. The clearances were calculated according to the open two-compartment model of Sapirstein et al., accepting the 90, 120 and 180 min samples as the last points of the biexponential curve. The clearance measurements were also performed according to the single-sample methods of Russell et al. and Bubeck using the fitted value at 44 min.

RESULTS

There was no significant difference between the two clearance measurements for all five samples (P>0.05). There was a systematic increase in clearance measurements of 8.0+/-2.7% from the 180 to 120 min samples and 4.8+/-2.0% from the 120 to 90 min samples. Both single-sample methods (Bubeck and Russell et al.) gave more divergent results than multi-sample methods. The mean and standard deviation (%) of the normalized differences between two successive tests were -3.9+/-12.6, -2.4+/-13.1, -1.9+/-14.9, -4.1+/-53.5 and -13+/-82.1 for 90, 120 and 180 min samples and the Russell et al. and Bubeck methods, respectively.

CONCLUSION

Single-sample methods give very poor reproducibility and accuracy and should not be used in patients with poor renal function. The reproducibility of 99mTc-MAG3 clearance using the multi-sample method (90 min) in patients with impaired renal function is 12.6%, which is similar to that in patients with good renal function and that obtained with other tubular agents. Whether this level of reproducibility is satisfactory for documenting serial changes in an individual patient with a 99mTc-MAG3 clearance below 100 ml/min/1.73 m2 depends on the expectation of the clinician.