Longer Tc-99m-mebrofenin labeling-to-administration time results in scintigraphic underestimation of liver function

Objective: Tc-99m-mebrofenin clearance rate is used to estimate hepatocellular function. This investigation studied effect of labeling-to-administration (LTA) time of Tc-99m-mebrofenin and its liver clearance rate. Methods: A total of 15 patients, age 46 ± 13 (range, 19-69) years, referred for routine gallbladder ejection fraction testing, were retrospectively studied. All had tests associated to normal liver, and no medical history of liver diseases was observed. Tc-99m-mebrofenin scintigraphic liver clearance (MSLC) rate was determined by the standard technique based on liver uptake rate. The radiopharmaceutical was prepared at an off-site central radiopharmacy. Linear regression was used to assess relationship of LTA time and MSLC. Results: The LTA was 7.6 ± 2.0 (range, 4-12) hours. The labeling efficiency was 99.0% ± 1.33%. The MSLC rate was 11.9%/min ± 2.7%/min (range, 6.4-18.3). There was an inverse relationship of LTA and MSLC, expressed in the following equation: y = -0. 97x + 19.25 (R² = 0.5076, P = 0.0028). The negative correlation with LTA remained when MSLC was corrected for body surface area (R² = 0.4241, P = 0.0085). Conclusion: There is a significant underestimation of MSLC with increasing LTA time. If liver function assessment is the purpose of a hepatobiliary study, Tc-99m-mebrofenin should be administered as close to the time of radiopharmaceutical preparation as possible, preferably within 1 hour.