PT  - JOURNAL ARTICLE
AU  - William C. Klingensmith III
TI  - <sup>99m</sup>Tc-Mercaptoacetyltriglycine Camera-Based Measurement of Renal Clearance: Should the Result Be Normalized for Body Surface Area?
AID  - 10.2967/jnmt.113.128124
DP  - 2013 Dec 01
TA  - Journal of Nuclear Medicine Technology
PG  - 279--282
VI  - 41
IP  - 4
4099  - http://tech.snmjournals.org/content/41/4/279.short
4100  - http://tech.snmjournals.org/content/41/4/279.full
SO  - J. Nucl. Med. Technol.2013 Dec 01; 41
AB  - Testing the rate of creatinine clearance by measuring the level of creatinine in the blood and in a 24-h urine collection is a common method of evaluating renal function. The result is routinely normalized for body surface area (BSA). Alternatively, renal clearance can be measured by 99mTc-mercaptoacetyltriglycine (MAG3) renal imaging without the need for urine collection. Frequently, the 99mTc-MAG3 camera-based result is also normalized for BSA. Methods: I evaluated the need for BSA normalization of renal clearance measurements in 99mTc-MAG3 imaging studies from both a conceptual and a mathematic point of view. Both approaches involved analyzing the effect of patient size, that is, BSA, on the factors blood volume, renal blood flow, and amount of test substance present in the blood in the creatinine clearance method compared with the 99mTc-MAG3 camera-based method. Results: Both the conceptual and the mathematic analyses were consistent with a significant difference between the creatinine and 99mTc-MAG3 approaches to measuring renal clearance. Larger patients have larger kidneys, greater renal blood flow, higher renal clearances, larger blood volumes, more muscle mass, and higher BSAs than smaller patients. However, the concentration of creatinine in the blood of patients of any size with normal renal function is similar because the amount of creatinine released into the blood varies with patient muscle mass, which varies with blood volume. Because normalization for BSA is needed for creatinine clearance, a single reference range can be used for all patients. In the case of measurement of renal clearance with 99mTc-MAG3 imaging (assuming a constant dose), the concentration of tracer in the blood will vary inversely with patient size because blood volume varies with patient size. Thus, as patient size increases, the blood concentration of tracer will go down and compensate for the increase in renal blood flow and renal clearance, and conversely. Consequently, the 99mTc-MAG3 renal imaging study is self-correcting for BSA and no additional correction is needed. Conclusion: A conceptual and mathematic analysis suggests that, although normalization for BSA is necessary in the measurement of renal clearance by the standard creatinine clearance test, such normalization is inappropriate in the 99mTc-MAG3 camera-based imaging study because the 99mTc-MAG3 method is inherently self-normalizing for BSA.