Simple sampling strategy for measuring inulin renal clearance

Abstract

Background

In the standard method of inulin clearance (Cin), three sets of serum and urine samples are collected during a 2-hour clearance period. For a practical use of this method, sampling should be the minimal number allowable while still providing enough accuracy. The aim of this study was to evaluate the validity of inulin renal clearance with assumed single urine collection with a period such as 30, 60 or 90 minutes.

Methods

Inulin clearance data collected by the standard method from 737 individuals were used. Changes of serum inulin concentrations between 45 and 105 minutes after the start of the infusion were analyzed. We used first urine collection to calculate the inulin clearance with single urine collection (Cin-30 min). We assumed single urine collection for 60 or 90 minutes by combining the urine data of the consecutive 30-minute periods. Inulin clearances (Cin-60 min, Cin-90 min) were calculated from the assumed single urine collections, respectively.

Results

Serum inulin concentration did not reach equilibrium during the clearance period. It increased in subjects with low glomerular filtration rate (GFR) and decreased in subjects with normal GFR. The amount of the change was small and −0.5 ± 12.6% in subjects with GFR over 30 ml/min per 1.73 m². Cin-30 min, Cin-60 min and Cin-90 min showed high correlation coefficients against Cin-ST (0.962, 0.988 and 0.998, respectively). Systemic biases in these clearances were negligible (under 1 ml/min per 1.73 m²). Root mean square error (RMSE) were 10.4, 5.3 and 2.3 ml/min per 1.73 m² for Cin-30 min, Cin-60 min and Cin-90 min, respectively. These data indicated that accuracy of inulin clearance depends on the duration of the urine collection period.

Conclusion

Inulin clearance with a single urine collection is a convenient method. We showed that single urine collection for 30 minutes or a longer period has reasonable accuracy in calculation of inulin clearance. We propose a method of inulin clearance with single urine collection for 60 minutes.

Appendix

The following investigators participated in the project for developing the Japanese Equation for estimating GFR: Asahikawa Medical University; Kenjiro Kikuchi, Masakazu Haneda: Hokkaido University Hospital; Seiji Hashimoto: Sapporo Medical University; Nobuyuki Ura: Tohoku University Hospital; Sadayoshi Ito, Hiroshi Sato: Fukushima Medical University; Tsuyoshi Watanabe: Jichi Medical University; Yasuhiro Ando, Eiji Kusano: Gunma University; Yoshihisa Nojima: University of Tsukuba; Kunihiro Yamagata, Chie Saitoh: Toride Kyodo General Hospital; Tatsuo Shiigai, Yoshitaka Maeda: Saitama Medical University; Hiromichi Suzuki, Yusuke Watanabe: Saitama Medical University; Tetsuya Mitarai, Hajime Hasegawa: The University of Tokyo; Toshiro Fujita: Jikei University; Tatsuo Hosoya: Nihon University; Koichi Matsumoto, Takayuki Fujita: Tokyo Women’s Medical University; Kousaku Nitta: Tokyo Women’s Medical University Medical Center East; Tsutomu Sanaka: Tokyo Medical and Dental University; Eiichiro Kanda, Sei Sasaki: Juntendo University; Yasuhiko Tomino: Tokyo Medical University Hospital; Toshiyuki Nakano: Showa University; Tadao Akizawa, Hirokazu Honda: Showa University Fujigaoka Hospital; Yoshihiko Inoue, Ashio Yoshimura: Toranomon Hospital; Hiroshi Tsuji: Toho University; Yasushi Ohashi: Teikyo University; Hideaki Nakajima Shunya Uchida: Kyorin University; Akira Yamada: Yokohama City University; Satoshi Umemura, Mai Yanagi: St. Marianna University; Hiro Yamakawa, Kenjiro Kimura: Niigata University; Shinichi Nishi, Fumitake Gejyo: Hamamatsu University; Hideo Yasuda, Tomoyuki Fujikura: Nagoya University; Seiichi Matsuo: Aichi Medical University; Hirokazu Imai, Wataru Kitagawa: Fujita Health University Hospital; Satoshi Sugiyama: Mie University; Shinsuke Nomura, Eiji Ishikawa: Toyama Prefectural Central Hospital; Masahiko Kawabata: Hiroyuki Iida: Kanazawa University Hospital; Takashi Wada: Kanazawa Medical University; Hitoshi Yokoyama: University of Fukui Hospital; Haruyoshi Yoshida: Shiga University of Medical Science; Takashi Uzu, Masayoshi Sakaguchi: Kyoto University Hospital, Atsushi Fukatsu: Osaka University; Yasuyuki Nagasawa, Shiro Takahara: Osaka City University; Eiji Ishimura,Yoshiki Nishizawa: Kobe University; Masafumi Fukagawa, Michio Umezu: Hyogo College of Medicine; Nakanishi Takeshi, Izumi Masaaki: Okayama University, Hitoshi Sugiyama, Hirofumi Makino: Kawasaki Medical School; Naoki Kashihara, Tamaki Sasaki: Hiroshima University; Noriaki Yorioka: University of Tokushima; Toshio Doi: Kagawa University; Masakazu Kono: Ehime University; Takafumi Okura: Kyushu University Hospital; Kazuhiko Tsuruya, Akiko Ono: Fukuoka University; Takao Saito, Yasuhiro Abe: Nagasaki University; Akira Furusu: Kurume University; Seiya Okuda: Kumamoto University; Kimio Tomita: University of Miyazaki; Shouichi Fujimoto: University Hospital of The Ryukyus; Iseki Kunitoshi, Schuichi Takishita: Koto Hospital; Isao Ebihara, Yuko Shima: Nara Medical University; Koji Harada, Yoshihiko Saito: Dokkyo Medical University; Atsushi Numabe, Toshihiko Ishimitsu: Kitano Hospital; Eri Muso, Toshiyuki Komiya: Musashino Red Cross Hospital; Ryoichi Ando:Toyonaka Municipal Hospital; Megumu Fukunaga: Ohmihachiman Community Medical Center; Tsuguru Hatta: Sendai Shakaihoken Hospital; Osamu Hota: Tosei General Hospital; Inaguma Daijo: Matsuyama Clinic; Kazuhiro Matsuyama: Rokko Island Hospital; Naoyuki Nakano: Shuwa General Hospital; Masashi Inoshita: Kanagawa Rehabilitation Hospital; Masahisa Kusaka, Masato Mizuguchi.