Influence of Temperature During Specimen Collection and Thawing on Plasma Renin Activity and Aldosterone Renin Ratio in Low Renin Hypertensive Patients

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 723-757-Renin-Angiotensin-Aldosterone System/Endocrine Hypertension
Bench to Bedside
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-738
Sarat Sunthornyothin*1 and Nawarat Pengpong2
1King Chulalongkorn Mem Hosp, Bangkok, Thailand, 2King Chulalongkorn Memorial Hospital
Background : Cryoactivation of prorenin and heat-related angiotensinogen degradation are the major concern in preanalytical condition of plasma renin activity (PRA) assay which can cause either overestimation or underestimation of PRA, respectively. To date, there is no study about the impact of preanalytical temperature on PRA in low renin hypertensive patients or patients who suspected primary hyperaldosteronism. We evaluate the impact of temperature during specimen collecting process and thawing on PRA assay. 

Methods : Five blood samples from each patients were collected into EDTA tubes at the room temperature. The first sample was processed within 30 minutes (control group). Other two blood samples were processed after freezing and thawing in ice bath (0°C) or room temperature (Group 2 and Group 3). The last two samples were kept in ice bath (0°C) or room temperature (25°C) for 6 hours then freezing and thawing in ice bath before PRA assay (Group 4 and Group 5).

Results :Two-hundred samples from 40 patients were collected for matched analysis. In control group, PRA was 0.635 ng/ml/hr. Freezing and thawing in ice bath or room temperature can significantly increase  PRA, 1.805 (p<0.001) and 1.470 (p<0.001) ng/ml/h, respectively. The blood samples which were kept in ice bath (0°C) or room temperature (25°C) for 6 hours significantly increased PRA , 2.055 ng/ml/hr  (p<0.001) and 1.915 ng/ml/hr (p=0.001) . There were no significant differences when group 2 and group 3 (p=0.181) or group 4 and group 5 (p=0.610) were compared. The ARR calculated from the sample with cryoactivation was significantly decreased from the baseline value which resulted in falsely negative results.    

Conclusion : Thawing process of plasma caused significant increment of plasma renin activity, both in ice bath(0°C) or at room temperature (25°C). There were no differences of PRA results between specimen collected in ice bath or room temperature for 6 hours. Therefore, the interpretation of PRA results from samples exposed to cold temperature, even in short period during thawing process, should be done with caution.

Nothing to Disclose: SS, NP

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Sources of Research Support: Ratchadapisek Sompoch Research Grant, Chulalongkorn University.