《黄帝内经·素问·病能论》
左脉主要的病症在肾脏，次要的病症在肺脏，所以当有腰痛的症状。
在左当主病在肾，颇关在肺，当腰痛也。
The main cause of the left pulse lies in the kidneys, while the secondary cause lies in the lungs. Hence, there should be symptoms of pain in the lumbar region.