threshold substance

thresh·old sub·stance

any material (for example, glucose) that is excreted in the urine only when its plasma concentration exceeds a certain value, termed its threshold.
Synonym(s): threshold body

thresh·old sub·stance

(thresh'ōld sub'stăns)
Any material (e.g., glucose) that is excreted in the urine only when its plasma concentration exceeds a certain value, termed its threshold.

threshold substance

A substance present in the blood that, on being filtered through glomeruli of the kidney, is reabsorbed by the tubules up to a certain limit, that being the upper limit of the concentration of the substance in normal plasma. High-threshold substances (such as chlorides or glucose) are entirely or almost entirely reabsorbed. Low-threshold substances (such as phosphates or urea) are reabsorbed in limited quantities. No-threshold substances (such as creatinine sulfate) are excreted entirely.