Question

The renal threshold value of glucose is normally
(A) $80mg/100ml$
(B) $160 - 120mg/100ml$
(C) $100 - 120mg/100ml$
(D) $80 - 110mg/100ml$

Answer 1

Hint: In anatomy, the term renal threshold can be defined as the concentration of a substance dissolved in the blood higher than which the kidneys will start to eliminate it into the urine.

Complete answer:
Glycosuria or glucosuria is the excretion of glucose into the urine. The proximal tubule can only reabsorb a limited amount of glucose. With normal kidney (renal) function, glucose is excreted in the urine only when there are abnormally elevated levels of glucose in the blood. However, in those with renal glycosuria, glucose is abnormally elevated in the urine due to improper functioning of the renal tubules, which are the primary components of the nephrons that act as the filtering units of the kidneys.

The renal threshold for glucose (RTg) corresponds to a blood glucose level of $^\~180mg/dL$, however, in hospitals, patients are often encountered who are hyperglycemic, but urine glucose test strip‐negative, who remain negative for urine glucose even at blood glucose concentrations $ > 180mg/dL$, implying a high RTg value. The proximal tubule can only reabsorb a limited amount of glucose. When the blood glucose level exceeds about $160 - 180mg/dl$ or $160 - 180mg/100ml$, the proximal tubule becomes overwhelmed and begins to excrete glucose in the urine. This point is called the renal threshold of glucose (RTG).

Therefore, from the above explanation the correct option is (B) $160 - 120mg/100ml$.

Note: The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of the loop of Henle. It can be further classified into the proximal convoluted tubule (PCT) and the proximal straight tubule (PST).