Ans. is 'b' i.e., 200 mg/dl * The transport maximum for glucose is 375 mg/min whereas the filtered load of glucose is only 125 mg/min.* Therefore, in normal conditions 100% of glucose is reabsorbed in proximal tubules.* When plasma glucose concentration is 100 mg/dl the filtered load is at its normal level, 125 mg/min, there is no loss of glucose in the urine.* However, when the plasma concentration of glucose rises above about 200 mg/dl, increasing the filtered load about 250 mg/min, a small amount of glucose begins to appear in the urine.* This point is termed as threshold for glucose.* Note that this appearance of glucose in the urine occurs before the transport maximum is reached.* The reason for the difference between threshold and transport maximum is that not all nephron have same transport maimum for glucose, and some of the nephron therefore begin to excrete glucose before others have reached their transport maximum.* The overall transport maximum for the kidneys, which is normally about 375 mg/min, is reached when all nephrons have reached their maximal capacity to reabsorb glucose.* That means, above filtered load of 250 mg/min of glucose, some glucose will appear in the urine (threshold level), whereas above filtered load of 375 mg/min, all the glucose will be excreted because all the nephrons have reached to their transport maximum.* Thus, Renal threshold for glucosei) At plasma levels - 200 mg/dlii) At filtered load - 250 mg/min