The PSA value used most frequently as the highest normal level is 4 ng/mL (nanograms per milliliter). However, since the prostate gland generally increases in size and produces more PSA with increasing age, it is normal to have lower levels in young men and higher levels in older men. Age-specific PSA levels are as follows (age group, upper normal): (40 – 49, ), (50 – 59, ), (60 – 69, ), (70 – 79, ). The use of age-specific PSA ranges for the detection of prostate cancer is controversial. Not all studies have agreed that this is better than simply using a level of 4 ng/mL as the highest normal value.