Final answer:
Specific gravity is the part of urinalysis that helps to detect the kidney's ability to concentrate or dilute urine. It measures the density of the urine compared to water and a specific gravity of 1.020 is considered normal after a renal concentration test.
Step-by-step explanation:
The part of urinalysis that helps to detect the ability of the kidneys to concentrate or dilute urine is specific gravity. Specific gravity refers to the ratio of the density of urine to the density of water. In a test of renal concentration ability, if the specific gravity is 1.020 after an injection of pituitrine and a 24-hour urine collection, the kidneys are considered to be functioning normally. However, if the specific gravity is lower, it may indicate a potential abnormality in the kidneys' ability to reabsorb water, thus affecting their ability to concentrate urine.
More precise measurements than specific gravity, like urine osmolality, provide an assessment of the number of dissolved particles in urine to evaluate kidney function further.
Normal kidneys are expected to produce urine with osmolality greater than 800 mOsm/kg of water under restricted fluid intake (concentration testing) and less than 100 mOSm/kg under increased fluid intake (dilution testing).