Urinalysis – Physical and Biochemical Practice Test

Urine concentration varies with collection time, so the first-morning sample is typically more concentrated because the body has been without fluid for several hours overnight. That higher concentration means more solutes per milliliter and a higher specific gravity, which can bias tests that depend on how concentrated the urine is. Because many urinalysis tests assume a sample that reflects typical daily excretion, a highly concentrated first-morning specimen can exaggerate or mask findings, making it less ideal for those tests. Some tests may benefit from concentration, but for routine analyses that aim to reflect average excretion, a different collection time helps provide a more representative result.