Fasting for a lab test typically lasts eight hours. Your doctor should give you any special instructions related to your tests, including fasting requirements.

Fasting means you don’t eat or drink anything but water usually for 8 to 12 hours beforehand. If your appointment is at 8 a.m. and you’re told to fast for 8 hours, only water is OK after midnight. If it’s a 12-hour fast, avoid food and drink after 8 p.m. the night before.

Results. Caffeine and its metabolites were detectable in the urine of most persons, generally at concentrations ≥1 μmol/L. Median concentrations (95% CI) ranged from 0.560 (0.497–0.620) μmol/L to 58.6 (48.6–67.2) μmol/L; median excretion rates from 0.423 (0.385–0.468) nmol/min to 46.0 (40.7–50.2) nmol/min.

If your urine is being tested only for a urinalysis, you can eat and drink normally before the test. If you’re having other tests at the same time, you may need to fast for a certain amount of time before the test.

Urine tests can be used to diagnose urinary tract infections, if bacteria or white blood cells are found. In patients who have already been diagnosed with chronic kidney disease, urinalysis may be ordered at intervals as a quick and useful way to monitor function.

Urine drug testing may screen for multiple substances, including amphetamines, methamphetamines, benzodiazepines, barbiturates, marijuana, cocaine, opiates, PCP, methadone, nicotine, and alcohol.

You can collect a urine sample at any time of day, unless your GP or practice nurse advises you otherwise. The types of urine sample you might be asked for include a random specimen, first morning specimen or timed collection.

Morning is when your urine will be most concentrated. So, if your morning urine is a pale, straw color, you’re probably well hydrated and healthy. At bedtime, it should look as clear as water or at least pale yellow. If it doesn’t, you may need to boost your fluid intake.

In this regard, the second morning spot urine may be particularly relevant, because it is easier to collect, and probably represents as uniform and achievable way as possible to collect urine among outpatients.

Refrigeration can result in the precipitation of urates or phosphates, which may obscure other pathologic constituents in the microscopic examination of the urine sediment. According to NCCLS, If the urine is also to be cultured, it should be refrigerated during transit and held refrigerated until cultured.

Any bacteria or cells present in a urine sample kept at room-temperature for more than one hour will continue to use glucose (sugar) in the urine. This may result in a falsely decreased urine glucose measurement. Also, bacteria produce ammonia which makes the urine more alkaline (increases pH).

If you can’t hand your urine sample in within an hour, you should keep it in the fridge at around 4C (39F) for no longer than 24 hours. Put the container of urine in a sealed plastic bag first. If the urine sample isn’t kept in a fridge, the bacteria in it can multiply.