Bicarbonate test
Quick answer: A bicarbonate test measures the amount of bicarbonate, which helps keep your blood's acid-base balance, in blood or urine. Doctors order it to check acid-base balance in kidney, lung or breathing problems, severe vomiting or diarrhoea, and to monitor some treatments.
- SampleBlood or urine
- TakesAbout 5 minutes for blood or spot urine; 24 hours for a full collection
- Before the testNo special preparation is usually needed; for a 24-hour test, collect all your urine as instructed.
How the test is done
- 1For blood, a needle draws a sample from a vein in your arm
- 2The tube is filled and capped quickly so gas does not escape
- 3For urine, you give a single sample or collect all urine for 24 hours
- 4The lab measures bicarbonate, often with other electrolytes
What your results can mean
Reading your report
Normal ranges differ between labs and by age and sex, so discuss your result with your doctor.
If the result is outside the usual range
A low blood level can be seen with kidney disease, diarrhoea, uncontrolled diabetes or some poisonings. A high level can be seen with repeated vomiting, some water tablets or long-term lung disease.
Who usually has this test
People with kidney or breathing problems, severe vomiting or diarrhoea, uncontrolled diabetes, or on medicines that affect acid-base balance.
Risks and aftercare
A blood sample may leave a small bruise; urine collection has no risk.
Names and options
Also called: HCO3, total CO2, bicarbonate
Options
- Blood (serum)
- Spot urine
- 24-hour urine
Listed by the hospital as
- BICARBONATE 24 HRS URINE
- BICARBONATE, SERUM
- BICARBONATE, URINE
Questions about this test
Is bicarbonate the same as total CO2?
In most lab reports they are treated as the same. Total CO2 is mostly made up of bicarbonate in the blood.
Why does vomiting change bicarbonate?
Vomiting removes stomach acid, which can leave the blood too alkaline and raise bicarbonate. Diarrhoea does the opposite and can lower it.
Why is urine bicarbonate tested?
Urine bicarbonate helps doctors see whether the kidneys are handling acid properly. It is used in some kidney tubule conditions.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.