What is bicarbonate?
Your metabolism makes acid all day long: when burning protein, during exertion, when fasting. Yet the acidity of your blood barely moves, and that is thanks to bicarbonate. It absorbs acid and then leaves your body as carbon dioxide through the lungs, while your kidneys make new bicarbonate and reclaim it from the pre-urine. Lungs and kidneys therefore turn one dial together: the lungs in minutes, by breathing faster or deeper, the kidneys in hours to days. The value in your blood is the level of that buffer. If it falls, more acid is being offered than is being removed, or the kidneys are holding on to too little bicarbonate. If it rises, acid is being lost or buffer is being added. The number says that the balance has shifted, not why; for that chloride, sodium, potassium and kidney function are needed beside it. Your report shows bicarbonate in mmol/L. Normal is about 24 to 28 mmol/L where the labs overlap; because one lab uses a narrow band and another a wide one, a value just under 24 is not called the same everywhere. It is measured in a separate tube that must stay closed, because bicarbonate escapes as carbon dioxide as soon as air gets to it.
Why is bicarbonate relevant?
For anyone healthy, bicarbonate is rarely the value that tells something new: the buffer works, and the number sits where it belongs. It becomes interesting in two situations. The first is a kidney function that is declining. Kidneys that filter less also excrete less acid, and bicarbonate then slowly falls with it; it is one of the first values to show that the kidney can no longer get rid of the acid, and a low value in turn speeds up bone loss and muscle breakdown. In chronic kidney disease it is therefore followed and topped up where needed. The second situation is a disturbance of the salt and fluid balance: persistent vomiting and diuretics make the value rise, severe diarrhoea makes it fall, and a ketogenic diet or prolonged fasting lowers it slightly, because ketones are acids. What food does to it is small but measurable. Protein, meat, cheese and grains deliver acid, vegetables and fruit deliver base; anyone who eats a lot of the first and little of the second asks more of the buffer, and at an older age and with weaker kidneys you see that back in a bicarbonate on the low side. More vegetables and fruit is then the lever, and that is the same lever as for blood pressure and bone. And then the most common reason for a low value, which has nothing to do with you: a tube that stood open too long. Bicarbonate disappears as carbon dioxide, and a result lower than expected more often says something about the logistics than about your kidneys.
Bicarbonate reference ranges
What counts beside the number:
- Whether the tube was closed and processed quickly, because bicarbonate escapes as carbon dioxide
- Creatinine and eGFR: kidneys that filter less excrete less acid
- Chloride, which moves along with loss through gut or kidneys and stays the same when acid is added
- Sodium and potassium, the rest of the salt and fluid balance
- Vomiting, diarrhoea, diuretics, antacids and a ketogenic diet or fasting
- What you eat: meat, cheese and grains deliver acid, vegetables and fruit deliver base
The band above is where the labs overlap; the range on your own report may be wider, and there is no national normal value. More important than the range is the tube: bicarbonate escapes as carbon dioxide as soon as air gets to it, so a low value from a tube that stood open or waited long says nothing about you.
What Dutch labs actually use
Three labs publish a range for bicarbonate and they differ mainly in how wide they draw it. Star-shl holds 20 to 31 mmol/L, Unilabs 22.0 to 29.0 and Certe 24 to 28. Star-shl's band is nearly three times the width of Certe's. A value of 22.0 mmol/L is normal at Star-shl and Unilabs and below the floor at Certe. The fourth lab publishes nothing at all. Clinical Diagnostics still lists bicarbonate in its lab guide, with the note that the test could no longer be collected through SCAL as of 10 April 2018, and gives no reference value with it.
24 – 28mmol/L
Between 20 and 24 and between 28 and 31 it depends on the lab, because each sets its limits on its own method and population. Above 31 every lab calls it abnormal.
every lab calls 24 – 28 mmol/L normal. Between 20 and 24 and between 28 and 31 it depends on the lab.
Bicarbonate high or low: what it means
A low bicarbonate is, in order of how often it occurs: a tube that stood open or waited too long, a kidney function that excretes less acid, severe diarrhoea, a ketogenic diet or prolonged fasting, and rarely a derailment of blood sugar in diabetes or a poisoning. Breathing too fast and deep, in panic or hyperventilation, lowers it too, because the lungs then remove too much carbon dioxide and the kidneys compensate. Chloride beside it helps: if that rises with it, it is usually loss through the gut or the kidneys; if it stays the same, acid has been added somewhere. A high bicarbonate means acid loss or extra buffer: persistent vomiting, diuretics, plenty of antacids or bicarbonate tablets, and in people with a lung disease the kidneys compensating for a chronically high carbon dioxide. In a healthy person it rarely occurs. What you do about it: with a low value first measure again with a properly closed tube. If it stays low, kidney function is the first question, and then more vegetables and fruit and less meat and cheese are the lever you have yourself; in chronic kidney disease bicarbonate as a tablet joins in where needed. A high value from vomiting or diuretics normalises once the cause is gone. Set bicarbonate beside chloride, sodium and potassium, and beside creatinine and eGFR. The number says the buffer is under pressure; the values beside it say why.
What lowers it
Often the tube, and beyond that more acid than the kidneys can get rid of.
| Cause | How often |
|---|---|
| A tube that stood open too longBicarbonate escapes as carbon dioxide as soon as air gets to it and the value falls by the minute; that is why it goes in a separate tube that stays closed until measurement | Often |
| Reduced kidney functionKidneys that filter less also excrete less acid; bicarbonate then slowly falls with it and speeds up bone loss and muscle breakdown | Sometimes |
| Heavy fluid loss from diarrhoeaGut fluid is rich in bicarbonate; with severe diarrhoea it is lost and the value falls | Sometimes |
| Ketogenic diet, fasting or breathing too fastKetones are acids and push the buffer down slightly; with hyperventilation the lungs remove too much carbon dioxide and the kidneys lower bicarbonate to compensate | Sometimes |
| A derailment of blood sugarIn diabetes with a severe insulin shortage ketones accumulate and bicarbonate falls fast; an emergency, with symptoms you do not miss | Rare |
What raises it
Acid loss or extra buffer, rare in a healthy person.
| Cause | How often |
|---|---|
| Persistent vomitingWith stomach acid, acid is lost and more buffer remains; chloride then falls with it | Sometimes |
| Diuretic medicationDiuretics make the kidneys excrete acid and chloride and hold on to bicarbonate | Sometimes |
| Antacids or bicarbonate tabletsPlenty of acid-binding agents or bicarbonate as a tablet deliver buffer from outside | Rare |
| Kidneys compensating for a lung diseaseWith a chronically high carbon dioxide, as in COPD, the kidneys hold on to extra bicarbonate to keep the acidity in place | Rare |
How does a bicarbonate blood test work?
- Referral
- Not needed, though not every lab still offers the test.
- Fasting
- Not needed.
- The draw
- A separate small tube that stays closed until measurement, because as soon as air gets to it bicarbonate escapes as carbon dioxide and the value falls by the minute. That is the reason a low result more often lies with the tube than with you.
- The result
- A single number in mmol/L, usually available the same day. The range differs per lab more than for most salts: one lab uses a narrow band, another a wide one.
- Repeating
- A low value again first, with a properly closed tube. If it stays low, kidney function follows the course.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is bicarbonate?
The main buffer in your blood. Your metabolism makes acid all day long, bicarbonate absorbs it and removes it as carbon dioxide through your lungs, while your kidneys make and reclaim new bicarbonate. That keeps the acidity of your blood within a very narrow margin. The value shows whether that buffer is under pressure.
What is a normal bicarbonate level in blood?
About 24 to 28 mmol/L, where the labs overlap. One lab uses exactly that band, another a wider one, so a value just under 24 is called low at one lab and normal at another. The range on your own report is the most useful here.
What does a low bicarbonate mean?
Often that the tube stood open or waited too long: bicarbonate escapes as carbon dioxide, and that is the first question with a low value. Otherwise it means there is more acid than the buffer absorbs or the kidneys hold on to too little: a kidney function that excretes less acid, severe diarrhoea, a ketogenic diet or fasting, or breathing too fast. Measure again first with a closed tube; if it stays low, kidney function is the first question.
What does a high bicarbonate mean?
That acid is being lost or buffer added: persistent vomiting, diuretics, plenty of antacids or bicarbonate tablets, and with a lung disease the kidneys compensating for a high carbon dioxide. In a healthy person it rarely occurs and normalises once the cause is gone.
Why must the tube stay closed for a bicarbonate test?
Because bicarbonate is in balance with carbon dioxide, and that gas escapes as soon as air gets to it. The value then falls by the minute, and a result lower than expected more often says something about the logistics than about you. That is why it goes in a separate tube that stays closed until measurement.
Can I do anything about my bicarbonate with food?
A little, and it is the same lever as for blood pressure and bone. Protein, meat, cheese and grains deliver acid, vegetables and fruit deliver base. Anyone who eats a lot of the first and little of the second asks more of the buffer, and with weaker kidneys you see that back in a value on the low side. More vegetables and fruit is then what you can do yourself; in chronic kidney disease bicarbonate as a tablet joins in where needed.
What does bicarbonate have to do with my kidneys?
Your kidneys excrete the acid your metabolism makes, and make and keep the bicarbonate that absorbs it. Kidneys that filter less can no longer get rid of the acid, and bicarbonate then slowly falls with it. A low value in turn speeds up bone loss and muscle breakdown, and that is why it is followed and topped up where needed in chronic kidney disease.
Do I need to fast?
No. What counts is that the tube stays closed and is processed quickly, and that chloride, sodium, potassium and your kidney function come from the same draw.
Which tests include bicarbonate?
Bicarbonate is part of Advanced, the broader panel. It is not orderable yet.
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): bicarbonate. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): bicarbonate (HCO3-). 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): bicarbonate. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): bicarbonate. 2026. clinicaldiagnostics.nl
- 5.NHG guideline on chronic kidney disease (M109), Dutch College of General Practitioners. 2026. richtlijnen.nhg.org
- 6.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
- 7.Khanna and Kurtzman, Metabolic alkalosis, Respiratory Care 46(4). 2001. pubmed.ncbi.nlm.nih.gov
- 8.Adeva-Andany et al., Sodium bicarbonate therapy in patients with metabolic acidosis, The Scientific World Journal. 2014. pubmed.ncbi.nlm.nih.gov
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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Bicarbonate is part of Advanced, the broader panel. It is not orderable yet.
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