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Minerals

Bicarbonate and the kidneys: what HCO3- says in kidney disease and high blood pressure

The kidneys can excrete bicarbonate (HCO3-), according to the NVKC the main form of carbon dioxide in the body, or hold on to it to keep the balance between acid and base. According to MedlinePlus, carbon dioxide itself is a waste product of metabolism.

According to the NVKC, in a metabolic disorder the kidneys cannot excrete the right amount of bicarbonate, and the NVKC names serious kidney problems as a possible cause of a metabolic acidosis with a lowered HCO3-. The bicarbonate level can only be determined by a blood test.

Unilabs uses 22.0 - 29.0 mmol/l for bicarbonate.

Doctor's Assessment Included

According to the NVKC, bicarbonate (HCO3-) is the main form of carbon dioxide in the body. The kidneys can excrete it or hold on to it to keep the balance between acid and base.

  • Star-SHL uses 20 - 31 mmol/l for bicarbonate, Unilabs 22.0 - 29.0 mmol/l, Certe 24 - 28 mmol/L and Diagnostiek voor U 21 - 28 mmol/L.
  • According to the NVKC, a raised bicarbonate together with a high pH fits a metabolic alkalosis, with prolonged vomiting among the possible causes.
  • According to the NVKC, a lowered bicarbonate together with a low pH fits a metabolic acidosis, with diabetes and serious kidney problems among the possible causes.

Bicarbonate: what Dutch laboratories use

There is no nationally agreed reference value; this is what individual laboratories publish.

The upper limit runs from 28 mmol/l at Certe to 31 mmol/l at Star-shl.

Reference ranges by group, in mmol/l
Star-shl · Everyone 20–31 mmol/l
20 31
Unilabs · Everyone 22–29 mmol/l
22 29
Certe · Everyone 24–28 mmol/L
24 28
Diagnostiek voor U · Everyone 21–28 mmol/L
21 28
0 34.1 mmol/l

Source: Star-shl

Source: Unilabs

Source: Certe

Source: Diagnostiek voor U

Each value as the laboratory itself publishes it, retrieved in 2026.

Bicarbonate: what this test measures

A bicarbonate level is given in millimoles per litre (mmol/l), and Unilabs measures bicarbonate in lithium heparin plasma with an enzymatic method (PEPC).

Bicarbonate: why this value matters

Bicarbonate matters because, according to the NVKC, the total CO2 test, with HCO3- as its main form, is also used to follow the course of kidney disease and high blood pressure.

Bicarbonate: how the blood test works

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Bicarbonate: when is testing worthwhile?

According to the NVKC, the CO2 test, which includes bicarbonate as its main form, can be ordered to judge whether medication for kidney disease or high blood pressure works.

Bicarbonate: symptoms of a high or low value

Low Levels

According to the NVKC, serious kidney problems are a possible cause of a metabolic acidosis, a low pH together with a lowered HCO3-, and Unilabs sets the lower limit for bicarbonate at 22.0 mmol/l. MedlinePlus also lists kidney or liver disease among the possible causes of a metabolic acidosis.

High Levels

The NVKC names an overdose of bicarbonate as a possible cause of a metabolic alkalosis, a high pH together with a raised HCO3-, and Unilabs sets the upper limit for bicarbonate at 29.0 mmol/l.

Bicarbonate: causes of a low or high value

What lowers the value

  • Diabetic ketoacidosis

    Too little CO2 in the blood may be a sign of diabetic ketoacidosis, a complication of type 1 and type 2 diabetes.

  • Serious kidney problems

    Serious kidney problems can be a cause of a metabolic acidosis: a low pH together with a lowered HCO3- in the blood.

  • Long-lasting diarrhoea

    Long-lasting diarrhoea is one of the possible causes of a metabolic acidosis, in which there can be too little CO2 in the blood.

  • Hyperventilation

    Too little CO2 in the blood may be a sign of a respiratory alkalosis, which comes from a lung or breathing problem, including hyperventilation: rapid, deep breathing.

  • A tube opened before analysis

    After the collection tube is opened, the bicarbonate concentration falls by about 6 mmol/L per hour; the tube must stay closed until analysis.

What raises the value

  • Prolonged vomiting

    Prolonged vomiting, with loss of acid from the stomach, can cause a metabolic alkalosis: a high pH together with a raised HCO3- in the blood.

  • An overdose of bicarbonate

    An overdose of bicarbonate can be a cause of a metabolic alkalosis with a raised HCO3-.

  • Cushing's syndrome

    Too much CO2 in the blood can be a sign of Cushing's syndrome.

  • Lung diseases

    Too much CO2 in the blood can be a sign of lung diseases.

Bicarbonate: lifestyle and this value

Discuss an abnormal bicarbonate with your GP, especially if you are being treated for kidney disease or high blood pressure, because the NVKC names the CO2 test for following those conditions.

Bicarbonate: frequently asked questions

Why does Unilabs ask for a separate tube for bicarbonate?

Unilabs asks for a separate small lithium heparin tube for bicarbonate that must stay closed until analysis, because after opening the concentration falls by about 6 mmol/L per hour.

Bicarbonate: sources

  1. Star-shl, Labbepalingen (referentiewaarden per bepaling), star-shl.nl, geraadpleegd 2026-10-01 (retrieved 2026) star-shl.nl
  2. Unilabs, Bepalingenklapper (referentiewaarden per bepaling), bepalingenklapper.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenklapper.nl
  3. Certe, Bepalingenwijzer (referentiewaarden per bepaling), bepalingenwijzer.certe.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenwijzer.certe.nl
  4. Diagnostiek voor U, eLabgids (Referentiewaarden DvU), diagnostiek.getincontrol.eu, geraadpleegd 2026-10-01 (retrieved 2026) diagnostiek.getincontrol.eu
  5. MedlinePlus, Carbon Dioxide (CO2) in Blood, medlineplus.gov, geraadpleegd 2026-10-19 (retrieved 2026) medlineplus.gov
  6. NVKC, Alles over testen: Bloedgassen, allesovertesten.nl, geraadpleegd 2026-10-19 (retrieved 2026) allesovertesten.nl

Test Products

This marker is included in the following test panels.

Heart and blood vessels

Complete Metabolic Panel

Comprehensive metabolic panel: electrolytes, kidney, liver, glucose, HbA1c, and protein.

HbA1c (Glycated Hemoglobin) ALT (Alanine Aminotransferase) Calcium ALP (Alkaline Phosphatase) AST (Aspartate Aminotransferase) Bilirubin (Total) Urea (BUN) Creatinine eGFR (Estimated Glomerular Filtration Rate) Glucose (Fasting) Bicarbonate Chloride Sodium Potassium Albumin Total Protein Bilirubin (Direct) Bilirubin (Indirect)
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Bicarbonate

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