Low bicarbonate in diabetic ketoacidosis (DKA) is the sign of the body losing a chemical tug-of-war against acid. Without enough insulin, the body burns fat so fast that acids flood the blood, and bicarbonate is spent soaking them up. The low number is not a missing nutrient to replace. It is a gauge of how much acid is present, which is why it rises on its own once insulin turns the acid supply off.
How Missing Insulin Turns Into Acid in the Blood
In DKA, cells can’t use sugar properly because insulin is too low, so the body acts as if it is starving for fuel.1PubMed. Pathophysiology of Ketoacidosis: Core Curriculum 2026 Fat cells respond by releasing huge amounts of fatty acids into the blood.2PubMed. Diabetic ketoacidosis Stress hormones such as adrenaline, cortisol and glucagon push this fat breakdown even harder.3PubMed. Pathophysiology of Ketoacidosis: Core Curriculum 2026 In the liver, glucagon steers those fatty acids into the cell’s energy factories, where they are turned into ketones.4Diabetes/Metabolism Research and Reviews. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes Ketones such as beta-hydroxybutyrate and acetoacetate then pour into the blood in large quantities.5Diabetes/Metabolism Research and Reviews. Ketone bodies: a review of physiology, pathophysiology and application of monitoring to diabetes Missed insulin doses, an infection or a first appearance of diabetes commonly set this off.
Ketones are the body’s backup fuel, and in small amounts, as during fasting, they are harmless. In DKA they are made far faster than the body can burn them. Beta-hydroxybutyrate is the main ketone, sometimes outnumbering acetoacetate about 10 to 1.6Endocrinología y Nutrición (English Edition). Capillary beta-hydroxybutyrate determination for monitoring diabetic ketoacidosis That’s why hospital finger-stick and blood ketone tests usually measure beta-hydroxybutyrate.
A keto diet also produces ketones, but there insulin is still present to keep them in check. With working insulin, ketone levels stay low and the blood stays near normal acidity. In DKA nothing applies the brakes, so levels climb many times higher. Seeing “ketones” on a strip is not the same as having DKA.
The body can’t switch back to sugar, because the sugar is stuck outside the cells. Nothing turns off the signal for fat breakdown until insulin returns, so ketones keep coming. Since ketones are acids, each one adds to the acid load that bicarbonate has to absorb.
How Bicarbonate Gets Used Up Neutralizing Ketones
Bicarbonate (often shown as “CO2” or “HCO3” on a lab report) is the blood’s main acid buffer. Its job is to soak up acid and keep blood acidity within a narrow safe range. When it meets acid, it forms carbonic acid, which splits into water and carbon dioxide.7PubMed Central. The Role of Bicarbonate Therapy in Diabetic Ketoacidosis: A Systematic Review and Meta‐Analysis The carbon dioxide leaves through the lungs, and the bicarbonate used in the reaction is gone.8PubMed Central. The Role of Bicarbonate Therapy in Diabetic Ketoacidosis: A Systematic Review and Meta‐Analysis So the more ketones the liver makes, the more bicarbonate disappears from the blood.
Each bicarbonate molecule can neutralize only one acid load before it is converted and breathed off, so the number falls in step with how much acid has been absorbed. The body makes new bicarbonate mainly through the kidneys, but that is slow compared with how fast ketones can be produced in DKA. Because supply is slow and demand is fast, the reserve can drop over hours from the normal range to very low values. Doctors watch it because it shows how much buffering reserve is left, it is quick to get on a routine blood panel, and it helps decide whether someone needs intensive care.
On the panel, “CO2” means bicarbonate, not the gas you exhale. A low CO2 on this panel means low buffer, not a breathing problem. The breathing-related carbon dioxide number comes from a separate blood gas test.
What Bicarbonate Numbers Mean for DKA Severity
- Normal: roughly 22 to 29 mmol/L.
- DKA: bicarbonate 18 mmol/L or lower, together with ketones in blood or urine.9PubMed Central. Is There Any Lower Limit of Serum Bicarbonate in Diabetic Ketoacidosis?
- Severe DKA: bicarbonate below 10 mmol/L.10PubMed Central. Is There Any Lower Limit of Serum Bicarbonate in Diabetic Ketoacidosis?
- Recovery target: commonly bicarbonate 18 or higher with blood ketones under 0.6 mmol/L, though some protocols use 15.11PubMed Central. Diabetic ketoacidosis12PubMed Central. Review of Evidence for Adult Diabetic Ketoacidosis Management Protocols
Labs print their own normal ranges beside results, so compare your number to the range on your own report. Doctors also weigh ketones and pH, not one value alone. A mildly low bicarbonate can also come from causes other than DKA, so ketone results help decide.
Your report may list an “anion gap,” calculated as sodium minus chloride and bicarbonate.13PubMed Central. Management of Diabetic Ketoacidosis in Adults: A Narrative Review When ketones use up bicarbonate, this gap widens, and above about 10 to 12 it points to an acid from something like ketones.14PubMed Central. Management of Diabetic Ketoacidosis in Adults: A Narrative Review Doctors also check blood acidity, or pH, where normal is about 7.35 to 7.45 and DKA pushes it lower.
The cutoff of 18 is a working definition, not a point where the body suddenly changes. A person at 19 with high ketones who looks very unwell is still treated seriously.
Why People With DKA Breathe Fast and Deep
As bicarbonate and blood acidity (pH) fall, the brain drives faster breathing to lower carbon dioxide.15PubMed Central. Effects of diabetic ketoacidosis in the respiratory system Breathing out carbon dioxide removes acid and slows the fall in pH.16PubMed Central. Effects of diabetic ketoacidosis in the respiratory system Breathing first gets faster, then deeper, and in serious cases becomes deep, labored “Kussmaul” breathing.17PubMed Central. Effects of diabetic ketoacidosis in the respiratory system Because this breathing is doing vital work, doctors try not to suppress it with a breathing machine in severe acidosis unless needed.18PubMed Central. Severe Diabetic Ketoacidosis With Extreme Acidemia and Preserved Consciousness: Intensive Care Management Guided by Pathophysiology Without Bicarbonate or Intubation
Kussmaul breathing is deep, sighing breaths that seem like air hunger, and it can be mistaken for an asthma attack or panic. The breath may smell fruity or like nail polish remover, from acetone. It is a reason to seek emergency care immediately.
Breathing can’t fully fix the problem. The lungs remove carbon dioxide but can’t stop the liver making ketones, and a person can only breathe so fast and deep before tiring. Only insulin treats the source of the acid.
How Bicarbonate Comes Back During Treatment
Once insulin is given, the liver stops overproducing ketones. As the body burns the remaining ketones, bicarbonate is regenerated and the acid clears.19PubMed Central. Bicarbonate in diabetic ketoacidosis – a systematic review Ketones lost in urine during DKA can’t be recycled, so that bicarbonate has to be rebuilt more slowly.20PubMed Central. Management of adult diabetic ketoacidosis
Treatment can add a second, milder acid problem. Large volumes of standard salt-water IV fluid add chloride, which the kidneys hold onto, keeping bicarbonate down.21PubMed Central. Management of adult diabetic ketoacidosis This chloride-driven acidity appears in over half of patients after 4 hours of treatment and over 90% by 8 to 20 hours.22PubMed Central. Bicarbonate in diabetic ketoacidosis – a systematic review Patients given a “balanced” IV fluid instead had lower chloride and higher bicarbonate, about 20 versus 17, after fluids.23PubMed. Resuscitation with balanced electrolyte solution prevents hyperchloremic metabolic acidosis in patients with diabetic ketoacidosis So a bicarbonate still low the morning after admission doesn’t necessarily mean ketones are still high. Doctors rely on blood ketone levels and pH rather than bicarbonate alone to judge recovery.24PubMed Central. Diabetic ketoacidosis Ketones usually clear before bicarbonate fully normalizes, and bicarbonate may take a day or more to reach normal.
Once ketones clear, the immediate danger is largely over even if bicarbonate hasn’t caught up. The kidneys then slowly clear extra chloride and rebuild bicarbonate over hours to days, so a patient may switch to injected insulin while bicarbonate is still below normal.
On repeated reports, the anion gap may return to normal while bicarbonate is still low, which shows the ketone acid is gone and only the chloride effect remains. A bicarbonate that falls again, or a rising anion gap, would suggest ketones are being made again, often because insulin was interrupted. Since recovery cutoffs differ, ask the team which criteria they are using for your case.
Why Doctors Rarely Give Bicarbonate Directly
In adults with severe DKA, those given bicarbonate recovered no faster than those who weren’t.25PubMed. Bicarbonate therapy in severe diabetic ketoacidosis One reason is that bicarbonate produces carbon dioxide that slips into cells faster than bicarbonate itself, which can make the inside of cells more acidic.26PubMed Central. The Role of Bicarbonate Therapy in Diabetic Ketoacidosis: A Systematic Review and Meta‐Analysis In children, giving bicarbonate was linked to more coma, fluid in the lungs and breathing failure.27PubMed. Reevaluating bicarbonate therapy in pediatric DKA: A propensity score-matched analysis of neurological and respiratory outcomes One hospital records analysis of adults, though, found less organ failure with bicarbonate and no difference in death.28PubMed Central. Therapeutic effectiveness of sodium bicarbonate in diabetic ketoacidosis: A retrospective cohort analysis using the marginal structural Cox model Whether to give it remains debated, and most use it only when acidity is extremely severe.29Frontiers in Diabetes. History of the Treatment of Diabetic Ketoacidosis
This surprises families, because adding back what’s low seems logical. But the low number reflects acid, not a shortage, and treating the gauge instead of the source can backfire.
What raises bicarbonate is the standard treatment. Insulin stops ketone production, the real fix. IV fluids correct dehydration and help the kidneys clear acid. Potassium is replaced because insulin shifts it into cells. Bicarbonate rises on its own as these work.
Doctors sometimes consider giving it when acidity is extremely severe and the person is at risk of dangerous heart rhythm or blood pressure problems. Even then it is usually given slowly and in limited amounts, with close monitoring, rather than to bring the number back to normal.
Why DKA Can Happen With Normal Blood Sugar
Medicines like empagliflozin, dapagliflozin and canagliflozin (SGLT2 inhibitors) lower sugar by spilling it into urine. They also make the kidneys flush ketones out as salts, indirectly costing the body bicarbonate when ketones are high.30PubMed Central. Euglycemic Ketoacidosis as a Complication of SGLT2 Inhibitor Therapy So low bicarbonate and ketones can appear while blood sugar looks reassuring.
The diagnosis can be delayed because the pills send sugar out in urine, so it looks fine even though the body is still short on insulin and making ketones. The reliable clues are the bicarbonate and ketone results, not the sugar reading.
Risk rises with surgery, fasting or a very low-carb diet, with acute illness and vomiting, and with reduced insulin doses. Doctors may advise pausing the pill before surgery.
If you take one of these and feel nauseated, short of breath or very tired, ask for a ketone test even if your sugar is normal. A home ketone meter can help, but a clearly raised reading means contacting urgent care promptly rather than waiting. In hospital, tell the staff about the pill by name, because it changes how they interpret a normal sugar level.
Why Two Bicarbonate Results Can Disagree
In the emergency room, a quick blood gas test from a vein often comes back before the full chemistry panel. Its bicarbonate read about 2.5 mmol/L higher on average than the lab panel in DKA patients.31PubMed Central. Comparison of bicarbonate values from venous blood gas and chemistry panels measured at the time of diagnosis and resolution of diabetes ketoacidosis In about 1 in 12 cases the blood gas value was above 18 and would have wrongly ruled out DKA.32PubMed Central. Comparison of bicarbonate values from venous blood gas and chemistry panels measured at the time of diagnosis and resolution of diabetes ketoacidosis Even so, blood gas results still identified nearly every DKA case in one emergency department.33PubMed. Diagnostic accuracy of venous blood gas electrolytes for identifying diabetic ketoacidosis in the emergency department
A blood gas machine measures acidity and carbon dioxide directly and then calculates bicarbonate, while the chemistry panel measures total carbon dioxide a different way. Small differences between methods are expected.
When results conflict, ask which test each number came from, and follow trends on the same test type. The chemistry panel is usually the reference for diagnosis, and ketone and pH results help settle disagreements.