Bicarbonate Is Rising in Blood Test Results: What the Data Shows

Almost every routine blood panel prints a line labelled CO2, or sometimes bicarbonate, or HCO3. Most people skim past it. On 15 August 2026 that line was suddenly the headline, after an analysis of two decades of American laboratory results reported that average serum bicarbonate has climbed by about 7 percent since 1999, while average calcium and phosphorus have fallen.

The finding is unsettling and it is easy to over-read. It says nothing about whether your own result is abnormal today, and if that is your question, our reference guide to what your bicarbonate level means answers it directly. What follows is the different question the new data raises: why the population average is moving at all, and whether it should change how you read the page.

What the analysis actually reported

Researchers from The Kids Research Institute Australia, Curtin University and the Australian National University used the US National Health and Nutrition Examination Survey, better known as NHANES. That survey draws blood from a nationally representative sample of Americans every two years. The team pulled results from roughly 7,000 people per cycle between 1999 and 2020 and looked at the trend line rather than at any individual.

Serum bicarbonate rose about 7 percent across that period. Calcium and phosphorus drifted down. Over the same years, atmospheric carbon dioxide went from roughly 369 parts per million to more than 420. The authors modelled the trends forward and suggested that, if they hold, average bicarbonate could approach the top of today’s accepted range within about 50 years, with calcium and phosphorus nearing the bottom of theirs later in the century.

The authors are explicit that this is a correlation across a population, not a demonstrated cause. Two things moved together over twenty years. Diet, kidney health, medication use, obesity rates and laboratory methods all changed over the same twenty years, and any of them can move these numbers.

What the CO2 line on your report is measuring

This is where most confusion starts. The CO2 on a standard metabolic panel is not the carbon dioxide gas you breathe out, and it is not the same as the CO2 measured in an arterial blood gas. It is total carbon dioxide content, which is overwhelmingly bicarbonate, the buffer your body uses to keep blood pH stable.

Bicarbonate is one of the four electrolytes reported together, and it is best read alongside the other three rather than on its own, as our page on the elektrolyyttipaneeli explains. Our guide to the kattava aineenvaihduntapaneeli shows where it sits among the other results.

Ranges vary between laboratories, so the numbers printed next to your own result are the ones that apply. A 7 percent population shift is small enough that it moves an average within the range rather than pushing individuals out of it.

The calcium and phosphorus part, and what the study did not show

Several news write-ups translated the falling calcium and phosphorus into bones dissolving to buffer acid. That mechanism is real and well described in the physiology literature, but it is not what this study measured. The study measured blood levels, not bone. It did not include bone density scans, fracture rates or any skeletal outcome.

The mechanism is worth knowing anyway, because it explains why these three lines belong together. When the body faces a sustained acid load, the skeleton acts as a buffer, and bone mineral dissolution releases phosphate, calcium, carbonate and citrate into the circulation, while the kidneys change how they handle all three. Notably, that process tends to raise blood calcium and phosphate in the short term, which is the opposite direction to the trend reported here. That tension is a good reason to treat the headline cautiously.

If your own calcium reading is what concerns you, it is rarely interpretable alone. It needs albumin, and often parathyroid hormone and vitamin D, as set out in our guides to the kalsium- ja luuston mineraalipaneelia sekä reading PTH alongside calcium.

Viimeisimmät tieteelliset edistysaskeleet selkokielellä

According to research indexed in PubMed and in the Consensus literature database, three threads from the last three years are worth knowing.

The first concerns whether breathing more CO2 actually does anything measurable in the short term. It appears not, at concentrations far above outdoor air. In a 2025 chamber study, twenty healthy adults spent eight hours at 3,000 parts per million, roughly seven times current outdoor levels, and showed no robust change in cognition, decision-making or physiological measures. A 2023 crossover experiment in 69 students found the same at up to 2,100 parts per million. A 2024 meta-analysis of brainwave studies did find changes in sleep and in EEG rhythms at elevated indoor CO2, so the picture is not uniformly reassuring, but nothing there points to acute harm at outdoor concentrations. Indoor air, incidentally, routinely runs far higher than outdoor air.

The second is that within the normal range, a higher bicarbonate has generally looked like the better place to be, not the worse one. Among 825 healthy young adults in the Qatar Biobank, each unit increase in serum bicarbonate was associated with a 17 percent lower likelihood of prediabetes in men, alongside lower markers of low-grade inflammation. A companion analysis of 2,989 healthy adults found higher bicarbonate associated with lower uric acid in men. Both are cross-sectional and neither proves cause. They are a useful counterweight to reading any upward drift as automatically bad.

The third is that the direction that clearly harms people is low bicarbonate, not high. In 3,229 cardiac intensive care admissions, metabolic acidosis with bicarbonate under 20 mmol/L was independently associated with higher in-hospital death, while metabolic alkalosis was not. In pre-dialysis chronic kidney disease, higher serum bicarbonate correlated with better bone density at the spine and hip. And a 2025 systematic review of 37 studies covering 24,782 dialysis patients concluded that the evidence on raising bicarbonate deliberately remains very uncertain, which is a fair summary of how much is still unknown about this marker.

What to do with your own result

Very little, if it is in range. This is a population trend measured over two decades, and it is not a reason to request a test or to change anything you are doing.

If your CO2 or bicarbonate is flagged, the useful questions are ordinary clinical ones rather than atmospheric ones. Persistently low bicarbonate points toward the kidneys, toward uncontrolled diabetes, toward chronic diarrhoea or toward certain medications, and is worth reading next to creatinine and eGFR on your munuaisten toimintapaneeli. A high value more often reflects vomiting, diuretics, potassium loss or a respiratory condition. Urine testing sometimes helps localise the cause, as covered in our guide to virtsan elektrolyytit.

If falling calcium and phosphorus are what caught your eye, the practical version of that concern is the boring one that already had good evidence behind it. Vitamin D status, protein and calcium intake, weight-bearing activity and, where indicated, a bone density scan. Our page on the vitamiini- ja ravintopaneelin covers the first of those, and a recent piece looks at vitamin D and belly fat after 50.

Usein kysytyt kysymykset

Is the CO2 on my blood test the same as the CO2 in the air?

No. The CO2 on a metabolic panel is total carbon dioxide content in your blood, which is almost entirely bicarbonate. It reflects how your body buffers acid, and it is influenced far more by your kidneys, your breathing and your medications than by the air outside.

Does this mean my old results are not comparable to new ones?

Not in any way that matters clinically. A 7 percent shift in a population average over twenty years is much smaller than the normal variation between two of your own samples, and smaller than the differences between laboratory methods. Compare your results to the reference range printed on the same report.

Should I ask for a bicarbonate test because of this study?

There is no reason to. Bicarbonate is already included in the standard metabolic panel most people receive, and testing it in isolation without a clinical question would not tell you anything useful.

Is a high bicarbonate dangerous?

A markedly high value, usually called metabolic alkalosis, does need explaining and is most often caused by vomiting, diuretics or low potassium. A value in the upper part of the normal range is not a finding in itself, and the intensive care evidence suggests the harmful direction is low, not high.

Does indoor air matter more than outdoor air here?

Indoor CO2 concentrations are routinely several times outdoor levels in poorly ventilated rooms. Chamber experiments at those higher concentrations have not shown consistent short-term effects on cognition or physiology in healthy adults, though ventilation remains worth attending to for other reasons.

Sanasto

• Bicarbonate, or HCO3: the main chemical buffer in blood, which keeps pH stable by absorbing or releasing acid.
• Total CO2: what the CO2 line on a metabolic panel measures, consisting mostly of bicarbonate rather than dissolved gas.
• NHANES: the US National Health and Nutrition Examination Survey, a long-running programme that collects blood samples from a representative sample of Americans.
• Metabolic acidosis: a state of too much acid or too little bicarbonate in the blood, usually from kidney, metabolic or gastrointestinal causes.
• Metabolic alkalosis: the opposite state, with bicarbonate too high, commonly from vomiting, diuretics or potassium loss.
• Anion gap: a value calculated from sodium, chloride and bicarbonate that helps narrow down the cause of an acid-base disturbance.
• Parts per million, or ppm: the unit used for atmospheric gas concentration, unrelated to the units on your blood test.
• Cross-sectional study: a study that photographs a population at one moment, which can show associations but cannot establish cause.

Ymmärrä omat tuloksesi

A CO2 or bicarbonate value tells you almost nothing by itself. It becomes meaningful next to your sodium, potassium and chloride, your calcium and phosphorus, your albumin, your creatinine and eGFR and the medications you take, and those arrive on the page in a mix of units and reference ranges that rarely explain themselves. AI DiagMe reads your complete lab report and explains, line by line, what each result means in your situation, including where a bicarbonate value sits relative to everything else. Upload your report at aidiagme.com for a clear reading before your next appointment.

Lisälukemista

• CO2 blood test: what your bicarbonate levels mean
• Kattava aineenvaihduntapaneeli: tulosten tulkinta
• Elektrolyyttipaneeli: natrium, kalium, kloridi ja bikarbonaatti
• Kalsiumin verikoe ja luu- ja mineraalipaneeli
• Munuaisten toimintakokeet: näin luet munuaisten verikoearvosi
• PTH blood test: reading your results with calcium

Lähteet

• The Kids Research Institute Australia. Scientists detect a surprising shift in human blood as atmospheric CO2 rises. ScienceDaily, 15 August 2026. sciencedaily.com
• Larcombe AN, Bierwirth PN. Carbon dioxide overload, detected in human blood, suggests a potentially toxic atmosphere within 50 years. Air Quality, Atmosphere and Health. 2026;19(3). DOI 10.1007/s11869-026-01918-5.
• Flagner S, et al. Cognition, economic decision-making, and physiological response to carbon dioxide. Indoor Environments. 2025. Lähde
• Chen D, et al. Effects of short-term exposure to moderate pure carbon dioxide levels on cognitive performance, health symptoms and perceived indoor environment quality. Building and Environment. 2023. Lähde
• Zhang N, et al. The impact of indoor carbon dioxide exposure on human brain activity: a systematic review and meta-analysis based on studies utilizing electroencephalogram signals. Building and Environment. 2024. Lähde
• Omar AA, et al. Association Between Serum Bicarbonate Levels and Prediabetes and Subclinical Inflammation in Young Healthy Adults. Diabetes, Metabolic Syndrome and Obesity. 2023. Lähde
• Ibrahim W, et al. Sex distinctive patterns in the association between serum bicarbonate and uric acid levels among healthy adults. Frontiers in Medicine. 2023. Lähde
• Canova TJ, et al. Admission Acid-Base Status and Mortality in Cardiac Intensive Care Unit Patients. Journal of Intensive Care Medicine. 2025;41(7):670-682. PubMed. DOI-koodi
• Azizudin AM, et al. The Effect of Dialysate Bicarbonate Concentration or Oral Bicarbonate Supplementation on Outcomes in Patients on Maintenance Dialysis: A Systematic Review and Meta-Analysis. Canadian Journal of Kidney Health and Disease. 2025. PubMed. DOI-koodi
• Salcedo-Betancourt JD, et al. The Effects of Acid on Calcium and Phosphate Metabolism. International Journal of Molecular Sciences. 2024. Lähde
• Abbas A, et al. Correlation Between Metabolic Acidosis and Bone Mineral Density in Pre-Dialysis Chronic Kidney Disease. Journal of Health, Wellness and Community Research. 2024. Lähde