Nearly half of kidney disease patients have an acid imbalance nobody is testing for

The test costs almost nothing. It is available in virtually every clinical laboratory. It takes minutes. And in Japan, fewer than one in ten chronic kidney disease patients receives it in any given year.

Serum bicarbonate measurement - the simple blood test that detects metabolic acidosis - is so infrequently ordered for CKD patients that an entire complication is hiding in the gap between what guidelines recommend and what clinicians actually do. A new study using Japan's nationwide Chronic Kidney Disease Database Extension (JCKDDBEx) has quantified just how wide that gap is.

The 10% problem

Mai Tanaka and colleagues at Niigata University extracted data from more than 21 university hospitals, evaluating bicarbonate measurement, diagnosis, and treatment patterns in adults with CKD stages 3a through 4 between 2014 and 2021. The annual measurement rate for serum bicarbonate was consistently below 10%.

Because almost nobody was being tested, the apparent prevalence of metabolic acidosis in the overall CKD population looked reassuringly low. But that number reflected measurement frequency, not disease frequency. When the researchers narrowed their analysis to the small subset of patients who actually had bicarbonate measured, the picture inverted. Nearly half met the clinical criteria for metabolic acidosis, and the prevalence climbed with advancing kidney disease.

"The rate of serum bicarbonate measurement was low in CKD patients, suggesting that more attention to metabolic acidosis is needed in routine CKD care," Tanaka said.

Diagnosed in 8.6%, treated in 7.5%

Even among patients whose bicarbonate levels had been measured and found to be below the 22 mEq/L threshold that triggers guideline-recommended treatment, the diagnosis rate was just 8.6%. The treatment rate was 7.5%. That means more than nine out of ten patients with laboratory-confirmed metabolic acidosis were neither formally diagnosed nor treated.

This matters because metabolic acidosis is not a benign finding. It accelerates kidney function decline through pathways that promote tubulointerstitial injury and fibrosis. It drives muscle wasting, bone disease, and insulin resistance. It correlates with increased mortality. And it is treatable - sodium bicarbonate therapy and dietary interventions have both shown promise in slowing kidney deterioration.

Not just a Japanese problem

If this were a quirk of Japanese clinical practice, it would be concerning but contained. It is not. A large real-world analysis across American and Canadian cohorts led by Abramowitz and Whitlock found a strikingly similar pattern: metabolic acidosis frequently goes unrecognized in CKD patients, fewer than 20% receive sodium bicarbonate therapy, and many cases remain invisible in administrative health records.

The consistency across different healthcare systems suggests a structural problem in how CKD is managed globally. Bicarbonate testing is not embedded in standard CKD monitoring panels the way creatinine or electrolyte panels are. It exists in guidelines but not in clinical workflows. The barrier is not technology or cost. It is habit.

An actionable quality target

The Japanese Society of Nephrology, like its international counterparts, recommends monitoring metabolic complications of CKD and correcting acidosis when serum bicarbonate falls below 22 mEq/L. The guidelines exist. The test is cheap. The treatment is available. What is missing is routine implementation.

For clinicians and health systems, the study identifies what the authors call an actionable quality improvement target: incorporate bicarbonate testing into standard CKD monitoring panels. As CKD prevalence rises globally - particularly in aging populations - this single addition to routine bloodwork could substantially improve detection rates and enable earlier intervention.

The study's limitations are worth noting. The data come from university hospitals, which may not reflect practice patterns in community settings. The retrospective design cannot establish whether routine bicarbonate screening would improve clinical outcomes - only that the current screening rate is far too low to detect a complication that affects roughly half of CKD patients when actually measured. Prospective trials testing the impact of routine screening on kidney outcomes would strengthen the case.

But the core message requires no further data to act on. A treatable complication that accelerates kidney failure, worsens quality of life, and increases mortality risk is being missed in the vast majority of patients because clinicians are not ordering a test that costs almost nothing. The fix is straightforward. The question is whether healthcare systems will implement it.