Chronic Kidney Disease & Acid-Base Interpretation
Classify chronic kidney disease using filtration and albuminuria, and read blood gases as a connected physiological pattern.
Quick revision ↓ Medical Dictionary
01Establish chronicity
CKD requires kidney structural or functional abnormalities with health implications persisting for more than three months. A single reduced estimated GFR during illness does not establish chronic disease. Use previous tests, albuminuria, imaging and the clinical history. Creatinine-based estimates are less reliable when kidney function changes rapidly or muscle mass is unusual; a deceptively low creatinine can coexist with impaired filtration in a frail patient.
02Assess risk and progression
Classify disease by cause, GFR and albuminuria, because filtration alone misses important risk. Confirm relevant abnormalities and assess blood pressure, diabetes, cardiovascular disease and medication exposure. Protein or albumin in urine may require a quantified ratio rather than a dipstick alone. Rate of decline, heavy albuminuria, haematuria and systemic features influence specialist referral and investigation of the underlying cause.
03Reduce harm and complications
Management addresses cardiovascular risk, pressure, albuminuria and suitable kidney-protective therapy, with potassium and renal monitoring. Review drug doses, over-the-counter medicines and contrast decisions. Anaemia, mineral-bone abnormalities, acidosis, fluid overload and nutrition need assessment as disease advances. Discuss replacement therapy or conservative kidney care early enough for informed decisions, avoiding the impression that dialysis is determined by one isolated eGFR value alone.
04Read a blood gas systematically
Start with pH, then carbon dioxide and bicarbonate to identify the main respiratory or metabolic process. Check whether compensation is broadly appropriate and consider a mixed disorder when it is not. Acidaemia is a low pH, whereas acidosis is a process that tends to lower pH; opposing processes can produce a near-normal pH. Interpret gases with oxygen delivery, electrolytes, lactate and the clinical story.
05Use the anion gap
A common formula is sodium minus the sum of chloride and bicarbonate: Na − (Cl + HCO3), using consistent units. An elevated gap can reflect unmeasured acids such as lactate or ketoacids; albumin affects interpretation. For sodium 140, chloride 104 and bicarbonate 16, the uncorrected gap is 20 mmol/L. Identify the cause rather than giving bicarbonate automatically, and seek urgent help for severe or mixed derangements.
High-Yield Revision
- CKD requires evidence of chronicity.
- Albuminuria adds risk information beyond eGFR.
- A near-normal pH does not exclude a mixed acid-base disorder.
Common Pitfalls
- Do not diagnose CKD from one acute creatinine rise.
- Do not prescribe bicarbonate solely because pH is low without evaluating the cause.
References & Further Reading
Read the relevant guideline sections alongside these original clinical teaching cases. Local pathways, available services and individual patient factors determine care.
Reference review: 27 September 2026. Consult current local protocols for prescribing, procedures and escalation.