A worked case showing how low albumin offsets acidifying effects, why a normal pH or anion gap can mislead, and what to check next.
Lactate is raised, but pH and SBE are within range
A synthetic adult critical-care case: lactate is 5 mmol/L, albumin 20 g/L, sodium 140 mmol/L and chloride 110 mmol/L. The arterial gas and chemistry are from the same sampling time.
A near-normal gas does not make the raised lactate unimportant. Check the measured contributors before calling the acid–base state normal.
Opposing metabolic effects; net SBE within the selected range
SBE is −0.2 mEq/L, within the default ±2 range. There is no net metabolic acidosis by that screen. Chloride relative to sodium and raised lactate have acidifying effects; low albumin has an alkalinising effect.
Full chemistry for this case
Same-time measurements · synthetic case
Measurement
Value
Unit
Sodium
140.0
mmol/L
Potassium
4.0
mmol/L
Chloride
110.00
mmol/L
Lactate
5.0
mmol/L
Albumin
20.0
g/L
Phosphate
1.0
mmol/L
Ionised calcium
1.2
mmol/L
Total magnesium
0.8
mmol/L
Lithium and sulfate are set to zero in this constructed example. Total magnesium approximates strong-cation charge.
Arterial sample; gas and chemistry from the same sampling time. Respiratory time course: Acute.
What low albumin changes
Albumin is a weak acid. A lower concentration reduces weak-acid charge and has an alkalinising direction. This can partly offset acidifying processes. It does not remove lactate or establish that the underlying illness has resolved.
Low albumin also lowers the conventional anion gap. That is a separate reason why an uncorrected gap can be misleading.
Here, AG is 5.8 mmol/L. Albumin correction adds 0.25 × (40 − 20) = 5.0 mmol/L, giving 10.8 mmol/L. Both fall within the app’s default 4–13 interval; this case does not demonstrate a raised corrected AG. The measured lactate and chloride pattern still require explanation.
What to check next
Raised lactate: assess perfusion, oxygen delivery, recent seizures, adrenergic drugs and impaired clearance. Use the clinical course and repeat measurements.
Chloride relative to sodium: review fluid composition, gastrointestinal losses, renal function and medicines.
Low albumin: review inflammation, dilution, hepatic synthesis and renal or gastrointestinal protein loss. The acid–base calculation does not identify the cause.
Reading the contribution chart
The simplified base-excess chart estimates a sodium–chloride effect of −8.0 mEq/L and an albumin effect of +5.5 mEq/L. The remaining +2.3 mEq/L includes other effects and approximation error. These three terms sum to SBE.
Lactate is already included in that remainder. Do not add a separate lactate term to this chart. The remainder is not SIG. The separate ion chart uses different reference anchors and balances the change in calculated bicarbonate.
Low albumin does not, by itself, account for the entire balance. These are estimates against stated comparison values, not a prediction of what albumin administration would do.