Albuminadjusted

Albuminadjusted is a term used in laboratory medicine to describe values that have been corrected for serum albumin concentration. Albumin is the main binding protein in blood, and many substances bind to it. When albumin levels are abnormal, the total measured concentration of those substances can diverge from the physiologically active free fraction, so an albumin-adjusted value provides a surrogate estimate.

The most common example is corrected calcium. Corrected calcium aims to estimate the ionized calcium by adjusting the total calcium for albumin level, typically using the formula: corrected calcium (mg/dL) = measured total calcium (mg/dL) + 0.8 × (4.0 − albumin (g/dL)). The value 4.0 g/dL is a reference normal albumin level, though specific practices vary. Corrected calcium is an approximation and may not be accurate in all situations; direct measurement of ionized calcium is preferred when precise assessment is needed, such as in critical illness or acid-base disturbances.

Albumin-adjusted concepts also appear in drug monitoring for highly protein-bound medications. In hypoalbuminemia, total concentrations may not reflect the unbound (pharmacologically active) portion. Formulas to estimate free drug levels exist for some drugs (for example, phenytoin and valproate), but they are drug-specific and imperfect. These adjustments serve as guidance rather than definitive measurements and should be interpreted in the context of clinical status and, when possible, direct free-drug assays.

Limitations include reliance on assumptions about binding and albumin status; factors such as pH, other binding proteins, and disease states can affect accuracy. See also corrected calcium, ionized calcium, and drug monitoring concepts.