Macro-alkaline phosphatase due to IgG kappa complex: demonstration with polyethylene glycol precipitation and
M C Owen1, L S Pike, P M George
1Clinical Biochemistry Unit, Canterbury Health Laboratories, Christchurch, New Zealand. Maurice.Owen@chmeds.ac.nz
Insights
Persistent high alkaline phosphatase (ALP) in a woman was due to macro-alkaline phosphatase, a complex with IgG. This finding clarifies a rare cause of elevated ALP levels.
Area of Science:
- Clinical Biochemistry
- Immunology
Background:
- Elevated plasma alkaline phosphatase (ALP) can indicate various health issues.
- Unexplained persistent hyperphosphatasia requires thorough investigation.
Observation:
- A 71-year-old woman presented with persistently elevated plasma ALP of unknown origin.
- Polyethylene glycol precipitation was used to investigate the cause.
Findings:
- The elevated ALP was attributed to macro-alkaline phosphatase.
- Gel filtration revealed two high molecular weight (MW) peaks (approx. 330 kDa and 560 kDa).
- Immunoelectrophoresis identified the ALP complex as a composite with immunoglobulin G (IgG) and kappa light chains.
Implications:
- Macro-alkaline phosphatase is a rare but significant cause of hyperphosphatasia.
- This case highlights the importance of characterizing ALP complexes in diagnosing unexplained elevations.
- Understanding ALP complex composition aids in differential diagnosis and patient management.
Abstract:
An otherwise unexplained, persistently elevated plasma alkaline phosphatase concentration in a 71-year-old woman was found to be attributable to the presence of macro-alkaline phosphatase using polyethylene glycol precipitation. Gel filtration showed two high MW peaks with masses of about 330 kDa and 560 kDa. The alkaline phosphatase (ALP) complex was characterized by immunoelectrophoresis as a complex with IgG with kappa light chains.
