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Serum alkaline phosphatase isoenzymes in childhood
Insights
Serum alkaline phosphatase (AP) in children was separated into three fractions: intestinal, hepatobiliary, and bone AP. Bone AP is the predominant fraction, and specific ratios aid in differentiating liver and bone isoenzymes.
Area of Science:
- Biochemistry
- Clinical Chemistry
- Pediatric Medicine
Background:
- Serum alkaline phosphatase (AP) is an enzyme with multiple isoenzymes originating from different tissues.
- Accurate differentiation of AP isoenzymes is crucial for diagnosing various diseases, particularly in pediatric populations.
Purpose of the Study:
- To develop and validate a semiquantitative method for separating serum AP isoenzymes in children.
- To establish the relative contributions of intestinal, hepatobiliary, and bone AP to total serum AP activity.
- To identify reliable ratios for differentiating bone and liver AP.
Main Methods:
- Utilized L-phenylalanine inhibition and heat inactivation to separate serum AP into three fractions: LPSAP, heat-stable non-LPSAP, and heat-sensitive non-LPSAP.
- Measured total AP activity and the activities of each fraction under optimized conditions.
- Calculated percentage ratios (Q value) of heat-stable non-LPSAP/non-LPSAP and heat-stable non-LPSAP/total AP.
Main Results:
- L-phenylalanine sensitive AP (LPSAP), primarily intestinal, constituted ~12% of total serum AP.
- Heat-stable non-LPSAP, mainly hepatobiliary, accounted for ~9% of total serum AP.
- Heat-sensitive non-LPSAP, predominantly bone AP, represented ~77% of total serum AP.
- Both determined quotients showed a significant negative correlation with total AP activity.
Conclusions:
- A semiquantitative method for separating serum AP isoenzymes is feasible in routine clinical laboratories.
- Bone AP is the major contributor to serum AP activity in healthy children aged 2-13 years.
- The established ratios provide valuable tools for differentiating bone and liver AP, aiding in clinical interpretation, especially when considering total AP levels.
Abstract:
Using a combination of L-phenylalanine inhibition and heat inactivation, the serum alkaline phosphatase (AP) in 2 to 13 year old children without evidence of hepatobiliary, osseous, or intestinal disease was separated in three fractions; i.e. L-phenylalanine sensitive AP (LPSAP), heat-stable non-L-phenylalanine sensitive AP (heat-stable non-LPSAP) and heat sensitive non-L-phenylalanine sensitive AP (heat-sensitive non-LPSAP). The activities of total AP and the different fractions were measured using optimized test conditions. LPSAP, (mainly intestinal AP), accounts for approximately 12% of the total serum AP activity, heat-stable non-LPSAP (mainly hepatobiliary AP) for approximately 9%, and heat-sensitive non-LPSAP (mainly bone AP) for approximately 77%. To give a better differentiation between bone and liver AP, the percentage ratios of heat-stable non-LPSAP/non-LPSAP (Q value), and heat-stable non-LPSAP/total AP, were determined. Both quotients showed a significant negative correlation with total AP, which has to be taken into account in the interpretation of the results of isoenzyme determinations of serum AP activity. The above semiquantitative separation of AP isoenzymes can be readily done in a routine clinical laboratory.