An investigation into the relationships between serum levels of C3, C4 and CH50

Aliquots of 213 specimens were assayed for C3, C4 and CH50. A graphical presentation of the data was obtained by a block diagram. This showed a generally flat plane with good agreement to quoted normal ranges. Only 2 of 68 specimens with C3 and C4 normal have a low CH50. If either the C3 or C4 is low then the CH50 may be normal or even high, but if both fractions are low then so is the Ch50. A low CH50 can occur with both C3 and C4 in the normal range or even higher. This implicates other complement factors as being deficient with a sufficiently high occurrence rate to require that the CH50 be kept as a routine laboratory procedure.