Serum methylmalonic acid before and after oral L-isoleucine loading in cobalamin-deficient patients.
Over a 1 1/2-year period, we measured concentrations of methylmalonic acid in serum before and after a standardized loading with oral L-isoleucine (100 mmol) in 13 patients admitted for evaluation of cobalamin deficiency. All patients had serum cobalamin values below 100 pmol l-1, but only 12 of the 13 patients were clinically confirmed cobalamin deficient. The clinically non-cobalamin-deficient patient had folate deficiency and was excluded. The serum methylmalonic acid concentrations before loading with isoleucine were above the upper reference limit (0.37 mumol l-1) in all the patients and L-isoleucine caused an increase in serum methylmalonic acid of more than 1.00 mumol l-1 in 11 of the 12 deficient patients. In the remaining patient the increase was 0.35 mumol l-1. The results show that a significant increase of an initially elevated serum methylmalonic acid concentration after isoleucine loading is a general finding in tissue cobalamin deficiency which strongly supports the diagnosis.
Moelby
L
L
Department of Medical Haematology, Aalborg Sygehus Syd (Aalborg-Hospital), Denmark.
Rasmussen
K
K
Jensen
M K
MK
Thomsen
L H
LH
Nielsen
G
G
D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007532:Isoleucine / Q000008:administration & dosage*; D008297:Male; D008764:Methylmalonic Acid / Q000097:blood*; D008875:Middle Aged; D014805:Vitamin B 12 / Q000097:blood; D014806:Vitamin B 12 Deficiency / Q000097:blood / Q000175:diagnosis*
D007532:Isoleucine; D008764:Methylmalonic Acid; D014805:Vitamin B 12