Lactate Dehydrogenase Levels and Isozyme Patterns

Lactate dehydrogenase (LDH) activity was determined in 24 cases of histologically proved retinoblastoma. The mean level was 1,825 IU/L, with a range of 10 to 15,920 IU/L. Twenty-two patients had elevated aqueous humor LDH levels. In two, the aqueous humor level was within the normal range. Student's t testing showed a highly significant difference between cataract and retinoblastoma aqueous humor. The retinoblastoma aqueous humor to blood ratio ranged from 0.045 to 58,529--not a good index of retinoblastoma. Isozyme patterns of retinoblastoma aqueous humor were statistically similar to those of normal cataract aqueous humor. The serum LDH level of cataract patients was not statistically different from that of retinoblastoma patients. The LDH 5/LDH 1 ratio of retinoblastoma aqueous humor ranged from 0.042 to 27.05--not a good index of retinoblastoma, as 28 of 34 aqueous samples of cataract patients had LDH 5 greater than LDH 1. Ten of 13 retinoblastoma patients had aqueous humor LDH 5 greater than LDH 1. The best index of the presence or absence of retinoblastoma is the total aqueous humor LDH level.