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Background: Lactate (L) and pyruvate (P) concentrations in cerebrospinal fluid (CSF) and the L/P ratio have diagnostic value in numerous primary and acquired disorders affecting the central nervous system, but age-related reference values are not available for children. Methods: We analyzed CSF and blood lactate and pyruvate concentrations and their ratio in a 4-year retrospective survey of a children’s hospital laboratory database. Reference intervals (10th–90th percentiles) were established from data on 197 hospitalized children. A recent regression modeling method was used to normalize and smooth values against age. The model equation of best fit was calculated for each variable. Results: Slight age-related variations were shown by the model, with an increase in lactate, a decrease in pyruvate, and a resulting increase in the L/P ratio with increasing age. However, the SD did not vary with age. We defined the upper limit of the reference intervals as the 90th percentiles, which from birth to 186 months of age varied continuously from 1.78 to 1.88 mmol/L (6%), 148 to 139 μmol/L (6%), and 16.9 to 19.2 (14%) for lactate, pyruvate, and the L/P ratio, respectively. At a threshold of 2 (in Z-score units), the sensitivity for a subgroup of inborn errors of metabolism (respiratory chain disorders) was 73%, 42%, and 31% for lactate, pyruvate, and the L/P ratio, respectively. Conclusions: In children, CSF lactate and pyruvate concentrations and their ratio appear to vary slightly with age. Average 90th percentile values of 1.8 mmol/L, 147 μmol/L, and 17, respectively, could be used in infants up to 24 months of age. In older children, age-adjusted reference intervals should be used, especially when values are close to the 90th percentile.

Several reports indicate that urinary growth hormone (GH) excretion might reflect central release of the hormone, and that measurement of urinary GH shows promise in the investigation of physiological and pathological GH secretion. We have developed and evaluated a direct immunoradiometric assay (IRMA) in which two monoclonal antibodies are used to measure GH in the urine of children. The detection limit is approximately 0.018 pmol/L for a sample volume of 2 mL. Within- and between-run variations (CVs) were 5.6% and 14.2%, respectively. Analytical recovery and dilution experiments showed the specificity of the method for GH. In normal-stature prepubertal children ages 3-12 years, 24-h urinary GH excretion was 0.189 (SD 0.100) pmol and correlated well with the amount of GH in the first morning miction, which showed wide day-to-day variations. Like others, we found a strong correlation between GH concentrations in serum and urine during stimulation tests with GH-releasing hormone (somatoliberin) and (or) during physiological nocturnal secretion, confirming that urinary GH measurement may be of help in investigating patients (particularly young children) with diseases in which GH secretion is impaired.