Ratzmann GW¹, Zöllner H ^{(+ in memoriam)}

MAGIP-Project Greifswald, Germany
¹ Pediatrician, Am Kohlgraben 22, 17498 Neuenkirchen (formerly Kinderklinik der Ernst-Moritz-Arndt-
Universität Greifswald)

Within the blood magnesium (Mg) is very strongly regulated by homeostatic functions. Therefore, lowered Mg
of serum or plasma certainly reflects a Mg deficiency; however, normal or even elevated Mg values do not
exclude Mg depletion. If in the state of Mg deficiency the renal Mg excretion is throttled, measurements could
be given additional informations about the Mg balance. In part, deficient reference data could be responsible
for failing of urinary Mg analysis in the clinical practice. - Before urinary chemical analysis is performed, latent
or chronic renal diseases must be excluded (micturition function, biochemical screenings, quantitative cytologic
and/or bacteriolo-gic diagnosis, renal sonography, blood pressure). Because of high variability of urinary
analytes (x) in sponta-neous urinary fractions sampling of the 24-hour urine (dU) is necessary. Data of body
length, body mass (BM), dU volume and measurements of creatinine, urea, Mg and other electrolytes of urine
and blood allow the calcu-lation of several renal functional parameters (e. g. dU-x-excretion, electrolytecreatinine-
ratio, clearances, FE values, THOMAS index). Calculation of dU-x per kg BM [ mmol/kg/24h ] helps to
reduce the range of measured values (by variability of urinary analytes, age-/body mass dependences, a. o.) for
better diagnostic classification. Within the first trimenon of infants such measured renal Mg-excretion amount
to 0.064+/-0.055, and such of school children (aged 6-17 years) 0.074+/-0.039 mmol/kg/24h, respectively. If in
Mg-deficient patients the renal dU-Mg is reduced to 0.047+/-0.032 (systemic jcA) or to 0.051+/-0.023
mmol/kg/24h (hyperventilation syndrome), the diagnostic value of urinary Mg measurements is made clear.