240 U/L) remain eonstant over a measurement time of 300 s
(l). However, forshorter measuring times catalytic activity
concentrations up to about 15 ykat/L (900 U/L) may be measu–
red before dilution with NaCl, 150 mrnol/L becornes necessary
(16).
2.10 Sample Volume Fraction
With the IFCC Reference Method a linear relationship has been
documented to exist between sample volume fractions of about
0.015 to 0.08 and reaction rates and this relationship prob–
ably extends to about 0.10 (l).
Likewise, dilutions of samples with buffer or NaCl, 150
mrnol/L do not result in significant errors (l).
3. REACTION BLANK RATES
3.1 Reagent Blank Rates
+
An LDH-MDH-2-oxoglutarate - NADH
+
H reagent blank reaction
is unavoidable.
Centamination of reagent enzymes, rnalate and lactate dehydro–
genases with ASAT will cause a reagent blank rate. If reagent
blank rates are higher than 60 nkat/L (about 4 U/L) corre–
sponding to a decrease of absorbance at 340 nm of 0.002 per
60 s, the reagent should be discarded.
3.2 Sample Blank Rates
Sam~le
blank rates may occur (l) . In the presence of sample
NH
concentrations compatible with life up to about l% of
4
high glutamate dehydrogenase cat alytic activity concentra-
tions may be measured. These conditions usually coincide with
highly increased ASAT and ALAT values, and thus may be consi–
dered of no clinical importance.
Klinisk kemi
i
Norden 2: supp/, 1990
49
