Examples of Preanalytical Factors
That May Affect Chemistry Results
Clinical Chemistry Review 70
FACTOR EFFECT
Use of isopropyl alcohol wipes to disinfect
venipuncture site
Squeezing site of capillary puncture
Pumping fist during venipuncture
Tourniquet >1 min
IV fluid contamination
Incorrect anticoagulant or contamination from
incorrect order of draw
Hemolysis
Exposure to light
Temperature between collection & testing
Can compromise blood alcohol determination
↑K+
↑K+, lactic acid, Ca2+, phosphorus; ↓pH
↑K+, total protein, lactic acid
↑glucose, K+, Na+, Cl–(depending on IV). Possible dilution of other analytes.
K 2 EDTA: ↓Ca2+, Mg2+; ↑K+
Sodium heparin: ↑Na+if tube not completely filled
Lithium heparin: ↑lithium
Gels: Some interfere with trace metals & certain drugs
↑K+, Mg2+, phosphorus, LD, AST, iron, ammonia (May be method dependent. Refer
to reagent package inserts.)
↓bilirubin, carotene
Chilling required for lactic acid, ammonia, blood gases
continued...
