Specimen requirement

Balanced heparin syringe  

(*Please note that different brands of syringe with different size and heparin content are used in NTEC hospitals.)

Minimum blood volume: 0.6 mL (using 1 mL syringe containing 30 IU balanced lithium heparin)

Minimum blood volume: 1.6 mL (using 3 mL syringe containing 80 IU balanced lithium heparin)

Authorisation code required

No

24 Hr available service

Yes

Precaution

Blood Taking Procedure

1. Appropriate volume of blood should be collected anaerobically in a special balanced heparin syringe. (Collect 0.6 mL blood for 1 mL syringe and 1.6 mL for 3 mL syringe so that the final concentration of the balanced heparin in sample is 50 IU/mL.)
    
2. Dispose the needle, tap syringe to move air bubble to the top and slowly advance plunger to expel air from sample, and then re-cap the syringe with a cap.
    
3. To ensure thorough mixing of blood with heparin, hold syringe in hand and rotate back and forth for 20 to 30 sec.
   
   
4. Send the blood sample in ice bath to the laboratory immediately for analysis.

At the dosage given as an antidote for cyanide poisoning, hydroxocobalamin may cause falsely low results in total haemoglobin, carboxyhaemoglobin and methaemoglobin measurement and falsely high results in oxyhaemoglobin measurement.

Method

Co-oximetry

Reference interval

(Source: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics 4th Edition, USA Elsevier Saunders, 2006: 2259, 2286, 2289)

Clinical indication

Investigation of unexplained central cyanosis; possible oxidant drug haemolysis (e.g. sulphonamides, aniline dyes, nitrates and nitrites)

Result interpretation

High methaemoglobin fraction concentrations, a condition called methaemoglobinemia, can produce hypoxia and cyanosis.     

Methaemoglobinemia can be the result of hereditary conditions (e.g. Hb M haemoglobinopathy or methaemoglobin-reductase deficiency) or of exposure to toxic substances (e.g. nitrates, nitrites, aniline dyes and their derivatives) and topical anesthetics (e.g. benzocaine).     

Infants and other individuals with significant fetal haemoglobin concentrations show increased susceptibility to methaemoglobinemia because fetal haemoglobin converts to methaemoglobin fraction more readily than adult haemoglobin.

Measurement of uncertainty

See table.

Frequency of measurement

Daily