A request for carboxy- and methaemoglobin on a 4y old Asian male child gave "interferences" on all the haemoglobin and derivative channels on Roche Omni blood gas analysers. Why? Suggestions gratefully received!
The child had been admitted with a 2 day history of diarrhoea and vomiting. Routine oximetry showed a saturation of 74% and oxygen was administered at 15L/min. The PO2 (not measured previously) was >30kPa, but the O2 saturation remained low. The metHb etc. were requested in an attempt to explain this disparity. (MetHb apparently interferes with pulse oximetry.)
There was no past medical history of note, and no exposure to medications (prescribed or not) or environmental or diagnostic agents was elicited.
The child was very anaemic with a Hb of 5.2g/dL. MCV, PCV and RBC count were all low, with 9% hypochromic cells and a retculocyte count of 2.1%. The total bilirubin was raised to 99umol/L and the LDH was high at 3,612 IU/L. The urea is slightly high at 6.8mmol/L. The Hb and O2 sats. responded to blood transfusion but the Hb is falling again.
The blood gas interferences were repeated on fresh pre-transfusion samples and another analyser of the same type, both of which are otherwise functioning well. Spectrophotometry of a haemolysate showed no abnormal peaks in the range 300 - 700nm, and that haemolysate produced the same interferences on the Omni. Known interfering substances such as methylene blue and lipid suspensions have been excluded.
Presumably the child is haemolysing, cause as yet unknown (direct Coomb's test negative). Possibly the cause of interference and the presence of this condition and the request for Hb derivatives is a rare coincidence. But neither we nor neighbouring colleagues are aware that this causes such interference, which persisted in a centrifuged haemolysate prepared off the analyser. If any colleagues have had such an experience or have any other comments I'd be pleased to hear from them.
Consultant Chemical Pathologist
Bradford Teaching Hospitals NHS Foundation Trust
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