Dear Heidi,

Thanks for this interesting question about the creatinine measurements. To me it raises three questions or issues.

1. I am pretty sure that the creatinine assay is not validated for ileostomy fluid, or indeed fluids other than urine or serum/plasma. This makes it an in-house IVD that we must take responsibility for. I note that you have also measured creatinine with the Enzymatic assay and also measured urea so there is not reliance on one result. However this leads into point 2, why are the creatinine results different?

2. Without knowing the Jaffe supplier, we can fairly safely assume that the assay is tweaked to give a reasonable result in a serum matrix, ie in the presence of the usual non-creatinine chromogens. It is also optimised for the concentrations usually seen in plasma. The issues are different when the same assay is used in urine as the creatinine is at much higher concentrations. For example some assays remove a fixed value from the Jaffe result (e.g. -26 umol/L). If there are no non-creatinine chromogens this is unnecessary and gives a falsely low result. Thus if the fluid is low in protein or low in some other normal plasma components this may be seen. Because of this some Jaffe assays have a lower reporting limit above 20 umol/L, which in this case may be a valid expression of the result.

3. Having said the above, it does seem that you can exclude the presence of urine with a high degree of confidence based on the other two results.

Regards,

Graham

Bilirubin?

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Dear Mailbase,

We had 3 clear yellow fluid sample in this week from a patient in ITU. Clinical details: ileostomy ?urine contamination

Results

Bilirubin checked on sample 1 and was 4 umol/L.

Presumably there is a substance in the fluid sample which is interfering in the Jaffe Creatinine assay. Here is a list of the medications/treatments the patient has been on in the last 5 days or so. Are any of these obvious culprits for interference?

Thanks!

Heidi

Heidi Mendoza PhD FRCPath

Principal Clinical Biochemist

Blood Sciences Department

Raigmore Hospital

Inverness IV2 3UJ

01463 - 705930

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