Hi Markus,

To my knowledge there is no formula, but maybe you could find elements of response at least in the following study "Capillary and venous haemoglobin levels in blood donors: a 42-month study of 36,258 paired samples".Tong E,et al  Vox Sang. 2010, 98:547-53. doi: 10.1111/j.1423-0410.2009.01285.x. 

BW. Gilles

Thanks a lot, Gilles!

It is always helpful to get an answer from you.

Best,

Markus

As far as I know no formula has ever been published, not even in the "grey" literature. I suppose that a correlation coefficient between methods should be defined through adequate comparison studies, which could also contribute to validate the methods. Some info can be found in an article by Irish colleagues - Tong and co-workers (Vox Sang. 2010 May;98(4):547-53). Ciao. Giuliano

Dear Giuliano,

Thank you very much.

Best,

Markus

I am not aware of a factor that can be used through the entire range of values observed among donors and patients. I  have attached an abstract of a paper published by the NIH Blood Bank group in Vox in 2013 that illustrates the problem.

Dear Celso,

Thanks a lot. Most useful citation.

Best from Frankfurt,

Markus

Dear Marcus,

I would like to add additional information on the topic.

http://www.ncbi.nlm.nih.gov/pubmed/23294266

It is well known that capillary hematocrit is lower than the hematocrit of systemic venous blood according to the Fahraeus effect.

Biorheology. 1980;17(1-2):183-9.

Flow of blood through narrow capillaries: rheological mechanisms determining capillary hematocrit and apparent viscosity.

Gaehtgens P.

Thanks a lot to Doris, Gregory and Hiromi for your valuable addition to this question. Our studies comparing different methods of capillary hemoglobin measurement with venous hemoglobin show differences, which in part can be explained by the Fahraeus effect as Hiromi pointed out correctly. However, some of the capillary methods are very close to the venous hemoglobin and differ significantly from other capillary methods, a fact, we cannot explain at the moment.

It can be imagined that distributions of both flow rate and capillary diameter would significantly affect on the strength of Fahraeus effect and the resulting capillary hematocrit on the average.

Dear Markus,

I would like to offer my own version of the explanation, I think that the results of the measurement of hemoglobin in the capillaries are heavily dependent on the depth of penetration. Therefore, the change in the measuring method or device leads to a change in the result. The deeper penetration - the less the difference between the results (venous vs capillaries hemoglobin value).

Dear Hiromi, dear Gregory,

Thank you very much for your valuable additions.

This is worthwhile to explore further.

Best,

Markus

Due to the wide range of haemodynamic changes that occur in circulation in the various regions of the body and at different times, I guess there may be subtle difference, but not like what is observed with blood glucose.

Thanks a lot!

Best,

Markus