Why is it that the plural of 'blood' is 'blood' in normal usage but 'bloods' (e.g. 'I'll be taking some bloods') is acceptable in a medical context? Are there any words with similar pluralisation anomalies?
This odd pluralisation may be confined to British English, here are some examples
UPDATE: I'm struggling to find online examples of this usage outside of midwifery as per the links above. Now I'm wondering if 'bloods' is actually a pluralisation that refers to both the mother and baby's blood. Has anyone an example of a medical usage outside of pregnancy?