Sullivan Nicolaides Pathology incorrectly quotes a limit of 15.0 umol/L for total homocysteine (so also does the RCPA Manual, reference AF05):

A homocysteine level of 15.0 umol/L is not considered safe by most experts, including authors of reference AE11 and AE12. Both of these expert groups recommend a maximum level of 12.0 umol/L. Here is the diagnostic flowchart for homocysteine, as shown in reference AE12:

As you can see, a level of > 12 umol/L is considered high for a healthy population; a level > 10 umol/L is high for those patients at risk for cardiovascular disease.

Another expert report by Rasmussen et al, reference AF01, provides a range of age and gender-specific reference intervals. For a male aged 30 to 59 years, the recommended limit is 11.2 umol/L.

Reputable laboratories use much lower levels than the 15.0 umol/L quoted by SNP; several are listed in reference AF8 to AF22. This table lists some of these limits, in umol/L:

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