TABLE 1.

Lipid categories and species quantified in the human plasma SRM

Lipid Category	Number of Species	Sum (nmol/ml)	Sum (mg/dl)
Fatty Acyls
Fatty Acids	31	214	5.82
Eicosanoids	76	0.071	0.002
Total	107	214	5.82
Glycerolipids
Triacylglycerols	18	1058	90.6
1,2-Diacylglycerols	28	39	2.36
1,3-Diacylglycerols	27	13	0.805
Total	73	1110	93.7
Glycerophospholipids
PE	38	435	32.7
LPE	7	36.6	1.78
PC	31	1974	157
LPC	12	103	5.25
PS	20	7.00	0.559
PG	16	6.12	0.480
PA	15	2.50	0.173
PI	19	31.5	2.74
N-acyl-PS	2	0.013	0.001
Total	160	2596	201
Sphingolipids
Sphingomyelins	101	303.468	22.817
Monohexosylceramides	56	2.3135	0.180
Ceramides	41	11.586	0.732
Sphingoid Bases	6	0.5678	0.02029
Total	204	318	23.7
Sterol Lipids*
Free Sterols	14	826	31.8
Esterified Sterols	22	2954	114
Total	36	3780	146
Prenol Lipids
Dolichols	6	0.025	0.003
Coenzyme-Q	2	4.59	0.394
Total	8	4.62	0.397
Total	588	8023	471

^*Sterols in plasma (nmol/ml) were determined as described in the supplementary experimental procedures. Weight calculations (mg/dl) were based on the sterol backbone for sterol esters. Additionally, total sterols were also measured by clinical laboratories following procedures certified by the Center for Disease Control and they reported similar plasma levels, though they are lower than the national average (National Health and Nutrition Examination Survey 2003–2006). The SRM consists of plasma pooled from individuals within a narrow age range. Thus, cholesterol values may deviate from other averages that include individuals from a wider age spectrum.