Dean F. Martin University of South Florida Tampa. Florida 33620 Thomas C. ~ a r t n e y M.D. . Medical Park Clinlcal labs. Inc. Tampa, Florida 33620
I
clinically significant constituents, I
I
chO1esterO1
I
Clinical Significance Cholesterol (I, see figure) is a major component of all mammalian plasma membranes. Though i t is vital to cell growth and survival (1,2), excessive amounts of the sterol can also be lethal in the instances when cholesterol deposits in arterial cells and contributes to the development of atherosclerosis. In man, cholesterol in plasma is associated with lipid-protein compounds. Linids are a class of oreanic comnounds that include oils. wax&, and fats. Lipids are esters firmed from two less rom: olex molecules.. fattv .acids. and an alcohol. With true fats. the alcohol is glycerine (glyc&ol), and the materials are &led trielvcerides. With waxes. the alcohol mav be somethine other tGglycerol, and the waxes may also inciude the steroiesters, the best known of which is cholesterol. In addition LO their chemical characteristics, serum lipids mas he differentiated bv their phssical prowrties: ~articularlv useful is density, a property that is me&able b; ultra-ceitrifugation. "High, low, very-low, and extremely-low density" lipids may be identified to be correlated with their physiologic effects. Three-fourths of man's serum cholesterol exists as low-density lipoprotein (LDL) ( I ) . Many conditions are associated with changes in lipid levels (Table I), but vascular disease is the main pathologic process to be correlated with a change in lipid levels (Table 2). Elements that characterize the type of hyperlipernia include cholesterol and triglyceride levels and plasma appearance, especially after a period of refrigeration. Table 1. Summary of the Cllnical SlgnHlcance of Cholesterol Levels ( 2 3 ) Cond'nion~Associated With Elevated Levels Reduced Levels Dietary and Metabolic Disordsm Diemv w Metabolic Dlsabsm Essential (Primary or familial)hyMalnulrition pwcholesterolemia Severe liver damage Mixed (familial with dietary corn Chronic anemla, including pemC ponent) hyperlipopotelnemia CIOYS anemla in relapse, hem* Carbohydrate-induced hyperlilytic anemia, marked hypo. pemia chromic anemia SelectedDiseases and Disorderr Spsciflc Diseases Alcoholism nrperlhyroidlsm Acute interminem pwphyria Diabetes mellihrs (lnsuiindepen- Spscific ChOlestemlLevels that Lower dent, uncontrolled) lnhibitlxs of chotesterolabsaptlon Glycogen storage dlseases (e.g. 6-sitosterol, neomycin) Hepatic disease inhibitors of cholesterol svnthesis Wpercalcemia, Idlopathlo 1e.g.. nicotinic aca, hydroxyWpothyroidism (myxedemia) amines, estragenlc subNephrotic syndmme stances) Pancreatiis Enhancers of cholesteml exaetlan other (e.g.. thyroid active substances Bilary obstnrctlon (stone,carcinosuch as demomyroxin, ilneOlamldes) ma of dm!, molangiolitlc cirmls) OlI~eragems*
-
~r~(mnancv -, 'Fore~*~bilsac~(~~chdsatemii.lhem~-'Llmnoued~ lmeractlon wnh an anlonexchsnge rmln chloosmine. Oueshan@(26)mlenlpal h y dr~niae.cota@mmepatimbgeahj. cha~ertorohnanagementagonBare descrlbsd in me PMI 121).
-,
Cholesteml (I) R = H. cholesterol ester R = R ' W bischolerterlenyl derlvatba, II (25):cholestane-hne, Ill.
Sampllng Precaullons The patient should he on a "normal-for-him" diet for a t least three days prior to sampling for cholesterol determination. No foods or liquids, other than water, should be permitted during a 14-hr interval prior to sampling. In practice, an early (5 p.m.) supper is recommended the night before testing. After supper, water only is permitted until blood samples are obtained 14 or more hours later. Cholesterol levels rise significantly during artificial venous compression (6); therefore, blood withdrawal should be accomplished as quickly as possible, and if multiple tubes are taken during samplihg, the portion that is drawn first should be resewed for cholesterol analvsis. Sodium azide (often used as a preservative for serum) seriously interferes with the analysis of cholesterol, so it should not be used (7). Test Prlncble Numerous analytical procedures are available for cholesterol because of its clinical significance. The goals of these procedures have been enhanced accuracy, improved precision, rapidity, and practicality, not all of which are mutually compatible. Considerable attention has been given to developing improved procedures for extracting cholesterol from serum prior to separate analysis of the extracted material (2).Other methods have been concerned with direct reaction mixture and bypass the extraction step. Most methods for cholesterol analysis use a colored com~ o u n dthat can he measured photometrically (8).The Lieherman-Burchard reaction, or a modification of it, probably has been the most popular procedure, which consists in mixing a chloroform solution of cholesterol with concentrated sulfuric acid in acetic anhydride. A green color results, and the maximum ahsorbance a t 620 nm is used to quantitate cholesterol (2). Disadvantages of the procedure include temperature dependence, light sensitivity, and color instability (6) as well as excessive sample volume (9).
Volume 55, Number 4, AprN 1978 / 239
Table 2. Famlllal Hyperllpmla Classlltcatlon Scheme (2-5) Type WHO Clas~ifi~~tim
Selected Synonyms
Triaivcerides -, Choiesteml el* mg % elevated mg % vated
Cause
I(rare)
Essential hyperiipemia Dietary fat not at-induced hyperiipemia cleared horn plasma
501.000
Iia (Common)
Essential Delay in LDC removal hyperchoiesterolemia metabolic ktyperbetaiipaprotein- ' defect? emia
3001800
ilb
Mixed hyperlipoprotein- Longterm dietary emia excess
I11 (Less com-
m n h n II and IV) IV (Probably most common type)
V (Uncommon)
N-++
+++
Plasma Appearance
Therapeutic Principle
1000- +++Cream layer on 30.000 top clear iniranate layer 150500
0-+ Unusualiy clear. may be slightly turbid
Restrict fat intake Medium chain higlycerides i h i diat Chemotherapy Attain and maintain normal weight Diet alone: chemotherapy may be needed.
Overindulgence hyperiipemia Woad beta disease Familial hvoerlioemia .. .
175- variable 2001500 to 1400
+t
+
+
+
Carbohydmte-induced Diwdered carbohydrate lipernla mtabolism, or Endogenous hyperlipemla exwssive Endogenous intake of carbohydrates hypertriglyceridemla or inc. in VLDL
1502.000
Mixed hyperlipidemla Mixed types I and tV
3001500
Metabolic defect? lnc. production of VLDL
+
17510,000
17510,000
+t
Usually turbid with faint chylomicron layer
Diet and chemotherapy reduw to ideal weight
Usually turbid Weight reduction with no cream layer Reduced carbohydrate
Cream layer on Diet and chemolhwspy top; turbid inhanate layer
+ elevated. ++ moderatelyelevated, +++ M e d l y elevsfsd. N rmrmai Errors in temperature control probably cause the largest concentration errors. Hewitt and Pardue ilOa) , . stress the importance of precise control in a fast kinetic method for cholesterol; kinetic equation and error analysis have been provided (lob). Another colorimetric procedure em~lovsoxidation of cholesterol with ferric ion tb produce colo~ed&mpounds(Zak reaction: FeCL-H&Oa method) (9). While this ~rocedure does not have
