Number 21 n March 1, 2010

Biological Variation of Laboratory Analytes Based on

the 1999–2002 National Health and Nutrition

Examination Survey

by David A. Lacher, M.D.; Jeffery P. Hughes, M.P.H.; and Margaret D. Carroll, M.S.P.H., Division of Health and

Nutrition Examination Surveys

Abstract

Objective—Biological variation consists of within-person (WP) and betweenperson (BP) variation. These components of biological variation are used to set

analytical goals for imprecision and bias, evaluate serial changes for individual

analytes, and assess the clinical utility of population-based reference intervals.

Estimates of WP coefficients of variation (CVw) and BP coefficients of variation

(CVg) for laboratory analytes were estimated from the 1999–2002 National

Health and Nutrition Examination Survey (NHANES).

Methods—NHANES is a survey of the noninstitutionalized civilian U.S.

population that uses a stratified, multistage probability design to collect a

nationally representative sample. Between- and within-person variations were

estimated for 34 laboratory analytes, including general biochemical, nutritional,

and environmental analytes. Between-person variation was estimated taking into

account the complex sample design of NHANES by Taylor series linearization.

For WP variation, a nonrandom sample was obtained with an average of 18.8

days (range: 3–51 days) between two analyte measurements. Data outliers were

excluded using Tukey’s method to obtain more stable estimates of variation.

Results—The BP and WP variations were estimated on as many as 18,761

and 853 sample persons, respectively. When compared with the BP sample, the

WP sample was older (mean age: 39 compared with 30 years) and had more

non-Hispanic white (45% compared with 37%) and fewer Mexican-American

(19% compared with 30%) persons. There was no statistically significant

difference in gender proportions between the BP and WP samples. Serum sodium

had the lowest CVg (1.8%) and the lowest CVw (1.0%). The index of

individuality (CVw /CVg) ranged from 0.20 for blood lead to 0.76 for serum iron.

The CVg exceeded the analytical method coefficient of variation for all analytes.

Within-person variation was also compared between males and females, and

several analytes revealed significant differences (p<0.01). Serum ferritin had the

greatest difference for CVw (males, 17.9% compared with females, 28.8%).

Keywords: within-person differences c between-person differences c laboratory

tests c survey

Introduction

Laboratory analytes for individuals

are subject to several sources of

variation, including biological,

preanalytical (specimen collection),

analytical (bias and imprecision), and

postanalytical variation (reporting of

results). Laboratory analytical bias is the

closeness of an analyte result to the

‘‘true value’’ of the result, and the true

value of a laboratory result is

established by a ‘‘gold standard’’

method using standard reference

materials. Bias is a measure of the

systematic error of laboratory

measurements. Precision is the

repeatability of an analyte result if the

same sample is tested many times, and

the imprecision of an analyte is a

measure of random errors. Biological

variation consists of within-person (WP)

and between-person (BP) variations,

which are used to set analytical goals

for bias and imprecision, assess serial

changes in individual analytes, and

gauge the clinical utility of populationbased reference intervals.

The goals of imprecision and bias

for a laboratory analyte differ depending

on its intended use in screening,

diagnosis, or monitoring the course of

diseases in patients. For example, the

WP variation, a component of

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Center for Health Statistics 
Page 2 National Health Statistics Reports n Number 21 n March 1, 2010

imprecision, should be smaller than BP

variation when monitoring serial

changes of laboratory analyte values in

an individual. Ideally, desirable goals for

imprecision (I) and bias (B) have been

related to the WP coefficient of

variation (CVw) and the BP coefficient

of variation (CVg) of laboratory analytes

(1–3). Between-person variation has

been studied extensively for

demographic differences including age,

sex, and, occasionally, race and

ethnicity. The WP variation has rarely

been evaluated by demographic

characteristics.

Imprecision should ideally be less than

one-half of the CVw , and bias should be

less than 0.25[(CVw)

2 + (CVg)2

]

1/2 (2). The

total error of a laboratory measurement

reflects the underlying bias and imprecision

of an analyte. The goal for total error

should be less than kI + B, where k = 1.65

at α = 0.05 (2). Analytical variation

includes the imprecision and changes in

bias (for example, changes in method

calibration), which are usually negligible.

Hence, the analytical coefficient of

variation (CVa ) is estimated by the method

imprecision coefficient of variation (CVi ).

The total coefficient of variation (CVt ) of a

laboratory analyte can be estimated

assuming that all sources of error are

measured at the same analyte mean and

that preanalytical and postanalytical sources

of variation are negligible. The CVt is

calculated as [(CVa )

2 + (CVw )2

]

1/2 (2).

The WP and BP variations have

been reported for selected analytes from

the Third National Health and Nutrition

Examination Survey (NHANES III)

conducted from 1988–1994 (4). In the

present study, BP and WP variations for

selected laboratory analytes are

presented for a nationally representative

sample based on the 1999–2002

National Health and Nutrition

Examination Survey (NHANES).

Gender differences for the WP variation

are compared.

Methods and

Procedures

Estimates of CVw and CVg for

laboratory analytes were calculated from

the 1999–2002 NHANES (5,6), a

cross-sectional survey that collected data

on the civilian noninstitutionalized U.S.

population through questionnaires and

medical examinations, including

laboratory analytes. NHANES 1999–

2002 used a stratified, multistage

probability design to collect a nationally

representative sample. Laboratory

methods for NHANES 1999–2002,

including imprecision, have been

described (5,6).

The BP and WP means, standard

deviations, and coefficients of variation

(CVs) for 34 general biochemical,

nutritional, and environmental analytes

are shown in Table 1. The BP variations

were estimated on 18,761 sample

participants from NHANES 1999–2002.

The WP variations were estimated for a

convenience sample of 853 individuals

based on NHANES 2000–2002 data. In

NHANES 1999–2002, different age

groups were selected for the various

analytes and the minimum age was 1

year (5,6). The WP sample participants

were recruited for a second analyte

measurement. The WP participants were

not selected randomly but recruited

according to several criteria, including

approximately equal proportions of

males and females with an

approximately uniform age distribution

of 16–69 years. Participants also were

recruited to obtain about equal numbers

of Mexican-American and non-Hispanic

black and white persons. The target size

of the WP sample was 5% of those

participants who had phlebotomy during

the initial visit to the NHANES mobile

examination center. The WP participants

were asked to return for a second

phlebotomy no sooner than 8 days after

their initial blood draw. Compared with

the BP sample, the WP sample was

older (mean age: 39 compared with 30

years) and had more non-Hispanic white

(45% compared with 37%) and fewer

Mexican-American (19% compared with

30%) persons. There was no statistically

significant difference in sex proportions

when comparing the BP and WP

samples.

The BP variation was estimated

taking into account the complex design of

NHANES by Taylor series linearization

(7). The BP standard deviation was

calculated as (SE2 + SDsrs2

)

1/2, where SE

is the standard error of the mean obtained

from the complex design and SDsrs

2 is the

square of the standard deviation assuming

a simple random sample. The WP

variation was estimated from a

nonrandom, unweighted sample with a

mean of 18.8 days (range: 3–51 days)

between two analyte measurements. The

CVw was calculated as [(CVt )

2

–

(CVa )

2

]

1/2. The distributions of several

analytes were nongaussian, and extreme

outliers were excluded to obtain an

approximately gaussian distribution with

more stable estimates of variation. Outliers

were eliminated by use of Tukey’s

method, which defines outliers as three

interquartile ranges below the 25th

percentile or above the 75th percentile (8).

Male and female WP variations were

compared. Ninety-five percent confidence

intervals were estimated for the CVw

using software developed by Verrill (9). A

likelihood ratio test was performed to

determine if the CVw for males and

females for a laboratory analyte were

equal (10). Statistical analyses were

carried out with SAS for Windows

software (SAS Institute) and SUDAAN

software (Research Triangle Institute).

Results and Discussion

The BP and WP means, standard

deviations, and CVs for 34 laboratory

analytes are shown in Table 1. The CVw

and CVg exceeded the laboratory CVi

for all laboratory analytes. For most

laboratory analytes, the mean BP and

WP analyte values were similar despite

some demographic differences between

the two groups. Analytical goals for

imprecision and bias can be judged by

use of the CVw and CVg. For example,

the observed serum total calcium

imprecision of 1.1% was less than the

precision goal of one-half of CVw

(2.3%), or 1.15%. The bias for serum

total calcium should ideally be

)

2

]

1/2 <0.25[(CVw)2 + (CVg , or

0.25[(0.023)2 + (0.042)2]

1/2, or 1.2%.

The total error is estimated as B +

1.65(I), or 1.2% + 1.65(1.15%), or

3.1%. Thus, the total-error serum total

calcium estimated at the BP mean of

9.47 mg/dL (Table 1) was 0.29 mg/dL

(9.47 mg/dL multiplied by 0.031). This

is less than 1.0 mg/dL, the total error

goal set by the Clinical Laboratory
150 

Repeat serum sodium (mmol/L)

140 

130 

120 

110 

0 

0 110 120 130 140 150 

Original serum sodium (mmol/L) 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2002 data. 

250 

200 

150 

100 

50 

0 

0 50 100 150 200 250 

Original serum iron ( μg/dL) 

Repeat serum iron ( μg/dL) 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2002 data. 

National Health Statistics Reports n Number 21 n March 1, 2010 Page 3

The ratio of CVw to CVg, also

known as the index of individuality, is

important in determining the use of

population-based reference (normal)

intervals in detecting changes of disease

status in individuals (13,14). When the

index of individuality is low (less than

0.6), the individual results stay within a

narrow range compared with the

population reference interval. Hence, a

low index suggests the utility of

evaluating serial changes in analyte

values in an individual, but populationbased reference intervals would be of

limited use. A high index (greater than

1.4) suggests that the population-based

reference interval is appropriate when

interpreting an individual’s laboratory

anlayte value. The index of individuality

ranged from 0.20 for blood lead to 0.76

for serum iron (Table 1).

The BP and WP variations were

analyzed by sex. The means, standard

deviations, and CVs for 34 laboratory

analytes are presented for males

(Table 2) and females (Table 3). Several

laboratory analytes had significant

differences (p<0.01) in the WP CV

when males and females were

compared. Females had higher CVw

than males for blood lead, red blood cell

folate, serum ferritin, homocysteine,

methylmalonic acid, albumin, alanine

aminotransferase, creatinine, gamma

glutamyl transferase, and potassium.

Males had higher CVw than females for

serum lactate dehydrogenase and

phosphorus. For ferritin (Figure 3), the

higher CVw for females may have

resulted from the lower average WP

ferritin (61 ng/mL for females compared

with 131 ng/mL for males), with

approximately the same WP standard

deviation for males and females. Lower

ferritin levels in females reflect lower

body iron storage, and females can have

more variable ferritin due to blood loss

during menstruation or increased iron

utilization during pregnancy. Borel et al.

also noted greater WP variation for

ferritin among females compared with

males (15). Feinleib et al. noted that

increased WP variances could lead to

overestimates of the prevalence of

disease (16). The WP variance alters the

BP distribution of analyte values if they

are based on a single measurement.

Figure 1. Original serum sodium compared with repeat serum sodium for sample persons

Improvement Amendments (CLIA) of individual variations due to sex, dietary

1988 (11). intake, diurnal variations, disease,

Serum sodium had the lowest BP outlying analyte values, or relatively low

CV (1.8%) and lowest WP CV (1.0%), analyte values. Serum iron (Figure 2)

as seen in Figure 1. For NHANES III, had the highest WP CV (31.9%),

serum sodium also had the lowest CVg reflecting its large diurnal variation (12).

(1.6%) and the lowest CV (1.3%) w (4). Serum ferritin had the highest BP CV

This reflects the narrow homeostatic

range for sodium that the body

maintains. High CVw and CVg values

were seen for several analytes, which

could result from natural population or

(89.8%). The BP and WP variations for

most analytes were similar to

corresponding variations seen in

NHANES III (4).

Figure 2. Original serum iron compared with repat serum iron for sample persons
Page 4	 National Health Statistics Reports n Number 21 n March 1, 2010

0 

100 

200 

300 

400 

500 

600 

Repeat serum ferritin (ng/mL) 

0 

100 

200 

300 

400 

500 

600 

0 100 200 300 400 500 600 

Repeat serum ferritin (ng/mL) 

Original serum ferritin (ng/mL) 

0 100 200 300 400 500 600 

Original serum ferritin (ng/mL) 

SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey, 1999–2002 data. 

Male

Female

Figure 3. Original seum ferritin compared with repeat serum ferritin for males and females

Increased WP variance makes the BP

distribution flatter and wider. This

results in more people being above or

below a cutoff value than distributions

based on only single measurements from

subjects.

In this study, BP and WP estimates

of CVs were obtained for general

biochemical, nutritional, and

environmental analytes. NHANES

1999–2002 provides a better estimate of

BP variation than other locally

representative studies because the

NHANES sample was nationally

representative (1,17,18). The WP

variation estimate was limited by the

nonrandom, self-selected design and

reflected a mean of 19 days between

two measurements. In addition, the WP

and BP CVs in NHANES were based on

a relatively healthy sample of the

population. The CVw and CVg would be

increased in a sample of unhealthy

individuals, as seen in a hospital

population. The BP sample contained

participants aged 1 year and over,

whereas the WP sample was restricted

to those aged 16–69. The estimate of

CVw could be improved by use of a

stratified, multistage probability design

over different time periods. Differences

for CVw and CVg among subpopulations

(sex, age, and race and ethnicity) can be

further investigated using NHANES

data. Additional WP and BP variation

data for other laboratory analytes based

on NHANES 1999–2002 will be

available in the future.

References

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appropriate use of normal intervals.

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JL. Day-to-day variation of ironstatus indices in healthy men and

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16. Feinleib M, Rifkind B, Sempos C, et

al. Methodological issues in the

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Accessed September 10, 2009.

Table 1. Between-person (CVg), within-person (CVw), and method (CVa) coefficients of variation and index of individuality (CVw/CVg)

Between-person Within-person Method1 Index2

Analyte (units) n3 Mean SD CVg (%) n Mean SD CVw (%) CVa (%) CVw/CVg

Albumin (g/dL). . . . . . . . . . . . . . . . . . . . . . . . . 13,082 4.39 0.33 7.5 831 4.27 0.16 3.5 1.3 0.46

Alkaline phosphatase (U/L) ................. 12,287 77.6 30.0 38.7 828 77.4 6.5 8.1 2.1 0.21

Alanine aminotransferase (U/L) .............. 12,728 22.4 9.7 43.4 796 22.4 4.6 20.3 4.0 0.47

Aspartate aminotransferase (U/L) ............. 12,757 22.7 6.2 27.1 795 22.3 3.5 15.5 3.1 0.57

Bicarbonate (mmol/L) .................... 13,116 23.7 2.3 9.7 835 23.5 1.5 5.1 3.9 0.53

Bilirubin, total (mg/dL) .................... 12,974 0.65 0.26 39.1 798 0.63 0.13 19.6 6.0 0.50

Blood urea nitrogen (mg/dL) ................ 12,968 13.4 4.3 32.4 822 12.7 2.3 17.9 2.7 0.55

Calcium, total (mg/dL) .................... 13,109 9.47 0.40 4.2 835 9.45 0.24 2.3 1.1 0.55

Chloride (mmol/L). . . . . . . . . . . . . . . . . . . . . . . 13,088 102.6 2.8 2.8 832 102.6 1.8 1.6 0.8 0.57

Cholesterol, total (mg/dL) .................. 13,108 193.6 40.8 21.1 835 192.1 13.5 6.9 1.5 0.33

Creatinine (mg/dL) ...................... 13,011 0.79 0.22 27.6 823 0.80 0.06 6.7 4.6 0.24

Ferritin (ng/mL) ........................ 15,992 83.9 75.3 89.8 796 94.1 20.8 21.8 3.2 0.24

Folate, red blood cell (ng/mL RBC) ............ 15,907 292.8 104.7 35.8 835 286.3 28.5 9.1 3.9 0.26

Folate, serum (ng/mL) .................... 15,750 14.85 7.23 48.7 827 13.16 2.92 21.5 5.4 0.44

Gamma tocopherol (μg/dL) ................. 14,645 226.03 115.32 51.0 265 236.04 55.35 23.2 3.4 0.45

Gamma glutamyl transferase (U/L) ............ 12,558 22.7 12.9 56.7 797 23.6 3.9 16.2 3.0 0.29

Glucose (mg/dL) ....................... 12,552 89.1 10.5 11.7 789 88.9 6.8 7.5 1.5 0.64

Homocysteine (μmol/L) ................... 15,880 7.508 2.786 37.1 832 7.641 0.982 12.2 4.0 0.33

Iron (μg/dL) .......................... 16,663 88.1 36.9 41.9 299 86.4 27.7 31.9 3.8 0.76

Lactate dehydrogenase (U/L) ............... 13,070 139.9 29.8 21.3 831 135.4 12.6 8.9 2.7 0.42

Lead, blood (μg/dL) ..................... 16,521 1.82 1.17 64.4 833 1.69 0.23 12.6 4.3 0.20

Methylmalonic acid (μmol/L) ................ 15,675 0.137 0.056 41.0 822 0.125 0.025 18.7 7.4 0.46

Phosphorus (mg/dL) ..................... 13,115 3.68 0.60 16.4 833 3.72 0.36 9.5 1.7 0.58

Potassium (mmol/L) ..................... 13,109 4.09 0.33 8.1 834 4.06 0.23 5.5 1.5 0.68

Protein, total (g/dL). . . . . . . . . . . . . . . . . . . . . . 13,108 7.42 0.46 6.2 833 7.37 0.26 3.3 1.3 0.53

Protoporphyrin (μg/dL RBC) ................ 16,592 49.6 16.3 32.9 300 51.0 5.4 9.8 4.1 0.30

Sodium (mmol/L) ....................... 13,105 139.1 2.5 1.8 834 138.6 1.7 1.0 0.8 0.55

Total iron binding capacity (μg/dL) ............ 16,588 370.6 59.7 16.1 294 373.1 37.0 9.0 4.2 0.56

Triglycerides (mg/dL)..................... 12,849 125.1 71.0 56.8 814 126.3 35.2 27.8 1.9 0.49

Uric acid (mg/dL) ....................... 13,115 5.33 1.46 27.4 835 5.35 0.50 9.3 1.2 0.34

Vitamin A (μg/dL) ....................... 15,784 56.05 17.37 31.0 297 55.38 6.03 10.4 3.3 0.33

Vitamin B12 (pg/mL) ..................... 15,736 527.4 229.8 43.6 831 497.9 74.3 14.6 2.9 0.34

Vitamin D, 25-hydroxy (ng/mL)............... 7,802 23.8 9.0 37.9 460 21.2 3.0 11.3 8.2 0.30

Vitamin E (μg/dL) ....................... 15,454 1,132.79 451.14 39.8 285 1,162.99 163.94 13.9 2.5 0.35

1

Method analytical CV is the laboratory method precision assuming no method bias exists.
 2

Index of individuality.
 3

Between-person sample size for each laboratory test varied by age of participant and response rate for the test.
 

NOTE: CV is coefficient of variation, n is the size of the subsample, and SD is standard deviation.
Page 6 National Health Statistics Reports n Number 21 n March 1, 2010

Table 2. Between-person (CVg), within-person (CVw), and method (CVa) coefficients of variation for males

Between-person Within-person Method1

Analyte (units) n2 Mean SD CVg (%) n Mean SD CVw (%) CVa (%)

Albumin (g/dL). . . . . . . . . . . . . . . . . . . . . . . . . 6,313 4.50 0.31 6.9 406 4.41 0.15 †3.22 1.3

Alkaline phosphatase (U/L) ................. 5,651 80.6 31.0 38.4 406 79.9 6.7 8.1 2.1

Alanine aminotransferase (U/L) .............. 6,035 25.8 10.2 39.6 380 26.1 4.9 ††18.2 4.0

Aspartate aminotransferase (U/L) ............. 6,083 24.5 6.3 25.6 376 24.4 4.0 16.0 3.1

Bicarbonate (mmol/L) .................... 6,321 24.1 2.2 9.3 408 24.0 1.6 5.3 3.9

Bilirubin, total (mg/dL) .................... 6,206 0.73 0.27 36.7 381 0.71 0.15 20.0 6.0

Blood urea nitrogen (mg/dL) ................ 6,245 14.3 4.3 29.8 399 13.8 2.5 18.2 2.7

Calcium, total (mg/dL) .................... 6,315 9.52 0.38 4.0 408 9.52 0.23 2.2 1.1

Chloride (mmol/L). . . . . . . . . . . . . . . . . . . . . . . 6,308 102.4 2.8 2.8 406 102.4 1.8 1.6 0.8

Cholesterol, total (mg/dL) .................. 6,314 192.0 41.2 21.5 408 187.3 13.0 6.8 1.5

Creatinine (mg/dL) ...................... 6,246 0.89 0.20 22.4 399 0.93 0.07 ††5.6 4.6

Ferritin (ng/mL) ........................ 7,624 112.3 82.8 73.7 373 130.9 23.8 ††17.9 3.2

Folate, red blood cell (ng/mL RBC) ............ 7,748 283.7 98.3 34.6 404 268.6 24.1 ††8.1 3.9

Folate, serum (ng/mL) .................... 7,686 14.13 6.74 47.7 405 12.42 2.61 20.3 5.4

Gamma tocopherol (μg/dL) ................. 7,118 226.60 114.39 50.5 119 239.92 60.55 25.0 3.4

Gamma glutamyl transferase (U/L) ............ 5,944 26.3 13.5 51.2 382 28.0 4.3 †15.0 3.0

Glucose (mg/dL) ....................... 6,017 90.7 10.2 11.3 380 91.0 6.6 7.1 1.5

Homocysteine (μmol/L) ................... 7,698 8.035 2.805 34.9 400 8.440 0.971 ††10.8 4.0

Iron (μg/dL) .......................... 8,144 93.9 37.0 39.4 136 94.5 30.0 31.5 3.8

Lactate dehydrogenase (U/L) ............... 6,286 141.3 29.9 21.1 405 136.6 13.5 †9.5 2.7

Lead, blood (μg/dL) ..................... 7,970 2.13 1.25 58.7 396 1.96 0.23 ††11.00 4.3

Methylmalonic acid (μmol/L) ................ 7,598 0.140 0.056 39.7 396 0.129 0.024 †17.3 7.4

Phosphorus (mg/dL) ..................... 6,319 3.65 0.64 17.7 408 3.68 0.38 †10.3 1.7

Potassium (mmol/L) ..................... 6,315 4.15 0.33 7.9 408 4.12 0.22 †5.1 1.5

Protein, total (g/dL). . . . . . . . . . . . . . . . . . . . . . 6,313 7.48 0.44 5.9 408 7.46 0.25 3.1 1.3

Protoporphyrin (μg/dL RBC) ................ 8,182 45.2 14.0 30.8 137 45.2 5.2 10.7 4.1

Sodium (mmol/L) ....................... 6,315 139.4 2.4 1.7 407 139.1 1.7 1.0 0.8

Total iron binding capacity (μg/dL) ............ 8,117 361.6 54.3 15.0 133 358.2 35.9 9.1 4.2

Triglycerides (mg/dL)..................... 6,140 131.4 74.8 56.9 395 133.0 38.6 28.9 1.9

Uric acid (mg/dL) ....................... 6,318 6.04 1.30 21.5 408 6.20 0.55 8.7 1.2

Vitamin A (μg/dL) ....................... 7,679 58.85 17.39 29.5 135 59.11 6.55 10.6 3.3

Vitamin B12 (pg/mL) ..................... 7,676 525.1 217.8 41.5 404 507.0 73.3 14.2 2.9

Vitamin D, 25-hydroxy (ng/mL)............... 3,781 24.2 8.5 34.9 212 21.7 3.1 11.6 8.2

Vitamin E (μg/dL) ....................... 7,548 1,111.43 442.23 39.8 128 1,128.07 145.51 12.7 2.5

† p < 0.01 for likelihood ratio of CVw for males equivalent to CVw for females.

†† p < 0.001 for likelihood ratio of CVw for males equivalent to CVw for females.
 1

Method analytical CV is the laboratory method precision assuming no method bias exists.
 2

Between-person sample size for each laboratory test varied by age of participant and response rate for the test.
 

NOTE: CV is coefficient of variation, n is the size of the subsample, and SD is standard deviation.
National Health Statistics Reports n Number 21 n March 1, 2010 Page 7

Table 3. Between-person (CVg), within-person (CVw), and method (CVa) coefficients of variation for females

Between-person Within-person Method1

Analyte (units) n2 Mean SD CVg (%) n Mean SD CVw (%) CVa (%)

Albumin (g/dL). . . . . . . . . . . . . . . . . . . . . . . . . 6,769 4.29 0.32 7.4 425 4.14 0.16 3.7 1.3

Alkaline phosphatase (U/L) ................. 6,636 74.8 28.8 38.5 422 75.0 6.3 8.1 2.1

Alanine aminotransferase (U/L) .............. 6,693 19.2 8.0 41.8 416 19.0 4.4 22.9 4.0

Aspartate aminotransferase (U/L) ............. 6,674 21.1 5.6 26.5 419 20.4 3.1 14.8 3.1

Bicarbonate (mmol/L) .................... 6,795 23.2 2.3 9.7 427 22.9 1.4 4.9 3.9

Bilirubin, total (mg/dL) .................... 6,768 0.59 0.22 38.1 417 0.56 0.11 18.5 6.0

Blood urea nitrogen (mg/dL) ................ 6,723 12.5 4.2 33.8 423 11.58 2.04 17.4 2.7

Calcium, total (mg/dL) .................... 6,794 9.41 0.40 4.3 427 9.39 0.25 2.4 1.1

Chloride (mmol/L). . . . . . . . . . . . . . . . . . . . . . . 6,780 102.8 2.8 2.7 426 102.73 1.81 1.6 0.8

Cholesterol, total (mg/dL) .................. 6,794 195.2 40.3 20.6 427 196.58 13.91 6.9 1.5

Creatinine (mg/dL) ...................... 6,765 0.69 0.19 26.8 424 0.68 0.06 8.1 4.6

Ferritin (ng/mL) ........................ 8,368 58.4 56.9 97.5 423 61.1 17.7 28.8 3.2

Folate, red blood cell (ng/mL RBC) ............ 8,159 301.5 109.9 36.4 431 302.9 32.1 9.8 3.9

Folate, serum (ng/mL) .................... 8,064 15.54 7.60 48.9 422 13.86 3.20 22.4 5.4

Gamma tocopherol (μg/dL) ................. 7,527 225.49 116.20 51.5 146 232.60 50.72 21.5 3.4

Gamma glutamyl transferase (U/L) ............ 6,614 19.5 11.4 58.4 415 19.5 3.5 17.5 3.0

Glucose (mg/dL) ....................... 6,535 87.6 10.4 11.9 409 87.1 6.9 7.8 1.5

Homocysteine (μmol/L) ................... 8,182 7.009 2.675 38.2 432 6.897 0.993 13.8 4.0

Iron (μg/dL) .......................... 8,519 82.6 36.0 43.6 163 79.3 25.7 32.1 3.8

Lactate dehydrogenase (U/L) ............... 6,784 138.5 29.7 21.4 426 134.2 11.6 8.2 2.7

Lead, blood (μg/dL) ..................... 8,551 1.53 1.01 66.1 437 1.45 0.22 14.5 4.3

Methylmalonic acid (μmol/L) ................ 8,077 0.133 0.056 42.1 426 0.122 0.026 20.0 7.4

Phosphorus (mg/dL) ..................... 6,796 3.71 0.56 15.2 425 3.75 0.34 8.8 1.7

Potassium (mmol/L) ..................... 6,794 4.04 0.33 8.1 426 4.00 0.24 5.9 1.5

Protein, total (g/dL). . . . . . . . . . . . . . . . . . . . . . 6,795 7.37 0.47 6.4 425 7.29 0.27 3.4 1.3

Protoporphyrin (μg/dL RBC) ................ 8,410 53.8 17.3 32.1 163 56.2 5.6 9.1 4.1

Sodium (mmol/L) ....................... 6,790 138.8 2.5 1.8 427 138.2 1.7 1.0 0.8

Total iron binding capacity (μg/dL) ............ 8,471 379.2 63.2 16.7 161 386.3 37.9 8.9 4.2

Triglycerides (mg/dL)..................... 6,709 119.3 66.9 56.1 419 119.9 31.7 26.4 1.9

Uric acid (mg/dL) ....................... 6,797 4.66 1.28 27.5 427 4.55 0.45 9.9 1.2

Vitamin A (μg/dL) ....................... 8,105 53.38 16.93 31.7 162 52.05 5.56 10.2 3.3

Vitamin B12 (pg/mL) ..................... 8,060 529.6 240.7 45.5 427 489.4 75.2 15.1 2.9

Vitamin D, 25-hydroxy (ng/mL)............... 4,021 23.4 9.5 40.6 248 20.7 2.8 11.0 8.2

Vitamin E (μg/dL) ....................... 7,906 1,153.34 458.66 39.8 157 1,194.11 177.55 14.7 2.5

1

Method analytical CV is the laboratory method precision assuming no method bias exists.
 2

Between-person sample size for each laboratory test varied by age of participant and response rate for the test.
 

NOTE: CV is coefficient of variation, n is the size of the subsample, and SD is standard deviation.
 
Page 8 National Health Statistics Reports n Number 21 n March 1, 2010

Suggested citation

Lacher DA, Hughes JP, Carroll MD. Biological

variation of laboratory analytes based on the

1999–2002 National Health and Nutrition

Examination Survey. National health statistics

reports; no 21. Hyattsville, MD: National

Center for Health Statistics. 2010.

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