Personalized and Population-Based Reference Intervals for 48 Common Clinical Chemistry and Hematology Measurands: A Comparative Study

BACKGROUND

Personalized reference intervals (prRIs) have the potential to improve individual patient follow-up as compared to population-based reference intervals (popRI). In this study, we estimated popRI and prRIs for 48 clinical chemistry and hematology measurands using samples from the same reference individuals and explored the effect of using group-based and individually based biological variation (BV) estimates to derive prRIs.

METHODS

143 individuals (median age 28 years) were included in the study and had fasting blood samples collected once. From this population, 41 randomly selected subjects had samples collected weekly for 5 weeks. PopRIs were estimated according to Clinical Laboratory Standards Institute EP28 and within-subject BV (CVI) were estimated by CV-ANOVA. Data were assessed for trends and outliers prior to calculation of individual prRIs, based on estimates of (a) within-person BV (CVP), (b) CVI derived in this study, and (c) publically available CVI estimates.

RESULTS

For most measurands, the individual prRI ranges were smaller than the popRI range, but overall about half the study participants had a prRI wider than the popRI for 5 or more out of 48 measurands. The dispersion of prRIs based on CVP was wider than that of prRIs based on CVI.

CONCLUSION

The prRIs derived in our study varied significantly between different individuals, especially if based on CVP. Our results highlight the limitations of popRIs in interpreting test results of individual patients. If sufficient data from a steady-state situation are available, using prRI based on CVP estimates will provide a RI most specific for an individual patient.

FUNCTIONAL VITAMIN B12 DEFICIENCY: IMPROVING METHYLMALONIC ACID REFERENCE INTERVALS IN URINE

BACKGROUND

AIM Most laboratory requests focus on the detection of possible vitamin B12 deficiency. In this context, methylmalonic acid (MMA) is reported as the best biomarker. The aim of our study was to establish the biological reference interval for MMA in urine, and assess the influence of age, sex, and vitamin B12 status on MMA concentrations.

METHODS

This is a prospective observational study considering individuals with normal results for blood count and liver and kidney function. Individuals who presented supplementation, any pathology or treatment that could cause cobalamin metabolism disorders, and pregnant women were excluded. Likewise, individuals whose vitamin B12 result presented antibody-mediated interference were excluded. Individuals were grouped by age-group and sex. Reference intervals were determined by non-parametric calculation (percentiles 1-99).

RESULTS

It was established a single reference interval [0.52 (CI_90%: 0.50-0.54) - 5.75 (CI_90%: 5.57-6.17) mmolMMA/mol creatinine], with 100% of individuals with MMA above the upper limit of reference presenting a total vitamin B12 concentration ≤238pmol/L.

CONCLUSION

The establishment of optimal reference intervals for methylmalonic acid excretion in urine is crucial in individuals with a suspicion of functional vitamin B12 deficiency. However, the possibility of establishing a cut-off value for total vitamin B12 suggesting subclinical deficiency remains a challenge for this magnitude.

Personalized reference intervals: from theory to practice

Using laboratory test results for diagnosis and monitoring requires a reliable reference to which the results can be compared. Currently, most reference data is derived from the population, and patients in this context are considered members of a population group rather than individuals. However, such reference data has limitations when used as the reference for an individual. A patient's test results preferably should be compared with their own, individualized reference intervals (RI), i.e. a personalized RI (prRI).The prRI is based on the homeostatic model and can be calculated using an individual's previous test results obtained in a steady-state situation and estimates of analytical (CV_A) and biological variation (BV). BV used to calculate the prRI can be obtained from the population (within-subject biological variation, CV_I) or an individual's own data (within-person biological variation, CV_P). Statistically, the prediction interval provides a useful tool to calculate the interval (i.e. prRI) for future observation based on previous measurements. With the development of information technology, the data of millions of patients is stored and processed in medical laboratories, allowing the implementation of personalized laboratory medicine. PrRI for each individual should be made available as part of the laboratory information system and should be continually updated as new test results become available.In this review, we summarize the limitations of population-based RI for the diagnosis and monitoring of disease, provide an outline of the prRI concept and different approaches to its determination, including statistical considerations for deriving prRI, and discuss aspects which must be further investigated prior to implementation of prRI in clinical practice.

Reference intervals of 14 biochemical markers for children and adolescence in China: the PRINCE study

OBJECTIVES

The Pediatric Reference Intervals in China (PRINCE) was initiated to establish the reference intervals (RIs) of Chinese children, as well as to make it possible to compare the variability of biochemical markers among countries internationally.

METHODS

Healthy participants, aged up to 20 years, from 11 provinces across China, were enrolled in PRINCE and according to a standard screening procedure, that included a questionnaire survey, physical examinations and laboratory tests. Fasting venous blood specimens were collected. All serum specimens were analyzed with Cobas C702 in the center laboratory, i.e. clinical laboratory of Beijing Children's Hospital, with certified qualification (ISO15189). The nonparametric method recommended by Clinical Laboratory Standards Institute guidelines, was used to calculate the age- and sex-specified RIs.

RESULTS

Among the 15,150 participants enrolled, 12,352 children (6,093 males and 6,259 females) were included to calculate RIs. The RIs for total protein, albumin, globulin, calcium, phosphate, potassium, sodium, chlorine, alkaline phosphatase, γ-glutamyl transpeptadase, alanine aminotransferase, aspartate aminotransferase, creatinine and urea were established by age- or sex-partitions. Most biochemical markers displayed larger variability and higher dispersion during the periods between 28 days and 1 year old, and included 4-6 age partitions commonly during 1 to <20 years old. In addition, differences of RIs between sexes usually occurs around the initiation of puberty at 12-13 years old.

CONCLUSIONS

The age- and sex-specified RIs of 14 biochemical markers in PRINCE study can provide a solid reference, which will be transferred into relevant RIs for other clinical laboratory's platforms according to the CLSI guidelines.

Prevalence and Correlates of Hypophosphatemia Among Type 2 diabetic patients attending the National Center for Diabetes, Endocrinology and genetics (NCDEG)

Objectives

To estimate the prevalence of hypophosphatemia and its associated factors among type 2 diabetic patients attending (NCDEG) in Amman-Jordan, and compare the prevalence of hypophosphatemia between diabetics, nondiabetic subjects.

Patients and methods

A case-control study was carried out at (NCDEG). A total of 1580 diabetic patients (59.7% females, 40.3% males), mean age (SD) of 55.15 ± 15.3 attended this center from January 1st, 2020 till March 31st, 2020 were included. Our study included 2155 non-diabetic from the national population-based multipurpose study in Jordan in 2017, to compare serum inorganic phosphate between diabetic, nondiabetic. Pregnant, those aged <18 or >80 years, GFR below 30 ml/min or those on hemodialysis were excluded. The data included patient's age, gender, smoking and medication, HbA1c. Statistical analysis were performed using the Package for Social Sciences (SPSS) version 21.

Results

The overall prevalence of hypophosphatemia in the diabetic patients was significantly higher (10.5% vs. 3.2%, P-value 0.001). Multivariate logistic regression analysis showed that in diabetic: males, current smokers, diabetic patients with HbA1c between 7 and 9% and >9%, those who on thiazide diuretics were 2, 1.9, 1.8, 1.7, and 1.9 times, more likely to have hypophosphatemia than their counterparts (P-values 0.001, 0.001, 0.006, 0.018 and 0.003), respectively, and it was found those on statin were less likely to have hypophosphatemia.

Conclusion

The prevalence of hypophosphatemia among type 2 diabetic patients is high. Factors independently related to hypophosphatemia in diabetic patients: male gender, smoking, poor glycemic control, taking thiazides and not being on statin.

•

The objectives is to estimate the prevalence of hypophosphatemia and its associated factors among type 2 diabetic patients. Also, to compare the prevalence of hypophosphatemia between diabetics, nondiabetic subjects.

•

The overall prevalence of hypophosphatemia in the diabetic patients was significantly 10.5%.

•

The overall prevalence of hypophosphatemia in the non- diabetic patients was 3.2%.

•

Factors independently related to hypophosphatemia in diabetic patients included: male gender, smoking, poor glycemic control.

Reference interval for type III procollagen (PIIINP) using the Advia centaur PIIINP assay in adults and elderly

OBJECTIVE

The amino-terminal peptide of type III procollagen (PIIINP) is a byproduct of type III collagen synthesis that exhibits promise as a biomarker of fibrosis, specifically in monitoring hepatic fibrosis in methotrexate treated patients. The Advia Centaur^® PIIINP assay is developed for track-based automated laboratory systems and is suitable for large volume analysis. Reference intervals in children and younger adults have been published previously. Here we measured PIIINP to determine reference ranges, specifically including elderly patients, for whom such are currently lacking.

METHODS

Samples were collected from subjects ranging from 20 to 98 years of age. Blood donors and clinical samples from primary care patients were used for reference interval calculation. Samples were analysed using the Advia Centaur^® PIIINP assay. After exclusion of samples high in alanine transaminase (AST), aspartate transaminase (ALT), and C-reactive protein (CRP) 386 samples were used in the reference interval calculation.

RESULTS AND CONCLUSION

We determined the following reference interval for the Advia Centaur^® PIIINP assay: the lower limit of the reference interval (2.5% percentile with 95% CI) was 4.42 (4.20-4.65) µg/L and the upper limit of the reference interval (97.5% percentile 95% CI) 16.0 (15.04-17.02) µg/L.No significant differences in mean PIIINP concentrations were found between men and women. While differing mean PIIINP concentrations were seen among subjects in different age groups, the differences were small and partitioning of reference range was determined not to be necessary.

Reference ranges for clinical electrophysiology of vision

Introduction

Establishing robust reference intervals for clinical procedures has received much attention from international clinical laboratories, with approved guidelines. Physiological measurement laboratories have given this topic less attention; however, most of the principles are transferable.

Methods

Herein, we summarise those principles and expand them to cover bilateral measurements and one-tailed reference intervals, which are common issues for those interpreting clinical visual electrophysiology tests such as electroretinograms (ERGs), visual evoked potentials (VEPs) and electrooculograms (EOGs).

Results

The gold standard process of establishing and defining reference intervals, which are adequately reliable, entails collecting data from a minimum of 120 suitable reference individuals for each partition (e.g. sex, age) and defining limits with nonparametric methods. Parametric techniques may be used under some conditions. A brief outline of methods for defining reference limits from patient data (indirect sampling) is given. Reference intervals established elsewhere, or with older protocols, can be transferred or verified with as few as 40 and 20 suitable reference individuals, respectively. Consideration is given to small numbers of reference subjects, interpretation of serial measurements using subject-based reference values, multidimensional reference regions and age-dependent reference values. Bilateral measurements, despite their correlation, can be used to improve reference intervals although additional care is required in computing the confidence in the reference interval or the reference interval itself when bilateral measurements are only available from some of subjects.

Discussion

Good quality reference limits minimise false-positive and false-negative results, thereby maximising the clinical utility and patient benefit. Quality indicators include using appropriately sized reference datasets with appropriate numerical handling for reporting; using subject-based reference limits where appropriate; and limiting tests for each patient to only those which are clinically indicated, independent and highly discriminating.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10633-021-09831-1.

Analysis of Primary Hyperparathyroidism Screening Among US Veterans With Kidney Stones

Importance

Approximately 3% to 5% of patients with kidney stones have primary hyperparathyroidism (PHPT), a treatable cause of recurrent stones. However, the rate of screening for PHPT in patients with kidney stones remains unknown.

Objectives

To estimate the prevalence of parathyroid hormone (PTH) testing in veterans with kidney stones and hypercalcemia and to identify the demographic, geographic, and clinical characteristics of veterans who were more or less likely to receive PTH testing.

Design, Setting, and Participants

This cohort study obtained Veterans Health Administration (VHA) health records from the Corporate Data Warehouse for veterans who received care in 1 of the 130 VHA facilities across the United States from January 1, 2008, through December 31, 2013. Historical encounters, medical codes, and laboratory data were assessed. Included patients had diagnostic or procedural codes for kidney or ureteral stones, and excluded patients were those with a previous serum PTH level measurement. Data were collected from January 1, 2006, to December 31, 2014. Data analysis was conducted from June 1, 2019, to January 31, 2020.

Exposures

Elevated serum calcium concentration measurement between 6 months before and 6 months after kidney stone diagnosis.

Main Outcomes and Measures

Proportion of patients with a serum PTH level measurement and proportion of patients with biochemical evidence of PHPT who underwent parathyroidectomy.

Results

The final cohort comprised 7561 patients with kidney stones and hypercalcemia and a mean (SD) age of 64.3 (12.3) years. Of these patients, 7139 were men (94.4%) and 5673 were white individuals (75.0%). The proportion of patients who completed a serum PTH level measurement was 24.8% (1873 of 7561). Across the 130 VHA facilities included in the study, testing rates ranged from 4% to 57%. The factors associated with PTH testing included the magnitude of calcium concentration elevation (odds ratio [OR], 1.07 per 0.1 mg/dL >10.5 mg/dL; 95% CI, 1.05-1.08) and the number of elevated serum calcium concentration measurements (OR, 1.08 per measurement >10.5 mg/dL; 95% CI, 1.06-1.10) as well as visits to both a nephrologist and a urologist (OR, 6.57; 95% CI, 5.33-8.10) or an endocrinologist (OR, 4.93; 95% CI, 4.11-5.93). Of the 717 patients with biochemical evidence of PHPT, 189 (26.4%) underwent parathyroidectomy within 2 years of a stone diagnosis.

Conclusions and Relevance

This cohort study found that only 1 in 4 patients with kidney stones and hypercalcemia were tested for PHPT in VHA facilities and that testing rates varied widely across these facilities. These findings suggest that raising clinician awareness to PHPT screening indications may improve evaluation for parathyroidectomy, increase the rates of detection and treatment of PHPT, and decrease recurrent kidney stone disease.

Estimating a normal reference range for serum B-cell maturation antigen levels for multiple myeloma patients

The serum B-cell maturation antigen (sBCMA) has been identified as a novel serum biomarker for patients with multiple myeloma. However, no study has yet established a reference range for sBCMA levels. Its levels were determined in 196 healthy subjects and showed a right-tailed distribution with a median value of 37·51 ng/ml with a standard deviation of 22·54 ng/ml (range 18·78-180·39 ng/ml). Partitioning of subgroup reference ranges was considered but determined to be irrelevant. A non-parametric method using the median ± 2 standard deviations suggests using a universal reference interval of <82·59 ng/ml.

Reference intervals for blood-based biochemical analytes of southern Beaufort Sea polar bears

Accurate reference intervals (RIs) for commonly measured blood-based analytes are essential for health monitoring programmes. Baseline values for a panel of analytes can be used to monitor physiologic and pathophysiologic processes such as organ function, electrolyte balance and protein catabolism. Our reference population includes 651 serum samples from polar bears (Ursus maritimus) from the southern Beaufort Sea (SB) subpopulation sampled in Alaska, USA, between 1983 and 2016. To establish RI for 13 biochemical analytes, we defined specific criteria for characterizing the reference population and relevant subgroups. To account for differences in seasonal life history characteristics, we determined separate RI for the spring and fall seasons, when prey availability and energetic requirements of bears differ. We established RI for five subgroups in spring based on sex, age class and denning status, and three subgroups in fall based on sex and age class in females only. Alkaline phosphatase activities were twice as high in subadult as in adult polar bears in spring (z _males = 4.08, P _males < 0.001, z _females = 3.90, P _females < 0.001) and did not differ between seasons. Denning females had significantly higher glucose concentrations than non-denning females (z = 4.94, P < 0.001), possibly reflecting differences in energy expenditure during lactation. A total of 10 of the 13 analytes differed significantly between seasons in either males or females; however, the physiologic importance of these differences may be minimal. Establishing these RIs allows for temporal monitoring of polar bear health in the SB and may prove useful for assessing and monitoring additional polar bear subpopulations in a changing Arctic environment.

An update on clinical biochemical RIs of rabbits with special consideration for age, gender, and size

BACKGROUND

Literature regarding the impact of age and breed size on clinical biochemical measurands in rabbits is scarce.

OBJECTIVES

We aimed to establish clinical biochemical measurand RIs for rabbits bred and kept under standard conditions and to evaluate the impact of gender, age, and breed size on the results using a Nova CRT8 analyzer (Nova Biomedical GmbH) and an ABX Pentra 400 analyzer (ABX Horiba, Axonlab).

METHODS

Serum samples were available from 122 adult rabbits (56 males, 66 females) of 10 different breeds and crossbreds with a mean age of 264 ± 21 days. The impact of age was evaluated by sampling 48 rabbits at weaning (8 weeks of age) and when they reached adulthood.

RESULTS

Significantly higher median values were obtained for ALT, glutamate dehydrogenase (GLDH), and potassium in adult males compared with adult female rabbits. Total bilirubin, cholesterol, creatinine, and urea were significantly higher in adult females than adult males. Juvenile animals at weaning revealed significantly higher median values for ALP, cholesterol, GGT, GLDH, glucose, phosphate, and triglycerides compared with their adulthood values. In contrast, lower median albumin, ALT, chloride, creatinine, globulin, ionized calcium, magnesium, potassium, total protein, urea, and calcium-phosphate ratios were seen at the time of weaning compared with adulthood values. Significantly lower median CK, creatinine, and ALT were found in dwarf/small rabbit breeds compared with intermediate/large breeds.

CONCLUSIONS

These RIs are especially useful for rabbit production and experimental studies. Age should be considered when evaluating clinical biochemical measurands. Creatinine, CK, and ALT are affected by organ mass.

Sources of variation analysis and derivation of reference intervals for ALP, LDH, and amylase isozymes using sera from the Asian multicenter study on reference values

BACKGROUND

Sources of variation (SV) of ALP, LDH, and amylase isozymes were explored.

METHODS

We analyzed 3511 sera from well-defined healthy individuals recruited during the 2009 Asian project for derivation of common reference intervals (RIs). Up-to-date electrophoresis auto-analyzer and reagents were employed for high resolution and reproducibility. SVs including sex, age, body mass index (BMI), ABO blood groups, and levels of drinking, smoking, and exercise were analyzed by multiple regression analysis. RIs were determined by parametric methods after refining healthy individuals by use of latent reference values exclusion method.

RESULTS

Age-related changes in ALP2-3 were different in females: ALP2, linear increase from 20-64y; ALP3, lowering until 45 y and rising steeply thereafter. ALP2 increased with BMI especially in females. ALP5 was barely detectable except in blood-types O and B. Age-related increases in LDH1-LDH3 were noted in females, whereas BMI-related increases were found only for LDH2-LDH5 in both sexes. Pancreatic amylase showed age-related increase in females and was slightly higher in blood-type O. RIs for absolute and relative activities of each isozyme were derived in consideration of sex and age.

CONCLUSIONS

Investigation of these isozymes revealed various age-, BMI-, and blood-type-related changes that are all relevant in clinical interpretation of enzyme test results.

Characteristics of hyperparathyroid states in the Canadian multicentre osteoporosis study (CaMos) and relationship to skeletal markers

CONTEXT

PTH is an essential regulator of mineral metabolism; PTH hypersecretion may result in hyperparathyroidism including normocalcaemic, primary and secondary hyperparathyroidism.

OBJECTIVE

To examine the characteristics of participants with hyperparathyroid states and the relationship to bone mineral density (BMD).

DESIGN AND PARTICIPANTS

A cross-sectional study of 1872 community-dwelling men and women aged 35+ years (mostly Caucasian) with available serum PTH from Year 10 Canadian Multicentre Osteoporosis Study follow-up (2005-07). PTH was determined using a second-generation chemiluminescence immunoassay.

OUTCOME MEASURES

L1-L4, femoral neck and total hip BMD.

RESULTS

We established a PTH reference range (2·7-10·2 pmol/l) based on healthy participants (i.e. normal serum calcium, serum 25-hydroxyvitamin D, kidney function and body mass index, who were nonusers of antiresorptives, glucocorticoids and diuretics and not diagnosed with diabetes or thyroid disease). Participants with PTH levels in the upper reference range (5·6-10·2 pmol/l), representing a prevalence of 10·7%, had lower femoral neck and total hip BMD, by 0·030 g/cm(2) [95% confidence interval: 0·009; 0·051] and 0·025 g/cm(2) (0·001; 0·049), respectively, than those with levels 2·7-5·6 pmol/l. Participants with normocalcaemic and secondary hyperparathyroidism also had lower total hip BMD than those with levels 2·7-5·6 pmol/l, and CaMos prevalences of normocalcaemic, primary and secondary hyperparathyroidism were 3·3%, 1·4% and 5·2%, respectively.

CONCLUSION

We found reduced BMD in participants with accepted hyperparathyroid states but also a notable proportion of other participants that might benefit from having lower PTH levels.

ASVCP reference interval guidelines: determination of de novo reference intervals in veterinary species and other related topics

Reference intervals (RI) are an integral component of laboratory diagnostic testing and clinical decision-making and represent estimated distributions of reference values (RV) from healthy populations of comparable individuals. Because decisions to pursue diagnoses or initiate treatment are often based on values falling outside RI, the collection and analysis of RV should be approached with diligence. This report is a condensation of the ASVCP 2011 consensus guidelines for determination of de novo RI in veterinary species, which mirror the 2008 Clinical Laboratory and Standards Institute (CLSI) recommendations, but with language and examples specific to veterinary species. Newer topics include robust methods for calculating RI from small sample sizes and procedures for outlier detection adapted to data quality. Because collecting sufficient reference samples is challenging, this document also provides recommendations for determining multicenter RI and for transference and validation of RI from other sources (eg, manufacturers). Advice for use and interpretation of subject-based RI is included, as these RI are an alternative to population-based RI when sample size or inter-individual variation is high. Finally, generation of decision limits, which distinguish between populations according to a predefined query (eg, diseased or non-diseased), is described. Adoption of these guidelines by the entire veterinary community will improve communication and dissemination of expected clinical laboratory values in a variety of animal species and will provide a template for publications on RI. This and other reports from the Quality Assurance and Laboratory Standards (QALS) committee are intended to promote quality laboratory practices in laboratories serving both clinical and research veterinarians.

Distribution of serum total protein in elderly Chinese

The serum total protein levels of the elderly possibly decrease gradually with aging. However, serum total protein levels are not suitable as a uniform reference standard for the elderly at different ages and genders. Thus, we investigated the total serum protein distribution in different gender and age groups of 11,453 elderly individuals aged ≥60 years and without liver or renal disease from Lianyungang, Jiangsu, China. The total protein levels (TPL) of these individuals exhibited normal distribution (Z = 1.206, P = 0.109), whereas the reference range (95% CI) was 54.1 g/L to 82.3 g/L. TPL was higher in females than in males for those aged between 60 and 75 years, whereas no significant difference was observed for those aged between 80 and 95 years. TPL was negatively correlated with age in males (r = −0.1342, P<0.05), females (r = −0.304, P<0.05), and the total group (r = −0.2136, P<0.05). TPL also decreased with aging and showed a faster rate in women than in men. These results indicated that an appropriate range of serum total protein based on age and gender differences should be used for clinical applications.

Reference intervals and factors contributing to serum cystatin C levels in a Chinese population

BACKGROUND

Serum cystatin C (Cys-C), an inhibitor of cysteine proteases, has been suggested as an ideal biomarker of glomerular filtration rate (GFR).

OBJECTIVES

The objective of this study was to describe the reference intervals of serum Cys-C and identify factors associated with serum Cys-C or its variability, including age, gender, creatinine (Crea), blood urea nitrogen (BUN), and uric acid (UA).

DESIGN AND METHODS

Serum Cys-C, Crea, BUN, and UA were measured in 4,517 healthy participants aged 8-89 years attending our hospital. Serum Cys-C was analyzed using a latex-enhanced immunoturbidimetric method. Crea were tested by picric acid jaffe method, BUN, and UA by kinetic UV assays.

RESULTS

The predominant characteristic of Cys-C distribution was that Cys-C concentration in age ≥60 years group was the highest (P < 0.05). The differences of Cys-C concentration between males and females existed for subjects aged from 30 to 59 years (P < 0.05). In a multiple model adjusted only for gender and age, gender (β = 0.007) has stronger effect on Cys-C levels, compared with age (β = 0.003). The clinical variables, comprised of age, gender, Crea, BUN, and UA, involved in the fully adjusted equation accounted for 37.6% of variation of Cys-C.

CONCLUSIONS

Ninety-five percent reference intervals for healthy population were partitioned into three categories only by age, 0.59-1.07 mg/L for subjects aged 19-59 years; 0.74-1.14 mg/L for the older aged ≥60 years; and 0.63-1.11 mg/L for children aged ≤18 years. Serum Cys-C is significantly related to gender, age, UA, Crea, and BUN. Besides, there are still other factors contributing to variation of Cys-C levels.

Age- and sex-specific reference intervals for blood copper, zinc, calcium, magnesium, iron, lead, and cadmium in infants and children

OBJECTIVES

Reference intervals for clinically important elements in infants and children are rarely reported, despite their importance for accurate clinical decision-making. The exploration of such reference intervals is essential.

DESIGN AND METHODS

Seven elements, including copper (Cu), zinc (Zn), calcium (Ca), magnesium (Mg), iron (Fe), lead (Pb), and cadmium (Cd), were analyzed on BOHUI 5100 and 2100 analyzers using blood samples from 4044 healthy infants and children.

RESULTS

Age- and sex-specific reference intervals were established for Cu, Zn, Ca, Mg, Fe, Pb, and Cd.

CONCLUSIONS

Established reference intervals for Cu, Zn, Ca, Mg and Fe can provide important guidance for the reasonable supplementation of trace elements and other essential elements in infants and children. Reference intervals for Pb and Cd can play a role in the surveillance and diagnosis of environmental overexposure.

Radioactive holmium acetylacetonate microspheres for interstitial microbrachytherapy: an in vitro and in vivo stability study

PURPOSE

The clinical application of holmium acetylacetonate microspheres (HoAcAcMS) for the intratumoral radionuclide treatment of solid malignancies requires a thorough understanding of their stability. Therefore, an in vitro and an in vivo stability study with HoAcAcMS was conducted.

METHODS

HoAcAcMS, before and after neutron irradiation, were incubated in a phosphate buffer at 37°C for 6 months. The in vitro release of holmium in this buffer after 6 months was 0.5%. Elemental analysis, scanning electron microscopy, infrared spectroscopy and time of flight secondary ion mass spectrometry were performed on the HoAcAcMS.

RESULTS

After 4 days in buffer the acetylacetonate ligands were replaced by phosphate, without altering the particle size and surface morphology. HoAcAcMS before and after neutron irradiation were administered intratumorally in VX2 tumor-bearing rabbits. No holmium was detected in the faeces, urine, femur and blood. Histological examination of the tumor revealed clusters of intact microspheres amidst necrotic tissue after 30 days.

CONCLUSION

HoAcAcMS are stable both in vitro and in vivo and are suitable for intratumoral radionuclide treatment.

Reference intervals for common laboratory tests in Melanesian children

Pediatric reference intervals for biochemical tests are often derived from studies in Western countries and may not be applicable to the developing world. No such intervals exist for Melanesian populations. The aim of this study was to provide specific reference intervals for children from Papua New Guinea (PNG). We assayed plasma from 327 healthy Melanesian children living in Madang Province for common biochemical and hematological analytes. We used well-validated commercially available assay methodology. Compared with reference intervals from children from Western countries and/or African children, there were substantial differences in hemoglobin, soluble transferrin receptor, ferritin, calcium, phosphate, and C-reactive protein. Differences in the upper limits of reference intervals for bilirubin and alanine aminotransferase were also observed. Available reference intervals from Western and African countries may be inappropriate in PNG and other Melanesian countries. This has implications for clinical care and safety monitoring in pharmaceutical intervention trials and vaccine studies.

Liquid chromatography-tandem mass spectrometry determination of oxalate in spot urine

BACKGROUND

For assessment of total oxalic acid (OX) status, reliable quantification of OX in both urine and plasma is important. For urine, but not plasma, a commercial kit is available. We have recently described a LC-MSMS method for OX in plasma. The aim of the present study was to evaluate the usefulness of this assay for urine. We also wanted to evaluate if 24 h urine collection could be substituted by OX/creatinine-ratio (U-OX/crea) in spot-urine, and establish precursory reference intervals for U-OX/crea in children and adults.

METHODS

Acidified urines were analysed and relevant validation parameters assessed. Diurnal excretion patterns were investigated in nine healthy volunteers on self-chosen diets. For method comparison, 29 urine samples were analysed with both the present method and a commercial urine-oxalate kit. Precursory reference values for U-OX/crea in children and adults (N=103, 1 month-76 years) were calculated.

RESULTS

The within-batch coefficient of variation (CV) was 2.5% and a relative recovery of 97% in urine spiked with 5-200 micromol/L OX was found. The LC-MSMS method gave 7.9% higher OX values compared to the kit. No significant diurnal pattern of U-OX/crea was observed. U-OX/crea in children decreases with age, with no gender dependency. In adults no age variation was found, but females had somewhat higher U-OX/Crea compared to males.

CONCLUSION

The LC-MSMS method has proven useful for urinary OX quantification. Random spot-urine samples can be used. Age-dependent reference limits for U-OX/crea must be applied in children, in contrast to adults.

An Improved Auto-Generation System to Obtain Reference Intervals for Laboratory Medicine

Objectives

Reference values are highly required parameters for all tests in the clinical laboratory, and the supplementary provision of reliable reference intervals is an important task for both clinical laboratories and diagnostic test manufacturers. Despite the progress that has been made in the conceptual aspects of reference intervals, in practice their use is still not completely satisfactory. Most of the laboratories have used various methods to calculate statistic-based reference intervals, and they have mainly focused on extracted data, yet its use is considerably limited. We had to deal with the inconvenience of using a number of programs (SPSS or SAS, MS Excel) in order to calculate the results of reference intervals.

Methods

In order to obtain standardized reference intervals, we developed an integrated program that can calculate, by a nonparametric method, reference intervals with using the Clinical and Laboratory Standards Institute (CLSI) processes as its guideline. We also developed a grouping interface that enables users to customize classification of each group (age, gender, blood group, race, etc) when calculating reference intervals.

Results

To verify the developed program, we compared the reference intervals of the current data on 281 persons for 8 total areas, and the reference intervals were was already calculated beforehand with by using this new program. As a result, both results perfectly matched.

Conclusions

This integrated program will be convenience for calculating reasonable values through continual datainspection at an inspection lab for calculating reference intervals. The newly developed program will improve the consistency and reliability of the statistics on reference intervals.

Predisposing chronic diseases and hypophosphatemia in patients with influenza

Almost half of the hospitalized influenza patients have a chronic disease, which increases the risk for secondary bacterial infections and for adults >65 years influenza is related to high mortality risk. The impact of diabetes mellitus (DM), asthma bronchiale, cardiovascular disease (CVD) and chronic obstructive pulmonary disease (COPD) on the risk of having a low serum phosphatemia (S-P) in addition to influenza is important to investigate as this increases both morbidity and mortality and can be prevented. Hypophosphatemia could be the explanation for reduced chemo-taxis and phagocytosis, which in addition to respiratory function may increase the risk of pneumonia and sepsis. Data for this study was collected from the medical journals retrospectively for 100 patients admitted to the Department of Infectious Diseases during the study period, 1992-94, with the clinical diagnosis influenza out of which seventy-two cases were used in the calculation. Forty-seven percent of the hospitalized influenza patients had a 2.7-fold risk of suffering from DM than of any other chronic disease and an almost significantly doubled risk of having a low S-P level with a chronic disease. The prevalence of hypophosphatemia (S-P<0.70 mmol/l) was high; 13.0% of the women and 15.0% of the men; 34.0% of all patients had S-P<0.82 mmol/l. Men, in contrast to women, showed clinical signs of a secondary bacterial infection more frequently (12/41 and 6/35, respectively). Our study gives indications for an involvement of low S-P with chronic disease.

An improved indirect approach for determining reference limits from intra-laboratory data bases exemplified by concentrations of electrolytes / Ein verbesserter indirekter Ansatz zur Bestimmung von Referenzgrenzen mittels intra-laboratorieller Datensätze am Beispiel von Elektrolyt-Konzentrationen

Background: The current dogma of establishing intra-laboratory reference limits (RLs) and their periodical reviewing cannot be fulfilled by most laboratories due to the expenses involved. Thus, most laboratories adopt RLs from external sources often neglecting the problems of transferability. Presently accepted validation concepts still require experimental expenses. Several attempts were undertaken to derive RLs from the large data pools stored in modern laboratory information systems. Former indirect procedures were not generally accepted, but were recently further developed and combined with direct exclusion criteria and applied to estimate RLs of the catalytic activity concentrations of enzymes. This approach was now applied to several electrolytes in serum and plasma most commonly applied in clinical chemistry.

Methods: A smoothed kernel density function was estimated for the distribution of the mixed data of the sample group (combined data of non-diseased and diseased subjects). It was assumed that the “central” part of the distribution of all data represents the non-diseased (“healthy”) population (non-pathological values) with high probability. The central part was defined by truncation points using an optimisation method, and was used to estimate a Gaussian distribution of the values of non-diseased subjects. This distribution was now considered as the distribution of the non-diseased subgroup. The percentiles of this parametrical distribution were calculated to obtain unimodal reference intervals.

Results: The RLs obtained from different laboratories were similar to recently published values established by direct procedures. Stratification for gender was not necessary, but in some cases for age. With rising age, an increase of the upper RL and of the reference range was observed for potassium. Hospitalisation affected the RLs of sodium, potassium, calcium and magnesium, but not of phosphate. In the case of sodium, the data of at least five regional laboratories could be combined to common RLs. The presented indirect procedure was further validated with a large dataset of potassium concentrations from the NHANES III study with five groups of different health status.

Conclusions: The proposed strategy of combining exclusion criteria with an indirect method led to RLs from intra-laboratory data pools for electrolytes which were plausible in comparison to published data obtained by the generally accepted direct approach. The combined concept, however, still requires further investigations. Therefore, it is presently only recommended for checking and reviewing already existing RLs.

Reference intervals: the way forward

New facts have recently enhanced interest in the topic of reference intervals. In particular, the International Organization for Standardization standard 15189, requesting that 'biological reference intervals shall be periodically reviewed', and the directive of the European Union on in vitro diagnostic medical devices asking manufacturers to provide detailed information on reference intervals, have renewed interest in the subject. This review presents an update on the topic, discussing the theoretical aspects and the most critical issues. The basic approach to the definition of reference intervals proposed in the original International Federation of Clinical Chemistry documents still remain valid. The use of data mining to obtain reference data from existing databases has severe limitations. New statistical approaches to discard outliers and to compute reference limits have been recommended. On the other hand, perspectives opened by the improvement in standardization through the implementation of the concept of traceability suggest new models to define 'common' reference intervals that can be transferred and adopted by different clinical laboratories in order to decrease the proliferation of different reference intervals not always justified by differences in population characteristics or in analytical methodology.

A plea for intra-laboratory reference limits. Part 1. General considerations and concepts for determination

Accurate results for quantitative procedures can be useless if the reference limits for the interpretation of laboratory results are unreliable. Recent concepts for quality management systems require that laboratories pay more attention to identification and verification of reference limits. Scientific recommendations often claim that each laboratory should determine intra-laboratory reference limits, which should be reviewed periodically. This recommendation is currently neglected by most laboratories; instead they use reference limits from external sources, despite various problems of transference. Prospective and retrospective methods either using or neglecting disease prevalences (polymodal or unimodal concepts, respectively) and applying different statistical approaches for determining reference limits have been described. The various procedures are reviewed with regard to their diagnostic sensitivity, specificity and (non-)efficiency. The present gold standard is the reference limit concept according to IFCC recommendations (a unimodal prospective approach). This concept, together with trueness-based standardization, is the most useful basis for harmonization of the decision-making process with laboratory results, despite complex problems of traceability and transference. This harmonization is at present only achieved for a limited number of analytes for which SI units and traceability can be technically realized. For the majority of measurands in laboratory medicine, much research is still required and results cannot be expected in the near future. For these measurands, a need remains for internal, efficient and simple identification of population-based reference limits. Therefore, newer retrospective concepts were developed that use large data sets from laboratory information systems to derive intra-laboratory reference limits. These approaches appear promising and should be further developed.

A plea for intra-laboratory reference limits. Part 2. A bimodal retrospective concept for determining reference limits from intra-laboratory databases demonstrated by catalytic activity concentrations of enzymes

BACKGROUND

The current recommendations for establishing intra-laboratory reference limits (RLs) cannot be fulfilled by most laboratories because of the expense involved. In the current study, a bimodal method was developed to derive RLs from data stored in a laboratory information system without any assumption concerning the distribution of the diseased subgroup.

METHODS

A smoothed kernel density function (D(mix)) was estimated for the distribution of combined data for non-diseased and diseased adult subjects. It was assumed that the "central" part of the distribution represents the non-diseased population, which was defined and used to estimate a Gaussian distribution of either the original values or Box-Cox transformed data. This normal distribution was now considered the distribution of the non-diseased subgroup (D(nd)). Percentiles were calculated to obtain retrospective RLs. The density function of the diseased subgroup (D(d)) was calculated by subtracting the non-diseased density function from D(mix) (D(d)=D(mix)-D(nd)). The intersection point of the D(nd) and D(d) curves identified the RL with the highest diagnostic efficiency.

RESULTS

The model was applied to catalytic activity concentrations of several enzymes with data from different laboratories. The RLs obtained were similar to recently published consensus values. Differences between laboratories were small but significant. Gender stratification was necessary for alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutymaltransferse (gamma-GT), not significant for lipase and amylase and inconsistent among the laboratories for alkaline phosphatase (AP) and lactate dehydrogenase (LDH). Age stratification was only tested for two groups (18-49 and >or=50 years) and was significant for AST (females only), gamma-GT and lipase, not significant for amylase and inconsistent for AP, LDH and ALT. For gamma-GT, further stratification for age in decades was necessary for males. Creatine kinase MB (CK-MB) values were not stratified owing to the low number of data available.

CONCLUSIONS

Retrospective RLs derived from intra-laboratory data pools for the catalytic activity concentration of enzymes using a modified procedure plausibly agreed with published consensus values. However, most RLs varied significantly among laboratories, thus supporting the "old" plea for intra-laboratory RLs.

Reference range for serum parathyroid hormone

OBJECTIVE

To determine whether the reference range for parathyroid hormone (PTH) should be lowered (from 65 pg/mL to a proposed value of 46 pg/mL) with use of the Allegro radioimmunometric assay.

METHODS

We examined the reference range for PTH, adjusted for serum 25-hydroxyvitamin D (25-OHD), in 503 healthy African American and white women, who were 20 to 80 years old. We also analyzed other factors that are thought to influence PTH levels.

RESULTS

Univariate predictors of PTH were identified, and a multivariate model was developed with use of the variables and PTH. Serum PTH was significantly higher in black study subjects than in white study subjects (P<0.02). Increasing PTH was also significantly correlated with increasing body mass index, age, and serum creatinine and with decreasing dietary calcium intake and serum 25-OHD levels. A stepwise multiple linear regression analysis yielded the following predictors of PTH: body mass index (R2=9.4%), age (R2=1.0%), and serum 25-OHD (R2=0.8%). In our study population, many PTH values were above the proposed new upper limit of 46 pg/mL.

CONCLUSION

The upper limit of the reference range for serum PTH should not be changed. Factors to be considered in analysis of serum PTH values in the upper reference range in patients with normocalcemia include obesity, race, 25-OHD levels, advanced age, serum creatinine, and dietary calcium intake.

Common biochemical markers of bone turnover predict future bone loss: a 5-year follow-up study

BACKGROUND

Bone mineral density (BMD) is used to follow gain or loss of bone mass but cannot detect changes within a short period of time. Biochemical markers of bone turnover may be of value for prediction of individual bone loss.

METHODS

We studied the relation between common inexpensive markers of bone turnover (serum alkaline phosphatase (ALP), osteocalcin (OC), urinary hydroxyproline (OHPr), and calcium (Ca)), BMD, age, and menopause in a combined cross-sectional and longitudinal design comprising 429 pre- and postmenopausal randomly selected women aged 21-79 years (mean 50 years). A follow-up was initiated after 5 years (including 192 of these women), which focused on changes in bone mass and the ability of these four common markers of bone turnover (sampled at baseline) to predict future bone loss.

RESULTS

A marked increase was observed for all markers at the beginning of menopause. During the postmenopausal period ALP and Ca decreased to near premenopausal levels, while OC and OHPr remained high even 15 years after menopause. We also found inverse correlations at baseline between the bone markers and BMD, independent of the selected marker or skeletal site, r=-0.14 to -0.46, P<0.05. The correlations between ALP, OC, OHPr, and subsequent bone loss over 5 years, was significant for arm, r=-0.23 to -0.36, P<0.01. Baseline levels of all bone markers correlated significantly at group level with the 5-year follow-up of BMD for all sites. The ability of markers to predict individual bone loss was estimated by a multivariate regression model, which included baseline BMD, age, and body mass index as independent variables. ROC analysis showed a validity of approximately 76% for the forearm model, but was lower for the hip (55%) and lumbar spine (65%).

CONCLUSIONS

These data show that the common inexpensive biochemical markers of bone turnover ALP, OC, OHPr, and Ca were related to the current bone mass and, moreover, provides information about future bone loss at the individual level. Future investigations should include an evaluation of the clinical relevance of markers of bone turnover in relation to fracture risk.

Partitioning biochemical reference data intosubgroups: comparison of existing methods

Four existing methods for partitioning biochemical reference data into subgroups are compared. Two of these, the method of Sinton et al. and that of Ichihara and Kawai, are based on a quotient of a difference between the subgroups and the reference interval for the combined distribution. The criterion of Sinton et al. appears rather stringent and could lead to recommendations to apply a common reference interval in many cases where establishment of group-specific reference intervals would be more useful. The method of Ichihara and Kawai is similar to that of Sinton et al., but their criterion, based on a quantity derived from between-group and within-group variances, seems to lead to inconsistent results when applied to some model cases. These two methods have the common weakness of using gross differences between subgroup distributions as an indicator of differences between their reference limits, while distributions with different means can actually have equal reference limits and those with equal means can have different reference limits. The idea of Harris and Boyd to require that the proportions of the subgroup distributions outside the common reference limits be kept reasonably close to the ideal value of 2.5% as a prerequisite for using common reference limits seems to have been a major improvement. The other two methods considered, that of Harris and Boyd and the “new method” follow this idea. The partitioning criteria of Harris and Boyd have previously been shown to provide a poor correlation to those proportions, however, and the weaknesses of their method are summarized in a list of five drawbacks. Different versions of the new method offer improvements to these drawbacks.

Objective Criteria for Partitioning Gaussian-distributed Reference Values into Subgroups

Background: The aim of this study was to develop new and useful criteria for partitioning reference values into subgroups applicable to gaussian distributions and to distributions that can be transformed to gaussian distributions.

Methods: The proposed criteria relate to percentages of the subgroups outside each of the reference limits of the combined distribution. Critical values suggested as partitioning criteria for these percentages were derived from analytical bias quality specifications for using common reference intervals throughout a geographic area. As alternative partitioning criteria to the actual percentages, these were transformed mathematically to critical distances between the reference limits of the subgroup distributions, to be applied to each pair of reference limits, the upper and the lower, at a time. The new criteria were tested using data on various plasma proteins collected from ∼500 reference individuals, and the outcomes were compared with those given by the currently widely applied and recommended partitioning model of Harris and Boyd, the “Harris-Boyd model”.

Results: We suggest 4.1% as the critical minimum percentage outside that would justify partitioning into subgroups, and 3.2% as the critical maximum percentage outside that would justify combining them. Percentages between these two values should be classified as marginal, implying that nonstatistical considerations are required to make the final decision on partitioning. The correlation between the critical percentages and the critical distances was mathematically precise in the new model, whereas this correlation is rather approximate in the Harris-Boyd model because focus on the difference between means in this model makes high precision hard to achieve. The application examples suggested that the new model is more radical than the Harris-Boyd model.

Conclusions: New percentage and distance criteria, to be used for partitioning gaussian-distributed data, have been developed. The distance criteria, applied separately to both reference limit pairs of the subgroup distributions, seemed more reliable and correlated more accurately with the critical percentages than the distance criteria of the Harris-Boyd model. As opposed to the Harris-Boyd model, the new model is easily adjustable to new critical values of the percentages, should they need to be changed in the future.

Hypophosphataemia in the metabolic syndrome. Gender differences in body weight and blood glucose

OBJECTIVE

We examined gender differences in the clustering of risk factors, especially regarding the possible role of serum phosphate (S-P) in obese patients who participated in a 4 week education programme to reduce their excess risk of cardiovascular disease (CVD).

RESULTS

Significantly higher body mass index (BMI) and concentrations of S-P and high density lipids (S-HDL) in serum were found in women (n=1272) than in men (n=993). In women, BMI was inversely correlated with S-P at the time of admission. Also in women (but not in men), changes in BMI and S-P over 1 or 1-1/2 y were inversely correlated. In men (but not in women), S-P level was inversely correlated with age, systolic blood pressure (SBP), diastolic blood pressure (DBP) and blood glucose at the time of admission. In women, S-P increased and DBP decreased, in addition to weight decrease over both 6 months and 1(1/2) y or 1 y. In women (but not in men), significantly higher age, S-P, S-chol, S-TG, S-urate, SBP and DBP values were found with the highest vs the lowest decile of S-Ca.

CONCLUSION

We conclude that higher S-P and S-Ca levels may contribute to the difference in metabolic disturbances occurring in obesity, seen in women vs men.

Standardization of Laboratory Data and Establishment of Reference Intervals in the Fukuoka Prefecture: A Japanese Perspective

Standardization of 22 clinical chemistry analytes and five serum protein constituents has been performed in the Fukuoka Prefecture, which has a population of approximately five million. The standardization project was established to determine reference intervals for these analytes by educating physicians, medical technologists and staff of medical institutions, and by daily or monthly monitoring the use of common control samples through e-mail. Standardization extended to 97% of the institutions in the prefecture. Results for 14 of the 22 clinical chemistry analytes have become highly reliable and differences between institutions decreased. Standardization of other analytes is now in progress. Regional collaboration based on international guidelines led to a significant improvement in interlaboratory comparability. Areas where further improvements are needed have been identified.

Calculating reference intervals for laboratory measurements

Reference intervals are used in laboratory medicine to detect measurements which are extreme, possibly abnormal. Methods of estimating reference intervals and age-specific reference intervals (where the measurement is dependent on a covariate, typically age) are reviewed. The issues of calculating confidence bands, determining appropriate sample sizes and assessing goodness-of-fit are discussed.

Hypophosphataemia in general practice patients

We compared plasma phosphate concentrations in general practice patients and hospital inpatients and outpatients over an 8-month period. The distribution of results in all three groups was similar and 12-16% of results were at or below 0.8 mmol/L. In general practice patients, 8.3% of results from males and 12.1% from females were below the lower limit of their respective reference ranges. Eighteen of these patients (0.2% of results) had plasma phosphate concentrations < or = 0.4 mmol/L. On follow-up, only two of these patients had any attributable cause for their severe hypophosphataemia; in the remainder, it was unexpected and unexplained. Hypophosphataemia in outpatients and general practice patients is more common than has previously been appreciated. We present a strategy for further investigation of these patients.

Reference intervals for some serum biochemical markers of bone metabolism in Kuwait

Using the Hitachi 717 Selective Multichannel analyser, we established reference intervals for serum albumin (37-9 g/l); measured serum calcium (2.14-2.54 mmol/l); corrected serum calcium (2.25-2.60 mmol/l); serum phosphate (0.74-1.60 mmol/l); and alkaline phosphatase (47.0-289.6 U/l) in the Kuwaiti population. The mean concentrations of calcium and phosphate decreased with increasing age in both sexes except for a sudden increase in women at about menopause. Although there was a skewed distribution of alkaline phosphatase in both sexes there was a significant increase in enzyme activity in women after the age of 50 years. Using corrected serum calcium we found that 15% of women in the reproductive age group in Kuwait had hypocalcaemia.

Immunoturbidimetry of serum apolipoproteins A-I and B on the Cobas Bio centrifugal analyzer: method validation and reference values

We describe an immunoturbidimetric assay for estimating the concentration of apolipoproteins (apo) A-I and B in serum with a Cobas Bio centrifugal analyzer. Several analytical variables were studied: pH, temperature, wavelength, reaction time, sample pretreatment, antisera dilution, concentration of NaCl, phosphate buffer, and PEG 6000; a good optical response was obtained with small volumes of sample and antisera. Imprecision was low, with intrarun coefficient of variance (CV) from 1.1 to 2.8% and interrun CV from 1.8 to 3.2%. We demonstrated a good correlation between our method and radial immunodiffusion for apo A-I (r = 0.975) and apo B (r = 0.980). Reference values were calculated from a sample of 494 healthy subjects, and separate intervals for the ratio of apo A-I to apo B in gender and age subgroups were established.

Essential fatty acid depletion of renal allografts and prevention of rejection

A central hypothesis in transplantation biology is that resident leukocytes expressing class II histocompatibility antigens may determine the immunogenicity of an organ. By means of a novel method to deplete the kidney of resident leukocytes, essential fatty acid deficiency (EFAD), this hypothesis was tested in an intact, vascular organ. Kidneys subjected to EFAD and thus depleted of resident Ia-positive macrophages survived and functioned when transplanted across a major histocompatibility antigen barrier in the absence of immunosuppression of the recipient. Control allografts were rejected promptly. Allografts from donors subjected to EFAD normalized their lipid composition and were repopulated with host macrophages by 5 days. Administration of Ia-positive cells at the time of transplantation established that the resident leukocyte depletion induced by EFAD was responsible for the protective effect. These observations may provide insights into the mechanisms underlying tissue immunogenicity and the population of normal tissues with resident leukocytes.