Organ weights are an essential part of autopsy analysis. Deviations from normal organ weights provide important clues to disease processes. The assessment of normal organ weights depends on reliable reference tables, but most widely available reference tables are based on data that are either decades old or derived from relatively small sample sizes.
To provide an updated reference table of organ weights based on contemporary sources and a large sample size.
Organ weights from 4197 carefully screened autopsies performed on adults at the Palm Beach County Medical Examiner's Office in West Palm Beach, Florida, and the Mayo Clinic Hospital in Rochester, Minnesota.
Height and body weight data in this study reflect the well-recognized increases in both variables, but most particularly in body weight, seen during the last decades. The study data show a strong positive association between organ weight and body weight for the heart, liver, and spleen. There is a similar but weaker association between body weight and the weight of the lungs and kidneys. Brain weight is independent of body weight but shows a strong negative association with age. Even when controlling for body weight, men's organs are heavier, except for the weight of the liver, which is comparable in men and women. These associations are in agreement with the findings of previous studies. The current study suggests that, for some of the commonly weighed organs, there has been an increase in median organ weight when compared with existing references.
The tables presented here provide an updated reference that should prove useful to autopsy pathologists in the forensic and hospital settings.
Organ weights are a cornerstone of autopsy gross pathology. By weighing the major organs with a simple hanging balance and comparing the results with standard tables, pathologists can draw inferences about disease processes (eg, hypertrophy, hyperplasia, atrophy, edema, infiltration). The quality of such inferences, however, depends in large part on the reliability and accuracy of the reference tables. Some autopsy references provide no normal organ weight reference values,1–3 whereas others4,5 use reference values that date back to the previous midcentury. Reliance on these tables presents several problems.
One potential problem with such references is that although anatomic relationships have remained constant for centuries, human body habitus has not. Large studies have shown striking changes across the world in average height during the last hundred years and measurable differences as recently as the last 50 years.6 Changes in human body weight have been even more dramatic.
American pathologist Henry Cattell's 1905 Post-Mortem Pathology listed average height and weight as 67 inches and 143 pounds for men and 63 inches and 121 pounds for women, figures that seem almost unimaginable by current standards.7 Morbid obesity was a comparatively rare event until the middle of the past century. The percentage of Americans in the obese range as measured by body mass index (BMI) remained fairly constant between 1960 and 1980, but it increased significantly between 1980 and 1991 (from 13% to 21% for men and from 17% to 26% for women). Between 2000 and 2018, the prevalence of obesity rose to 42.4% and the prevalence of severe obesity rose from 4.7% to 9.2%.8
Changes in average body weight are particularly pertinent to this discussion, because it is well established that, for many organs, normal organ weights vary directly with body weight. The increasing proportion of adults with obesity in modern Western civilization in general and in the United States particularly would be expected to affect organ weights.9
A second potential problem with historical references is the source of the organ weights. Some of the standard organ weight tables rely heavily on hospital-based populations or on tissue bank material. Organ weights may be influenced by a variety of disease processes.10 Although the authors of these tables took steps to exclude weights of organs with known disease from their data sets, the subjects in these studies were inpatients and by definition sick enough to require admission. Prolonged hospitalization often entails changes in fluid balance and diet. If the goal is to create a standard reference of normal organ weights in disease-free individuals, then prioritizing data from ambulatory subjects and patients with short hospital admissions offers clear advantages.
Some recent studies have attempted to establish a modern reference range of autopsy organ weights using data from forensic autopsy series.11–15 These studies, however, suffer from relatively small sample sizes, particularly when subcategorizing the sample by sex, age, or body weight/length.
The purpose of this study was to address the problems with existing references and establish a large database of normal organ weights in adults from a contemporary control group of deceased individuals. The results will provide updated standards against which to compare organs during autopsy gross examination. This paper will first review existing compilations of organ weights in normal adults. It will then provide normal organ weight ranges based on sex and either body weight or age in adults from the current era.
MATERIALS AND METHODS
Prior to data collection and screening of decedents in this study, a systematic review of historical normal autopsy organ weights from reference textbooks and articles was conducted. The purpose was to review previous segmentation approaches and to garner estimates of variability by organ in order to calculate minimum sample sizes required for each data cell in the reference tables. Using the larger studies with weights on the larger organs, an average SD of 55 g was used for sample size calculations. Therefore, 95% confidence intervals of the mean of ±5, ±10, and ±15 g would require minimum data cell sample sizes of 200, 75, and 50 cases, respectively. This study was designed to have minimum data cell sample sizes of 75.
Organ weights, body weight, and body length were collected retrospectively from decedents age 18 or older from the Palm Beach County Medical Examiner Office in West Palm Beach, Florida, between 2009 and 2017, and from the Mayo Clinic Hospital in Rochester, Minnesota, between 2013 and 2014. During evisceration, the organs were separated from their major attachments and stripped of adherent soft tissue. The following nonembalmed organs were weighed for each decedent: brain, heart, right lung, left lung, liver, spleen, right kidney, and left kidney. The brain weight included the cerebral and cerebellar hemispheres, midbrain, pons, medulla, and leptomeninges, excluding the dura. The aorta and pulmonary artery were cut 1 to 2 cm above the aortic and pulmonic valves and blood was removed prior to weighing. The liver was weighed with the gallbladder intact. The organs were weighed on an electronic digital scale and weights were recorded in grams. Unclothed body weight was obtained using an electronic digital floor scale and recorded as the nearest whole number in pounds. The body length was measured with the shoeless decedent in the anatomic position to the nearest half inch using a standard measuring stick.
All cases included in the investigation met strict criteria and were reviewed as directed by the authors. This included a review of the autopsy report, prior clinical and medical information, and, if applicable, hospital records. All decedents were refrigerated prior to autopsy, and autopsies were performed within 24 hours after death. Grossly abnormal remains (eg, visibly edematous, putrefied, or severely burned or charred bodies) were excluded. Patients who had been hospitalized for more than 2 days were excluded.
Organs that were severely injured, decomposed, or determined to be anatomically or pathologically abnormal such that weight would be affected were excluded. In cases where a specific organ or set of organs was affected by disease or injury, those organ weights were omitted, leaving the remaining unaffected organs eligible for inclusion in the study. For example, if the death was from an opiate overdose, the lung weights were excluded, because pulmonary edema is a common finding in fatal opiate overdose and this would increase the lung weights above normal. The rest of the organs from that opiate overdose would be included in the study. The common exclusionary criteria are listed in Table 1.
There are some published data to suggest that opioid overdose may have an effect on brain weight. Molina et al16 compared the brain weights of people who died of opioid overdoses, cardiovascular causes, and motor vehicle crashes (approximately 80 subjects in each group). The brains of subjects in the opioid overdose group were slightly but significantly heavier than the brains of subjects in the motor vehicle crash group (1380 versus 1328 g). Interestingly, there was no significant difference in brain weight between people who died of opioid overdoses and those who died of cardiovascular causes (1380 versus 1369 g). The study groups, however, were limited in size, and the magnitude of the differences between the groups was small. We decided not to exclude the brain weights of subjects who died of opioid overdoses.
The were no exclusion criteria for body weight or BMI. As a result, the study data include organ weights from subjects who would meet published criteria for obesity. Because obesity has been shown to be associated with a wide variety of morbid conditions, an argument could be made that data from obese individuals should not be included in a collection of normal organ weights. The decision to include these data was made principally for 2 reasons: (1) the difficulty of unequivocally identifying obese subjects and (2) the definition of the term normal.
First, defining and identifying obesity is not a straightforward process. Although the Centers for Disease Control and Prevention uses BMI cutoffs as a convenient way to define categories such as overweight and obese, its Web site acknowledges that “For individuals, BMI is a screening tool, but it does not diagnose body fatness or health. A trained health care provider should perform appropriate assessments to evaluate an individual's health status and risks.”8 Some of the additional information that might enable a more reliable assessment of obesity in our cohort (body fat content, waist circumference) was not readily available. Excluding subjects based on BMI criteria alone would exclude some number of athletic individuals with increased lean muscle mass.
Second, there is the question of whether reference data should represent desirable target values for a population or the values most commonly found in that population. The former approach would produce a table of ideal organ weights that would exclude not only obesity, but also other factors potentially associated with disease states (alcohol use, tobacco use, chronic illness). Although there are advantages to that approach, there are practical barriers to defining such an ideal population and to identifying adequate numbers of subjects who meet those standards. By choosing the latter approach, we have produced tables of organ weights that we believe could be considered usual, typical, or routine, the dictionary definition of normal. It is this definition of the word normal that is used to describe the organ weights in this study.
Before data summarization of organ weights, clear outliers were excluded from the distribution of overall reported weights; between 1 and 5 individual weights were excluded per organ. No subsequent outliers were removed, in an effort to include all reasonable normal organ weights. The final presentation of the reference tables is summarized with nonparametric statistics to avoid the influence of any potential outliers to the summarization estimates.
All data summarizations were generated using SAS (Cary, North Carolina). Reference tables were initially generated in 2 ways, first by sex and body weight categories and second by sex and age range categories. The categories for body weight ranges were less than 131, 131 to 150, 151 to 170, 171 to 190, 191 to 210, 211 to 230, and more than 230 pounds. The categories for age ranges were 18 to 30, 31 to 40, 41 to 50, 51 to 60, 61 to 70, and more than 70 years. For the final reference tables, 3 nonparametric statistics are presented (median, 10th percentile, 90th percentile) for each data cell, along with the number of weights for each organ.
The data from a total of 4197 decedents are included in the reference tables for normal organ weights from 2 institutions: Palm Beach County Medical Examiner Office in West Palm Beach, Florida (n = 3863), and Mayo Clinic Hospital in Rochester, Minnesota (n = 334). The distributions of decedents by sex and body weight categories and by sex and age categories are summarized in Tables 2 and 3, respectively. Of the 4197 decedents in the study, 2999 (71.5%) were male and 1198 (28.5%) were female. There was a higher percentage of women in the lower weight categories. Women represented 67.2% of decedents less than 130 pounds but only 37.8% of decedents who weighed between 131 and 150 pounds. In the higher weight categories (greater than 151 pounds), the percentage of women ranged between 15.6% and 25.6%. The percentage of women in each age category ranged from 22.6% to 36.3% and generally increased when moving to higher age categories.
Based upon the systematic review and the desire to have 95% CIs of the mean at ±10 g for the higher-weight organs, the goal was to attain a minimum sample size of 75 for each data cell of the sex and body weight category. This minimum sample size requirement was met for every data cell, except for women in the 211- to 230-pound weight category. In many data cells, especially for the men and women in the weight categories less than 170 pounds, the number of decedents exceeded 200, which was the minimal sample size for confidence limits at ±5 g. However, the actual number of weights for each organ may be lower, because not every organ weight was obtained for every decedent.
Two reference tables were generated, first by sex and body weight ranges and second by sex and age range categories. When deciding upon the best reference table structure for each organ, the authors chose the reference table format with lower organ weight SDs and the format that most clearly trended differences in organ weight distributions when moving across either the age or body weight categories for each sex (comparative data not shown).
In addition, the reference table design from the manuscripts in the systematic analysis helped inform the final decision. The reference table designs of the historical reference textbooks and articles were reviewed (Table 4), and of the 14 references, 6 (42.9%) used sex/body weight, 4 (28.6%) used sex/age, and 4 (28.6%) used sex/other factor. The authors found that the sex and body weight ranges provided a more useful reference table for each organ, except for brain, which was broken out by sex and age ranges.
The data set that forms the basis for this study is very rich. The organ weight tables could also have been segregated by height or BMI, and there are arguments to be made for alternative designs. For example, creating tables organized by BMI would have the benefit of allowing users to decide for themselves if they wanted to include potentially obese patients in their definition of normal. Space does not allow for a comprehensive presentation all of the data tabulated and graphed in alternative formats here. We propose releasing those alternative graphs and tables at another time.
The historical references were also reviewed to see which used parametric summary statistics (mean, SD, and/or CI) and which used nonparametric summary statistics (medians and percentiles) in their reference tables. Of the 14 historical reference tables, 8 (57.1%) used parametric summary statistics and 6 (42.9%) used nonparametric summary statistics. The authors decided to use nonparametric summary statistics because not all of the organ weights were normally distributed. Nonparametric statistics best described the central 80% (10th–90th percentile) of all the reported weights without potential outlier biases that could affect the parametric means and SDs.
The final normal organ weight reference tables are shown in Tables 5 and 6. Table 5 is the reference table for all organs, except for brain, defined by sex and weight categories, and Table 6 is the reference table for brain weights defined by sex and age categories. For each data cell in both tables, the median organ weight, number of cases, and 10th and 90th percentiles are shown. For all 7 organs in Table 5, the organ weights increase as the body weight categories increase for both men and women, although the rate of increase is less for right and left lung and right and left kidney. Men demonstrate 10% to 20% heavier organ weights than women, controlling for body weight category, for each organ except for liver, where the weights are similar between sexes at each body weight category. Lastly, right lung is 10% to 20% heavier than left lung across sex and weight categories and left kidney is approximately 10 g heavier than right kidney across sex and weight categories. This is the reason that right and left lung and right and left kidney are provided separate normal organ weight ranges. For brain in Table 6, the weights decrease across increasing age categories for both men and women. Male brain weights are 10% to 15% heavier than female brain weights for any given age category.
Table 7 shows the distribution of height, body weight, and BMI for our data set. The best-fit regression lines for median organ weight by body weight (as well as the regression lines for the 10th, 25th, 75th, and 90th percentiles) are shown for the heart, lungs, liver, and spleen for both men and women in Figures 1 and 2. Figure 3 shows similar graphs for the distribution of brain weight by age.
The use of simple balance scales to weigh commercial goods dates back to about 2000 BCE.17 By the time of the publication of the first real collection of clinical pathologic correlations using autopsy (Morgagni's De Sedibus in 1761), scales of all sizes and of surprising accuracy were in widespread use at docks, markets, jewelers, and apothecaries throughout Europe. But another 100 years would pass before organ weights would become a routine part of an autopsy assessment. Rokitansky and Virchow in the mid-1800s and later, for example, gave descriptive and comparative assessments of organ findings, but reports of actual weights were rare. Autopsy pathology, like medicine more generally, was slow to adopt a quantitative approach. This appears to have been a matter of choice rather than the result of a lack of technology. Qualitative assessments were quick, convenient, and tried-and-true. Widespread change had to overcome considerable inertia.
Contributions of the Study
The motivation for the current study's collection of body weights and organ weights is largely twofold: to respond to the changes in average body habitus that have occurred during the last decades and to expand and improve upon the reference data set used for autopsy practice. It is, in essence, a recalibration of baseline, the sort of analysis that is second nature to our colleagues in clinical pathology. But it is also an opportunity to reevaluate basic autopsy procedure, an important exercise for the continued health and relevance of the field.
The trend of increasing organ weights for all 7 organs in Table 5 with increasing body weight categories for both men and women is consistent with the historical references and conventional wisdom. The same is true for decreasing brain weights with successively higher age categories for both men and women in Table 6. The finding that organ weights for men (except for liver) are consistently 10% to 20% higher when controlling for body weight or age is also consistent with historical reference tables and publications.
The aggregate data for height, body weight, and BMI in this study, in agreement with other studies, show an increase in body weight out of proportion to an increase in height, with a resulting increase in mean BMI, compared with data from the last several decades. Our results for BMI for men (26.8 kg/m2) and women (26.0 kg/m2) align with national data reported by the Centers for Disease Control and Prevention (26.6 kg/m2 for men and 26.5 kg/m2 for women). A comparison of our results for organ weights with those of previous reports suggests that there may have been increases in organ weights as recently as the last 40 years. Heart weights in our data set, for example, run about 20% heavier compared with data collected by Kitzman and colleagues18 at the Mayo Clinic in 1988. Unfortunately, a rigorous head-to-head statistical comparison of our data set with prior data sets is not possible without additional analysis and is beyond the scope of this paper.
It was the purpose of this study to compile the most complete and modern normal organ weight reference tables using the largest number of cases for the most important organs weighed at autopsy. Almost all of the historical publications listed in Table 4 used fewer than 1000 cases. The largest studies had 3432 and 1333 cases, but analyzed only one organ each. Although there were some additional historical studies that provided weights on multiple organs (not listed in Table 4), they still did not reach the number of cases in this study and provided only normal reference ranges overall or by sex. The strength of this study is that it has the largest number of cases that provide robust normal reference ranges across body weight or age categories for 8 major organs of interest, including both left and right lungs and kidneys. Although there have been some more recent studies with fewer than 1000 cases, those publications focus on one specific organ. The 2 studies with more than 1000 cases were published in the 1970s. This study also used individual case‐ and organ-level screening for disease, producing the most nearly “normal” data set currently in use.
Comparison to Other Studies
When comparing the normal weight ranges for heart with the other historical heart weight studies, our median weight ranges (270–440 g) are generally tighter. Our 10th and 90th percentile difference from the median of 60 to 90 g across our data cells is slightly higher than the data cell SDs for the Zeek19 study (when correcting for the difference in measures); consistent with the data cell ranges, SDs, and CIs for the studies by Kitzman et al,18 Hanzlick and Rydzewski,20 Smith,21 and Vanhaebost et al22 (when correcting for the difference in measures); and slightly better than the SD and percentile ranges in the Gaitskell et al9 and Skurdal and Nordrum23 studies. When comparing the brain weights in Table 6 with those in the 1978 Dekaban24 historical publication, our median brain range of 1218 to 1444 g across the data cells is slightly tighter than their range of means, but our data cell 10th and 90th percentile difference from the median of ±110 to 190 g is larger than their data cell SD range of ±10 to 50 g, even when approximating for the different measure definitions. This difference may be due to case selection or other measurement differences. When comparing the spleen weights in Table 5 with the 3 historical studies, the median range of spleens across the sex and weight data cells is 108 to 260 g, which is heavier than those in the previous studies. In addition, the 10th and 90th percentile difference from the median of ±40 to 140 g is larger than those in the Boyd25 (1933) and Myers and Segal26 (1974) studies, but slightly better than that in the Sprogoe-Jakobsen and Sprogoe-Jakobsen27 (1997) study. The heavier spleen ranges and higher percentile variability ranges may reflect a trend of heavier and more variable spleen weights using a more modern population. For liver, the only major historical reference is the Boyd25 study from 1933. The median ranges in Table 5 represent heavier liver weights and demonstrate a much higher variability range. This was also seen for kidney weights when comparing Table 5 with the historical 1937 Wald28 study. Our data reflect heavier kidney weights with greater variability ranges, but they are difficult to compare with such an early study. It should be noted that Table 5 separates right and left kidney because there is an approximate 10-g difference, whereas the Wald study used combined kidney weight. Lastly, when comparing right and left lung weights with one historical (1974) study by Whimster and Macfarlane,29 the range of lung weights in Table 5 is 340 to 580 g, which is heavier than the mean range in the Whimster and Macfarlane study (342–456 g), and the data cell 10th and 90th percentile difference from the median in Table 5 of ±110 to 320 g is also greater than the data cell SD ranges of ±80 to 117 g in the Whimster and Macfarlane publication when correcting for the different measurements.
Like all such data sets, this one has its limitations. Although every effort was made to eliminate any diseased organs from this retrospectively collected data set, we cannot exclude the possibility of undiagnosed or unreported illness. It is also not clear if the demographics of this set reflect the demographics of the general US population. For example, the data are not broken down by ethnicity or national origin. Even if the data set were a good reflection of trends in the general population in the United States, it is not clear how far beyond the United States the findings would apply. Ideally these shortcomings would be addressed by ongoing, large-scale data collection by region everywhere across the world, perhaps compiled by an international agency such as the World Health Organization.
In conclusion, the normal organ weight tables presented in this study represent modern organ weight reference ranges with the highest number of total decedent cases for the 8 most important organ weights at autopsy. For all organs except brain, the best classification was by sex and body weight categories; for brain, the best classification was by sex and age categories. The high number of decedent cases allows for robust normal organ weight reference ranges by the classification categories that can be used in any medical examiner or hospital institution. It would be useful for an autopsy laboratory to have these reference ranges posted physically or electronically to guide pathologists as to normal or abnormal organ weights at autopsy.
Long is an employee of the College of American Pathologists.
The authors have no relevant financial interest in the products or companies described in this article.