Factors contributing to variation in lipoprotein (a) in Melbourne Anglo-Celtic population

AIM

The purpose of this report is to survey the factors contributing to variation in lipoprotein(a) (Lp(a)) in a population-based sample of Anglo-Celtic Melburnians.

RESULTS

The plasma Lp(a) levels were highly skewed towards low levels in this population, with a median of 156 mg/l and a mean of 262 mg/l. Approximately 33% had plasma Lp(a) above the threshold value of 300 mg/l, while 35% had Lp(a) levels below 100 mg/l. The most commonly occurring phenotype was apo(a) S3. In this phenotype, Lp(a) concentrations ranged from 10 to 596 mg/l. Lp(a) was consistently associated with diastolic blood pressure, systolic blood pressure, total protein, albumin and nitrogen excretion in the 40-60 y age group. Multiple stepwise regression analyses, in non-dietary factors, were used to explain about 13% of the variance in Lp(a) (19% in men and 23% in women). Remarkably, in the <40 y age group, non-dietary factors may account for 86% of the variance in Lp(a) and dietary factors, analysed separately, 46%. Thus, although Lp(a) is mainly genetically determined, there are clearly other factors which contribute to variations in Lp(a) concentrations.

Total body dual X-ray absorptiometry is a good measure of both fat mass and fat-free mass in liver cirrhosis compared to "gold-standard" techniques. Melbourne Liver Group

Liver cirrhosis is a condition in which overnutrition, edema, and undernutrition can coexist simultaneously, or successively, over a period of time, giving rise to alterations in body composition, as well as systemic and multiorgan manifestations. We undertook a cross-sectional study of body composition in 198 adult patients with liver cirrhosis (140 males, mean age 53.6, range 31-85 years; and 58 females, mean age 58.4, range 36-79 years). The patients had cirrhosis of differing etiology and different stages of severity. They were gathered from seven different hospital clinics in the city of Melbourne, Australia, but all the body composition measurements were performed in one body composition laboratory. A variety of body composition techniques were used to identify which commonly available ones could best assess both fat-free mass and fat mass relative to a criterion "gold-standard" method available in a specialist laboratory. A gold-standard fat-free mass (FFMGS) was defined as the sum of total body protein, measured by in vivo neutron activation analysis (IVNA), plus total body water, measured by D2O dilution, plus bone mineral content, measured by dual X-ray absorptiometry (DXA). A gold-standard fat mass (FATGS) was defined as the difference between body weight and FFMGS. "Usual" fat mass and fat-free mass were defined by different techniques including DXA, anthropometry (ANT), single-frequency bioelectrical impedance (SFBIA), multiple-frequency bioelectrical impedance spectroscopy (MFBIA), and whole body gamma counting (TBK). The FFMGS was overhydrated in both sexes, relative to the usual value of 0.73, but women were significantly overhydrated compared to men. Relative to the gold-standard deuterium oxide dilution method for measuring total body water, SFBIA slightly overestimated TBW, whereas MFBIA slightly underestimated TBW, with both methods having wide limits of agreement for any single estimate. In comparing FFM to FFMGS, only DXA showed a small negative bias, in both males and females, with modest limits of agreement for any single estimate. All other methods showed a large negative bias (ANT, SFBIA, and MFBIA) or a large positive bias (TBK) relative to FFMGS, with wide limits of agreement. In comparing FAT with the FATGS, only DXA showed a small positive bias, in both males and females, with modest limits of agreement for any single estimate. All other methods showed a large positive bias (ANT, SFBIA, and MFBIA) or a large negative bias (TBK) relative to FATGS, with wide limits of agreement. In cirrhosis, DXA is a good and widely available method to assess both fat mass and fat-free mass. However, it cannot give information about the quality of the FFM, particularly its water content. The bedside methods of anthropometry and bioelectrical impedance, both SFBIA and MFBIA, are poor methods of measuring body composition in patients with liver cirrhosis, whereas whole body gamma counting, although not widely available, also significantly differs from the gold-standard method of assessment of fat-free mass and fat mass in liver cirrhosis.

Total body protein status assessed by different estimates of fat-free mass in adult peritoneal dialysis patients

OBJECTIVE

To assess the usefulness of fat-free mass (FFM) as an index of total body protein (TBPr) status in continuous ambulatory peritoneal dialysis (CAPD) patients.

DESIGN

TBPr was measured by in vivo neutron activation analysis (IVNAA) and expressed as a standardised protein index (PI). FFM was estimated by dual energy X-ray absorptiometry (DXA), whole body counting of total body potassium (TBK), and creatinine kinetics (CK), and expressed as a standardised FFM index (FFMI). FFM was also determined by a criterion method based on four compartment model (4CM) which is defined as the sum of total body water determined by D2O dilution, TBPr determined by IVNAA, bone mineral determined by DXA, and glycogen estimated to be 4.4% of TBPr. Each patient was measured within a four hour period by all methods.

SETTING

Body Composition Laboratory, Monash Medical Centre.

SUBJECTS

Six male and twelve female CAPD patients (33-77 years).

RESULTS

FFMI assessed by DXA and by TBK agreed with measurements of PI on identifying the mean TBPr status of the CAPD group as significantly below a comparable normal reference population (mean Z score: PI = -1.01 (P < 0.05); FFMI by DXA = -0.50 (P < 0.05); FFMI by TBK = -1.24 (P < 0.05)). In contrast, FFMI assessed by CK did not reveal a significantly reduced TBPr status (mean Z score: -0.70 (NS)). Furthermore, significant linear correlations were noted between PI and FFMI estimated by DXA and by TBK (r = 0.57 (P < 0.05) vs r = 0.69 (P < 0.05)) however no significant correlation was observed between PI and FFMI estimated by CK (r = 0.36 (NS)). Moderate variation in FFM hydration did not compromise the ability of DXA, TBK or CK to differentiate between protein deleted, normal and enriched patients. Comparison of FFM estimates between the criterion method and either DXA, TBK or CK revealed no significant bias (+ 1.8 kg vs -2.0 kg vs +0.8 kg) and respective SEE values of 3.8 kg (8.3%), 5.9 kg (14.3%) and 9.6 kg (21.7%).

CONCLUSION

The findings of this study indicate that FFM estimated by either DXA or the whole body counting of TBK is a useful index of TBPr status in CAPD patients. However, FFM assessed by CK does not appear to be an appropriate index of TBPr status in CAPD patients.

Kt/V in CAPD by different estimations of V

This study compared the measurements of total body water (TBW) by 58% body weight (TBW58%), the Watson equation (TBWWV) and bioelectric impedance (TBWBIA) with the gold standard, Deuterium oxide (TBWD2O) dilution method in twenty continuous ambulatory peritoneal dialysis (CAPD) patients. TBW volumes were highest when calculated as TBW58% (42.6 +/- 9.4 liter) and lowest when calculated from TBWWV (34.6 +/- 6.8 liter). TBWBIA underestimated TBW when compared to TBWD2O, although the difference was not statistically significant (37.1 +/- 9.8 liter and 38.8 +/- 9.3 liter, respectively). In fact, TBWBIA correlated strongly with TBWD2O (r = 0.8, P < 0.0001). These discrepancies resulted in significant differences when Kt/V week-1 derived from the four methods were compared. To determine the effect of percent fat mass on the estimation of TBW by each method, we compared TBW and Kt/V week-1 derived from the four methods in nine CAPD patients who had normal percent fat mass (Non-Obese) and 11 CAPD patients who had greater than normal % fat mass (Obese). In the Non-Obese group, there was close correlation of TBWBIA, TBWWV and TBW58% when compared with TBWD2O (r = 0.93, P < 0.001, r = 0.89, P < 0.01 and R = 0.86, P < 0.01, respectively. Also, Kt/V week-1 derived from TBWBIA, TBWWV and TBW58% correlated strongly with Kt/V week-1 from TBWD2O (r = 0.93, P < 0.0005, r = 0.83, P < 0.01 and r = 0.8, P < 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Quality control in body composition measurements

The principles of quality control (QC) are not new; they have always been with mankind. At the most fundamental level QC can be defined as a state of mind in which we continually strive to analyse what we are doing in order to produce a 'product' which our peers will judge to be 'better' . Paradoxically, this simple concept is expressed in many different ways within the multi-disciplinary team that makes up a body composition laboratory and very careful discussion is needed to ensure uniformity of technique and results. The situation is made even more difficult by the large range of equipment and techniques that are now available for the measurement of body composition. It is necessary to have a detailed understanding of the equipment and techniques and to have good communication within the group of workers. Good communication is essential to ensure that all members of the group have a clear understanding of the relevant guidelines and principles of QC and measurements, and to ensure that they are applied consistently throughout all the work of the laboratory. A detailed understanding of the equipment is necessary in order to define and implement simple tests that will monitor the most sensitive or troublesome features without imposing an undue burden upon the operator. There is a need for such tests to be automated as much as possible and, in general, there is a need for a more professional approach to the analysis of error and its propagation throughout an experiment. Inter comparisons of results between centres is a logical, but generally difficult requirement and some of the problems that arise would be simplified if equipment designs were more standardized. Finally, all these requirements need to be achieved within an environment that is continually changing with respect to the aims of the laboratory and the funding bodies.