Multicentric evaluation of the homogeneous LDL-cholesterol Plus assay: comparison with beta-quantification and Friedewald formula

Reliability of Friedewald formula in patients with type 2 diabetes mellitus and its relation to lipid profile in diabetes regulation

Introduction: Many laboratories utilize Friedewald formula (FF) to analyze LDL cholesterol levels of patients including diabetes mellitus (DM). Therefore, it is essential to consider the coherence of results acquired by FF and direct measurement. The number of studies that investigated the effect of lipid parameters, especially TG/HDL cholesterol ratio, on the difference between the two methods is limited. The study was designed to compare LDL cholesterol values obtained by using FF with direct measurement, and to evaluate the relationship between diabetes regulation and lipid profile.

Material and Methods: In the cross-sectional study, 529 type 2 DM patients and 1703 non-DM subjects were divided into four groups regarding TG concentrations. Unlike other studies, the study focuses on direct LDL (DLDL) cholesterol levels obtained with the help of different DLDL cholesterol kits (n=20). The correlations were implemented between HbA1c and lipid profiles.

Results: It was determined that the bias% was over 10% in 24% of patients with 100-199 mg/dL TG levels. The parameter revealed that the most significant difference and the strongest correlation with HbA1c was TG/HDL cholesterol ratio in patients with type 2 DM.

Conclusions: In patients with type 2 DM, even if it was TG <200 mg/dL, LDL calculated with FF should be evaluated together with the TG/HDL cholesterol ratio. Otherwise, direct measurement can be recommended. This ratio is related to diabetes regulation and may be used to monitor patients..

Evaluation of a new equation for estimating low-density lipoprotein cholesterol through the comparison with various recommended methods

Introduction

The accurate estimation of low-density lipoprotein cholesterol (LDL) is crucial for management of patients at risk of cardiovascular events due to dyslipidemia. The LDL is typically calculated using the Friedewald equation and/or direct homogeneous assays. However, both methods have their own limitations, so other equations have been proposed, including a new equation developed by Sampson. The aim of this study was to evaluate Sampson equation by comparing with the Friedewald and Martin-Hopkins equations, and with a direct LDL method.

Materials and methods

Results of standard lipid profile (total cholesterol (CHOL), high-density lipoprotein cholesterol (HDL) and triglycerides (TG)) were obtained from two anonymized data sets collected at two laboratories, using assays from different manufacturers (Beckman Coulter and Roche Diagnostics). The second data set also included LDL results from a direct assay (Roche Diagnostics). Passing-Bablok and Bland-Altman analysis for method comparison was performed.

Results

A total of 64,345 and 37,783 results for CHOL, HDL and TG were used, including 3116 results from the direct LDL assay. The Sampson and Friedewald equations provided similar LDL results (difference ≤ 0.06 mmol/L, on average) at TG ≤ 2.0 mmol/L. At TG between 2.0 and 4.5 mmol/L, the Sampson-calculated LDL showed a constant bias (- 0.18 mmol/L) when compared with the Martin-Hopkins equation. Similarly, at TG between 4.5 and 9.0 mmol/L, the Sampson equation showed a negative bias when compared with the direct assay, which was proportional (- 16%) to the LDL concentration.

Conclusions

The Sampson equation may represent a cost-efficient alternative for calculating LDL in clinical laboratories.

Which of low-density lipoprotein cholesterol estimates can be used in children with type 1 diabetes?

BACKGROUND

One of the strongest risk factors of cardiovascular disease is a high concentration of low-density lipoprotein cholesterol (LDL-C); thus, the accurate measurement of LDL-C concentration in children is important. The aim of this study was to compare the concentration of LDL-C measured by direct method and the LDL-C concentration estimated by different formulas with the modified β-quantification method in children with type 1 diabetes.

METHODS

Thirty-one serum samples received from diabetic children (15/18; M/F) and 26 serum samples taken from nondiabetic children (18/14; M/F) were used in the study. LDL-C concentrations were determined by direct enzymatic method (LDL-CD) and the modified β-quantification method (LDL-CmBQ). The concentration of LDL-C was also calculated by different formulas.

RESULTS

The results of LDL-CmBQ and LDL-CD correlated. However, the correlation coefficient obtain in the nondiabetic samples was much higher (r=0.927; p<0.001) than the correlation coefficient for LDL-CmBQ and LDL-CD concentration obtained in the diabetic samples (r=0.691; p<0.001). Additionally, the coefficients of correlation between the LDL-CmBQ concentration and the LDL-C concentrations calculated by different formulas were lower in diabetic (range: 0.514-0.693) than in nondiabetic samples (range: 0.834-0.937). Bland-Altman plots showed much higher confidence intervals for 95% limits of agreement for the differences between LDL-CmBQ and LDL-CD as well as for the differences between LDL-CmBQ and LDL-C estimated by different formulas for samples from the diabetic samples compared with nondiabetic samples.

CONCLUSIONS

The limitations of methods measurement and of each of the formulas should be taken into account when a medical decision to lower LDL-C is made in the treatment of diabetic children.

Extreme concentrations of high density lipoprotein cholesterol affect the calculation of low density lipoprotein cholesterol in the Friedewald formula and other proposed formulas

OBJECTIVES

To investigate the effect of extreme levels of high density lipoprotein cholesterol (HDL-C) in the calculation of low density lipoprotein cholesterol (LDL-C) using Friedewald's formula (FF) and other formulas proposed recently.

DESIGN AND METHODS

Lipoprotein profile was performed in 2603 samples with HDL-C ≤ 20 mg/dL and 1953 samples with HDL-C ≥ 100 mg/dL.

RESULTS

Wilcoxon's and Student's t-tests showed significant differences (p<0.001) between calculated LDL-C by different formulas and direct determination in the two groups of HDL-C values. Passing-Bablok regression and Bland-Altman plot showed disagreement for the four formulas studied, except for Vujovic formula in the HLD-C ≥ 100 mg/dL group.

CONCLUSIONS

Our results suggested that none of the formulas under analysis should be used for estimating LDL-C in samples with extreme HDL-C concentrations due to absence of statistical correlation with LDL-C direct measurement.

Blood glucose and nocturnal blood pressure in African and Caucasian men: The SABPA study

AIM

To investigate the relationship between nocturnal blood pressure and chronically elevated blood glucose to determine if these elevated blood glucose concentrations contribute to a non-dipping blood pressure, especially in high-risk groups such as Africans.

METHODS

Nocturnal blood pressures and blood glucose levels of 41 non-dipping African and 28 non-dipping Caucasian men were investigated. Ambulatory systolic (SBP) and diastolic blood pressure (DBP) were measured and blood collected in sodium fluoride tubes from the antebrachial vein to determine serum glucose and glycosylated hemoglobin A1c (HbA1c) percentage. The estimated average glucose (eAG) was determined from HbA1c percentage with a regression formula.

RESULTS

The African non-dippers had higher blood pressures (p<0.001) and elevated HbA1c (p=0.037) and eAG (p=0.041) levels compared to the Caucasians. In single, partial and multiple regression analyses nighttime (00:00-04:00) SBP correlated positively with HbA1c (p=0.069) and eAG (p<0.001) in the African men. No correlations were found in the Caucasian men. Sensitivity analysis confirmed that the association between nighttime SBP (00:00-04:00) and eAG was independent of carotid intima-media thickness in the African men (R(2)=0.617; β=0.438; p=0.008).

CONCLUSION

The blunted nocturnal decline in SBP during the early morning hours is associated with chronically elevated blood glucose in non-dipper African men.

Associations of cholesterol and glucose with cardiovascular dysfunction in black Africans: the SABPA study

The aim was to determine whether blood glucose or cholesterol is the more prominent contributor to cardiovascular dysfunction in 101 African men and 99 African women. We measured ambulatory daytime blood pressure (BP), carotid intima-media thickness (CIMT), and determined blood glucose and lipids in serum. High-density lipoprotein cholesterol (HDL) (p = 0.002) and HDL: total cholesterol (HDL:TC) (p ≤ 0.001) were significantly lower, while serum glucose (p ≤ 0.001) was significantly higher in men. In single, partial, and multiple regression analysis, BP correlated positively with blood glucose in men. Furthermore, CIMT (B = -0.50; p = 0.009) correlated negatively with HDL:TC in men. While in women CIMT (B = 0.346; p = 0.015) correlated positively with glucose. In conclusion, subclinical atherosclerosis is significantly related to an unfavorable HDL profile in men, whereas in women, this link is stronger with fasting glucose.

Method of LDL cholesterol measurement influences classification of LDL cholesterol treatment goals: clinical research study

BACKGROUND

Low-density lipoprotein cholesterol (LDL-C) has been clearly associated with the risk of developing coronary heart disease. The best and most convenient method for determining LDL-C has come under increased scrutiny in recent years. We present comparisons of the Friedewald calculated LDL-C (C-LDL-C) and direct LDL-C (D-LDL-C) using 3 different homogenous assays. This highlights differences between the 2 methods of LDL-C measurement and how this affects the classification of samples into different LDL-C treatment goals as determined by the National Cholesterol Education Program Adult Treatment Panel III guidelines thus potentially affecting treatment strategies.

METHODS

Lipid profiles of a total of 2208 clinic patients were retrieved from the Central Arkansas VA Healthcare System clinical laboratory database. Samples studied were of 1-week period during the 3 periods studied: 2000 (period 1), 2002 (period 2), and 2005 (period 3). Different homogenous assays for D-LDL-C measurement were used for each of the 3 periods.

RESULTS

There is a fundamental disagreement between D-LDL-C and C-LDL-C, although Pearson correlation coefficients are 0.93, 0.97, and 0.98 for periods 1, 2, and 3, respectively. Using the model for period 1, when C-LDL-C is 70 mg/dL, the predicted D-LDL-C is 95 mg/dL (36% higher). The differences between C-LDL-C and predicted D-LDL-C progressively decrease at higher LDL-C cut points. In the assay used in period 3, there are 290 samples with D-LDL-C values between 100 and 130 mg/dL. Of these, only 182 samples show agreement with C-LDL-C values, whereas 90 samples with a D-LDL-C in the 100- to 130-mg/dL range are in the 70- to 100-mg/dL range using the C-LDL-C assay. Although the κ statistics suggests the LDL-C measures have relatively high levels of agreement, the significant generalized McNemar tests (P < 0.01) provide additional evidence of disagreement between C-LDL-C and D-LDL-C during all the 3 periods.

CONCLUSIONS

Our results highlight D-LDL-C measurements using 3 different assays during 3 different periods. In all assays, there is a substantial lack of agreement between D-LDL-C and C-LDL-C, which, in most cases, resulted in higher D-LDL-C values than C-LDL-C. This leads to clinically significant misclassification of patient's LDL-C to a different LDL-C treatment goal, which would potentially result in more drug usage, thus exposing patients to more potential adverse effects and at a much greater cost with little evidence of benefit.

Agreement Between Fasting and Postprandial LDL Cholesterol Measured with 3 Methods in Patients with Type 2 Diabetes Mellitus

BACKGROUND

LDL cholesterol (LDL-C) is a modifiable cardiovascular disease risk factor. We used 3 LDL-C methods to study the agreement between fasting and postprandial LDL-C in type 2 diabetes (T2DM) patients.

METHODS

We served 74 T2DM patients a standardized meal and sampled blood at fasting and 1.5, 3.0, 4.5, and 6.0 h postprandially. We measured LDL-C by use of modified β quantification (MBQ), the Friedewald equation (FE), and a direct homogeneous assay (DA). We evaluated agreement using 95% limits of agreement (LOA) within ±0.20 mmol/L (±7.7 mg/dL).

RESULTS

LDL-C concentrations at all postprandial times disagreed with those at fasting for all methods. In 66 patients who had complete measurements with all LDL-C methods, maximum mean differences (95% LOA) in postprandial vs fasting LDL-C were −0.16 mmol/L (−0.51; 0.19) [−6.2 mg/dL (−19.7; 7.3)] with MBQ at 3 h; −0.36 mmol/L (−0.89; 0.17) [−13.9 mg/dL (−34; 6.6)] with FE at 4.5 h; and −0.24 mmol/L (−0.62; 0.05) [−9.3 mg/dL (−24; 1.9)] with DA at 6.0 h. In postprandial samples, FE misclassified 38% of patients (two-thirds of statin users) into lower Adult Treatment Panel III (ATP III) risk categories. Greater disagreement between fasting and postprandial LDL-C was observed in individuals with postprandial triglyceride concentrations &gt;2.08 mmol/L (&gt;184 mg/dL) and in women (interactions: P ≤ 0.038).

CONCLUSIONS

Differences up to 0.89 mmol/L (34 mg/dL) between fasting and postprandial LDL-C concentrations, with postprandial LDL-C concentrations usually being lower, were found in T2DM by 3 different LDL-C methods. Such differences are potentially relevant clinically and suggest that, irrespective of measurement method, postprandial LDL-C concentrations should not be used to assess cardiovascular disease risk.

Validation of the Friedewald formula for the determination of low-density lipoprotein cholesterol in renal transplant recipients

In large patient populations, it has been established that calculated (c) and measured (m) plasma levels of low-density lipoprotein cholesterol (LDL-C) were comparable, but this issue is not known to be tested in renal transplant recipients (RTRs). Herein we aimed to compare the plasma levels of LDL-C that was calculated by Friedewald formula (FF) and direct measurement in RTRs.

METHODS

LDL-C was measured by direct method and by FF in 193 fasting venous blood samples obtained from 103 RTRs. Patients had triglyceride (TG) levels <400 mg/dL. Patients were treated with prednisolone, calcineurin inhibitors (CNIs), and/or sirolimus and everolimus.

RESULTS

The mean plasma levels of LDL-C for calculated and direct measurement were 100.81 +/- 32.79 mg/dL and 107.82 +/- 33.23 mg/dL, respectively (p < 0.01). The differences between cLDL-C and mLDL-C were similar according to usage of angiotensin receptor blockers (ARB)/angiotensin-converting enzyme inhibitors (ACEI), CNI, or mammalian target of rapamycin inhibitor (mTOR), tacrolimus or cyclosporine, and serum creatinine levels. mLDL-C and cLDL (FF) were highly correlated (r = 0.977). The mLDL-C level was calculated by following formula: LDL-C = 8.018 + (0.99 x FF cLDL-C) and the mean difference was 0 for last formula.

CONCLUSION

The LDL-C can be calculated by the following formula: LDL-C = 8.018 + (0.99 x FF LDL-C). The coefficient of determination correlation (r) for this regression was 0.977, which indicates that the calculated LDL-C levels can be used in RTRs with TG lower than 400 mg/dL. mLDL-C was significantly higher than cLDL-C. We observed that difference between cLDL-C and mLDL-C levels were not affected by serum creatinine levels and usage of CNIs, sirolimus, everolimus, ACEI, and ARB in RTRs.