Adjustment of direct high-density lipoprotein cholesterol measurements according to intercurrent triglyceride corrects for interference by triglyceride-rich lipoproteins.

BACKGROUND: Low plasma levels of high-density-lipoprotein cholesterol (HDL-C) and high triglyceride (TG) are strongly associated with cardiovascular disease (CVD). Clinical recognition of this high-risk population demands accurate measurement of HDL-C, whereas cost and clinical demand dictate that optimal HDL-C measurement requires fully automated methods that avoid manual precipitation. Commercial techniques use specific reagents to selectively expose and "directly" measure cholesterol in HDL. However, these "direct" methods may experience interference from the cholesterol content of triglyceride-rich-lipoproteins (TRL), leading to analytical overestimation of HDL-C, with subsequent underestimation of low-density-lipoprotein cholesterol (LDL-C) and of CVD risk. OBJECTIVE: The aim of this study was to develop a method to overcome this interference. METHODS: Serum/Li+-heparin plasma samples from consecutive patients were analyzed for HDL-C by the comparison of three generations of the Roche Diagnostics, HDL-C assay on a Hitachi-917 or Modular-PPE analyzer. HDL-C measurement was performed before and after removal of TRL by ultracentrifugation ("direct" HDL-C and HDL-UC, respectively). We examined the effect of TG on the relationship between HDL-UC and "direct" HDL-C. Analysis of variance multiregression analysis was performed for each generation of the commercial assay. RESULTS: We observed progressive TG interference that increased "direct" HDL-C by 10% to 15% or more in moderately hypertriglyceridemic samples (<600 mg/dL). Predictive equations were derived for each generation of the assay to estimate HDL-C in the absence of TRL. CONCLUSIONS: This study casts doubt on the specificity of "direct" HDL-C assays in the presence of hypertriglyceridemia. The use of assay-specific correction formulae to adjust for interference from TRL reduces the overestimation of HDL-C that influences CVD risk calculation, treatment, and follow-up of patients.

Butyrylcholinesterase (BCHE) genotyping for post-succinylcholine apnea in an Australian population.

BACKGROUND: Measurement of plasma butyrylcholinesterase (BChE) activity and inhibitor-based phenotyping are standard methods for identifying patients who experience post-succinylcholine (SC) apnea attributable to inherited variants of the BChE enzyme. Our aim was to develop PCR-based assays for BCHE mutation detection and implement them for routine diagnostic use at a university teaching hospital. METHODS: Between 1999 and 2002, we genotyped 65 patients referred after prolonged post-SC apnea. Five BCHE gene mutations were analyzed. Competitive oligo-priming (COP)-PCR was used for flu-1, flu-2, and K-variant and direct DNA sequencing analysis for dibucaine and sil-1 mutations. Additional DNA sequencing of BCHE coding regions was provided when the five-mutation screen was negative or mutation findings were inconsistent with enzyme activity. RESULTS: Genotyping identified 52 patients with primary hypocholinesterasemia attributable to BCHE mutations, and in 44 individuals the abnormalities were detected by the five-mutation screen (detection rate, 85%). Additional sequencing studies revealed mutations in eight other patients, including five with novel mutations. The most common genotype abnormality was compound homozygous dibucaine and homozygous K-variant mutations. No simple homozygotes were found. Of the remaining 13 patients, 3 had normal BChE activity and gene, and 10 were diagnosed with hypocholinesterasemia unrelated to BCHE gene abnormalities. CONCLUSION: A five-mutation screen for investigation of post-SC apnea identified BCHE gene abnormalities for 80% of a referral population. Six new BCHE mutations were identified by sequencing studies of 16 additional patients.