In light of this, a combined approach to laboratory diagnosis is required to reach a differential diagnosis.CBS deficiency may be diagnosed by routine metabolic biochemistry. Genetic testing may be used to screen for known SNPs (mutations). In the first instance, plasma or urine amino acid analysis will frequently show an elevation of methionine and the presence of homocysteine. Many neonatal screening programs include methionine as a metabolite. The disorder may be distinguished from the re-methylation defects (e.g., MTHFR, methionine synthase deficiency, or the cobalamin defects) in lieu of the elevated methionine concentration. Additionally, organic acid analysis or quantitative determination of methylmalonic acid should help to exclude cobalamin (vitamin B12) defects and vitamin B12 deficiency giving a differential diagnosis.The laboratory analysis of homocysteine itself is complicated because most homocysteine (possibly above 85%) is bound to other thiol amino acids and proteins in the form of disulphides (e.g., cysteine in cystine-homocysteine, homocysteine in homocysteine-homocysteine) via disulfide bonds. Since as an equilibrium process the proportion of free homocystene is variable a true value of total homocysteine (free + bound) is useful for confirming diagnosis and particularly for monitoring of treatment efficacy. To this end it is prudent to perform total homocyst(e)ine analysis in which all disulphide bonds are subject to reduction prior to analysis, traditionally by HPLC after derivatisation with a fluorescent agent, thus giving a true reflection of the quantity of homocysteine in a plasma sample.
"Prevalence, characteristics and natural course of inappropriate sinus tachycardia". Europace. 7 (2): 104–12. doi:10.1016/j.eupc.2004.12.007. PMID 15763524. Leon, Hernando; Guzman, Juan Camilo;  et al. (2005). "Impaired Baroreflex Gain in Patients with Inappropriate Sinus Tachycardia". Journal of Cardiovascular Electrophysiology. 16 (1): 64–8. doi:10.1046/j.1540-8167.2005.04441.x. PMID 15673390. Sanchez-Quintana, D; Cabrera, JA;  et al. (2005). "Sinus node revisited in the era of electroanatomical mapping and catheter ablation". Heart. 91 (2): 189–94. doi:10.1136/hrt.2003.031542. PMC 1768731. PMID 15657230. Cruz Filho, Fernando E. S.; Maia, Ivan G.;  et al. (1998). "Modificação do nódulo sinusal via cateter por energia de radiofreqüência em paciente com taquicardia sinusal inapropriada. Avaliação dos resultados imediatos e tardios" [Sinus node modification by catheter using radiofrequency current in a patient with inappropriate sinus tachycardia. Evaluation of early and late results]. Arquivos Brasileiros de Cardiologia (in Portuguese). 70 (3): 173–6. doi:10.1590/S0066-782X1998000300006. PMID 9674178. Lee, SH; Cheng, JJ;  et al. (1997). "Radiofrequency catheter modification of sinus node for inappropriate sinus tachycardia: A case report". Zhonghua Yi Xue Za Zhi. 60 (2): 117–23. PMID 9360339.