We describe an enzymatic method for rapid, precise measurement of serum triglycerides with use of sample:reagent ratios as large as 1:200. Hydrolysis of triglycerides is catalyzed by lipase to produce glycerol and free fatty acids. The glycerol generated is then phosphorylated by adenosine 5'-triphosphate in the presence of glycerol kinase. Oxidation of the resulting glycerol 3-phosphate to produce hydrogen peroxide is catalyzed by L-alpha-glycerophosphate oxidase. An intense red chromogen is produced by the peroxidase-catalyzed coupling of 4-aminoantipyrene and sodium 2-hydroxy-3,5-dichlorobenzenesulfonate with hydrogen peroxide. This sensitive chromogen system not only permits use of unusually small sample volumes, it also facilitates a linear response to serum triglyceride concentrations up to at least 10 g/L while displaying good Ringbom (measure of accuracy) characteristics.

A peroxidase-coupled method for the colorimetric determination of serum triglycerides.

PHYSIOLOGY Creatine is synthesised by the body in a two-step process (Fig. 1) involving the initial synthesis of guanidinoacetate, which takes place in the kidneys, small intestinal mucosa, pancreas, and probably the liver. The reaction between glycine and arginine is catalysed by a transamidase, which is subject to feedback inhibition by increased creatine levels. Guanidinoacetate is transported to the liver where it is methylated to creatine, which then enters the blood to be widely distributed, chiefly to muscle cells, in which it is converted to creatine phosphate-a source of high energy phosphate bonds for the immediate reformation of ATP during muscular contraction. Creatinine is formed by a spontaneous and irreversible conversion from creatine and creatine phosphate. Formation of creatinine is reasonably constant, and about 2% of whole body creatine is so transformed every 24 h. Consequently, creatinine formation also has a direct relationship to total muscle mass and roughly to the body weight. Creatinine production rate therefore remains approximately the same from day to day unless the muscle mass changes. It is not altered significantly by illness, sepsis, trauma or fever, nor by the state of hydration; however, increased protein intake can result in increases in creatinine production of the order of 10%.

https://journals.sagepub.com/doi/pdf/10.1177/000456328602300101

Analytical Reviews in Clinical Biochemistry: The Estimation of Creatinine:

A method for determining the presence of an analyte in a fluid is described along with various components of an apparatus specifically designed to carry out the method. The method involves taking a reflectance reading from one surface of an inert porous matrix impregnated with a reagent that will interact with the analyte to produce a light-absorbing reaction product when the fluid being analyzed is applied to another surface and migrates through the matrix to the surface being read. Reflectance measurements are made at two separate wavelengths in order to eliminate interferences, and a timing circuit is triggered by an initial decrease in reflectance by the wetting of the surface whose reflectance is being measured by the fluid which passes through the inert matrix. The method and apparatus are particularly suitable for the measurement of glucose levels in blood without requiring separation of red blood cells from serum or plasma.

Minimum procedure system for the determination of analytes

Interference by endogenous and exogenous substances with assays for clinical analytes is a common problem in laboratory medicine. For this review, we defined interference as "the effect of a substance present in the sample that alters the correct value of the result, usually expressed as concentration or activity, for an analyte." There are four major endogenous compounds that consistently interfere with laboratory results: hemoglobin, bilirubin, lipids, and paraproteins. The major exogenous sources of interference are drugs prescribed for the patient; and there are several excellent compendia of the effect of drugs on clinical laboratory tests. We recommend determining whether the interference is dependent or independent of the analyte for the assay. Further, we propose an approach to the identification and resolution of an interference problem for the clinical laboratory and make recommendations to manufacturers.

R.J. Thibert

Papers

Interesting interferences in a direct serum creatinine reaction

Study of various substrates for peroxidase-coupled peroxide oxidations

Spectrophotometric study of bilirubin and hemoglobin interactions in several hydrogen peroxide generating procedures

Determination of iron, copper, and zinc in a single aliquot of serum sample using 4-[(5-bromo-2-pyridyl)azo]resorcinol

Spectrophotometric study of total protein-albumin methods applied to cerebrospinal fluid