Liver function testing

Abstract

The investigation of the functional capacity of the liver has long exorcised the ingenuity of the medical world, and as knowledge of liver physiology has advanced so have the liver function tests increased both in number and in complexity, but the results of so much observation and experiment have, up to the present time, been disappointing - it may be that in seeking a sign the ardour of the workers has outstripped their wisdom.The study of liver function has been retarded by the striking signs which failure of one function - an that not the most important one - produces, namely, the classical picture of jaundice with the staining of the integuments, the coloration of the urine, and the discoloration at times of the stools; the easy recognition of this trilogy of signs for many centuries satisfied the curiosity of the medical world, and it was not until patient pathological research showed that liver insufficiency of a degree incompatible with life could occur without jaundice, and that jaundice was frequently a manifestation, not of liver disease, but of disorders of the haemopoietic system, or of impermeability of the binary passages, that attention became directed to the possibilities of studying other liver functions than those of bile production.The researches of many workers in many countries have placed the study of kidney function in the clinic upon a rational basis, and analogous teste of liver function are an urgent necessity, a little study will show, however, that the problems are entirely different, and that their solution cannot be expected along similar lines. It is quite possible, by means of a few simple tests, to estimate the capacity of the kidney with regard to its three great functions - urea excretion, salt excretion, and water excretion, and even to estimate its power of dealing with ingested or injected dye -stuffs - on the other hand the functions of the liver are legion, and so vital that nature has not only endowed this organ with vast ressrve capacities, but it has given the extra- hepatic tissues of the organism the power, under certain circumstances to usurp the liver's part in practically every process with which it is concerned. How, then, can it ever be possible to gain an intimate knowledge of the workings of the hepatic cellule by the use of such simple tests as the exigencies of the clinic demand?It will be the purpose of this thesis to deal in turn with each liver function, to discuss its physiology in the light of modern knowledge, and to point out the methods which have been adopted to elucidate its functional capacity; it will be most convenient to reserve the criticism of each test until the end of the appropriate section, but at thisjuncture a short review of the subject will be given in order to correlate what would otherwise appear to be an incohesive mass of details.Firstly as regards liver physiology, in none of the standard textbooks on physiology to which the author has had access has a connected account been given, but crumbs of information have had to be culled from various sections; the best account is probably to be found in the Traite de Pathologie Medicale et Thera - peutique Appliquée - Foie et Pancreas (Paris, 1923) by Brule, but this represents the somewhat too isolate French views upon the subject. From this and from other sources of information that are quoted elsewhere the following account has been compiled, and whilst it may contain matter which is of a controversial nature, it is at least a working basis for an understanding of the subject.This - the function whose derangement is most easily investigated - whereby bile salts and bile pigments are discharged into the intestine, has been regarded variously as an excretory and as a secretory one; the evidence is discussed at some length in the special section on the subject, but a brief account will be given here.The bile pigments are produced by the disintegration of the haemoglobin of the effete erythrocytes, and all the evidence points to the conclusion that the Kuppfer cells of the reticulo- endothelial system are responsible for this; the pigments thus formed are carried, to the liver, taken up by the hepatic cells, and discharged into the bile passages for excretion.The bile salts - compounds of Cholalic acid with two amino acids taurine and glycine - are of quite unknown origin, but it is suggested that they also may beof extrahepatic origin, and that their formation has some relation to cholesterin metabolism.Urobilin and urobilinogen are decomposition products of bilirubin perhaps formed as the result of bacterial action in the intestine, with reabsorption from the intestine and reexcretion by the liver. Evidence that urobilin can be formed in any of the body tissues is forthcoming, but knowledge is in so chaotic a state that judgment as to the correctness of any of the numerous theories must be withheld.Uroerythrine is a brick red urinary pigment chemically related to haemoglobin and bilirubin and said to be formed when the metabolism of bile pigments is imperfect.