Icterus index

Recently, this problem has been approached by reverting to reading the color of the bilirubin directly. This used to be called an "Icterus Index", in which the color of the serum was compared to a dilute dichromate solution (39). However, the new approach has been to use two wavelengths. This can be used in either of two different procedures. In one procedure the reading is made at the peak for bilirubin which is at 453 nm and at an isosbestic point for hemoglobin (40). The effect on the reading due to hemoglobin is subtracted from the bilirubin value. Commercial instruments based on this principle have not been successful. 

In humans, early symptoms of intoxication may include headache, dizziness, nausea, vomiting, malaise, and myoclonic jerks of the limbs clonic and tonic convulsions and sometimes coma follow and may occur without the premonitory symptoms. A suicidal person who ingested 25.6mg/kg developed convulsions within 20 minutes that persisted recurrently until large amounts of barbiturates had been administered. Hematuria and azotemia occurred the day after ingestion and continued for 18 days. Liver function studies were within normal limits except for an elevated icterus index an electroencephalogram revealed generalized cerebral dysrhythmia, which returned to normal after 5 months. ... 

The use of the icterus index, as described by Meulengracht, for the assessment of jaundice has fallen into disrepute because of the errors caused by the presence of lipochromes, carotenoids, and other yellow pigments. Josephson (J6) in his survey found that the correlation coefficient between icterus index and serum bilirubin concentration was 0.69 in 360 healthy subjects and 0.84 in 40 jaundiced subjects. In newborn infants however, bilirubin is the only yellow pigment likely to be present and the possibility of determining serum bilirubin concentrations by direct measurement has again been re-examined. Abelson and Boggs (Al) diluted serum from infants with erythroblastosis 1 in 50 and studied the absorption curves. They found that in addition to the bili-... 

J6. Josephson, B., The icterus index as a measure of serum bilirubin concentration. Acta Genet. Statist. Med. 4, 231-235 (1953). 

Ingestion of carotenes alone does not cause vitamin A toxicity, probably because of markedly decreased absorption at high doses and feedback inhibition of carotene conversion to retinaldehyde, but can cause harmless carotene-mia with yellowing of the skin, particularly on the palmar and plantar surfaces. Carotenemia can cause falsely elevated values for the icterus index or for other direct reading methods for estimating serum bilirubin (Chapter 29). 

Refractometry Refractometry is a quick and reasonably accurate alternative to chemical analysis for serum total protein when a rapid estimate is required. The refractive index of water at 20°C is 1.330 if solute is added to the water, the refractive index of a dilute solution increases linearly and proportionally to the solute concentration at higher concentrations of dissolved solids (50-200gl ), the increase is nearly linear. Temperature affects appreciably the refractive index of a solution, so refracto-meters for clinical use compensate for temperature effects. Serum contains dissolved solids in concentrations of 80-100 gl, most of which are proteins. In the refractometry of serum, it is assumed that the concentration of inorganic electrolytes and nonprotein organic compounds does not vary appreciably from serum to serum and that the differences in the refractive index reflect primarily the differences in protein concentrations. The assumption has been shown to be reliable for clear, nonpigmented samples, but hemolysis, lipemia, icterus, and azotemia produce erroneously high results. The method cannot be used for urine protein measurement because of excess solutes in relation to the protein. 

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