Management - Diagnosis
Management
Diagnosis
The diazo reaction, described by van den Bergh in 1916, is the basis for most clinical bilirubin testing. It involves hydrolysis of bilirubin's central methene bridge yielding 2 dipyrroles. One reacts with the diazo dye to form an azodipyrrole, which is red and can be quantified colorimetrically. The other dipyrrole reacts with half of another previously hydrolyzed bilirubin molecule to reform bilirubin which can further react. In stepwise fashion all the available bilirubin is converted to azodipyrroles.Upon adding water and a diazotizing agent, usually diazosulfanilic acid, to serum, some of the bilirubin, the direct-reacting fraction, reacts immediately. The remainder requires addition of an accelerator, usually alcohol or caffeine, which displaces bilirubin from albumin. This results in all the available bilirubin reacting, yielding the total bilirubin. Normally, the direct bilirubin is < 1 mg/dL. In patients with high total bilirubins, any direct < 10 - 20% of the total is considered normal. (NOTE: 1 mg/dL of bilirubin = 17 mmol/L)Transcutaneous bilirubin measurements are being studied with increasing frequency. The 2 best studied devices are the Minolta JM-103 and the BiliChek. They tend to overestimate the serum bilirubin in black babies, although since bilirubin levels are usually lower in blacks, this is unlikely to be clinically significant. They are also unreliable when the bilirubin is above 15 mg/dL. They can be used as noninvasive screening tools prior to hospital discharge. However, remember that the risk zone nomogram, as well as all the clinical guidelines for treatment, use serum bilirubins.Return to top of page