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The issue of whether 99m Tc-DTPA can replace 51 Cr-EDTA for measurement of plasma clearance as a surrogate for glomerular filtration rate (GFR) is of great relevance to daily clinical practice. Prompted by the shortage of 51 Cr-EDTA we conducted a head-to-head comparison in patients attending our department for GFR determination. The two tracers (3.7 MBq of 51 Cr-EDTA and 8 MBq of 99m Tc-DTPA) were administered intravenously immediately after each other, and the standard number of blood samples were drawn. Fifty-four patients were enrolled. In 51 of these, single-sample measurement was performed with the following results: GFR EDTA was 84.6 ± 23.3 mL/min, GFR DTPA was 84.2 ± 24.7 mL/min. The mean difference was 0.4 ± 2.8 mL/min, p  = 0.32, and results based on the two tracers were highly correlated ( r  = 0.995). GFR DTPA exceeded GFR EDTA at high GFR values (difference < 0 at GFR EDTA >91.4 mL/min) and vice versa (difference > 0 at GFR EDTA < 91.4 mL/min). However, differences fell within few GFR units that most often will have no clinical consequence. We therefore conclude that 99m Tc-DTPA can replace 51 Cr-EDTA for single-sample determination of GFR in a clinical setting.

A radioimmunoassay for quantitation of serum myoglobin in healthy individuals and patients with different diseases is described. Purified myoglobin was labelled by an 125I-labelled ester (N-succinimidyl 3-(-4 hydroxy, 5-[125I]iodophenyl) propionate), a commercially available antiserum was used, and the antigen-antibody complex was precipitated with polyethylene glycol 6000. The rapid assay can be performed within 1 h at 37 degrees C with a detection limit of 45 micrograms/l. Prolonged incubation at 4 degrees C for 18 or 72 h gives a detection limit of 6 and 2 micrograms/l, respectively. The mean coefficient of variation of the routine assay was 11%. In healthy human subjects a significant difference in mean serum myoglobin concentration was found between 43 women (34 +/- 17 micrograms/l) and 51 mean 47 +/- 15 micrograms/l). In twenty patients admitted to hospital with the clinical diagnosis acute myocardial infarction, the serum myoglobin concentration profiles were in close agreement with the final diagnosis. In three patients with myocardial infarction serum samples were taken every 2 h after the acute episode, and serum myoglobin levels were compared with the levels of creatine kinase, lactate dehydrogenase, aspartate aminotransferase and creatine kinase isoenzyme-MB.

A latex agglutination test for detection of elevated levels of myoglobin in serum has been studied, and its clinical value in diagnosis of acute myocardial infarction (AMI) has been evaluated on a retrospective material of fifty-five patients consecutively admitted to hospital on suspicion for AMI within 4 h after onset of symptoms. The analysis time was less than 10 min. There was no evidence of interference with other related proteins, as judged from analysis of sera with high content of aspartate and alanine aminotransferase, lactate dehydrogenase and creatine kinase, nor was the test sensitive to haemolysis. However, unspecific agglutination was seen with some sera containing a high concentration of rheumatoid factors. In sera with known concentrations of myoglobin, quantitated by a radioimmunoassay, the test was negative in all sera below 80 micrograms/l (n = 187), and positive in all sera above 140 micrograms/l (n = 209). In the range 80-140 micrograms/l the latex test could be either positive or negative (n = 105). The day-to-day reproducibility was high in the ranges below 80 micrograms/l and above 140 micrograms/l, but range 80-140 micrograms/l. In the diagnosis of AMI the predictive value of a positive result was 0.64, and the predictive value of a negative result was 1.0. The latex agglutination test is therefore clinically useful as an emergency test, and as a very early and sensitive indicator for AMI. Patients with a negative test result during the first 12 h after debut of symptoms can with great certainty be identified as not suffering from AMI, whereas patients with a positive test result should be monitored by further laboratory analyses.