Negative interference from immunoglobulin M paraproteinaemia on the Roche enzymatic creatinine method.

Although enzymatic creatinine methods are subject to fewer interferences than traditional Jaffe creatinine methods, every method in clinical chemistry has limitations. We report, for the first time in the literature, a case of an immunoglobulin M (IgM) paraproteinaemia causing an undetectably low creatinine result on the Roche enzymatic assay. This interference did not occur with other enzymatic creatinine methods produced by Abbott and Siemens or the Roche Jaffe, VITROS dry slide and liquid chromatography with tandem mass spectrometry (LC-MS/MS) creatinine methods. IgM interference was confirmed as patient serum precipitated with polyethylene glycol (PEG) and anti-IgM antiserum yielded detectable Roche enzymatic creatinine results comparable to unaffected methods. The patient's serum formed an obvious precipitate when mixed with reagent one of the Roche enzymatic creatinine method. This is in contrast to a report of positive interference from IgM paraproteinaemia in a different enzymatic creatinine method, which showed that a precipitate formed when mixing blood with reagent two. As each patient's paraprotein has a unique structure, it is possible that there are variations in the chemical characteristics of IgM paraproteins between patients. This, as well as IgM-class antibodies' tendency to form multimers and aggregates, can lead to unpredictable assay interferences and precipitation tendencies between different manufacturers of enzymatic creatinine reagents and their incubation steps. This case highlights the importance of continuing to question and investigates results that do not fit the clinical picture, especially as more laboratories switch from primarily using traditional Jaffe creatinine methods to enzymatic creatinine methods.

Assessment of GFR by four methods in adults in Ashanti, Ghana: the need for an eGFR equation for lean African populations.

BACKGROUND: Equations for estimating glomerular filtration rate (GFR) have not been validated in Sub-Saharan African populations, and data on GFR are few. METHODS: GFR by creatinine clearance (Ccr) using 24-hour urine collections and estimated GFR (eGFR) using the four-variable Modification of Diet in Renal Disease (MDRD-4)[creatinine calibrated to isotope dilution mass spectrometry (IDMS) standard], Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Cockcroft-Gault equations were obtained in Ghanaians aged 40-75. The population comprised 1013 inhabitants in 12 villages; 944 provided a serum creatinine and two 24-hour urines. The mean weight was 54.4 kg; mean body mass index was 21.1 kg/m(2). RESULTS: Mean GFR by Ccr was 84.1 ml/min/1.73 m(2); 86.8% of participants had a GFR of >/=60 ml/min/1.73 m(2). Mean MDRD-4 eGFR was 102.3 ml/min/1.73 m(2) (difference vs. Ccr, 18.2: 95% CI: 16.8-19.5); when the factor for black race was omitted, the value (mean 84.6 ml/min/1.73 m(2)) was close to Ccr. Mean CKD-EPI eGFR was 103.1 ml/min/1.73 m(2), and 89.4 ml/min/1.73 m(2) when the factor for race was omitted. The Cockcroft-Gault equation underestimated GFR compared with Ccr by 9.4 ml/min/1.73 m(2) (CI: 8.3-10.6); particularly in older age groups. GFR by Ccr, and eGFR by MDRD-4, CKD-EPI and Cockcroft-Gault showed falls with age: MDRD-4 5.5, Ccr 7.7, CKD-EPI 8.8 and Cockcroft-Gault 11.0 ml/min/1.73 m(2)/10 years. The percentage of individuals identified with CKD stages 3-5 depended on the method used: MDRD-4 1.6% (7.2 % without factor for black race; CKD-EPI 1.7% (4.7% without factor for black race), Ccr 13.2% and Cockcroft-Gault 21.0%. CONCLUSIONS: Mean eGFR by both MDRD-4 and CKD-EPI was considerably higher than GFR by Ccr and Cockcroft-Gault, a difference that may be attributable to leanness. MDRD-4 appeared to underestimate the fall in GFR with age compared with the three other measurements; the fall with CKD-EPI without the adjustment for race was the closest to that of Ccr. An equation tailored specifically to the needs of the lean populations of Africa is urgently needed. For the present, the CKD-EPI equation without the adjustment for black race appears to be the most useful.

Intraindividual hormonal variability in ultrasonographically timed successive ovulatory menstrual cycles is detected only in the luteal phase in infertility patients.

OBJECTIVE: To assess intraindividual variation of follicle stimulating hormone, luteinising hormone, estradiol, progesterone, inhibin A, and inhibin B in three successive ovulatory cycles correlated with transvaginal ultrasound monitored morphological changes in the ovary. METHODS: Serial transvaginal color and pulsed Doppler ultrasound and serum hormone analysis were performed during midfollicular, periovulatory, and midluteal phase for three consecutive cycles in 19 patients with normal menstrual cycles. RESULTS: Luteinising hormone and progesterone showed significant differences in the midluteal phase between the 1st and 2nd cycle (luteinising hormone p = 0.007 and progesterone p = 0.02). Progesterone showed a similar significant change (p = 0.013) between the 2nd and 3rd cycle. No significant differences were seen in the midfollicular or periovulatory phases or between the 1st and 3rd cycle. CONCLUSIONS: Luteal phase progesterone and luteinising hormone concentrations showed individual variation in successive cycles suggesting early or late corpus luteolysis. Follicular and periovulatory hormone levels were similar in subsequent ovulatory cycles.