Useful Information
Hormone Assay Interference
Interference in immunoassay is a well recognised problem. This may be due to a number of factors such as non-specificity of antibodies used in the assay method or Interference from a component in the patient sample such as circulating antibodies. These interfering antibodies are specific to an individual patient and have the potential to interfere in an unpredictable way. The reported prevalence of such interfering antibodies varies from 0.05 to more than 2%. Our experience with thyroid hormones and gonadotrophins is that interference occurs in approximately 0.5% clinical samples.
The approach to detection of interference that we have taken is:
1: alertness to the problem
2: to use an alternative analytical method either a different immunoassay method, or by organic extraction prior to analysis or by mass spectrometry.
3: to use PEG precipitation to remove interfering proteins
4: to use commercially available anti-animal antibody coated tubes to remove any endogenous antibody
References
Gynaecological Endocrinology
Day 21 progesterone (nmol/L) for evaluation of the function of the corpus luteum:
Day 21 progesterone is a misnomer as it is only correct for women with 28 day cycles. In order to assess optimal luteal function, progesterone measurements should ideally be made 7 days prior to the next menstrual bleed.
|
<35 |
poor luteal function: ovulation unlikely |
|
35-70 |
optimal luteal function indicating ovulation likely |
|
>70 |
may indicate suboptimal luteal function unless there is multiple ovulation due to either spontaneous occurrence or due to induction by clomiphene |
Amenorrhoea
|
|
LH & FSH |
Oestradiol |
|
Premature ovarian insufficiency |
both high but usually FSH > LH |
low |
|
Weight loss associated amenorrhoea |
FSH > LH |
low |
|
Polycystic ovary syndrome |
LH: FSH ratio is > 2.5:1 in many cases but is an unreliable test for the diagnosis of PCO |
variable |
|
Pregnancy |
low LH and FSH |
|
|
Oestrogen-secreting tumour |
low |
high |
|
Prolactinoma (see below) |
|
|
Prolactin
Mildly elevated values ie 600-900 U/L may be due to the stress of venepuncture; samples with values in this range should be checked on a repeat sample.
Elevated levels of prolactin may be due to pregnancy, hypothyroidism and drugs eg phenothiazines, haloperidol, tricyclic anti-depressants, metoclopramide, methyl DOPA & high dose oral contraceptives.
Elevated prolactin levels in the absence of the above conditions requires further investigation for prolactinoma eg full pituitary function tests and imaging.
Biochemical changes during pregnancy
|
Real changes |
§ elevation in hCG § increase in alkaline phosphatase due to placental production of the isoenzyme § decrease in albumin, creatinine and urea |
|
Apparent changes |
§ There is an oestrogen-induced increase in several plasma binding proteins which apparently increases the levels of protein bound substances although their activity is unchanged as the free levels are unchanged. This may result in an elevation in plasma thyroxine, T4 > 200 nmol/L. |
Investigation of the hirsute woman
|
Clinical evaluation |
First line investigations |
Second line investigations |
|
long-standing hirsuties, regular menstrual cycles, no virilism |
none necessary |
|
|
long-standing hirsuties, irregular menstrual cycles, no virilism |
investigate for PCO (ovarian ultra-sound or LH: FSH ratio). Testosterone >5.5 nmol/L |
if Testosterone > 5.5 nmol/L proceed as below for CAH or tumour |
|
severe hirsuties, irregular menstrual cycles and virilism |
investigate for CAH if long history and for adrenal or ovarian androgen-secreting tumour if history is short |
